Poly(ethylene-block-vinylalcohol) film with amphiphilic surface at high temperature

Poly(ethylene-block-vinylalcohol) (PE/PVA), which consisted of both hydrophobic and hydrophilic blocks, was prepared by using polyethylene single crystals as starting material. Polyethylene single crystals were reacted with fuming nitric acid resulting in long methylene chains with functional groups such as COOH and NO₂ at the ends (the chain lengths were almost the same as the lamellar thickness of polyethylene single crystal). The functionalized methylene chains were allowed to react with 4-aminostyrene to give corresponding amides, i.e. methylene chains with vinyl groups at the ends (macromer). The macromers were extended by block-copolymerization with vinyl acetate, then saponified resulting in PE/PVA block copolymer. The block copolymer was molded into sheets which were subsequently heat-treated in contact with hydrophilic or hydrophobic media. Depending on the media, the sheet surface changed at high temperature reversibly from hydrophilic to hydrophobic and vice versa. The surface property was fixed by quenching because both blocks were able to crystallize. Thus the surface of this material can be tailored for various purposes at high temperature, and then used in stable condition at room temperature.