The effect of polydispersity on structure of ultrasonically treated rubbers

Structure of ultrasonically treated rubbers, as recently shown by us, can be analyzed using the classical theory of rubber network statistics. This theory allows one to calculate gel fraction and crosslink density of a rubber network, provided, in particular, that molecular weight distribution (MWD) of the rubber chains is given. In previous studies, the initial MWD of ultrasonically treated rubbers was assumed to be of Floryʹs type in order to facilitate calculations. The present paper demonstrates that shape of the initial MWD insignificantly affects calculations of gel fraction and crosslink density if rubber network degradation proceeds through random scissions of main chains and crosslinks as in the case of continuous (with flow) ultrasonic treatment. MWD has been demonstrated to affect kinetics of rubber network degradation if a partial depolymerization of broken chains (thermal degradation) takes place during the ultrasonic treatment, which might happen under the static (no flow) conditions of treatment. The results of illustrative calculations are presented on structure of ultrasonically treated unfilled styrene-butadiene rubber.