SURFACE-STRUCTURE AND DYNAMICS OF BLOCK AND GRAFT-COPOLYMERS HAVING FLUORINATED POLY(ETHYLENE OXIDE) CHAIN-ENDS

The surface compositions of poly(styrene-b-ethylene oxide) and poly(st yrene-g-ethylene oxide) films were found to be largely determined by t he nature of the poly(ethylene oxide) (PEO) chain ends. Angle-dependen t X-ray photoelectron spectroscopy revealed that polystyrene (PS) domi nated the surfaces of the copolymers having PEO chain ends terminated by hydroxyl groups (SEO). Also, the PEO content decreased with decreas ing sampling depth. In contrast, the surface regions of the correspond ing copolymers having fluorinated PEO chain ends (fSEO) were dominated by PEO, and the PEO content increased with decreasing sampling depth. The fluorine content of fSEO also increased with decreasing sampling depth, indicating that the fluorinated chain ends were segregated at t he outermost surface. The studied fSEO block copolymer seemed to have a higher surface concentration of fluorinated chain ends than the fSEO graft copolymers. Although it is likely that the fSEO surfaces were f ully covered by fluorinated chain ends, the advancing water contact an gles on fSEO films were markedly lower than on the corresponding SEO f ilms. Moreover, low contact angles were retained even after prolonged annealing of the fSEO films in a vacuum. The surface behavior of BEO m ay be explained by the presence of flexible, fluorinated PEO chain end s, providing a highly dynamic surface. When fSEO films are immersed in water, the surfaces can rapidly restructure and expose PEO.