Free radical polymerization in the presence of non‐solvents, 1. Styrene

During styrene (STY) polymerization, initiated by radicals formed by thermal or photochemical decomposition of 2,2′‐azoisobutyronitrile (AIBN) the overall polymerization rate constant K defined by relation K = R p /([AIBN] 0,5 [STY] η ) and the ratio k p /(2 k t0 ) increase with decreasing styrene concentration by hexane or benzene ( R p is the polymerization rate and η MIX the viscosity of the reaction system). In the thermally initiated polymerization K = k p (2 f k d /(2 k t0 )) 0,5 and in the photochemically initiated polymerization K = k p (2,303 ϕ I 0 ϵ d /(2 k t0 )) 0,5 where k d , k p , and k t0 are respectively, the rate constants of AIBN decomposition, of propagation, and of termination (for a system of the viscosity 1 mPa·s) reactions, ϕ is the quantum yield of radicals entering into reaction with the monomer, I 0 the intensity of the incident light, ϵ the molar absorption coefficient of AIBN, and d the path length of the light. The increase of K and of k p /(2 k t0 ) with decreasing monomer concentration is more marked for the system styrene/hexane than for styrene/benzene and this increase is greater at 30°C than at 60°C. For Θ‐systems formed by binary mixtures like styrene/hexane, styrene/decane and styrene/C 1 – C 4 alcohols the values of k p and k t0 at 30°C range between 57 and 91 dm 3 ·mol −1 ·s −1 and (0,9 to 2,2)·10 7 dm 3 ·mPa·mol −1 , i.e. they are in principle identical with the tabulated values of these rate constants for styrene bulk polymerization.