Abstract
Lowβdensity polyethylene was blended in various proportions with an ethylene/propylene/1,4βhexadiene copolymer having an ethylene/propylene mole ratio of 4.5 and a low level of crystallinity. The DSC melting peak of polyethylene was decreased, the unit cell was expanded, and the spherulitic development was disturbed. The temperature of a dynamic mechanical loss peak varied smoothly with composition between the T~g~ of the copolymer and the Ξ²βrelaxation of the polyethylene, but the glass temperature of the copolymer measured by DSC was unchanged. These effects were all diminished when the ethylene/propylene ratio of the copolymer was reduced. Blends with highdensity polyethylene showed little depression of the melting point or change in crystal structure and much less effect on the dynamic mechanical behavior. However, the behavior of copolymers of ethylene with low levels of vinyl acetate or methyl methacrylate was similar to that of lowβdensity polyethylene. Therefore, the ability to cocrystallize is an important factor for limiting the tendency of nonpolar polymers to separate, thereby facilitating the preparation of blends with desirable combinations of properties.