Structural Defects in Poly(vinyl chloride) and the Mechanism of Vinyl Chloride Polymerization: Comments on Recent Studies

Investigations in the title areas within the past ten years are summarized and critiqued. The polymerizations studied were performed by conventional free-radical methods. A new mechanism, not yet confirmed, is suggested to explain a reported enhancement in the chloromethyl branch concentration of poly(vinyl chloride) (PVC) prepared at high conversions of monomer. This mechanism involves an intramolecular 1,5 hydrogen shift in a 1,3,5,6-tetrachlorohexyl radical. Evidence showing that most of the internal double bonds in PVC are not formed via intermolecular H abstraction from internal monomer units is tentatively rationalized, in part, by hydrogen transfer via at least one cyclic transition state containing more than eight members. The absence of free chlorine atoms from polymerizations of vinyl chloride (VC) is reaffirmed, and the copolymerization of VC with the chloroallylic chain ends of PVC is argued to be insignificant. New information in the literature does not invalidate the currently accepted mechanism of vinyl chloride polymerization.