γ‐Irradiation of polystyrene emulsions

Abstract

AbstractAqueous polystyrene emulsions were subjected to γ‐irradiation at 30°C and 0.6 Mrad/hr dose rate. Analogy with water‐soluble systems suggests that such conditions might suppress chain scission and favor crosslinking. The (extrapolated) infinite‐dose gel content and gel‐permeation analysis of the polymer in the pre‐gel region indicate that the extent of chain scission was negligible. The G (crosslink) value obtained from the dose for incipient gelation and molecular weight variations in the pre‐gel region is 0.051. Charlesby‐Pinner plots were linear, but linearity cannot be construed as indicating that chain scission has produced an effective random molecular weight distribution. Our results are consistent with the conclusions that crosslinking events are random and directly proportional to dose. The probability that a given crosslink is effective in increasing the gel content decreases with dose past the incipient gel point, however, because of cyclization on preformed gel. The crosslink density/dose ratio is a decreasing function of dose in this range. Attempts to predict dose–gel relations with assumptions of various initial molecular weight distributions were unsuccessful, possibly because of the neglected influence of cyclization on the measured gel content.