Vinyl chloride studies. Part 1.—Kinetics of polymerization of vinyl chloride in chlorobenzene solution

Abstract

The polymerization of vinyl chloride has been studied dilatometrically in chlorobenzene using azoisobutyronitrile as an initiator at temperatures between 30 and 45°C and with monomer and initiator concentrations varying from 1.0 to 8.1 M and from 0.005 to 0.1 M respectively. Molecular weights of the polymers have been determined by viscometry. At monomer concentrations above 7 M the polymerization is heterogeneous and the rate depends on the extent of conversion to polymer. Below this monomer concentration the polymerization is homogeneous, its rate is independent of the extent of conversion and is well represented by the expression 10^–15R_p= 3.63 [I]^0.56[M]^1.23 exp (–101,500/RT). Here R_p is the rate of polymerization in mole 1.^–1 h^–1, R is the gas constant in joules (mole)^–1 deg.^–1 and [I] and [M] are the initiator and monomer concentrations in mole 1.^–1 The deviation of the orders in initiator and monomer from 0.5 and 1.0 can both be explained by degradative reaction of polymer radicals with the solvent which can also account for the difference of the overall activation energy from that obtained in the bulk polymerization. Molecular weight determinations favour copolymerization rather than transfer as the degradative reaction. A high value, 1.9 × 10^–3, is obtained for the transfer constant to monomer and can be explained by complex formation and a transfer reaction involving abstraction of hydrogen from the growing polymer chain.