Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl metacrylate). VII. Determination of the rate constants for template polymerization

Abstract

AbstractThe separate rate constants kp and kt for propagation and termination of radical template polymerization of methyl methacrylate along isotactic poly(methyl methacrylate) as a polymer template have been determined. The polymerizations were carried out in the strongly complexing solvent dimethylformamide at 5°C. For the evaluation of k/kt from stationary kinetic experiments, the rates of initiation were determined by employing a scavenger method. The nonstationary experiments yielding kp/kt were performed by means of the rotating sector technique. As the template rate effects increased with decreasing initiator concentration, the rotating sector curves were corrected for variation in light intensity. It appeared that the radical lifetime increases from 8.4 sec for normal or blank polymerization to 64 sec for template polymerization. The calculated values of kp are 26.6 and 5.9 l./mole‐sec and of kt 140 × 104 and 1.7 × 104 l./mole‐sec for blank and template polymerization, respectively. The changes in kp and kt, due to the presence of template polymer, are explained in terms of an extra loss of activation entropy in the stereoselective propagation step and a strong hindrance of segmental diffusion for the termination reaction of the chains growing along the polymer template.