On the Configurational Statistics of Ethylene-Propylene Copolymers

Abstract

Mean‐square unperturbed dimensions 〈 r 2 〉 0 and their temperature coefficient d ln 〈 r 2 〉 0 /dT have been calculated for ethylene‐propylene copolymers by means of the rotational isomeric state theory of chain molecules. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of polyethylene and polypropylene, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the propylene sequences. It is shown that 〈 r 2 〉 0 and d ln 〈 r 2 〉 0 /dT for these copolymer chains should be most sensitive to chemical sequence distribution in the case where propylene sequences are highly isotactic in stereochemical structure. Calculations carried out using values of these variables thought to be appropriate for ethylene‐propylene polymers experimentally investigated give values of d ln 〈 r 2 〉 0 /dT which are in good agreement, in general, with those obtained from previously published force‐temperature measurements on elongated networks of ethylene‐propylene chains.