SYNTHESIS OF SILOXANE-ORGANIC BLOCK POLYMERS WITH ORGANOMETALLIC INITIATORS.

The synthesis of siloxane-organic block polymers with organometallic initiators is discussed. The effects of initiator structure and metal counter-ion, of solvent polarity, of Lewis base promoters, and of cyclosiloxane monomer type on siloxane polymerizations with respect to block polymer formation are reviewed. Particularly, the synthesis of acrylic-siloxane block copolymers with ambident initiators via homogeneous anionic polymerization techniques is described. The variables controlling the reproducible synthesis of block polymers are outlined. Some of these variables are the temperature of the siloxane polymerization, the MWD of the PMMA block, the total mol. wt, and the composition and composition distribution of the block polymers. Polydimethylsiloxane domains in a PMMA matrix are observed by electron microscopy and are less than 400 A, thus accounting for the optical clarity of these block polymers.