The Configuration, Conformation and Degradation of Polyvinyl Chloride

The proton spectrum of poly(vinyl chloride) prepared by free-radical polymerization has been studied at 220 MHz and interpreted in terms of pentads for the x-protons and tetrads for the n-protons. The chemical shifts are in good agreement with those reported elsewhere using selectively deuterated polymers. The magnitudes of the vicinal coupling constants indicate that in the solvents employed, the isotactic dyads are in approximate equilibrium between the conformations which, if repeated, result in a helix, whereas syndiotactic dyads are probably in the conformation with the backbone in a planar zigzag structure. The tetrad and pentad relative intensities are consistent with Bernoullian chain propagation statistics, with a value m(the probability of isotactic placement) of 0.43. Radiolysis of poly(vinyl chloride) (PVC) was studied by ultraviolet and visible spectroscopy following post-irradiation storage at selected temperatures in a cryostatic cell. A sequence of alkyl, allyl and polyenyl radicals followed by chain transfer to PVC leads to polyene formation. Allyl, dienyl and trienyl radicals were associated with absorption bands at 2520, 2910, and 3300 A, respectively. Radical intermediates react readily with oxygen. INTRODUCTION In this paper, I wish to report on recent work carried out at the Bell Telephone Laboratories on the structure and chemical reactivity of polyvinyl chloride. Although many techniques and types of spectroscopy have been applied to this polymer in this and other laboratories, our principal tools in this work have been high resolution nmr for the study of its configuration and conformation and esr and uv spectroscopy for the study of its chemical behaviour, in particular the dehydrochlorination reaction which is initiated by high energy radiation. STEREOCHEMICAL CONFIGURATIONf Interpretation of the nmr data for polyvinyl chloride has been protracted and controversial, in part because of ambiguities in the spectra and in part t In the following discussion, familiarity with the basic concepts used in interpreting the nmr spectra of vinyl polymers will be assumed. For those needing it, a review of these concepts can be found in Acc. Chem. Res. 1, 175 (1968).