Analysis and properties of ethylene-propylene copolymers

Copolymers of ethylene and C14‐labeled propylene were prepared with a metal‐oxide catalyst which polymerizes ethylene to a high density polymer. Methyl branches arising from the propylene were counted radiochemically and then related to the infrared absorption of films at 8.7 μ. This band was then used independently to determine methyl branching of a series of ethylene‐propylene copolymers that differed in density and stiffness. Both properties decrease in value with an increase in branching.