Random-Coil Dimensions and Dipole Moments of Vinyl Chloride Chains

A rotational isomeric state model with neighbor interactions is used to calculate mean-square unperturbed dimensions and dipole moments for vinyl chloride chains CHa-(CHCI-CH,,)zH having degrees of polymerization x ranging from 1 to 150 and stereochemical structures ranging from perfect syndiotacticity to perfect isotacticity. Conformational energies used in the calculation were those which had been established in an analysis based on the stereochemical equilibration of 2, 4-dichloro-n-pentane by Flory and Williams. The calculations indicate that the dimensions of poly(vinyl chloride) chains of large x should decrease significantly with increasing isotacticity; this dependence of chain dimensions on stereochemical structure is the opposite of that calculated for vinyl chains having alkyl side groups, such as polypropylene. The dipole moments of poly (vinyl chloride) chains are also predicted to decrease with increasing isotacticity and both the dimensions and dipole moments are expected to decrease with increasing temperature, the largest dependence occurring in the case of perfectly syndiotactic chains. The marked differences in configurational characteristics of poly(vinyl chloride) and polypropylene chains are primarily due to the significant difference in size between Cl atoms and CHa groups; the electrostatic interactions present in poly(vinyl chloride) chains are of relatively minor importance. The predicted results for large x are in good agreement with published experimental results on poly (vinyl chloride).