AbstractDensity, infrared, and creep studies have been made of ethylene–propylene copolymers containing up to about 50 mole‐ propylene and their homopolymers. The degree of crystallinity (volume fraction of polyethylene crystals), as measured by density and x‐ray studies, decreases with increased propylene content. This change is also reflected in the intensity of the 13.7 μ band in the infrared spectra of the polymers. The measured amount of unsaturation (0.1–0.2) in the copolymers is too small to account for the presence of several infrared bands which are often attributed to unsaturation. An unsaturation of 0.90 was obtained for a terpolymer where the third component was unsaturated. Indentation–creep studies showed the creep to be nearly proportional to the logarithm of time with a slope of 10 creep per decade for 0.1–10 min. Compliance–temperature graphs were found to be quite similar to those for the styrene–butadiene
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