Effect of Polymerization Temperature on Polymethylmethacrylate Stereochemistry and Molecular Weight: A Polymer Chemistry Laboratory Procedure

Polymethylmethacrylate (PMMA) is a popular commercial polymer commonly referred to as acrylic, plexiglass, or Perspex. PMMA\u27s applicative versatility can be sourced back to its bulk structure, which 14 refers to the ratio of crystalline to amorphous regions within a sample and is directly related to physical and mechanical properties. Chain tacticity is a determining factor of crystalline and amorphous proportions, as it influences ordered stacking and entanglement, therefore effecting bulk structure. Tacticity can be described as having isotactic, syndiotactic, or atactic patterns that can typically be observed by1H NMR. The relationship between polymerization temperature and tacticity in PMMA has already been observed and reported, so the purpose of this project was to reproduce the trend and construct a laboratory procedure for an upper-level polymer chemistry course. This relationship entails as polymerization temperature decreases, syndiotactic patterns dominate. To begin the experiment, PMMA samples were synthesized at various temperatures ranging from 60°Ϝ-100°Ϝ (15.55℃-37.77℃). These samples were then analyzed by viscometry to determine the average molecular weight per chain and construct a pattern with respect to change in polymerization temperature (supplemental information). The resulting pattern demonstrated a slight inverse relationship between temperature and average molecular weight. Regarding the1H NMR analysis, peaks within the region of 0.5-1.5 ppm were integrated, followed by taking the ratio of these values that corresponded to the 3 tacticity patterns. The consensus regarding H1 NMR data is still being discussed and analyzed by both advisor and experimenter (as of 3/18/2022)