Stereochemical Effects on Polymethylmethacrylate: Temperature's Impact on Polymerization -, Lab Reports of Chemistry

Download Stereochemical Effects on Polymethylmethacrylate: Temperature's Impact on Polymerization - and more Lab Reports Chemistry in PDF only on Docsity! Stereochemical Effects on the Physical Properties of Polymethylmethacrylate Each lab section will polymerize methyl methacrylate at five different temperatures and compare the results. The tacticity of the polymers will change as a result of the reaction temperature and you will compare the effects of this on molecular weight and glass transition temperatures. Depending on the number of students in the lab section, you may team up with another student to perform a polymerization at a temperature as determined by the TA. Polymerizations will be performed at 138, 110, 85, 25, and 5 oC. In some cases more than one person or team may perform the polymerization at the same temperature. If so, that data should be included as separate data except for the 1H NMR where a small amount of polymer from both groups will be combined for the NMR analysis due to time constraints. Polymerization at 138 oC Combine 100 mg of 2,2-azobisisobutyronitrile (AIBN), 5 ml of xylene and 5 ml of freshly distilled methyl methacrylate into a 25 ml round-bottomed flask. Add a stir bar and assemble a reflux apparatus fitted with a drying tube. Reflux for 2 hours 45 minutes and allow the solution to cool to room temperature. Continue with the precipitation from cold methanol according to the workup procedures. Polymerization at 110 oC Combine 100 mg of 2,2-azobisisobutyronitrile (AIBN), 5 ml of toluene and 5 ml of freshly distilled methyl methacrylate into a 25 ml round-bottomed flask. Add a stir bar and assemble a reflux apparatus fitted with a drying tube. Reflux for 2 hours 45 minutes and allow the solution to cool to room temperature. Continue with the precipitation from cold methanol according to the workup procedures. Polymerization at 85 oC Combine 100 mg of 2,2-azobisisobutyronitrile (AIBN), 5 ml of toluene and 5 ml of freshly distilled methyl methacrylate into a 25 ml round-bottomed flask. Add a stir bar and assemble a reflux apparatus fitted with a drying tube. Heat the reaction mixture to 85 oC with a water bath for 2 hours 45 minutes; use a Pyrex crystallization dish for the water bath. Keep some ice nearby in case you need to cool the water bath until the temperature stabilizes. Once the reaction is complete allow the solution to cool to room temperature. Continue with the precipitation from cold methanol according to the workup procedures. Polymerization at 25 oC Combine 100 mg of 2,2-azobisisobutyronitrile (AIBN), 5 ml of toluene and 5 ml of freshly distilled methyl methacrylate into the reaction tube. Add a stir bar and fit the tube with a rubber septum and needle leading to a drying tube. Wipe the tube clean of any fingerprints and carefully place it into the Rayonet photochemical apparatus taking care not to touch the lamps. Wrap some aluminum foil around the rubber septum and turn on the cooling fan. Adjust the air outlet so that the stir bar is activated and then turn on the UV lamps. CAUTION – Do not stare at the lamps when lit as the UV-light can damage your retina. Place a cardboard protector around the opening of the Rayonet apparatus. Irradiate the solution at 350 nm for 2 hours 45 minutes and then turn off the lamps, fan, and air outlet. Continue with the precipitation from cold methanol according to the workup procedures. Rinse the reaction tube with fresh toluene to clean it for the next class. Polymerization at 5 oC Combine 100 mg of 2,2-azobisisobutyronitrile (AIBN), 5 ml of toluene and 5 ml of freshly distilled methyl methacrylate into the reaction tube. Add a stir bar and fit the tube with a rubber septum and needle leading to a drying tube. Wipe the tube clean of any fingerprints and carefully clamp it into the immersion tube apparatus. Wrap some aluminum foil around the rubber septum and turn on the circulating bath and add water to the immersion reservoir until it is 2/3 full. Clamp the medium-pressure mercury lamp so that it is about 2 cm from the immersion apparatus and the lamp is directed at the reaction tube. After the reservoir has reached the desired temperature, then turn the lamp on and place the cardboard protectors around the apparatus. CAUTION – Do not stare at the lamp when lit as the UV-light can damage your retina. Irradiate overnight and label a flask or vial so that the TA can transfer your solution the next day. Proceed to the workup procedure in week 2. Workup Procedures Add the reaction mixture slowly via a disposable pipette to a vigorously stirred solution of 100 ml methanol, which is cooled in an ice bath. Note: you should start cooling the methanol about 20-30 minutes before the polymerization is complete. Allow the solution to stir for 10 minutes and then perform a vacuum filtration with a Buchner funnel; use a Hirsch funnel if you have only a small amount of precipitate. Rinse the PMMA with fresh methanol. Once the solution has been filtered, discard the filtrate and suck air through the funnel for up to 20 minutes to ensure evaporation of the methanol from the precipitate. Place the PMMA on a watch glass or in a beaker and allow it to dry until next week. Collect the white powder, weigh it and transfer to a labeled vial. NMR Sample preparation Add several grains of PMMA to an NMR tube and fill it ¼ full with CDCl3. Place a plastic cap on the tube and write your initials on the cap with a Sharpie pen. The NMR director, Dr. Bill Stevens, will take you down to the NMR facility in small groups and assist you in collecting a 1H spectrum. Save your spectrum with the following file name: PMMA5CSec1 to signify that 5 oC was the reaction temperature and this was section 1; modify this name for your temperature and section (e.g. Sec 2 at 85 oC would be PMMA85CSec2). The TA’s will transfer your data so that