SURFACE CHARACTERIZATION OF 2-HYDROXYETHYL METHACRYLATE STYRENE BLOCK-COPOLYMERS BY TRANSMISSION ELECTRON-MICROSCOPIC OBSERVATION AND CONTACT-ANGLE MEASUREMENT

The surface structures of poly(HEMA-block-styrene-block-HEMA)s and poly(HEMA-ran-styrene) (where HEMA denotes 2-hydroxyethyl methacrylate) are characterized by TEM observation and contact angle measurements using sessile drop method and Wilhelmy plate technique under the dry and wet conditions. One (T-60) of the triblock copolymers is produced by the addition reaction of telechelic polystyrene with isocyanate terminals and semitelechelic PHEMA with an amino group at one chain end, and the others (L-50, L-60) are synthesized by anionic living polymerization. The random copolymer (R-50) is prepared by radical polymerization. L-50, L-60,T-60, and R-50 contain 45, 61, 63, and 47 wt % of PHEMA segments, respectively. From the TEM observation, the outermost surface of the as-cast L-50 him is found to be completely covered with polystyrene layer, while the microdomains of polystyrene and PHEMA are mixed in the top surface area of the as-cast T-60 film. By use of the staining technique, thewet surface structures of L-60 and T-60 are also observed. At the hydrated top surface, the polystyrene microdomains wrapped with PHEMA segments are stretched toward the water side, while the microphase separated structure in bulk remains intact. The contact angle measurements elucidates that the hydrophobic surfaces are replaced with hydrophilic ones by soaking the L-50 and T-60 films in water and that the hydrated surface of L-50 reverts to the hydrophobic one again by annealing. The surface of R-50 does not show a drastic restructuring in response to the environmental change.