Copolymerization of vinyl chloride with sulphur dioxide—I molecular association between vinyl chloride and sulphur dioxide

The formation of VC-SO₂ and VC-(SO₂)₂ complexes in liquid mixtures of vinyl chloride (VC) and sulphur dioxide has been shown by (a) the freezing point composition diagram and (b) chemical shifts in the PMR spectrum of VC over the complete composition range. It is postulated that SO₂ can associate with the CC bond and the Cl atom. These complexes may be involved in the copolymerization and influence the composition and stereochemistry of the product. PMR spectra of VC-SO₂-ethane(E) mixtures with SO₂] ? E] ? VC] gave K_v = 2·0 ± 0·5, 1·5 ± 0·1 and 1·1 ± 0·3 at 232·6, 272·6 and 301·3 K with ΔH_f⁰H_f = ?6·6 ± 1·4 kJ mol^?1 for the VC -(SO₂)₂ complex. The chemical shift of the trans β-proton was twice that of the other two protons. indicating that SO₂ adopts an asymmetric orientation to the double bond.