ELASTOMERIC BLENDS OF HOMOGENEOUS ETHYLENE-OCTENE COPOLYMERS

An elastomeric ethylene-octene copolymer was compared with binary blen ds of ethylene-octene copolymers formulated to have the same crystalli nity as the target copolymer. Copolymers having narrow molecular weigh t distribution, homogeneous comonomer distribution and homogeneous lon g chain branching structure were prepared by Dow's INSITE(TM) constrai ned geometry catalyst and process technology (INSITE(TM) is a trademar k of The Dow Chemical Company). A copolymer of higher comonomer conten t than the target was blended with the appropriate amount of a lower c omonomer content copolymer to obtain the target level of crystallinity . Thermal analysis indicated that the components crystallized separate ly in all the blends. The stress-strain behaviour of the copolymers an d their blends was evaluated as a function of temperature. At ambient temperature, the total amount of crystallinity primarily determined th e 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. Howeve r, if the branch concentration of the blended copolymers was too diffe rent, the non-crystalline regions were immiscible,and the copolymer bl end had a lower tensile strength than the target at higher temperature s. (C) 1997 Elsevier Science Ltd.