Elastomeric blends of homogeneous ethylene-octene copolymers

An elastomeric ethylene-octene copolymer was compared with binary blends of ethylene-octene copolymers formulated to have the same crystallinity as the target copolymer. Copolymers having narrow molecular weight distribution, homogeneous comonomer distribution and homogeneous long chain branching structure were prepared by Dow's INSITE(TM) constrained geometry catalyst and process technology (INSITE(TM) is a trademark of The Dow Chemical Company). A copolymer of higher comonomer content than the target was blended with the appropriate amount of a lower comonomer content copolymer to obtain the target level of crystallinity. Thermal analysis indicated that the components crystallized separately in all the blends. The stress-strain behaviour of the copolymers and their blends was evaluated as a function of temperature. At ambient temperature, the total amount of crystallinity primarily determined the stress-strain relationship regardless of whether the material was a single copolymer or a copolymer blend. Any effects of phase morphology were subtle at ambient temperature. At higher temperatures, where the network junctions started to melt, miscibility of the non-crystalline regions produced a synergistic effect on the tensile strength. However, if the branch concentration of the blended copolymers was too different, the non-crystalline regions were immiscible,and the copolymer blend had a lower tensile strength than the target at higher temperatures. (C) 1997 Elsevier Science Ltd.