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

Abstract

High resolution PVC and PVC reduced with Bu,SnH. The reduction is never complete and CHzCl groups preferentially remain. It causes almost complete formation of cyclopentane structures from both internal and chain end unsaturation. as chain end unsaturation except if there are interferences with initiator residues : in that case, its combination with 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. 'H NMR of reduced PVC can be used to get the total non-reduced structures, both -CH,Cl 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.'H and 13C NMR data were obtained on 'H NMR gives total unsaturation as well 13C NMR of reduced PVC gives the

New Insight into the Formation of Structural Defects in Poly(Vinyl Chloride)

“…Assignment of the signals in the 1 H spectra (known from literature 19 ) was confirmed by 1 H homonuclear COSY experiments. 20 Proton-decoupled 13 C spectra of reductively dehalogenated samples were run at 120°C for approximately 10% w/ solutions in the mixture of 1,2,4-trichlorobenzene and benzene-d6 (3:1). The tip angle was 60°, pulse repetition time was 5 s, and , only branches up to 5 carbons can be distinguished using 13 C spectra of reductively dehalogenated PVC.…”

“…20 Proton-decoupled 13 C spectra of reductively dehalogenated samples were run at 120°C for approximately 10% w/ solutions in the mixture of 1,2,4-trichlorobenzene and benzene-d6 (3:1). The tip angle was 60°, pulse repetition time was 5 s, and , only branches up to 5 carbons can be distinguished using 13 C spectra of reductively dehalogenated PVC. 8 This structure would give the same peaks as long branches formed by intermolecular transfer.…”

“…Radical suspension polymerization, which is the most common process in the PVC industry, is known to give rise to a lower concentration of unsaturations and branches (especially butyl branches) than solution polymerization. 13 In this work, we study the effect of monomer conversion on the nature and concentrations of structural defects in radical suspension polymerization of vinyl chloride. Although the conversion dependence has been studied previously, this was done in a completely different polymerization system at subsaturation conditions when special precautions were taken to avoid diffusion control of the propagation.…”

“…Although the conversion dependence has been studied previously, this was done in a completely different polymerization system at subsaturation conditions when special precautions were taken to avoid diffusion control of the propagation. 6,14 PVC made by suspension polymerization was also analyzed in the past, but the conversion range was not covered completely and the low-molecular-weight part was extracted 13 or only some of the defects were taken in account. 15 There does not appear to be any detailed information on the formation of structural defects at high conversion under conditions that would normally be encountered in the industrial production of PVC via radical suspension polymerization.…”

“…The formation of structural defects as a function of monomer conversion was monitored using 1 H and 13 C NMR spectrometry. To assist in the interpretation of the results, the 1,2-intramolecular and corresponding intermolecular hydrogen abstraction reactions were also studied using high-level ab initio molecular orbital calculations.…”