Surface characteristics of polydimethylsiloxane—poly(methyl methacrylate) block copolymers and their PMMA blends



To draw a relationship between surface concentration of the siloxane segment and adhesion performance, surface properties of the polydimethylsiloxane—poly(methyl methacrylate) block copolymers(PDMS-b-PMMA) prepared via poly(azo-containing siloxaneamide)s and their PMMA blends have been studied by measurements of FT-IR spectra, water contact angle, ESCA spectra and 180° peel strength toward pressure-sensitive adhesive tape. The water contact angles of the chloroform-cast blend films increased abruptly with siloxane bulk concentrations, or siloxane contents, particularly, on the air-side surfaces to reach almost 100° in low siloxane content. A marked increase of the contact angle was observed in the blends containing siloxane chain length (SCL) of longer than 2000. ESCA data evidently confirmed for these blend systems that the siloxane segments with low surface energy were accumulated or enriched mainly on the air-side surface, and that, on the other hand, polar PMMA segments with high surface energy were oriented to the glass-side surface and the inside of the films. This surface accumulation behavior of the siloxane segments reflected the 180° peel strength, as a measure of adhesion performance. The water contact angle and 180° peel strength were unequivocally correlated to the siloxane surface concentration estimated from ESCA data. Conversely, in the compression-molded blend films made by a hydraulic press between a Teflon and a stainless steel plate, the extent of surface accumulation of the PDMS segment was lower than that of the chloroform-cast films, suggesting lower degree of segment migration in hot-press films, probably due to substrate surface energy and lower relaxation in the blend melts.