The Unique Versatility of the Double Metal Cyanide (DMC) Catalyst: Introducing Siloxane Segments to Polypropylene Oxide by Ring-Opening Copolymerization.

Abstract

The combination of hydrophobic polydimethylsiloxane (PDMS) blocks with hydrophilic polyether segments plays a key role for silicone surfactants. Capitalizing on the double metal cyanide (DMC) catalyst, the direct (i.e., statistical) copolymerization of cyclic siloxanes and epoxides is shown to be feasible. The solvent-free one-pot copolymerization of hexamethylcyclotrisiloxane and propylene oxide results in the formation of gradient propylene oxide (PPO)-PDMS copolymers. Copolymers with up to 46% siloxane content with low dispersities (Ð<1.2) are obtained in the molecular weight range of 2100-2900gmol-1 . The polymerization kinetics are investigated by pressure monitoring and in situ 1 H and in situ 29 Si NMR spectroscopy. Contact angle measurements reveal the impact of siloxane incorporation manifest in strongly increased hydrophobicity of PPO-PDMS copolymers and a glass transition of -95°C for 46% SiO content. This unusual copolymerization offers promise for the synthesis of silicone/polyether polyols.