Selectively Thermally Cleavable Fluorinated Side Chain Block Copolymers: Surface Chemistry and Surface Properties

Abstract

A series of monodisperse poly(styrene-b-isoprene[-g-perfluoroacyl]) block copolymers was synthesized by sequential anionic polymerization of styrene and isoprene. The perfluorinated ester side chains were attached to the remaining double bonds of the isoprene block via oxidative hydroboration and esterification of the resulting alcohol by the corresponding perfluorinated acid chloride. Surfaces of the pure polymers or blends in polystyrene exhibit a notable fractional surface excess of the perfluorinated side chains within the uppermost 100 Å depending on the surface preparation and the block copolymer composition. Thus, these surfaces are highly hydrophobic having advancing water contact angles of up to 122°. When samples are heated to 340 °C, the perfluorinated side chains can be selectively cleaved off by a thermal ester cleavage, leaving the backbone of the polymer completely intact. As a result, the hydrophobicity of the resulting poly(styrene-b-isoprene) polymer surface is reversed to an advancing water contact angle < 90°. The selective thermal ester cleavage in combination with a subsequent chemical surface derivatization may have the potential to selectively change the surface functionality. If the thermal cleavage is done locally, patterning of the surface functionality seems possible.