Behavior of primary radicals in vinyl polymerization

The reciprocal of the viscosity‐average degree of polymerization ( P̄ v −1 ) vs. rate of polymerization ( V ) relation is expressed as: equation image where [η] = K ′ P̄ v α , β = k td / k t , k = rate of primary radical formation out of cages/concentration of initiator, {article}{empty}{document}∑ ᵢ k' ₚᵢ [Rᵢ ·][ M] = rate of initiation of polymerization{document} , {article}{empty}{document}∑ ᵢ k' ₜᵢ [Rᵢ ·][ M ·]{document} = rate of termination of growing chains M· by reaction with primary radicals R i ·. From this equation, several, important constants can be determined. In the polymerization of styrene at 60°C. with 2,2′‐azobisisobutyronitrile, the results obtained are as follows: k p 2 / k t = 5.52 × 10 −4 (or 5.86 × 10 −4 ) l.‐mole. −1 ‐sec. −1 . k tr M / k p = 6 × 10 −5 , k tr S / k p 1.1 × 10 −2 (carbon tetrachloride as solvent), k = 1.57 × 10 −5 (or 1.48 × 10 −5 ) sec. −1 , {article}{empty}{document}∑ ᵢ k' ₚᵢ [Rᵢ ·]/∑ ᵢ k' ₜᵢ [Rᵢ ·] = 1.20 × 10- 7{document} . These values agree well with those obtained by the other authors. The rate of initiation {article}{empty}{document}∑ ᵢ k' ₚᵢ [Rᵢ ·] -[ M]{document} and the rate of termination {article}{empty}{document}∑ ᵢ k' ₜᵢ [Rᵢ ·][ M ·]{document} between the growing chains and primary radicals are calculated, respectively, from the equations: equation image The rate of disappearance of the primary radicals through the reaction among themselves is negligible in comparison with the other termination rates in the usual conditions. The ratio of concentrations of the primary radicals R· and growing chains M· is expressed under an ordinary condition as: equation image where V R is the rate of primary radical formation and k ′ p the rate constant of initiation.