Polymer NSR spectroscopy. III. The rates of the propagation steps in the isotactic and syndiotactic polymerization of methyl methacrylate

Abstract

AbstractBy measurement of peak areas in the α‐methyl region of the NSR spectra of 15% chloroform solutions of methyl methacrylate polymers prepared by free radical initiation over a 178° range of polymerization temperatures, it has been found that syndiotactic propagation becomes increasingly dominant as the polymerization temperature is decreased and that propagation tends toward randomness as the polymerization temperature is increased. We report the first experimental measurement of the difference in activation enthalpies and entropies for syndiotactic and isotactic monomer placement. It is found that there is no difference in the activation entropies of these processes, but that isotactic placement requires an additional activation enthalpy of 775 ± 75 cal./mole.