SYNTHESIS OF POLYSILOXANES WITH ELECTRON-DONATING GROUPS BY ANIONIC RING-OPENING POLYMERIZATION

Anionic kinetically controlled ring opening polymerization of cyclotri siloxane is explored as a method of synthesis of copolymers having the chain composed of dimethylsiloxane units and siloxane units bearing a n uncharged nucleophilic (electron-donating, ED) group. Model monomers for these studies are derived from hexamethylcyclotrisiloxane (D3) in which one methyl group is replaced by the organophosphorus group of g eneral formula -(CH2)nP(X)Ph2 where X is lone pair, O or S. This metho d is shown to give significant advantages over the thermodynamically c ontrolled homopolymerization and copolymerization of nucleophile-subst ituted cyclosiloxanes which have so far been used for synthesis of ED substituted siloxane copolymers. The yield of the copolymers is much h igher and the molecular weight distribution is narrow. The arrangement of the ED substituents along the chain, although not purely uniform, is much more regular as compared with the statistical distribution. Th e content of cyclic oligomers was higher than in the polymerization of unsubstituted D3, which is rationalized on the basis of intramolecula r interaction of the counter-ion with the ED groups.