Anionic polymerization of a series of 5-membered cyclocarbosiloxanes

A study has been made on the anionic polymerization of a series of 5-membered cyclocarbosiloxanes with methyl and/or phenyl substituents. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. Six 5-membered cyclocarbosiloxanes (2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane; 2,2,5- trimethyl-5-phenyl-1-oxa-2,5-disilacyclopentane; 2,5-dimethyl-2,5-diphenyl- 1-oxa-2,5-disilacyclopentane; 2,2-dimethyl-5 ·,5-diphenyl-1-oxa- 2,5-disilacyclopentane; 2-methyl-2,5,5-triphenyl-1-oxa-2,5-disilacyclopentane; 2,2,5,5-tetraphenyl-1-oxa-2,5-disilacyclopentane) were synthesized. Since the chemical shifts of the protons of the cyclic monomers and the polymers formed were different, the rate of polymerization of the cyclic monomers was measured utilizing an NMR spectrometer. The effects of tetrahydrofuran concentration, initiator concentration and water concentration on the rate of polymer formation and on the molecular weight of the polymer formed are reported for a cyclocarbosiloxane 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane. Both monomodal and bimodal distributions of molecular weights were obtained on the polymers depending on the relative concentrations of initiator and water. The formation of this type of molecular weight distribution is explained. The rate of polymerization of phenyl substituted cyclocarbosiloxanes is also reported. This study shows that the structure of the growing chain end is important in determining the rate of polymerization. The apparent activation energy of polymerization for the cyclocarbosiloxanes studied was found to be in the range 10 - 14 kcal/mole --Abstract, page ii