Bulk Polymerization of Styrene
Bulk polymerization of styrene will be conducted with different initial initiator concentrations. The polymers will be analyzed for their MW and PDI by size exclusion chromatography (SEC) using a calibration curve. The MW dependence on conversion will be investigated. The effect of the initiator concentration on polymer MW will be examined.
Materials.
Azobisisobutyronitrile (AIBN) and toluene (HPLC) were purchased from Sigma-Aldrich and used as received. Styrene (Sigma-Aldrich) was purified by passing through a silica column to remove inhibitors. CDCl3 was purchased from Cambridge Isotope and was used as received.
Methods.
Reaction procedure. To a vial charged with freshly purified styrene (10 g) was AIBN (0.7g, 0.35g or 0.17g) added at room temperature. The mixtures are then heated at 80˚C in an oil bath. Seven aliquots of the reaction mixture are removed at fixed time intervals (e.g., 0, 20, 40, 60, 80,100 min, 1 week) and analyzed by 1H NMR spectroscopy for conversion and SEC for polymer MW and PDI.
Sample preparation for SEC analysis. An aliquot of the reaction mixture (3mg) is dissolved in THF(1mL) and was filtered through a syringe membrane filter prior to injection into SEC column.
Sample preparation for 1H NMR analysis. An aliquot of the reaction mixture (0.1-0.5 mg) is dissolved in CDCl3 (1mL) and is transferred into a NMR tube for conversion analysis.
Lab report write-up.
Summarize and discuss your experimental results and describe the characterization techniques you used for this lab. The following questions should be addressed in the report.
(1) How does SEC characterization of polymer MW and PDI work? What are the advantage and limitation of this technique?
(2) How is a calibration curve constructed?
(3) What is the mechanism for the bulk polymerization of styrene?
(4) How did you obtain the conversion data?
(5) How does the polymer MW depend on conversions? Why?
(6) How does the polymer MW depend on the initiator concentration? why?