Horseradish peroxidase mediated free radical polymerization of methyl methacrylate

This paper reports the free radical polymerization of methyl methacrylate ( MMA) catalyzed by horseradish peroxidase (HRP). A novel method was develope d whereby MMA polymerization can be carried out at ambient temperatures in the presence of low concentrations of hydrogen peroxide and 2,4-pentanedion e in a mixture of water and a water-miscible solvent. Polymers of MMA forme d were highly stereoregular with predominantly syndiotactic sequences (syn- dyad fractions from 0.82 to 0.87). Analyses of the chloroform-soluble fract ion of syndio-PMMA products by GPC showed that they have number-average mol ecular weights, M-n, that range from 7500 to 75 000. By using 25% v/v of th e cosolvents dioxane, tetrahydrofuran, acetone, and dimethylformamide, 85, 45, 7 and 2% product yields, respectively, resulted after 24 h. Increasing the proportion of dioxane to water from 1:3 to 1:1 and 3:1 resulted in a de crease in polymer yield from 45 to 38 and 7%, respectively. Increase in the enzyme concentration from 70 to 80 and 90 mg/mL resulted in increased reac tion kinetics. By adjustment of the molar ratio of 2,4-pentanedione to hydr ogen peroxide between 1.30:1.0 and 1.45:1.0, the product yields and M-n val ues were increased. On the basis of the catalytic properties of HRP and stu dies herein, we believe that the keto-enoxy radicals from 2,4-pentanedione are the first radical species generated. Then, initiation may take place th rough this radical or by the radical transfer to another molecule.