THE MECHANICAL-PROPERTIES OF RANDOM COPOLYMERS OF ETHYLENE - FORCE-ELONGATION RELATIONS

Utilizing a newly developed apparatus, force‐length measurements were performed on a series of unfractionated random ethylene copolymers having different counit types and a wide composition range. By controling crystallization conditions, crystallinity levels could be varied over wide extremes and a complete repetoire of superstructures was developed. Emphasis was on key mechanical properties such as the initial modulus, yield stress, and the ultimate properties of draw ratio at break and tensile stress. Except for the ethylene‐methacrylic acid copolymers, which behaved in a unique manner, the properties were found to be independent of the chemical nature of the counit and the particular supermolecular structure that was developed. The initial modulus and the yield stress were found to be very dependent on the crystallinity and phase structure. On the other hand, except for the decrease at low counit content, the draw ratio at break was found to be invariant with counit type, crystallinity level, supermolecular structure, and molecular weight. The results are discussed in terms of the molecular constitution of the copolymer and the structure in the crystalline state. Copyright © 1990 John Wiley & Sons, Inc.