SOLVENT EFFECTS ON FREE-RADICAL POLYMERIZATION .6. SOLVATOCHROMIC (LSER) ANALYSIS OF THE SOLVENT EFFECT ON THE HOMOPOLYMERIZATION RATE ON THE BASIS OF THE REACTION-SOLVENT COMPLEX MODEL

摘要

Evaluation results of the homopolymerization rate in solution taken from previous papers are analyzed by two solvatochromic correlation methods taking into account the scale E(T) by Dimroth and scales by Taft. From available data a nearly linear correlation between log(1/r(11')) (r(11') = relative monomer reactivity change increment) and ET is found for styrene (St) and methyl methacrylate (MMA). Linear solvent susceptibility equations are established for these monomers and tentatively estimated for N-vinylpyrrolidone (NVP), ethyl acrylate (EA), and acrylonitrile (AN). It follows from solvatochromic analyses of St and MMA polymerizations by Taft that the aliphatic, more polar, and electron-deficient MMA is 3 times more susceptible against solvent polarity and is considerably more susceptible against solvent nucleophilicity than St. St is about 5 times more susceptible against solvent polarizability than MMA. Furthermore, two independent methods of separate radical susceptibility estimation are presented. Polar solvents reduce the reactivity of growing PMMA radicals. This reactivity lost is recompensed by a much stronger reactivity increase of the monomer. [References: 33]