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.