CHAIN FOLDING IN CRYSTALLINE SYNDIOTACTIC POLYVINYL-CHLORIDE)

Potential-energy calculations seem to be capable of providing information about the structural characteristics of the folds in crystalline polymers. This paper deals with the conformational analysis of syndiotactic poly(vinyl chloride) (PVC) chains in order to reproduce satisfactory models of folding in the (010), (400), and (2bar10) crystallographic planes. The results imply that tight (010) and (400) folds and, hence, adjacent reentry may occur. The folds are probably stabilized by a weak hydrogen-bond type of interaction. Moreover - ChCl-Ch//2-CH//2-CHl - segments in the folds have been taken into account, thus obtaining more energetically favored models. The crystal lattice energy has been computed as a function of the PVC unit-cell parameters a and b, releasing the fold's constraint of the stems. The energy minimum corresponds to a noticeable decrease of a in comparison with the experimental value, although the potentials used in the calculations are hard and have van der Waals radii greater than those usually accepted.