MOLECULAR-WEIGHT AVERAGES AND DISTRIBUTIONS OF UNSATURATED POLYESTERS - THEIR EFFECT ON THE PROPERTIES OF STYRENE-CROSSLINKED NETWORKS

Unsaturated polyesters have been synthesized and modified to determine the effect of number-average molecular weight (M//n) and molecular weight distribution (MWD) on the following properties of the polyesters after crosslinking with styrene: (i) water absorption, (ii) initial mechanical properties and (iii) property retention after immersion. The most important factor was found to be the very low molecular weight 'tail' which adversely affected behavior in several respects. Above a certain M//n, initial mechanical properties were insensitive to the variables mentioned, but mechanical property retention after immersion closely reflected the water absorption behavior by its dependence on the average chain length and the low molecular weight constituents.