Living synthesis of silicone polymers controlled by humidity

The preparation of hydrophobic silicone (co)polymers generally requires acid- or base-catalyzed equilibration reactions that, in addition to polymer formation, generate undesired low molecular weight cyclic species. We report that living polymerization of hydrosiloxanes, controlled by the presence of water (bulk water/humidity/wet solvent) and 0.01–0.5 mol% B(C6F5)3, arises from facile SiH hydrolysis to the silanol and, subsequently, a more rapid reaction with remaining SiH groups leading to chain extension without significant accompanying cyclic monomer formation. The interaction between hydrophobic silicone and hydrophilic water plays a role in reaction rates. In the case of (accidental) introduction of excess water, SiH groups are quickly converted to SiOH, halting polymer growth. Polymerization of the ‘dead’ SiOH terminated polymers can be re-initiated using small quantities of telechelic HSi oligomers. This mild (room temperature and pressure in an open flask) method may be used to synthesize, in high yield, low molecular weight branched polymers, chain-extended SiH telechelic silicones to give linear homo or alternating silicone block copolymers with dispersities < 2 and molecular weights ranging from ∼2k to 250k g mol−1, and resins or foams.