Investigations on surface-modified bulk polymers .1. Copolymers of styrene with a styrene moiety containing a sugar monomer

Copolymers containing vinyl sugar units were synthesized by copolymerizing 2,3;4,5-di-O-isopropylidene-1-(4-vinylphenyl)-D-gluco(D-manno)pentitol (1) with styrene. Films and plates of the copolymers and blends were prepared by casting solutions on glass plates or by hot-pressing. Isopropylidene groups, the hydrophobic protecting groups of the sugars (1), were hydrolyzed only in the sample surface layers by treating the films and plates with aqueous acid. The surfaces showed hydrophilic properties afterward and were studied by water contact angle measurement. The accumulation and reorientation of the hydrophilic sugar segments at the surface was demonstrated by a decrease of the receding contact angle and found to depend on the copolymer composition and on sample preparation. The surface compositions of the solution-cast copolymer films were investigated by means of X-ray photoelectron spectroscopy (XPS). The results clearly showed that the isopropylidene groups at the surfaces were removed and the percentage of the sugar carbon at the surfaces accordingly increased. Angle-dependent XPS measurements indicated that the hydrolysis took place evenly to a depth of 10 nm. The surface conductivity of the copolymer plates increased by several orders of magnitude owing to adsorption of water on the hydrolyzed, hydrophilic surfaces under defined air humidities.