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 ana lysis is reported. The polymer films are immersed in water, the time-d ependent advancing and receding contact angles are observed, and the c ontact angle hysteresis is reported. The initially hydrophobic polymer surfaces are observed to become more hydrophilic with long-term expos ure to water. The advancing contact angles are relatively constant wit h immersion time; the receding contact angles decrease to some equilib rium value after a few days' exposure to water. It is proposed that th e surfaces reorganize by a mechanism in which the hard block urethane- urea domains migrate through the soft block silicone to the polymer-wa ter interface. The surface reorganization kinetics are discussed in te rms of the effects of annealing as well as the average molecular weigh t of the soft block.