FREE-RADICAL POLYMERIZATION OF ACRYLATES ALPHA-SUBSTITUTED BY TRIMETHYLSILOXY SUBSTITUENTS - DRAMATIC INFLUENCE OF THE SIZE OF THE ESTER SUBSTITUENT ON THE POLYMERIZABILITY

alpha-Trimethylsiloxyacrylates H2C=C(OSiMe(3))COOR (R = methyl, ethyl, propyl, isopropyl, isobutyl, and trimethylsilyl) were synthesized and polymerized under free-radical conditions. Despite the 1,1-disubstitu tion by large substituents, all olefins were found to homopolymerize. Polymerizability is very dependent on the bulkiness of the ester subst ituent, the olefins with the largest ester groups being very reluctant to react. Polymerization of the methyl ester at 60 degrees C was kine tically investigated. The rate dependence deviates from a first-order kinetics with respect to monomer concentration (n = 1,81 (benzene solu tion) and 2,36 (DMF solution)), but follows the expected square-root d ependence with respect to the initiator (AIBN). A solvent dependence u pon the rate of polymerization was also found. Copolymerization of the methyl ester (M(1)) with styrene (M(2)) was carried out at 60 degrees C: r(1) = 1,42, r(2) = 0,46, Q = 0,47, and e = 0,04. Experimental res ults are rationalized on the basis of the steric hindrance introduced by the substituents and the high captodative stabilization of the prop agating radicals.