Polydimethylsiloxane–polyurethane elastomers: Synthesis and properties of segmented copolymers and related zwitterionomers

A series of polyurethane block polymers based on hydroxybutyl‐terminated polydimethyl‐siloxane soft segments of molecular weight 2000 were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) which was chain extended with either 1,4‐butanediol (BD) or N ‐methyldiethanolamine (MDEA). The MDEA‐extended materials were ionized by using 1,3‐propane sultone. The weight fraction of hard segments was in the range 0.13–0.39. The morphology and properties of these polyurethane elastomers were studied by a variety of techniques. All of these short‐segment block copolymers showed nearly complete phase separation. The zwitterionomer materials exhibited ionic aggregation within the hard domains. Hard‐segment crystallinity or ionic aggregation did not affect the morphology. Hard‐domain cohesion was found to be a more important factor than hard‐domain volume fraction in determining the tensile and viscoelastic properties of these elastomers.