Surface study of ladderlike polyepoxysiloxanes

By using the two-liquid geometric method and the three-liquid acid-base method, we are the first to determine the surface tensions of ladderlike polyepoxysiloxanes by the measurement of contact angles on thin films. Three kinds of ladderlike polymers have been synthesized: A-C (which has the alkyl group and the epoxy group graft to the ladderlike polysilsesquioxane chain), A-C-P (which has the alkyl group, phenyl group, and epoxy group graft to the ladderlike chain), and A-P (which has the phenyl group and epoxy group in the ladderlike side chain). The results showed that when different liquids and different theories are chosen to determine the surface energies, there are some minor differences in the values but a similar trend is still exhibited. The surface energies of these three polymers are in the following order of γ_SA-C<γ_SA-C-P<γ_SA-P. Interestingly, the surface energy increases for these polymers are mainly from the nonpolar part of the polyepoxysiloxanes. XPS surface analysis indicated that the Si and O ratios of these polymers at the air-polymer interface were in the order of A-C>A-C-P>A-P, suggesting Si atoms were more likely to migrate to the polymer surface and the bulky effect of the phenyl groups could also interfere with the migration of the Si atoms. As a result, Si and O ratio at the interface determines the order of apparent surface energy for these three polymers. Experimental data also reflect that there are differences between the ladderlike polyepoxysiloxanes and the commercially available linear polysiloxanes.