Water-induced surface structure of poly(dimethylsiloxane)-containing block copolymers

Two triblock copolymers, polyester-b-poly(dimethylsiloxane) (PDMS)-b-polyester, were synthesized by the ring-opening polymerization with both hydrophobic and water-repellent hydroxyl-terminated PDMS and hydrolytically degradable ester monomers. The T (g) s of the polyester blocks were controlled by E >-caprolactone/lactide mixture or lactide only. The surface composition of the triblock copolymers was measured by angle-dependent electron: X-ray photoelectron spectroscopy. The results showed that the PDMS block with a low surface energy in the copolymers was quite segregated in the surface region; the copolymer films showed significantly higher mole fractions of PDMS (0.78-0.86) at a low takeoff angle compared with their bulk mole fractions (0.015-0.02). When the films were exposed to water at 20 A degrees C for 70 min, the mole fractions of surface PDMS were decreased to 0.3-0.5 because of the water-repellent hydrophobicity and the chain mobility of both blocks.