Environmentally induced macromolecular rearrangement on the surface of polyurethane–polysiloxane block copolymers

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Abstract
The surface of polyurethane–polysiloxane block copolymers with a controlled polysiloxane block segment length and defined siloxane content has been studied in dry and in wet states. The top surface of a cast block copolymer film was covered completely with the polysiloxane component in the dry state and the thickness of the top polysiloxane layer ranged from > 100 Å to < 20 Å depending on the block segment length and on the total siloxane content. Along with the change of contacting medium from dry to aqueous phase, a dynamic surface rearrangement occurred from a polysiloxane surface to polyurethane-like surface and the dynamics were monitored by means of contact-angle measurements with a captive bubble technique. The dynamics of this surface rearrangement process were systematically correlated with the total siloxane content and with the polysiloxane segment length. The type of polysiloxane segment, either block or graft, affected the surface dynamics markedly.