KINETICS OF ULTRASONIC AND TRANSIENT ELONGATIONAL FLOW DEGRADATION - A COMPARATIVE-STUDY

The kinetics of ultrasonic degradation has been investigated for dilut e polystyrene solutions in decalin. The increase in the scission rate constant (K) with initial molecular chain length was systematically in vestigated over 2 decades of molecular weight by using narrow polymer fractions with M = 50 x 10(3) - 8.5 x 10(6) Da. An empirical relation of the form K similar to (M - M-lim)(1.9), with M-lim = 30 000, was fo und for 50 x 10(3) < M < 2.2 x 10(6). The rate constant becomes indepe ndent from M at higher molecular weight. This complex behaviour is rat ionalized by establishing a parallelism between transient elongational flow and ultrasonic degradation. (C) 1997 Elsevier Science Ltd.