CRYSTALLIZATION-INDUCED GELATION OF ETHYLENE/1-BUTENE COPOLYMERS OVER A WIDE CRYSTALLINITY RANGE

The crystallization-induced gelation from decalin solutions of a series of ethylene-butene random copolymers covering the range of crystal weight fraction 0.32-0.74 and having nearly equal molar weights has been investigated as a function of concentration. Swollen as well as dried gels have been characterized by means of differential scanning calorimetry, mechanical tests and scanning electron microscopy. The critical concentration for gelation is shown to be strongly dependent on the crystallinity of the polymers. On the contrary, the critical concentration for chain entanglement is quite invariant. A liquid-liquid phase separation phenomenon prior to the crystallization upon cooling is disclosed for the more crystalline materials. The better solubility of the co-unit rich copolymers is ascribed to a more favorable interaction parameter towards decalin with increasing co-unit content. Common aspects of the gelation process of the copolymers with that of atactic amorphous and isotactic semi-crystalline polystyrene are discussed.