Electron beam crosslinking of rigid-rod polyesters with flexible aliphatic side chains

Abstract

The crosslinking of a series of thermotropic LC polyesters, consisting of a poly(p-phenylene terephthalate) backbone and flexible aliphatic side chains, by electron beam irradiation was studied as a function of the side-chain composition, side-chain length, and irradiation temperature. For a comparison of the effect of irradiation the G(S)/G(X) ratio, as determined from sol-gel or GPC measurements, was used. Crosslinking dominates if this value is smaller than 1, which is the case for four out of five polyesters studied. Only the polyester with hexyloxy side chains shows a slight tendency to degradation. Crosslinking is stimulated by longer side chains and the introduction of hetero atoms that are more easily ionizable, like oxygen. The introduction of an unsaturation has the largest effect and boosts the crosslinking process. Raising the irradiation temperature increases the tendency to crosslinking or degradation already present. For most of the polyesters studied, irradiation slightly improves the mechanical properties of cast films. © 1996 John Wiley & Sons, Inc.