Theoretical Study of the Conformational Behaviour of Poly(oxypropylene) Chains

Abstract

The present paper describes the calculation of the conformational behaviour of isotactic, syndiotactic and atactic poly(oxypropylene) (POP) chains, using rotational-isomeric-state (R-I-S) theory in the form of BIOSYM's Polymer computer-software. It is found that the conformational behaviour of the POP chain, in the region of an R methyl-substituted skeletal carbon atom, differs from that in the region of the corresponding S carbon, due to the differences in the steric interactions between the methyl side-group and the methylene group two skeletal atoms away in the POP backbone. Thus, the isotactic and syndiotactic chains have markedly different values of Cn, the characteristic ratio. Accordingly, Cn was calculated for isotactic, syndiotactic and atactic POP chains of various numbers of skeletal bonds, n. The results showed that the isotactic chains occupy more extended conformations (with the highest values of Cn), compared with the highly-coiled syndiotactic chains (lower values of Cn). For the atactic POP chains, Cn was found to lie between the two extremes of the isotactic and syndiotactic forms. The value of C* for the infinite atactic POP chain was found to be consistent with values determined from experimental measurements.