DEFORMATION OF ELASTOMERIC ETHYLENE-OCTENE COPOLYMERS

The elastomeric behavior of low-crystallinity ethylene-octene copolyme rs prepared by Dow's INSITE constrained geometry catalyst technology i s described. Deformation in uniaxial tension was examined as a functio n of comonomer content and molecular weight. Within the melting range of copolymers, temperature was used as an experimental variable to rev eal the relationship between crystallinity and stress response. The co ncept of a network of flexible chains with fringed micellar crystals s erving as the multifunctional junctions provided the structural basis for analysis of the elastic behavior. The rubber modulus scaled with c rystallinity. Furthermore, the dimension of the fringed micellar junct ion obtained from the modulus correlated well with the average crystal lizable sequence length of the copolymer. Because classical rubber the ory could not account for the large strain dependence of the modulus, a theory which incorporates the contribution of entanglements to the n etwork response was considered. Slip-link theory described the entire stress-strain curve. The slip-link density correlated with crystallini ty; the cross-link density did not depend on crystallinity and appeare d to represent a permanent network. The latter was further revealed by the effect of molecular weight on the stress-strain behavior. It is p roposed that lateral attachment and detachment of crystallizable chain segments at the crystal edges provide the sliding topological constra int attributed to slip-links, and entanglements that tighten into rigi d knots upon stretching function as permanent network junctions.