SELECTIVITY OF SILOXANE-SILOXANE COPOLYMER SYNTHESIS BY RING-OPENING POLYMERIZATION

Anionic ring-opening polymerization of 1,1-diphenyl-2,2,3,3-tetramethy lcyclotetrasiloxane was studied as a model polymerization of cyclic, s iloxane with mixed siloxane units. Sequencing of siloxane units was in vestigated by Si-29 NMR. Various initiator-promoter-solvent systems we re used. In most cases reaction was highly chemoselective, as sequenci ng were not affected by back biting, chain transfer and terminal unit exchange processes. Reactions showed, however, low regioselectivity in monomer ring opening. The coordination of the metal counter-ion to mo nomer plays a considerable role in propagation and affects sequencing of the polymer.