Polymerization control through the free‐radical retrograde‐precipitation polymerization process

In this article, we present results of our work in a novel polymerization process [called the free‐radical retrograde‐precipitation polymerization (or FRRPP) process] that occurs at temperatures above the lower critical solution temperature. In this process, conversion‐time plots for styrene polymerization in ether show autoacceleration at the beginning, followed by a relatively long period of reduced conversion rate starting at conversions as low as 30% and at operating temperatures way below the glass transition of the reacting system. Molecular weight and polydispersity index data also indicate early autoacceleration (in the form of overshoots in these values), whereas the latter period of slow conversion rate is accompanied by stable levels of molecular weight and polydispersity index. Polymer radical concentration measurements show an initial sharp rise, followed by an asymptotic value, even after almost all the initiator molecules have already decomposed into radicals. With end‐group analyses of product polystyrene and polymer radical data, we calculate a proportion of live polymeric radicals to asymptote at levels of 80–84% of all polymeric species, even after almost all initiator molecules have already decomposed into radicals. All the data presented herein verify the postulate of a controlled polymerization mechanism for the FRRPP process. Our results have become the basis for an anti‐gel effect phenomenon that is derived from prior theoretical and experimental observations, in which phenomenological diffusivities vanish at the spinodal curve of the phase envelope. The universality of this behavior in FRRPP systems is manifested from similar observations in styrene polymerization in acetone and methacrylic acid polymerization in water. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 761–774, 1999