MOLECULAR TOPOLOGY IN ETHYLENE COPOLYMERS STUDIED BY MEANS OF MECHANICAL TESTING

The molecular topology of melt-crystallized ethylene-1-butene copolymers has been investigated by means of mechanical testing with the aid of suitable models. The number of regular folds between two consecutive interlamellar tie molecules has been estimated by means of a theoretical relationship of the tensile modulus as a function of temperature. In addition, the molecular weight between entanglements of the copolymers has been determined from an analysis of the post-yield strain-hardening, assuming an ideal network behaviour. It has been shown that the regular folded chain macroconformation turns gradually into a fringed micellar macroconformation as the co-unit concentration increases. The entanglement density increases in parallel. These results confirm the conclusion of a previous work stating that the rejection of the co-units within the amorphous phase disturbs the basic chain folding mechanism of crystallization and hampers the reeling-in motion of the chains from the melt onto the growth surfaces. Criticisms of the models have been developed taking into account some inconsistent aspects with regard to the experimental data.