Polymer Exemption Guidance Manual, Slides of History

Download Polymer Exemption Guidance Manual and more Slides History in PDF only on Docsity! United States Office of Pollution EPA 744-B-97-001 Environmental Protection Prevention and Toxics June 1997 Agency (7406) Polymer Exemption Guidance Manual POLYMER EXEMPTION GUIDANCE MANUAL 5/22/97 A technical manual to accompany, but not supersede the "Premanufacture Notification Exemptions; Revisions of Exemptions for Polymers; Final Rule" found at 40 CFR Part 723, (60) FR 16316-16336, published Wednesday, March 29, 1995 Environmental Protection Agency Office of Pollution Prevention and Toxics 401 M St., SW., Washington, DC 20460-0001 Copies of this document are available through the TSCA Assistance Information Service at (202) 554-1404 or by faxing requests to (202) 554-5603. 1. INTRODUCTION The Environmental Protection Agency (EPA) published a series of proposed rules (USEPA 1993a-1993d) in the Federal Register on February 8, 1993 to announce the Agency’s plan to amend premanufacture notification (PMN) regulations for new chemical substances under §5 of the Toxic Substances Control Act (TSCA). Included were proposed amendments to the polymer exemption rule originally published on November 21, 1984 (USEPA 1984) under the auspices of § 5(h)(4) of TSCA and entered into the Code of Federal Regulations (CFR), the administrative rules under which the U.S. Government operates, at 40 CFR Chapter I, Subchapter R, part 723.250. After the proposed polymer exemption rule was published, the Agency considered public comments, consulted with European counterparts, and utilized the experience gained in the review of over 12,000 polymers in publishing its new final rule for polymer exemptions on March 29, 1995, amending 40 CFR §723.250 (USEPA 1995). The new polymer exemption rule is notably different from that originally published in 1984 and it is the purpose of this technical manual to provide the regulated community with additional insight, so that manufacturers and importers will be able to determine if their new chemical substances are eligible for the polymer exemption under the new rule. Substances submitted before May 30, 1995 are subject to the original rule (USEPA 1984) and its requirements. On or after that date, all polymer exemptions are subject to the new rule and its requirements. A few notable features of the 1995 Polymer Exemption are as follows: • Manufacturers and importers are no longer required to submit notice prior to manufacture or import. However, manufacturers and importers must submit an annual report for those exempt polymers whose manufacture or import has commenced for the first time during the preceding calendar year, as stipulated in §723.250(f), and the manufacturer or importer of an exempt polymer must comply with all recordkeeping requirements at §723.250(j). • A new method can be used for determining which monomers and reactants are considered part of the polymer’s chemical identity (modification of the so-called "Two Percent Rule"). • More polymers are now eligible for exemption because previous exclusions have been modified or eliminated. Some of the changes are in regard to halogens, cyano groups, biopolymers and reactive group limitations. • Certain high molecular weight polymers once considered eligible for submission under the 1984 exemption are not eligible for this exemption. The EPA hopes this technical manual will: (1) assist the chemical manufacturer or importer in determining whether the PMN substance is a polymer as defined by the polymer exemption rule, (2) guide the manufacturer or importer in determining whether the polymer meets the exemption criteria of the rule and (3) assist the manufacturer or importer in determining whether the polymer is excluded from exemption by certain factors. In addition, this manual provides technical guidance and numerous pertinent examples of decision-making rationales. The Agency hopes that after reviewing this document prospective manufactures and importers will be able to decide easily whether the polymer exemption is applicable to any of their new substances. This technical guidance manual is not intended to substitute for or supersede the regulations as found at 40 CFR §723.250 and the Federal Register (USEPA 1995). Manufacturers and importers must read those provisions to assure compliance with all the procedural and recordkeeping requirements of the polymer exemption. 1 2. HISTORY Section 5 of TSCA contains provisions that allow the Agency to review new chemical substances before they are manufactured or imported. Section 5(a)1 of TSCA requires that persons notify EPA at least 90 days prior to the manufacture or import of a new chemical substance for commercial purposes. A "new" chemical substance is one that is subject to TSCA but is not already included on the TSCA Chemical Substance Inventory. If the Agency determines that a new chemical substance may present an unreasonable risk of injury to human health or the environment or if there is insufficient information to establish that no such risk exists, the Agency may limit the manufacture, processing, distribution in commerce, use, or disposal of the new chemical substance under the authority provided in TSCA §5(e). From the beginning of the PMN program in 1979 until 1984 all new chemical substances, including polymers, were subject to the full reporting requirements of the premanufacture notification process. Under §5(h)(4) the Agency has authority to promulgate rules granting exemptions from some or all of the premanufacture requirements for new chemicals if the Agency determines that the manufacturing, processing, distribution in commerce, use, or disposal of a new chemical substance will not present an unreasonable risk of injury to human health or the environment. Through its experience in reviewing new chemical substances, the Agency identified certain criteria to determine which polymers were most unlikely to present an unreasonable risk of injury to human health or the environment. This experience led to the original polymer exemption rule under §5(h)(4) allowing polymers that met certain criteria under these conservative guidelines to be exempt from some of the reporting requirements for new chemicals (USEPA 1984). Since the EPA published the 1984 TSCA polymer exemption rule, the Agency has reviewed over 10,000 polymer submissions under the standard 90 day PMN review process and an additional 2,000 polymer exemption notices. With the experience gained by the review of this large number of submissions, the Agency reevaluated the criteria used to identify those polymers which were unlikely to present unreasonable risks. This led to the proposal of a revised polymer exemption rule that would increase the number of polymers qualifying for exemption and enable the Agency to concentrate its limited resources on those polymers that do not meet the polymer exemption criteria and on non- polymeric new chemical substances that may present greater risks. The amendments are expected to result in resource savings for industry as well as the EPA. The new polymer exemption rule amends appropriate sections of 40 CFR 723.250 to allow certain polymers to be exempt from the reporting requirements for new chemicals and imposes new restrictions on a limited set of polymers that were previously eligible for the exemption (USEPA 1993d). To be eligible for the exemption, a new chemical substance must: 1) meet the polymer definition, 2) meet one of three exemption criteria and 3) not be excluded. The definition of polymer, for purposes of the new exemption, is found at 40 CFR §723.250(b). There are now three exemption types, located at 40 CFR §723.250(e)(1), (e)(2), and (e)(3), subsequently referred to as the (e)(1), (e)(2), and (e)(3) criteria. Excluded categories are listed at 40 CFR §723.250(d) of the new rule. The definition of polymer, the key components of each of the three exemption types, and the categories excluded from the exemption are discussed below. The remainder of this technical manual provides prospective submitters with information helpful for establishing whether or not their new chemical substances meet the exemption criteria. The (e)(1) exemption concerns polymers with a number-average molecular weight (NAVG MW) in a range that is greater than or equal to 1,000 (≥ 1000) daltons and less than 10,000 (<10,000) daltons. Dalton - precisely 1.0000 atomic mass unit or 1/12 the mass of a carbon atom of mass 12. Hence, a polymer with a molecular weight of 10,000 atomic mass units has a mass of 10,000 daltons. 2 For the (e)(1) exemption, oligomer content must be less than 10 percent by weight below 500 daltons and less than 25% by weight below 1,000 daltons. The polymer must also meet functional group criteria to be described in a later section of this manual. Oligomer (in the context of the rule and this manual) - a low molecular weight species derived from the polymerization reaction. The Organization for Economic Cooperation and Development (OECD) has a draft guidelines document1 for determining the low molecular weight polymer content. For the (e)(2) exemption, the NAVG MW for eligible polymers must be greater than or equal to 10,000 daltons and these polymers must have oligomer content less than two percent below 500 daltons and less than 5 percent below 1,000 daltons. The (e)(3) exemption concerns certain polyester polymers (as defined at §723.250(b)) composed solely of monomers and reactants from the list as found at §723.250(e)(3). In addition to meeting the specific criteria of one of the three exemption types described above, the new polymer must not fall into any of the prohibited categories listed at §723.250(d) of the new rule. This section of the amended rule specifically excludes certain polymers from the reduced reporting requirements of the polymer exemption: certain cationic polymers; polymers that do not meet elemental restrictions; polymers that degrade, decompose, or depolymerize; and polymers that are produced from monomers and/or other reactants that are not on the TSCA inventory or otherwise exempted from full PMN reporting under a §5 exemption. Some highly water- absorbing, high molecular weight polymers are also specifically prohibited. Any new chemical polymer substance that does not meet the polymer definition, does not meet any of the (e)(1), (e)(2), or (e)(3) exemptions, or is specifically excluded from the polymer exemption is subject to the full PMN reporting requirements. 3. DEFINITIONS For a new polymer to be eligible for the exemption it must meet distinct criteria set forth in the 1995 polymer exemption rule. Much of the terminology used in these criteria is explained in this and subsequent sections of the guidance manual. Note that the definitions provided herein are those used in the new polymer exemption rule, and that these terms may not necessarily have the same meaning as commonly used in an academic or industrial setting. Careful attention must be paid to the definitions contained in the new polymer exemption rule when determining eligibility. The polymer definition has been revised to conform with the international definition recently adopted by the OECD as a result of the Experts on Polymers Meetings held in Toronto, Canada (January 1990), Paris, France (October 1991), and Tokyo, Japan (April 1993), in which the Agency participated. The definition was agreed upon in May 1993 by the OECD member countries, including the United States, Canada, Japan, and member nations of the European Union. The definitions of polymer and other important terms as used in the new polymer exemption rule are: Polymer - a chemical substance consisting of molecules characterized by the sequence of one or more types of monomer units and comprising a simple weight majority of molecules containing at least 3 monomer units which are covalently bound to at least one other monomer unit or other reactant and which consists of less than a simple weight majority of molecules of the same molecular weight. Such molecules must be distributed over a range of molecular weights wherein differences in the molecular weight are primarily attributable to differences in the number of monomer units. 3 Example 3: Figure 3 Ethoxylated Glycerol: CH2O CHO CH2O (CH2CH2O)2H (CH2CH2O)2H (CH2CH2O)2 CH2CH2OH o.r. 2 m.u. m.u. Example 3 meets the sequence criterion and would be considered a polymer molecule. If polymer formation is desired, at least 7 equivalents of EO should be charged to the reactor. With less EO charged, each hydroxyl may only be ethoxylated twice or less, which would not satisfy the sequence criterion. Example 4: Figure 4 Glycerol Triester: CH2O CHO CH2O CO(CH2)16-18CH3 CO(CH2)16-18CH3 CO(CH2)16-18CH3 o.r. o.r. Example 4 does not meet the sequence criterion. There are no repeating units. Neither the glycerol other reactant nor the fatty acid other reactant can repeat under the reaction conditions. Methylene (CH2) is not a monomer unit, because it is not the reacted form of a monomer present in the polymer. Example 5: Figure 5 Epoxy Resin: CH2 CH CH2 OH O CH2CHCH2O CH3 CH3 OOC O H3C o.r. m.u. m.u. m.u. 6 Example 5 meets the sequence criterion and therefore would be a polymer molecule. It has an unbroken chain of three monomer units and one other reactant. Examples 6, 7, and 8: Examples 6-8 illustrate the sequence and distribution criterion of the new polymer exemption rule. Table 1 Distribution Criteria Examples 6, 7, and 8: Ethoxylated Alcohols SPECIES o.r. + m.u. EXAMPLE 6 EXAMPLE 7 EXAMPLE 8 RO.EO.H 1 + 1 5% 25% 8% RO.EO.EO.H 1 + 2 20% 35% 20% RO.EO.EO.EO.H 1 + 3 30% 20% 52% RO.EO.EO.EO.EO.H 1 + 4 40% 10% 10% RO.EO.EO.EO.EO.EO.H 1 + 5 5% 10% 10% For these examples, ’EO’ is a monomer unit derived from ethylene oxide, and ’RO’ is an other reactant derived from an alcohol. Example 6 meets the definition of a polymer because >50 percent of the substance has molecules of at least 3 monomer units in sequence and <50 percent of each species (same molecular weight components) is present. Example 7 does not meet the definition of polymer because <50 percent of substance has molecules of at least 3 monomer units plus at least one additional monomer unit or other reactant. Example 8 does not meet the definition of polymer because >50 percent of one molecular weight species is present. Example 9: Consider the enzyme pepsin and the sequence and distribution criteria of the new polymer exemption rule’s definition of a polymer substance. Although pepsin meets the sequence requirements of the polymer definition, the molecules will always have the same distinct molecular weight, corresponding to the sum of the molecular weights of the amino acid monomer units which comprise the specific protein sequence of the enzyme. As such it has a majority of molecules having identical weight and will not meet that portion of the new rule’s definition of a polymer. On the other hand, a lipoprotein or mucoprotein with its attachments intact might satisfy the sequence and distribution criteria. The lipo- or muco- portions can be quite variable in quantity and this could cause enough variation in weight of the polymer molecules. 4.2. SUBSTANCES EXCLUDED FROM THE EXEMPTION AT 40 CFR §723.250(d) Certain categories of polymers are ineligible for exemption under the new polymer exemption rule because the Agency cannot determine whether these substances can be reasonably anticipated to present an unreasonable risk of injury to human health or the environment. For a discussion of the history behind the selection of these categories consult the preamble to the 1995 polymer exemption rule (USEPA 1995). The following sections discuss the excluded categories. 7 4.2.1. EXCLUSIONS FOR CATIONIC AND POTENTIALLY CATIONIC POLYMERS Cationic polymers and those polymers which are reasonably anticipated to become cationic in the natural aquatic environment are excluded from the exemption and may not be manufactured under it. The principal concern is the toxicity toward aquatic organisms. Cationic polymer - a polymer that contains a net positively charged atom(s) or associated group(s) of atoms covalently linked to the polymer molecule. This includes, but is not limited to phosphonium, sulfonium, and ammonium cations. Potentially cationic polymer - a polymer containing groups that are reasonably anticipated to become cationic. This includes, but is not limited to, all amines (primary, secondary, tertiary, aromatic, etc.) and all isocyanates (which hydrolyze to form carbamic acids, then decarboxylate to form amines). Reasonably anticipated means that a knowledgeable person would expect a given physical or chemical composition or characteristic to occur, based on such factors as the nature of the precursors used to manufacture the polymer, the type of reaction, the type of manufacturing process, the products produced in the polymerization, the intended uses of the substance, or associated use conditions. 4.2.1.1. CATIONIC POLYMERS NOT EXCLUDED FROM EXEMPTION Through its experience reviewing thousands of polymers, the Agency has determined that two categories of cationic and potentially cationic polymers would not pose an unreasonable risk of injury to human health or the environment. These two types are not excluded from consideration for the exemption and are as follows: • Cationic or potentially cationic polymers that are solids, are neither water soluble nor dispersible in water, are only to be used in the solid phase, and are not excluded from exemption by other factors, and • Cationic or potentially cationic polymers with low cationic density (the percent of cationic or potentially cationic species with respect to the overall weight of polymer) which would not be excluded from the exemption by other factors. For a polymer to be considered to have low cationic density, the concentration of cationic functional groups is limited to a functional group equivalent weight of greater than or equal to 5,000 daltons. Functional group equivalent weight (FGEW) - the weight of polymer that contains one equivalent of the functional group; or the ratio of number-average molecular weight (NAVG MW) to the number of functional groups in the polymer. The methods for calculating the FGEW are described in a later section. Example 10: As an example of the cationic density requirement, consider the reaction of precisely equal molar amounts of ethanediamine and phthalic acid, resulting in a polyamide (polymer) with an equal number of unreacted amine and unreacted carboxylic acid groups. This would be equivalent to a sample of polymer molecules that would have (on average) one end group that was an unreacted amine (potentially cationic) and the other end group an unreacted carboxylic acid. For this polymer to be eligible for the exemption it must have a minimum NAVG MW of 5,000 daltons which would give the amine FGEW as 5,000 daltons (1 amine termination per 5,000 MW of polymer). 8 4.4.1.1. LOW-CONCERN FUNCTIONAL GROUPS AND THE (e)(1) EXEMPTION Low-concern functional groups defined in §723.250(e)(1)(ii)(A) may be used without limit. These groups are so categorized because they generally lack reactivity in biological settings. The low-concern reactive functional groups are: carboxylic acid groups; aliphatic hydroxyl groups; unconjugated olefinic groups that are considered "ordinary;" butenedioic acid groups; those conjugated olefinic groups contained in naturally-occurring fats, oils, and carboxylic acids; blocked isocyanates (including ketoxime-blocked isocyanates); thiols; unconjugated nitrile groups; and halogens (not including reactive halogen-containing groups such as benzylic or allylic halides). Ordinary olefinic groups - unconjugated olefinic groups that are not specifically activated either by being part of a larger functional group, such as a vinyl ether, or by other activating influences, such as the strongly electron-withdrawing sulfone functionality (in a vinyl sulfone system). In addition, carboxylic esters, ethers, amides, urethanes and sulfones are implicitly permitted because polyesters, polyethers, polyamides, polyurethanes, and polysulfones are among the types of polymers allowed under the exemption, as long as these functional groups have not been modified to enhance their reactivity. One such group that would not be allowed is the dinitrophenyl ester of a carboxylic acid, which is far more reactive due to the activating functionality. In summary, if a substance (1) meets the definition of a polymer, (2) is not excluded by §723.250(d), (3) has a NAVG MW greater than or equal to 1000 daltons and less than 10,000 daltons, (4) contains only the low-concern reactive functional groups, and (5) meets oligomer content criteria (<10 percent below 500 daltons and <25 percent below 1000 daltons), the new substance may be manufactured under a polymer exemption. 4.4.1.2. MODERATE-CONCERN FUNCTIONAL GROUPS AND THE (e)(1) EXEMPTION Moderate-concern groups defined in §723.250(e)(1)(ii)(B) may be used with functional group equivalent weight (FGEW) constraints. Each functional group present from category (B) must have a FGEW of greater than or equal to 1,000 daltons. For a polymer containing no type (C) groups (see section 4.4.1.3 for when type (C) groups are present), the FGEWcombined must be greater than or equal to 1,000 daltons. (The method for calculating a FGEWcombined is covered in section 5.3. of this manual). The moderate-concern reactive functional groups are: acid halides; acid anhydrides; aldehydes; hemiacetals; methylolamides; methylolamines; methylolureas; alkoxysilanes bearing alkoxy groups greater than C2; allyl ethers; conjugated olefins (except those in naturally-occurring fats, oils, and carboxylic acids); cyanates; epoxides; imines (ketimines and aldimines); and unsubstituted positions ortho- and para- to a phenolic hydroxyl group. In summary, if a substance (1) meets the definition of a polymer, (2) is not excluded by any of the provisions of §723.250(d), (3) has a NAVG MW greater than or equal to 1000 daltons and less than 10,000 daltons, (4) has individual FGEWs and a FGEWcombined greater than or equal to 1,000 daltons for moderate-concern groups (when high-concern groups are not present, but low- concern groups may be present without limit), and (5) meets oligomer content criteria (<10 percent below 500 daltons and <25 percent below 1000 daltons), the new substance may be manufactured under a polymer exemption. 4.4.1.3. HIGH-CONCERN FUNCTIONAL GROUPS AND THE (e)(1) EXEMPTION Reactive groups not defined by (e)(1)(ii)(A) or (B) fall into category (e)(1)(ii)(C), the high-concern reactive functional groups. These may be used with more restriction than moderate-concern groups alone. If a polymer contains type (C) reactive functional groups, each type (C) functional group present must meet a 5,000 dalton minimum permissible limit, each type (B) group present must meet the 1,000 dalton limit and the polymer must have a 11 FGEWcombined of greater than or equal to 5,000 daltons. A FGEWcombined calculation takes into account all type (C) and type (B) reactive groups. (This type of calculation is covered in section 5.3. of this manual.) Therefore, if a substance containing category (e)(1)(ii)(C) functional groups meets the definition of a polymer, is not excluded by any of the provisions of §723.250(d), has a NAVG MW greater than or equal to 1,000 daltons and less than 10,000 daltons, has a FGEWcombined greater than 5,000 daltons, meets the individual type (B) and (C) FGEW limits of 1,000 and 5,000, respectively, and the polymer meets oligomer content criteria (<10 percent below 500 daltons and <25 percent below 1000 daltons) the new substance may be manufactured under a polymer exemption. Table 2 summarizes the FGEWcombined minimum permissible levels as discussed in the preceding (e)(1) exemption criteria section of this manual. In the table, the ’X’ marks which type of group (or groups) is present from the categories: low-concern, moderate-concern, and high-concern. Table 2 FGEWcombined Summary Low- Concern X X X X Moderate- Concern X X X X High- Concern X X X X Minimum FGEWcombined None* 1,000 5,000 1,000** 5,000** 5,000 5,000** * There are no FGEW limits for polymers containing only low-concern (type A, also known as (e)(1)(ii)(A) ) functional groups. ** When calculating FGEWcombined for substances with moderate (Type (B)) and/or high-concern (Type (C)) functional groups, low-concern groups (Type (A)) are not included in the calculation. 4.4.2. THE (e)(2) EXEMPTION CRITERIA Those polymers having NAVG Mws exceeding the limits of §723.250(e)(1) are subject to §723.250(e)(2). Hence, this section covers polymers with NAVG Mws greater than or equal to 10,000 daltons. The oligomeric content of these higher molecular weight polymers must be less than two percent for species with molecular weight less than 500 daltons, and must be less than 5 percent for species of molecular weight less than 1,000 daltons. There are no functional group restrictions for the (e)(2) exemption, but the substance must not be excluded from exemption by any of the provisions found at §723.250(d). For example, water-absorbing polymers and cationic or potentially cationic polymers in this weight range are excluded from exemption by §723.250(d). Therefore, if a substance meets the definition of a polymer, is not excluded by any of the provisions of §723.250(d), has a NAVG MW greater than or equal to 10,000, and meets the oligomer content criteria (less than two percent below 500 daltons and <5 percent below 1,000 daltons), the new substance may be manufactured under a polymer exemption. 4.4.3. THE (e)(3) EXEMPTION CRITERIA Section 723.250(e)(3) provides for the exemption of manufactured or imported polyesters which have been prepared exclusively from a list of feedstocks identified in section (e)(3) of the new rule. To qualify for this exemption, each monomer or reactant in the chemical identity of the polymer (charged at any level) must be on the list. At this writing (5/22/97), six entries on the list are not on the TSCA Inventory. Therefore, these six monomers and reactants are not allowed for use in domestic manufacture. 12 Just as for all other exempted polymers, polyesters that are allowed an exemption under (e)(3) must meet the definition of a polymer and must not be excluded from exemption by §723.250(d). For example, excluded from an (e)(3) exemption are biodegradable polyesters and highly water-absorbing polyesters with number-average molecular weights (NAVG MW) greater than 10,000 daltons. The following is the list from which all monomers and reactants in (e)(3)-exempted polymers must be taken. They are listed by Chemical Abstracts Index Names and Registry Numbers (where available). A "√" identifies the six substances not on the TSCA Inventory, as of this writing. Table 3 The (e)(3) Monomer and Reactant List (in order by CAS Registry Number) [56-81-5] 1,2,3-Propanetriol [57-55-6] 1,2-Propanediol [65-85-0] Benzoic acid [71-36-3]** 1-Butanol [77-85-0] 1,3-Propanediol, 2-(hydroxymethyl)-2-methyl- [77-99-6] 1,3-Propanediol, 2-ethyl-2-(hydroxymethyl)- [80-04-6] Cyclohexanol, 4,4’-(1-methylethylidene)bis- [88-99-3] 1,2-Benzenedicarboxylic acid [100-21-0] 1,4-Benzenedicarboxylic acid [105-08-8] 1,4-Cyclohexanedimethanol [106-65-0] Butanedioic acid, dimethyl ester [106-79-6] Decanedioic acid, dimethyl ester [107-21-1] 1,2-Ethanediol [107-88-0] 1,3-Butanediol [108-93-0] Cyclohexanol [110-15-6] Butanedioic acid [110-17-8] 2-Butenedioic acid (E)- [110-40-7] Decanedioic acid, diethyl ester [110-63-4] 1,4-Butanediol [110-94-1] Pentanedioic acid, [110-99-6] Acetic acid, 2,2’-oxybis- [111-14-8] Heptanoic acid [111-16-0] Heptanedioic acid [111-20-6] Decanedioic acid [111-27-3] 1-Hexanol [111-46-6] Ethanol, 2,2’-oxybis- [112-05-0] Nonanoic acid [112-34-5] Ethanol, 2-(2-butoxyethoxy)- [115-77-5] 1,3-Propanediol, 2,2-bis(hydroxymethyl)- [120-61-6] 1,4-Benzenedicarboxylic acid, dimethyl ester [121-91-5] 1,3-Benzenedicarboxylic acid [123-25-1] Butanedioic acid, diethyl ester [123-99-9] Nonanedioic acid [124-04-9] Hexanedioic acid [126-30-7] 1,3-Propanediol, 2,2-dimethyl- [141-28-6] Hexanedioic acid, diethyl ester [142-62-1] Hexanoic acid [143-07-7] Dodecanoic acid [144-19-4] 1,3-Pentanediol, 2,2,4-trimethyl- [505-48-6] Octanedioic acid [528-44-9] 1,2,4-Benzenetricarboxylic acid [624-17-9] Nonanedioic acid, diethyl ester [627-93-0] Hexanedioic acid, dimethyl ester [629-11-8] 1,6-Hexanediol [636-09-9] 1,4-Benzenedicarboxylic acid, diethyl ester [693-23-2] Dodecanedioic acid [818-38-2] Pentanedioic acid, diethyl ester [1119-40-0] Pentanedioic acid, dimethyl ester [1459-93-4] 1,3-Benzenedicarboxylic acid, dimethyl ester 13 Equation 1: Equation 2: Example 11: The reason for using the NAVG MW instead of the WAVG MW in the criteria is best demonstrated by an example. Suppose a polymer contains 200 molecules that weigh 1,000 daltons, 300 molecules that weigh 1,500 daltons, 400 molecules that weigh 2,000 daltons and 2 molecules that weigh 1,000,000 daltons. In this case 99.8 percent of the molecules in this sample weigh ≤ 2000 daltons. Clearly, one might say that typically, the polymer has a molecular weight from 1,000 to 2,000 daltons. The NAVG MW and the WAVG MW are calculated below: Of these two calculations, the Mn at 1503 daltons more accurately represents 99.8 percent of the molecules in the polymer batch. The Mw is biased by the two incidental 1,000,000 dalton molecules to the extent that the Mw average is a considerably greater weight than 99.8 percent of the sample. The Agency requires that the manufacturer of an exempt polymer keep records of the "lowest" number-average molecular weight at which the polymer is to be made. This is not the value for the lowest MW species in a sample, but rather the lowest value of the NAVG MW obtained from polymer samples taken from a series of batches in the production of the polymer. There are several analytical techniques for determining NAVG MW. Two literature references4,5 as well as OECD’s guidelines document for testing of chemicals3 discuss methodologies in some detail and provide additional references. Brief summaries of the information provided in these references are given below. The techniques are based on molecular size (a function of the NAVG MW); colligative properties of polymer solutions (osmotic pressure, boiling point, freezing point, vapor pressure, etc.); or the number of chemically reactive groups present in the polymer. Any method that can be verified is acceptable for purposes of the polymer exemption. The following are most commonly used: • Gel permeation chromatography (polymer size), • Membrane osmometry (colligative property), • Vapor-phase osmometry (colligative property), • Vapor pressure lowering (colligative property), • Ebulliometry (colligative property), • Cryoscopy (colligative property), and • End-group analysis (chemical reactivity). 16 5.1.1. GEL PERMEATION CHROMATOGRAPHY Gel permeation chromatography (GPC), the most frequently used and generally most reliable method for determining NAVG MW of polymers and oligomer content below 500 and 1000 daltons, is suitable for substances ranging from very low to very high molecular weights. In an ideal situation, separation of the polymer sample is governed by hydrodynamic radius (size) of each molecular species as it passes through a column filled with porous material, typically an organic gel. Smaller molecules penetrate the pores and thereby travel a longer path and elute after larger molecules. The GPC column must be calibrated using polymers of known weight and, ideally, similar structure. Polystyrenes are used quite extensively as internal standards. Detection techniques used for GPC are refractive index and UV-absorption. One potential problem with GPC is band broadening, especially when measuring low molecular weight polymers, or as the result of unevenly packed columns or dead volumes. Empirical calibrations of the instrument can be made to minimize broadening6, but become unimportant when the ratio of the WAVG MW to the NAVG MW is greater than two. Another limitation with GPC is that many high molecular polymers are insoluble in usable solvents, and therefore can’t be analyzed by GPC. 5.1.2. MEMBRANE OSMOMETRY Membrane osmometry exploits the principle of osmosis for determining NAVG MW7. Polymer is placed in a membrane osmometer on one side of a semi- permeable membrane while a solvent is placed on the other. Solvent is drawn through the membrane as the system progresses toward equilibrium, creating a pressure differential that is dependent on the concentration difference and the molecular weight of the polymer. The major disadvantage to this method is that accuracy and reliability may be compromised by diffusion of low weight oligomers through the membrane. Generally, diffusion is absent for unfractionated polymers with NAVG MWs greater than 50,000 daltons. The upper limit of the NAVG MW that may be measured with confidence is generally 200,000 daltons (OECD guidelines3). 5.1.3. VAPOR-PHASE OSMOMETRY This method is based on the comparison of evaporation rates for a solvent aerosol and at least three other aerosols with varying polymer concentration in the same solvent. The technique is most accurate for polymers with NAVG MW less than 20,000 daltons (OECD guidelines3). This method is best applied to samples with molecular weight too low to be measured in a membrane osmometer. 5.1.4. VAPOR PRESSURE LOWERING For this technique the basic principle is similar to vapor phase osmometry, however, vapor pressure is measured instead of the rate of aerosol evaporation. The vapor pressure of a reference solvent is compared against the vapor pressure of at least three concentrations of the polymer mixed with the solvent. Theoretically this technique may be applicable for polymers of up to 20,000 dalton NAVG Mws. In practice, however, it is of limited value. 5.1.5. EBULLIOMETRY This technique exploits the boiling point elevation of a solution of a polymer to determine NAVG MW8. This method makes accurate determinations for polymers with NAVG MW approaching 30,000 daltons; however, it is limited by the tendency of polymer solutions to foam upon boiling. The polymer may even concentrate in the foam due to the foam’s greater surface area, making the observed concentration of the polymer in solution less than the actual. It is customary to calibrate the ebulliometer with a substance of known molecular weight. Octacosane, with a molecular weight of 396 daltons, is a common choice. 17 5.1.6. CRYOSCOPY Freezing point depressions of polymer solutions can also be used to determine NAVG MW. Although the limitations associated with cryoscopy are fewer than those of ebulliometry, care must be taken to avoid supercooling. The use of a nucleating agent to provide controlled crystallization of the solvent is helpful. Reliable results may be obtained for molecular weights of up to 30,000 daltons. As with ebulliometry, calibration with a substance of known molecular weight is customary. 5.1.7. END-GROUP ANALYSIS This method is generally the least useful since a fair amount of prior knowledge, such as overall structure and the nature of the chain-terminating end groups, is needed about the polymer. Basically, end-group analysis methods take into account the number of molecules in a given weight of a sample, which in turn, yields the NAVG MW. End-group analysis is best suited to linear condensation polymers. For branched condensation polymers or addition polymers no general procedures can be established because of the variety and origin of the end-groups. However, when the polymerization kinetics are well known, the degree of branching may be estimated based on the amount of feedstock charged. For addition polymerization, end-group analysis can be used to determine molecular weight by analyzing for specific initiator fragments containing identifiable functional groups, elements, or radioactive atoms; for chain terminating groups arising from transfer reactions with solvent; or for unsaturated end groups such as in polyethylene and poly-α- olefins. The analytical method used must distinguish the end groups from the main polymer skeleton. The most widely used methods are NMR, titration, or derivatization. For example, carboxyl groups in polyesters are usually titrated directly with a base in an alcoholic or phenolic solvent. Infrared spectroscopy is used when the polymer cannot be titrated due to insolubility in certain solvents. This technique is useful for NAVG MWs up to 50,000 daltons (with decreasing reliability as the NAVG is increased). 5.2. THE TWO PERCENT RULE AND CHEMICAL IDENTITY According to the polymer exemption rule at §723.250(d)(4), a polymer is not eligible for exemption if it contains at greater than two weight percent monomers and/or reactants that are not: included on the TSCA Inventory, manufactured under an applicable TSCA §5 exemption, excluded from exemption, or an non-isolated intermediate. Monomers and reactants at greater than two percent make up the "chemical identity" of the polymer. For an exempt polymer, monomers and reactants at less than or equal to two weight percent are not considered part of the "chemical identity" of the polymer; and the use of these monomers and reactants creates a different set of issues, which are discussed below. A manufacturer or importer must carefully decide at what weight percent level each monomer or other reactant is to be used in the preparation of the exempt polymer. This choice (which must be obvious from the manufacturing data kept by the manufacturer or importer) limits the manufacturer or importer of an exempt polymer in two major ways. First, if a certain monomer or reactant is used in an exempt polymer at less than or equal to two weight percent, the manufacturer may not later use that reactant at greater than two weight percent (under the exemption for the same polymer). The new polymer substance that results when the reactant is increased to greater than two weight percent is different, by definition, from the polymer that contains the reactant at less than or equal to two weight percent. Second, if a reactant or monomer is used at greater than two weight percent in an exempt polymer, the reactant or monomer must not be eliminated completely from the polymer (if the manufacturer is trying to satisfy the exemption for the same polymer). If either of these "identity-changing" events occur, the manufacturer must do one of the following: 1) find the new polymer identity on the TSCA Inventory, 2) submit a PMN at least 90 days prior to manufacture if the new polymer is not 18 5.2.2. PERCENT INCORPORATED METHOD In the percent incorporated method, as stated in the 1995 PMN rule amendments, "the weight percent is based on...the minimum weight of monomer or other reactant required in theory to account for the actual weight of monomer or other reactant molecule or fragments chemically incorporated (chemically combined) in the polymeric substance manufactured." Therefore, if a percent incorporated is to be calculated for a monomer or reactant, the degree of incorporation of the fragment resulting from the monomer or reactant must be measured. It is not always possible or feasible to determine analytically the degree of incorporation for every type of reactant, especially for random polymerizations where no repeating subunits exist and for polymerizations using chemical reactants where the structures are not completely specified (such a reactant as conjugated sunflower-oil fatty acids, for example). Complete or efficient incorporation cannot be assumed, even if the reaction equilibrium and kinetics predict a certain result. It is also necessary to identify a structural unit within the polymer that corresponds to the specific monomer from which it came. Often the same monomer unit may originate from more than one monomer. For example, empirically determining the exact chemical incorporation of oxirane, methyloxirane, ethylene diamine, and epichlorohydrin in a polymer would require a complicated study, perhaps using radioisotope-labeled reactants. If the percent incorporated cannot be deduced by measurement or reliably estimated, the manufacturer must use the percent charged method. In order to calculate a weight percent incorporated for a reactant, certain data must be known: the molecular weight of the reactant charged; the molecular weight of the fragment that is incorporated into the polymer (if the feedstock is not entirely incorporated); and the analytically determined amount of the incorporated reactant that is present in the polymer (the weight percent of the polymer that consists of the fragment). From these data the number of moles of fragment present in the polymer can be calculated, which is proportional to the amount of feedstock that reacted to form the polymer. The following ratio is useful: Equation 4: The weight percentage of reactant incorporated is calculated by converting moles of incorporated fragment per 100 g of polymer (Ratio A), to moles of reactant and then multiplying by the reactant molecular weight. (The specific units used are irrelevant; gram-moles per 100 grams or ton-moles per 100 tons are equally valid for the calculation.) This is accomplished by the following equation: Equation 5: Example 13: For an example of the calculation for the percent incorporated method consider the polymerization of ethylene glycol with a dialkyl terephthalate. It is known that both oxygen atoms of the glycol are incorporated into the resulting polyester while two alkoxy groups of the terephthalate ester are lost in the process. The following calculation determines the weight 21 percentage incorporated for dialkyl terephthalate: The polymer was empirically shown to contain 13.2 percent by weight of the terephthaloyl unit [-C(=O)-C6H4-C(=O)-], which has a MW of 132 daltons. Ratio A for terephthaloyl is calculated as follows: The weight percent of reactant incorporated is calculated as shown below. Each mole of parent dialkyl terephthalate ester would result in one mole of fragment, so the molar conversion factor is 1. If the dialkyl terephthalate charged is dimethyl terephthalate, the MW used for the calculation is 194 g/mole. Example 14: For a comparison to Example 13, consider if the dialkyl terephthalate charged were diethyl terephthalate. The MW for the diethyl terephthalate is 222 g/mole. The calculation would show a weight percent of reactant incorporated as 22.2 percent. This would mean that diethyl terephthalate would have to be charged to the reaction vessel at 22.2 percent for the terephthaloyl fragment to be incorporated into the polymer at 13.2 percent; whereas dimethyl terephthalate would have to be charged at only 19.4 percent to have the terephthaloyl fragment incorporated at 13.2 percent. These percentage values make sense because a larger alkoxy group is lost when the diethyl terephthalate is the source of the terephthaloyl group than when dimethyl terephthaloyl is the source of the terephthaloyl groups and the methoxy group is lost. Therefore, to provide the same fragment incorporated in the polymer, more weight of diethyl terephthalate would have to be charged in comparison to dimethyl terephthalate. Example 15: Neutralizers are often used in considerable excess over the amount actually incorporated into the polymer. If the amount of incorporation is two percent or less, neutralizer may be omitted from the identity of the polymer. A sample calculation of the "weight percent incorporated" for a neutralizing base is given below: A polymer containing free carboxylic acid functional groups was neutralized using a large excess of sodium hydroxide (NaOH; formula weight = 40); the total amount of base charged to the reactor was 10 percent. Analysis of the resulting polymer salt revealed that the polymer contained 0.92 weight percent of sodium (atomic weight = 23), coming only from the base. This amount of sodium corresponds to 0.04 moles of sodium per hundred grams of polymer, or 1.6 grams of NaOH per hundred grams of polymer -- that is, 1.6 weight percent NaOH incorporated, despite the large excess charged. Because the weight percent of NaOH is not greater than two percent, the polymer substance would not have to be described as the sodium salt. 22 If sodium bicarbonate (NaHCO3; formula weight = 86) had been the neutralizing agent, the same number of moles of sodium per hundred grams of polymer would have corresponded to 3.36 weight percent of NaHCO3. Because the weight percent of NaHCO3 is greater than two percent, the polymer substance must be described as the sodium salt. If a combination of bases is used for neutralization, the amounts incorporated should be prorated according to the mole ratios of the neutralizing agents charged if the reactivities are similar. Otherwise, assume the most reactive neutralizing agents is consumed first, etc. Example 16: For calculating the weight percent incorporated of an initiator, the computation will be similar to that for an excess neutralizing base. Initiator may be charged to the reaction vessel at a higher percentage than what is actually incorporated into the polymer. If the amount of incorporation is consistently below two percent, the initiator will not be in the chemical identity of an exempted polymer. (For polymers with PMNs and NOCs, the submitter has the option of leaving the initiator out of the identity, or including it.) In the case where initiator is not in the identity of the either an exempted polymer or in the identity of a polymer covered by a PMN and NOC, a change in initiator could be made without having to establish another polymer exemption or PMN for the change in the polymer manufacture, as long as the alternate initiator remained at or under two percent and in the case of the exemption, the initiator did not exclude the polymer in other ways. A sample calculation of the "weight percent incorporated" for an initiator is given below: A polyolefin with a NAVG MW of 9,000 daltons was produced using azobis[isobutyronitrile] (AIBN, MW = 164) charged at 3 percent. This class of initiator is known to produce radicals that contain the nitrile moiety (CN, FW = 26), which can be analytically determined. The polymer sample was found to contain 0.29 weight percent nitrile, which was assumed to originate only from AIBN. This 0.29 g of fragment in 100 g of polymer corresponds to 0.011 moles of fragment [(0.29 g / 26 g/mol) = 0.011 moles] in 100 g of polymer. Since every 1 mole of AIBN reactant produces 2 moles of fragment, a molar conversion factor of 1/2 is used to relate the amount of fragment present to the amount of reactant incorporated. The weight percent of reactant incorporated is calculated as follows: 23 Table 4 Allowable Thresholds for Reactive Functional Groups Moderate-Concern: The minimum permissible FGEW is 1,000 daltons. Acid halides Acid anhydrides Aldehydes Alkoxysilanes where alkyl is greater than C2 Allyl ethers Conjugated olefins Cyanates Epoxides Hemiacetals Hydroxymethylamides Imines Methylolamides Methylolamines Methylolureas Unsubstituted position ortho- or para- to phenolic hydroxyl High-Concern: The minimum permissible FGEW is 5,000 daltons.* Acrylates Alkoxysilanes where alkyl = methyl or ethyl Amines Aziridines Carbodiimides Halosilanes Hydrazines Isocyanates Isothiocyanates .alpha.-Lactones; .beta.-Lactones Methacrylates Vinyl sulfones * For polymers containing high-concern functional groups, the FGEWcombined must be greater than or equal to 5,000 daltons taking into account high-concern (e)(1)(ii)(c) and, if present, moderate-concern (e)(1)(ii)(b) functional groups. Unless a functional group equivalent weight can be determined empirically by recognized, scientific methodology (typically titration), a worst-case estimate must be made for the FGEW, in which all moderate- and high-concern functional moieties must be factored. A generalized approach for performing equivalent weight estimations with specific methods and examples is provided below. The following is limited guidance on how to calculate functional group equivalent weights. The methods discussed are end-group analysis (Section 5.3.1), calculation based on percent charged (Section 5.3.2.), and nomograph use (Section 5.3.3.). 5.3.1. END-GROUP ANALYSIS Most condensation polymers (polyesters, polyamides, etc.) contain reactive functional groups only at the chain ends, because all other reactive functionality in the monomers is consumed to produce the condensation polymer backbone in the final product. For this type of polymer, FGEW determination may be as simple as theoretical end group analysis and can be performed regardless of the reactive group type. For a linear polymer (two reactive groups per monomer) with either the nucleophilic or electrophilic reagents in excess, the FGEW is half the NAVG MW, as described. 26 EXAMPLE 17: A polyamide with a NAVG MW of 1000 daltons, made from excess ethylene diamine (two nucleophiles) and adipic acid (two electrophiles), would be anticipated to be amine-terminated at both ends, assuming a worst case scenario (the greatest content of reactive functional groups present). The amine equivalent weight would be 1/2 the NAVG molecular weight, or 500 daltons. For simple, branched condensation polymers (having only one monomer possessing more than 2 reactive sites), the FGEW must be calculated from the total number of end groups present in the polymer. This is calculated from an estimated degree of branching, which is derived by knowing the number of reactive groups in the polyfunctional monomer. If reasonable, it should be assumed that the monomer responsible for the branching will be incorporated in its entirety to form the polymer. The mathematics for estimating the FGEW for simple branched condensation polymers follows. The equivalent weight of the monomer is the molecular weight of the monomer divided by the weight percent charged to the reaction vessel. The monomer equivalent weight of 1000 daltons means that there is one mole of monomer for every 1000 daltons of polymer. Equation 6: The degree of branching is calculated by dividing the NAVG MW value by the monomer equivalent weight, multiplied by the number of reactive groups that are not used to make the polymer backbone, which is (NRG - 2). (The NRG value is the number of reactive groups originally in the monomer.) Equation 7: The total number of end-groups in the polymer is the degree of branching value plus two, where the two in this equation is the number of end-groups of the polymer backbone. Equation 8: The FGEW is then derived by simply dividing the NAVG MW by the number of end- groups in the polymer. Example 18: Consider the polymerization of pentaerythritol (PE, 4 reactive groups) with polypropylene glycol (PPG, 2 reactive groups) and an excess of isophorone diisocyanate (2 reactive groups). The polyfunctional feedstock (PE) is added to the reaction at 10 percent by weight to produce an isocyanate-terminated polymer having a NAVG molecular weight equal to 2720 daltons. The monomer 27 equivalent weight of pentaerythritol is 1360, obtained by dividing the monomer molecular weight by the weight percent charged (136 ÷ 0.10). PE has four reactive alcohol moieties, two are used to form the polymer backbone and the other two form branches. Following the equations given above, the degree of branching for this polymer example is [(2720 ÷ 1360) x (4 - 2)] = 4. The total number of end-groups is [4 + 2] = 6. Due to the excess of isophorone diisocyanate, we assume that each end-group is an isocyanate group. Finally, the FGEW can be calculated by simply dividing the NAVG MW by the total number of end groups theoretically present. Therefore, FGEW = (2720 ÷ 6) = 453 daltons. Figure 7 Isocyanate-Teriminated Urethane and Functional Group Equivalent Weight: HO OH HO OH O=C=N N=C=O HO[ CH3 O]x H + + O C N Chain-NCO OCN-Chain O[ CH3 O]x N N C O C O OCN-Chain O O OO N C O Chain-NCO OCN-Chain OCN-Chain O O OO For condensation polymers derived from a more complex mixture of feedstocks, computer programs that simplify the complicated FGEW calculations may be used. (There are a few commercial programs which perform a "Monte Carlo" simulation of a random condensation polymerization that directly estimates the NAVG MW and FGEW from the types of data described earlier.) Analytical data should be used periodically to confirm computer estimates and verify eligibility. 5.3.2. MORE COMPLEX FGEW CALCULATIONS Some condensation and addition reactions create polymers where not all reactive functional groups along the backbone of the polymer are consumed during the reaction, so a simple end-group analysis will not suffice for determining an accurate FGEW. In many of these cases the equations in this section may be used to estimate FGEWs. These equations aid in calculating FGEWs for elements (for example, basic nitrogen), for reactive groups that are unchanged under the reaction conditions and for multiple types of functional groups that remain in the polymer molecule. Equation 9 can be used for any reactive functional group in a polymer. This may even be an atom, such as basic nitrogen, as in an example that follows. In the equation, ’FWG’ is the formula weight of the group; and ’W%G’ is the weight percent of the group: 28 With a FGEWcombined of 2,792 daltons, this polymer would be eligible for exemption because the FGEW combined is greater than the required 1,000 minimum permissible equivalent weight (threshold level). Although there are two reactive functional groups from the moderate-concern list, there are no high- concern groups present. However, note that if instead of epichlorohydrin, 1 percent of acryloyl chloride (high-concern reactant with a molecular weight 90.5) had been used, the same type of calculation would produce a polymer that is excluded from the exemption. In this further example, groups from (e)(1)(ii)(B) and (e)(1)(ii)(C) are both present and give a FGEW combined of 2,774 daltons. The threshold of 5,000 is daltons is not satisfied. Example 22: Similar calculations may be done for addition reaction polymers. Consider a radical polymerization of acrylates, which react via the alkene leaving reactive functionality in the molecule. In this case it would be reasonable to assume that each monomer charged to the reaction vessel will be incorporated in its entirety to form polymer. Assume that polyacrylate was produced from 10 percent glycidyl methacylate (MW = 142), two percent hydroxymethyl acrylamide (MW = 101) and 88 percent acrylic acid. (See Figure 9). The reactive functional groups of concern are the epoxide (1,000 dalton threshold) from glycidyl methacrylate and the hydroxymethyl amide from the acrylamide (1,000 dalton threshold). The carboxylic acid moiety from acrylic acid may be used without limit. (See the rule, section (e)(1)(A); and also the tables in this manual.) Using Equation 11, one can calculate the FGEW for the epoxide to be 1,420 daltons (142 / 0.10), and the FGEW for hydroxymethyl amide to be 5,050 daltons (101 / 0.02). (If either of these monomers had been used separately in the stated proportions, the polymer FGEW eligibility restrictions would have been met.) The FGEWcombined for the polymer calculated using Equation 12 is 1,108 daltons ( 1 / [(1/1420) + (1/5050)] ). This polymer would be eligible for the exemption because the 1,000 dalton threshold for two or more moderate- concern reactants was met. Because 1,108 daltons is fairly close to the 1,000 dalton threshold, the manufacturer will not have a lot of flexibility to increase the epoxide or amide in future batches. Also, each batch must meet the exemption. If it is anticipated that some batches will not qualify for the exemption, the manufacturer or importer must file a regular PMN 90 days prior to the manufacture of the commercial product, to cover those particular production runs. 31 Figure 9 Acrylate with Multiple Functional Groups: HO O HN O OH O O O CH3 + + 10% Charged 2% Charged 88% Charged O O O CH3 [CH2 C] CH][CH2 OH O HN CH][CH2 O HO ChainChain In some addition reactions the reactive groups that effect the desired polymerization reaction are consumed and in others they are not. Examples 23 and 24 contrast these two types. Example 23: An example of an addition reaction that consumes the reactive functional groups is the addition of an amine to an isocyanate molecule. The reactive amine adds to the isocyanate to produce a "urea" polymeric backbone which is unreactive. Typically, an end-group analysis would be used to determine if the FGEW falls within the allowable limits for the exemption. Example 24: An addition reaction where the reactive group involved in the polymerization is not consumed (is still considered reactive) involves a more complicated calculation of FGEW. Figure 10 Unconsumed Amines and Combined Functional Group Equivalent Weight: 70% Charged30% Charged O OH O H [N N O OHOHH N]xNHH H + O OO H2N NH2 Consider the reaction between ethanediamine (MW = 60) charged at 30 percent, and diglycidyl ether (MW = 130) charged at 70 percent. In the reaction, amine nitrogens react with the epoxides. This results in consumption of the epoxide to form an aliphatic alcohol, which is on the low-concern list and may be present in any quantity. The amine functionality remains intact and the FGEW 32 for the amine is proportional to the amount of feedstock containing the amine charged to the reaction vessel. The FGEW for the amines in this type of reaction is estimated using Equation 11, the molecular weight of the feedstock (60), the percent of the monomer charged to the reaction vessel (30), and the number of reactive functional groups in the feedstock (2): The minimum permissible equivalent weight for amines is 5,000 daltons. Because adding more groups to the FGEWcombined calculation can only lower the value, no further calculation would be necessary since the polymer would not be eligible by amine content alone. This is demonstrated by factoring in the epoxide contribution. The polymer would likely be epoxide-terminated because of the excess molar amount of glycidyl ether charged. If this polymer had a NAVG MW = 5,000 daltons, the epoxide FGEW would be 2,500 daltons by end group analysis, assuming linear polymerization. The epoxide-terminated polymer containing reactive amines would have a FGEWcombined equal to 96 daltons [1 ÷ [(1/100) + (1/2500)]]. In some addition polymer processes one reactant (or group of reactants) is used in large excess compared to the other reactants. The reporting of residual amounts of monomers or other reactants is not required under the new rule. (The amount of reactant that does not form polymer is not regulated by the new polymer exemption rule, since these residual, unreacted materials must be on the TSCA inventory and are covered by different Agency authority, as existing chemicals.) For polymers made under these conditions, a simple repeating unit of known molecular weight can be assumed. The FGEW can be calculated by dividing the unit molecular weight by the number of groups in the unit. Example 25: A polyamine was made from the addition of 70 weight percent 1,2- benzenediamine (MW = 108) to 30 weight percent of diglycidyl ether (MW = 130). The diamine:diepoxide ratio equals about 3:1, as charged to the reaction vessel. A linear polymer of a 1:1 adduct (MW = 238) is the most likely Figure 11 Repeating Units, A Polyamine and Functional Group Equivalent Weight: NH2 NH2 O OO + H OH OH ON [NChain H ] Chain 3:1 Mole Ratio 1:1 Linear Adduct representative repeating unit. The amine FGEW would be 119 daltons (the repeating unit MW of 238 daltons divided by two, the number of reactive amines in the repeating unit). The FGEW will not change regardless of the number of repeating units in the polymer or the amount of excess diamine monomer. 33 7. COMMON QUESTIONS AND ANSWERS POLYMER DEFINITION: 1. In determining whether a polymer is on the Inventory, does the "new" polymer definition under the polymer exemption apply? For example, if I manufacture a substance of the type R(OCH2CH2)nOSO3Na where n = an average of 7, will I have to submit a PMN even though >3 units of consecutive monomer are present? The Inventory currently considers all the ethoxylates with >3 units as polymeric, and therefore as the same substance. What if n = exactly 7? Exactly 15? The alkyl ethoxylate sulfates with definite numbers of repeating units that you describe would not meet the polymer definition, because they would consist of molecules of a single molecular weight. Chemical Abstracts nomenclature rules and the TSCA Inventory nevertheless does treat some of these as though they were polymers. For example, "laureth sulfate", which corresponds to the formula above where R = C12H25 and n = x, is on the Inventory (CASRN 9004-82-4). Variations in the number of ethylene oxide units, as long as n is either >10 or variable or represents an average value, will not produce a new (that is, non-Inventory) substance. Thus laureth sulfate with n averaging 7 is considered an existing substance, as is laureth sulfate with n = exactly 15. However, the case where n = exactly 7 is considered a discrete chemical substance, not a polymer, and would not be considered the same. It would have a different name and CASRN, and would be a new chemical if it is not already on the Inventory elsewhere. This has always been true, and is unchanged by the polymer exemption. The "new" polymer definition does not affect the Inventory status of existing polymers or of new polymers submitted under the PMN rule. The polymer definition, which applies only to polymers manufactured under the polymer exemption, therefore does not have the effect of creating a set of "no longer polymers". 2. Would the following example count as a "polymer molecule?" (The longest straight chain is 1+1+2=3+1.) H(oxypropylene)-O-sorbitol-O-(propyleneoxy)2-H No. Sorbitol cannot be a repeating unit under the conditions of the relevant polymerization reaction (propoxylation), so it is considered an "other reactant". Therefore the longest sequence of monomer units (considered as derived from propylene oxide) is two. A continuous string of at least three monomer units is required, plus one additional monomer unit or other reactant. 3. How do you apply the molecular weight distribution requirement of the polymer definition (i.e., <50 percent of any one MW) to highly cross- linked polymers of essentially infinite MW? For polymers of "essentially infinite" MW, unless the entire mass of polymer produced were in one continuous phase, the actual molecular weight would be limited by the size of the individual droplets, beads, pellets, flakes, etc. No two of these would be likely to have exactly the same mass, and the distribution criterion would be met. For that matter, the molecular weight determination itself would produce a range of values because of the finite precision of the instrument. ELEMENTAL EXCLUSIONS: 4. Regarding elemental limitations, why was fluorine not included in 723.250(d)(2)(B) but included in ii(C)? 36 Fluoride ion (F-) has a high acute toxicity, and would therefore be unacceptable as a counterion in a substance that is supposed to present no unreasonable risk to human health. Fluorine covalently bound to carbon is either unreactive and thus not available in the form of F-, or is part of a reactive functional group such as acyl fluoride (COF) and subject to the reactive functional group criteria. 5. Can you give an example of F- (anion) that is not allowed? Consider a cationic ion exchange resin that would otherwise have been eligible (because it meets the criterion of insolubility). If the counterion is fluoride (F-), it will be ineligible. 6. Ammonium is not listed as an acceptable monatomic counterion. Does this mean a polymer may be made under the exemption, but not its ammonium salt? No; Ammonium may be used as a counterion. It is not monatomic, and is not excluded under section (d)(2)(ii). 7. Are only monatomic counterions allowed? What about CO3 2-, HCO3 -, NO3 -, etc.? Monatomic counterions are allowed only if they are on a list of specifically allowed ones. All other monatomic counterions are excluded. The polymer exemption says nothing whatsoever about polyatomic counterions as such; they are permitted if they do not otherwise render the polymer ineligible. Carbonate (CO3 2-) is allowed, for example; perchlorate (ClO4 -) is not, because the chlorine is neither a monatomic ion nor is it covalently bound to carbon; trichloroacetate (CCl3CO2 -) is allowed. 8. Are monomers that have CF2 or CF3 groups allowed? Monomers that contain CF2 or CF3 groups are acceptable, provided that the groups are not part of a reactive functional group. -CF2- is not generally a monomer unit because it is not "the reacted form of the monomer in the polymer"; however, -CF2CF2- groups derived from the polymerization of tetrafluoroethylene certainly could be monomer units. EXCLUSION FOR DEGRADABLE POLYMERS: 9. What is the time frame for "polymers that do not degrade, decompose or depolymerize?" Does EPA want us to synthesize polymers that bioaccumulate in the environment? Does the term "degrade" apply to biodegradation or other degradation in waste treatment systems? This restriction is essentially unchanged from the 1984 polymer exemption. While EPA recognizes in principle the beneficial effects of biodegradability, it commented in the discussion section of that rule that the Agency "...has little experience reviewing the mechanism by which breakdown may occur, the decomposition products that may result, and the potential uses of such polymers. ... Because of the complexity of review necessary for many of these polymers and the lack of EPA review experience, the Agency did not believe that an expedited review period was sufficient to adequately characterize risk." The Agency acknowledged in that discussion that essentially all polymers degrade or decompose to a limited degree over time. It gave as examples the normal fate of polymers in landfills and the weathering of paint, and specifically stated that the exclusion was not intended to address such degradation. Substantial biodegradation in a waste treatment system would render a polymer ineligible for the exemption. 37 10. How does EPA define "degrade," "decompose," and "depolymerize?" If these are by-product minor reactions of a polymer, can the polymer still be eligible for the exemption, assuming other criteria are met? The definitions are provided at §723.250(d)(3), and read: "For the purposes of this section, degradation, decomposition, or depolymerization mean those types of chemical change that convert a polymeric substance into simpler, smaller substances, through processes including but not limited to oxidation, hydrolysis, attack by solvents, heat, light, or microbial action." Minor byproduct degradative reactions will not exclude a polymer from the exemption; see the answer to the previous question, for example. 11. Starch is a polymer that readily degrades in the environment. If it were not listed on the TSCA Inventory, would starch be eligible for the exemption? No; polymers that readily degrade are excluded from the exemption. 12. What does the Agency mean by "substantially" in the phrase "substantially degrade..."? Does this refer to any specific conditions (e.g., sunlight, water, low pressure) or under normal environmental conditions? By "substantially," the Agency means considerably; meaningfully; to a significantly large extent. The restriction refers to polymers that undergo considerable degradation, under normally anticipated conditions of use or disposal, and in a reasonable length of time. 13. Will a polymer that is designed to be pyrolyzed or burned when it functions as intended be excluded from the exemption by the "degrade, decompose or depolymerize" conditions? Yes, if that is the normal way it is used. A polymer propellant or explosive would be excluded. However, a plastic used for (say) garbage bags would not be excluded merely because it might under some circumstances be incinerated. 14. A manufacturer produces a polymer that is otherwise eligible for the exemption. It is readily biodegradable by the OECD test. There are two uses for the product. In one use, the manufacturer can reasonably anticipate that the polymer will eventually find itself in aqueous systems where it may degrade. In the second use, the polymer will be formulated into articles at a low percentage such that the articles themselves would not be anticipated to degrade once they are disposed of in a landfill. Provided that the manufacturer could control customer sales to assure that the polymer would only be used in the second use, could the polymer exemption apply? Yes; provided that the use is restricted to conditions under which the polymer would not be expected to degrade, decompose or depolymerize, it would not be excluded from the exemption. 15. Will EPA specify testing conditions for evaluating "degradation"? Will manufacturers using the exemption have to test to prove their polymers don’t degrade? Can we rely on intent to degrade? This guidance document does not specify test conditions for degradability; there is no testing requirement to establish nondegradability; and, as the rule says in section (d)(3), polymers are excluded "...that could substantially decompose after manufacture and use, even though they are not actually intended to do so." In other words, it is what can actually be expected to happen to the substance, rather than just the intent of the manufacturer, that determines whether this criterion is met. 16. Are Diels-Alder polymers (for example, dicyclopentadiene polymers) considered degradable? 38 polymers. Whatever standard is used, however, should be applied to the commercial material as manufactured and sold. If an aqueous emulsion is the commercial form of the substance, the solubility criterion should be applied to that, rather than to a dried film of the final, end-use product. (An aqueous emulsion is a water-dispersed material, and a substance in that form would be considered to be soluble or dispersible; it therefore would not qualify.) REACTIVE FUNCTIONAL GROUPS: 25. Please confirm that amine salts are permitted, as well as confirming that sulfonic and sulfuric acids (-SO3H and -OSO3H) and their salts are considered non-reactive. Amine counterions are permitted for anionic polymers. Sulfonate salts are not considered reactive. However, sulfonic and sulfuric acids are considered reactive (they were specifically designated as such in the 1984 polymer exemption rule, and the interpretation has not been changed in the new rule). 26. Regarding (e)(1) criteria, what are a few examples of "high concern" and "low concern" functional groups. Would acrylate, epoxide or isocyanate groups be considered "high" or "low" concern? Epoxides are listed in (e)(1)(ii)(B), the list of "moderate concern" groups for which concerns exist at a functional group equivalent weight of 1,000 or less. Acrylate and isocyanate are not listed either in (e)(1)(ii)(B) or in (e)(1)(ii)(A), the "low concern" group list; they are therefore considered "high concern" groups and fall under (e)(1)(ii)(C), for which the functional group equivalent weight concern level is 5,000 or less. Sections (e)(1)(ii)(A) and (B) contain lists of all the "low concern" and "moderate concern" groups, respectively. Any reactive group not on either list is considered to be "high concern." 27. The nitro group does not appear on the low- or moderate- concern list of reactive functional groups. Does this mean that nitro would fall into the high-concern category by default? This is counter-intuitive, because I wouldn’t consider the nitro group to be very reactive and of much concern. Numerous groups were not listed because they were not considered to be reactive functional groups (for example, ester and ether groups). Nitro groups are also not considered to be reactive functional groups, unless they are specially activated (certain aromatic nitro groups are readily displaced by nucleophilic substitution reactions). 28. Is the amine group considered a high-concern reactive functional group? It is not listed specifically at either 40 CFR §723.250(e)(ii)(A) or (B), which would by default place it in category (C). However, because the criteria for a substance that "may become cationic in the environment" appears to address the concerns that EPA would have for amine groups in limiting the amount of amine in a polymer to one in 5,000 daltons, it does not seem that the amine group, in and of itself, should be regarded as a reactive functional group. Would the amine group be used in the calculation for FGEWcombined? The amine group is considered a high-concern reactive functional group and therefore should be used in the calculation. It is reactive in undergoing condensation reactions to form polyamides and polyimides and, unlike the aliphatic hydroxyl group, was not identified as a low-concern functional (category (A)) group. The Agency has concern for this group as a reactive functional group unrelated to considerations of its aquatic toxicity. For polymers that are not water-soluble or -dispersible and that will be used only in the solid phase, the limitation on cationic functional groups (such as quaternary ammonium) would not apply; but the limit on amine groups as reactive groups would still apply. 41 29. Regarding FGEW of high concern groups vs. low concern groups, does one need to combine all high concern groups and separately combine all low concern groups - or add both together? If any "high concern" (that is, (e)(1)(ii)(C)) groups are present, one needs to calculate the combined functional group equivalent weight of any "moderate concern" (that is, (e)(1)(ii)(B)) and "high concern" groups together. To meet the criterion, the resulting FGEW must be no less than 5,000. "Low concern" (that is, (e)(1)(ii)(A)) groups are not included in the computation. 30. If a polymer with a number-average molecular weight >10,000 meets the reactive functional group and oligomer content criteria of (e)(1), but not the more stringent oligomer content criterion of (e)(2), it seems to fall into a gap between (e)(1) and (e)(2). Is it therefore not eligible for the exemption? If is isn’t, does the Agency plan to amend the (e)(1) criterion to omit the phrase "and less than 10,000 daltons"? The (e)(1) and (e)(2) exemptions are indeed mutually exclusive. Polymers with molecular weight of more than 10,000 are eligible only for the (e)(2) exemption, which has lower allowable concentrations of oligomer than does (e)(1). A polymer like the one described would not be eligible for either the (e)(1) or (e)(2) exemption. The Agency received no comment on this issue from the time the rule was proposed on February 8, 1993 until after the final rule became effective on May 30, 1995. A modification of the criteria seems reasonable, but additional rulemaking rather than a simple correction would be required. The issue is under discussion, and Agency resource constraints may rule out near-term action. THE TWO PERCENT RULE (AND NON-INVENTORY REACTANTS): 31. Please explain the changes in the "Two Percent Rule" for polymers. The "Two Percent Rule," which has been in effect since 1977, allows manufacturers and importers of polymers to add monomers or other reactants to an Inventory-listed polymer at levels of two percent or less (based on the dry weight of the manufactured polymer) without making a polymer with a different chemical identity than the Inventory-listed polymer. It also serves as a basis for determining the identity of a polymer. Before May 30, 1995, the effective date of the PMN Rule amendments, the monomer content of a polymer was always calculated based on the weight percentage of monomer or other reactant "charged" to the reaction vessel. The 1995 amendments allow persons greater flexibility in determining the percentage composition and whether monomers and other reactants are present at more than two percent. In addition to being able to use the "charged" method, the 1995 amendments allow persons to use an alternative method, i.e., to determine the amount of monomer or other reactant that is present "in chemically combined form" (incorporated) in a polymer and to report the minimum weight percent of that monomer or reactant that is needed in theory to account for the amount incorporated. A manufacturer is free to use either method to determine a two percent level; however the "incorporated" method, while providing more flexibility, also requires supporting analytical data or theoretical calculations. This change in the "Two Percent Rule" applies to all polymers under TSCA, including Inventory listings, PMN submissions, and polymer exemptions. 32. If I use the "chemically combined" method and claim that two percent or less of a reactant is incorporated in my polymer even though I charge a higher level to the reaction vessel, what records am I required to maintain to support this claim? Your records must contain analytical data or appropriate theoretical calculations, if such an analysis is not feasible, to demonstrate that the minimum weight of monomer/reactant required to account for the monomer/reactant fragments chemically incorporated is two percent or less. Your records should take into account potential batch-to-batch variation. 42 33. It appears from the polymer exemption rule and the technical guidance manual that a person does not have the option of including a reactant/monomer at less than or equal to two percent in the polymer identity. Is this true? Yes, this statement is true. Polymers covered by a polymer exemption do not have a formal name. The "identity" is established by the percentages of monomers/reactants charged or incorporated in the polymer, as cited in the exemption-holder’s records. If a polymer has less than or equal to two percent of a monomer/reactant, the identity does not contain that monomer/reactant. If an otherwise identical polymer is made, and the same monomer/reactant is a greater than two percent, the identity of the second polymer is different from the first. Two exemptions would have to be claimed to cover both polymers. For polymers for which a PMN is submitted, the submitter does have the option of including a reactant/monomer at less than or equal to two percent in the polymer identity. 34. Does a manufacturer need to test every batch of polymer to prove that less than two percent is incorporated, or would one documented test on a typical batch be sufficient? A company is not required to test every batch but is required to maintain in its records analytical data or theoretical calculations to demonstrate compliance with the "Two Percent Rule" when using the "incorporated" method. If the amount normally incorporated is expected to be close enough to two percent that occasional batches might exceed that level, either more frequent testing, or always considering the reactant to be part of the chemical identity, or manufacturing a separate exempt polymer with the reactant present at greater than two percent and included in the polymer identity, might be appropriate. 35. I use a prepolymer that is on the Inventory to make my polymer. The prepolymer contains a non-Inventory monomer, and the final polymer contains greater than two percent of that monomer. Will my polymer be ineligible for the exemption? Not on the basis of the non-Inventory monomer; §(d)(4) bars the use of "monomers and/or other reactants... that are not already included on the TSCA Chemical Substance Inventory...", but the prepolymer is a reactant that is on the Inventory. The identity of the final polymer will probably include the non-Inventory monomer, though; see the answers to related questions in the section on Inventory Status of Reactants (questions 45-49). 36. If an initiator is incorporated at no more than two percent, does it have to be on the TSCA Inventory? An initiator or other reactant present at no more than two percent does not have to be on the Inventory for a polymer to be eligible for the exemption. However, if the reactant is not on the Inventory, it cannot be used for commercial manufacture in the United States. Consequently, this provision will for all practical purposes be applicable only to imported polymers. 37. Can I use less than or equal to two percent of any monomer that is on the Inventory? Yes, as long as that monomer doesn’t introduce elements, groups or properties that would render the polymer ineligible at the concentration of monomer used. Note, though, that for the (e)(3) "polyester" exemption, all components of the polymer must be on the list of allowable reactants. In this case the use of non-listed monomers, even at two percent or less, would render the polymer ineligible for the (e)(3) exemption. 38. I wish to import a substance containing greater than two percent of a reactant not on the public TSCA inventory, but which may be on the 43 but rather according to the structural repeating unit (SRU) and end groups present: α-Hydro-ω-hydroxy-poly(oxy-1,2-ethanediyl). Similarly, polydimethylsiloxane is named on the basis of its SRU: di-Me Siloxanes and Silicones (and is considered to be end-capped with trimethylsilyl groups). If a prepolymer is named so as to represent a certain structural feature or definite repeating unit, its name cannot be decomposed into ultimate monomers for the purpose of naming the final polymer. The Agency’s conventions for representation of polymeric substances are discussed in greater detail in a 1995 paper, "Toxic Substances Control Act Inventory Representation for Polymeric Substances," available from the TSCA Hotline: phone (202) 554-1404; fax (202) 554-5603. 48. Does the "Two Percent Rule" apply to the actual reactants used, or to the ultimate or putative reactants? Consistent with the answer above, the ultimate reactants should be the basis of the chemical identity of the polymer. Thus, if a new polymer is made from the polymer in the answer above, plus additional dimethyl terephthalate and ethylene glycol, the final polymer name would be based on three constituents, and the total amount of dimethyl terephthalate would be the sum of the separate contributions. Ultimate reactants that contribute no more than two percent by weight to the final polymer may be omitted from the identity. If a homopolymer is used as a prepolymer constituent, the identity of the derived polymer should be based on the ultimate monomer, except where CA practice differs due to the applicability of SRU nomenclature (see the paper referenced in the answer to the previous question). Although calculation of the percentage composition of a polymer may be based on analysis (that is, "incorporated"), the identity should be based on the ultimate precursors. 49. In light of the modified "Two Percent Rule," which now allows reporting of polymers as incorporated as well as charged, can all polymer listings on the Inventory now be read either as incorporated or as charged? Yes; polymers on the Inventory can be interpreted either as incorporated or as charged. Remember that "incorporated" means the minimum amount that theory requires to be charged in order to account for the amount monomer or reactant molecules or fragments found in the polymer itself. 50. If I import a polymer that is described as a sodium salt and I can determine analytically that sodium is present at two percent or less, can I assume that sodium hydroxide was the neutralizing agent used to produce that material, and should I use the sodium hydroxide molecular weight in determining the percent incorporated (and hence the chemical identity)? Yes; in the absence of information about the source of the sodium ion, sodium hydroxide should be used as the default source and the calculations should be based on the molecular weight of sodium hydroxide. The hydroxides of magnesium, aluminum, potassium and calcium should also be used as the default sources of the respective ions. POLYESTER CRITERION: 51. Some of the reactants on the polyester list are not on the TSCA Inventory. Am I allowed to use these to manufacture a polyester under the polymer exemption? Yes, for imported polymers. Under the 1984 exemption those reactants were placed on the polyester ingredients list, even though they were not on the Inventory, because there was no exclusion for non-Inventory reactants. The Agency is continuing to allow these specific reactants , because the Agency has already made the determination that no unreasonable risk will be incurred by a polymer that contains residual amounts of these reactants. For domestic manufacture, you may use only substances that are on the Inventory or are otherwise exempt or excluded from reporting. 46 52. If a monomer in my polyester is used at less than or equal to two percent and is not on the (e)(3) list, is the polymer eligible for the exemption if it meets all the other criteria and is not otherwise excluded from the (e)(3) exemption? No, the polyester would not be eligible for the exemption. Only monomers and reactants on the (e)(3) list may be used for this category of polymer regardless of the percentage charged or incorporated. 53. Is there to be a mechanism to add new reactants to the polyester reactants list? If so, what is expected to be required? The list of permissible ingredients in the present exemption has already been enlarged since the 1984 version. To quote from the Agency’s response to a comment addressing this specific issue in the preamble to the final rule, "The Agency believes that it would be appropriate in the future to propose amendments to this section to allow expansion of the list of eligible precursors, when additional candidates have been identified. To support requests for additional reactants, petitioners should provide health and environmental effects information on the candidate reactants, which must be already on the Inventory." No specific mechanism has yet been put in place. The Agency would prefer not to deal with such reactants piecemeal, but rather as part of a systematic process, perhaps initiated by trade organizations or consortia of interested companies. OTHER ISSUES: 54. If a polymer contains a gel fraction (presumably high MW>10,000) of 10 to 20 percent and the MW of the soluble fraction is <10,000, is it no longer exempt? Or is the gel fraction an impurity? Or by-product? Since the two polymeric fractions have the same chemical identity and are not separately prepared, they would usually be considered as a single substance, for which one (not two) number-average molecular weight would be measured. However, impurities are not considered part of a polymer composition; if the 10-20 percent gel portion is undesirable, it may be considered an impurity. In that case, the appropriate number-average molecular weight would be for the portion below 10,000, and the polymer would have to meet the (e)(1) criteria. Whether the gel portion is considered an impurity does not depend upon whether it is a minor component; it depends upon whether it is not intended to be present. 55. Are inventory-listed monomers which have allowed groups, and a 5(e) order attached, eligible for the new polymer exemption? Yes, as long as the use of the monomer is in accordance with the conditions of the 5(e) order. 56. There is no guidance on measurement of oligomer content. Is accumulated weight fraction on a GPC trace an adequate determination? In the absence of GPC, how can this be done? Cumulative weight fraction is a commonly accepted method. The Agency has not prescribed any analytical methodology; others may be acceptable, depending on circumstances. 57. Do polymers made by "reactive processing" of two or more other polymers (both on TSCA) fall under the polymer exemption? If not otherwise excluded, yes, as long as they meet the necessary criteria. There is no exclusion for polymers made from other polymers, nor is there any restriction on method of preparation. 58. What are the analytical requirements with respect to insoluble polymers? Can inference from melt flow data and comparison to other polymers be 47 adequate? Can I use Monte Carlo simulation methods (such as Oligo 5) to estimate the MW of an insoluble polymer theoretically? The Agency does not require any specific analytical methodology. Inference from physical behavior, from comparison to close analogues, and from theoretical calculation is acceptable where appropriate or where other methods are inapplicable. Monte Carlo methods, while widely used, have not been subjected to much experimental verification; if your polymer is expected to have values of MW or oligomer content near the allowable thresholds, you should probably not rely too strongly on such methods. For a discussion of analytical methods in general, see the relevant section of this guidance manual. 59. For persons who choose to use the "chemically combined" method for determining the amount incorporated in a manufactured polymer, does EPA prescribe a specific analytical method for this determination? No. The rule does not specify any particular method. Guidance on this issue is found in this guidance manual. 60. If you make a new polymer in the laboratory which meets the exemption rule, do you need to send a research and development letter to the customer? Substances considered to be research and development (R&D) chemicals are subject to the Research and Development Exemption, and must follow the conditions of that exemption. Polymers should be handled according to the R&D requirements until they reach the stage of being commercial products eligible for the polymer exemption. When the commercial activity is no longer R&D, provisions of that exemption no longer apply. 48