Water-Induced Surface Rearrangements of Poly(dimethylsiloxane−urea−urethane) Segmented Block Copolymers

An investigation of the surfaces of linear, segmented block copolymers of poly(dimethylsiloxane−urea−urethanes) by dynamic contact angle analysis is reported. The polymer films are immersed in water, the time-dependent advancing and receding contact angles are observed, and the contact angle hysteresis is reported. The initially hydrophobic polymer surfaces are observed to become more hydrophilic with long-term exposure to water. The advancing contact angles are relatively constant with immersion time; the receding contact angles decrease to some equilibrium value after a few days' exposure to water. It is proposed that the surfaces reorganize by a mechanism in which the hard block urethane−urea domains migrate through the soft block silicone to the polymer−water interface. The surface reorganization kinetics are discussed in terms of the effects of annealing as well as the average molecular weight of the soft block.