THERMAL-DEGRADATION OF POLY(2,2-DIALKYL-3-HYDROXYPROPIONIC ACID) .1. LIVING DEPOLYMERIZATION

Poly(2,2-dialkyl-3-hydroxypropionic acid)s (usually prepared by living anionic polymerization of the corresponding 2,2-dialkyl-3-propiolactone) thermally degrade by two independent mechanisms depending on the state of the carboxylate group at the termination end of the polymer chain. When the carboxylate is deprotonated (X = Li+, Na+, K+, Cs+, R4N+, or R4P+) the polymer degrades predominantly by reverse polymerization. This paper concentrates on the reverse polymerization mechanism for polymer degradation. Reverse polymerization is dependent on the nucleophilicity of the terminal carboxylate group. This is demonstrated by the effect of the terminal counterion on the rate of degradation. Furthermore, reverse polymerization is shown to be a “living depolymerization”. By living depolymerization we mean that all polymer chains degrade simultaneously from the living ends of the chains. Kinetics, change in MW distributions, and degradation of block copolymers are consistent with a living depolymerization. © 1990, American Chemical Society. All rights reserved.