13C and 1H NMR analysis of structural defects in PVC: Application to the production of defects at various polymerization stages

Abstract

AbstractHigh resolution 1H and 13C NMR data were obtained on PVC and PVC reduced with Bu3SnH. The reduction is never complete and CH2Cl groups preferentially remain. It causes almost complete formation of cyclopentane structures from both internal and chain end unsaturation. 1H NMR gives total unsaturation as well as chain end unsaturation except if there are interferences with initiator residues; in that case, its combination with 13 C NMR of reduced PVC gives the chain end unsaturation. By the last method short branches and long ends are determined. Residual primary chlorine in all kinds of branches (methyl, ethyl, butyl, long ends) is taken into account. Long end contents are to be corrected (factor around 1.5), due to incomplete relaxation in standard analysis conditions. 1H NMR of reduced PVC can be used to get the total non‐reduced structures, both ‐CH2Cl and ‐CHCl‐. PVC was prepared by suspension or solution (trichlorobenzene) polymerization at 55° C, using dicetyl peroxydicarbonate as an initiator. The initiator residue content is higher in suspension PVC at very low conversion, and then levels off at a low value; in solution polymerization, it chiefly depends on the monomer/initiator ratio. At low conversion, more chain end and less short branches are present in suspension polymerization. Otherwise, only the butyl branch content shows a definite trend to increase with conversion. In solution polymerization, the number of defects is chiefly dependent on the initial monomer concentration; it is generally much higher than in suspension, except for the chloromethyl branches where both processes give about the same results.