KINETICS OF HIGH-CONVERSION FREE-RADICAL POLYMERIZATION .1. UNDERSTANDING KINETICS THROUGH STUDY OF PSEUDOINSTANTANEOUS MOLECULAR-WEIGHT DISTRIBUTIONS

Study of molecular weight distributions provides a more informative an d discriminating approach to uncovering the nature of the gel effect t han analysis of rate or molecular weight average data. Analysis of pse udoinstantaneous molecular weight distributions, calculated from cumul ative molecular weight distributions, is used in this work to provide new insights into the nature of the gel effect in free-radical polymer ization. Pseudoinstantaneous molecular weight distributions from sever al methyl methacrylate polymerizations have been studied, revealing th ree distinct instantaneous molecular weight distributions are produced at different times during the polymerization; a single distribution c haracterizes the low-conversion regime, while two distributions are sh own to exist during the high-conversion regime. The evolution of these constituent distributions over the course of the polymerization is de scribed, and the implications of this behavior as it pertains to the g el effect are discussed.