INFLUENCE OF POLY(ARYLETHER SULFONE) MOLECULAR-WEIGHT DISTRIBUTION ONMEASURES OF GLOBAL THERMAL-STABILITY

The dependence of the thermal stability of high-performance poly(aryle ther sulfones) (PAES) on the initial molecular weight distribution and backbone structure was assessed experimentally and through computer s imulation. Reaction of PAES polymers resulted in the formation of an i nsoluble gel fraction and significant changes in weight and number ave rage molecular weights of the sol fraction. A PAES with alternating et her and sulfone linkages formed a larger fraction of gel at a given re action time than a PAES with the hydroquinone moiety. For a given chem ical composition, more rapid molecular weight changes and gel fraction formation were observed for the polymer with the higher value of the initial weight average molecular weight. The growth of molecular weigh t was also faster for the polymer with the broader initial distributio n. The simultaneous increase in M(w) and decrease in M(n) suggested th e occurrence of two types of overall reactions: scission and addition. Simulation of these reactions using Monte Carlo kinetics allowed esti mation of the range of probability for bond scission, R, of 0.5 < R ( 0.8 capable of accounting for the observed experimental behavior. The dependence of the simulated molecular weight changes on the initial mo lecular weight distribution agreed qualitatively with the experimental trends. (C) 1995 John Wiley & Sons, Inc.