Effect of solvent on the termination rate constant in initial stages of free radical polymerization

The effect of solvent on the termination rate constant K_t, in the initial stages of free radical polymerizations has been estimated by considering its effect on the viscosity of the medium and on the overall dimensions of the macroradicals. The expression derived predicts that K_t is inversely proportional to the viscosity of the reaction medium, η₀, and that K_t, increases as the overall dimensions of the radicals decrease in poorer solvents. The effect of solvent on the η₀K_t, product depends on the average size and concentration of polymer in the system. For relatively high concentrations of high-molecular-weight polymers η₀K_t can be greater in a better solvent than in a poorer solvent. This trend would be reversed for low concentrations and/or low polymer molecular weights. Good agreement has been found between experimental and estimated values of η₀K_t.