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-disubstitution by large substituents, all olefins were found to homopolymerize. Polymerizability is very dependent on the bulkiness of the ester substituent, the olefins with the largest ester groups being very reluctant to react. Polymerization of the methyl ester at 60 degrees C was kinetically investigated. The rate dependence deviates from a first-order kinetics with respect to monomer concentration (n = 1,81 (benzene solution) and 2,36 (DMF solution)), but follows the expected square-root dependence with respect to the initiator (AIBN). A solvent dependence upon 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 results are rationalized on the basis of the steric hindrance introduced by the substituents and the high captodative stabilization of the propagating radicals.