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MECHANISTIC ASPECTS OF THE CATIONIC POLYMERIZATION OF PARA-SUBSTITUTED - ALPHA-METHYLSTYRENES
Abstract
Mechanistic studies were carried out on the cationic polymerization reactions of a series of para-substituted alpha-methylstyrenes, including p-fluoro-, p-chloro-, p-bromo- and p-isopropyl-alpha-methylstyrene, using Friedel-Crafts initiators. Solvent polarity was found to have a large effect on polymer yield, molecular weight and tacticity for the more electron withdrawing p-chloro monomer but not for the p-fluoro monomer. These results were interpreted in terms of free ion and ion pair reaction mechanisms and carbenium ion stabilization by the p-fluoro group. Polymers with bimodal molecular weight distributions (MWD's) were fractionated by preparative gel permeation chromatography and analyzed for tacticity by nuclear magnetic resonance spectroscopy. The two modes were postulated to have been formed by free ions and by ion pairs. Polymerization reactions producing polymers with very narrow MWD's were found not to be living polymerization systems on the basis of copolymerization and polymer conversion studies. Theoretical calculations by Morawetz predicting narrow MWD's in the presence of chain termination were investigated and found not to apply to these systems. The presence of sterically hindered bases such as 2,6-di-tert-butyl-4-methylpyridine (DBMP) had a profound effect on the polymerization reaction. A reaction mechanism was proposed to account for the observations. As a sidelight, studies of some crystalline properties of these polymers showed that crystallinity could be enhanced by annealing or dilute solution crystallization of polymers already showing signs of crystallinity by differential scanning calorimetry. The addition of 15% meta-substituted monomer units was found to completely disrupt crystallinity in p-methyl-alpha-methylstyrene.
Subject Area
Polymers
Recommended Citation
JONTE, J. MICHAEL, "MECHANISTIC ASPECTS OF THE CATIONIC POLYMERIZATION OF PARA-SUBSTITUTED - ALPHA-METHYLSTYRENES" (1982). Doctoral Dissertations Available from Proquest. AAI8219818.
https://scholarworks.umass.edu/dissertations/AAI8219818