Adsorption of polymers at the solution/solid interface, 15. Styrene-vinylferrocene copolymers

A series of styrene-vinylferrocene random copolymers is synthesised and characterised. Their adsorption from carbon tetrachloride and from chloroform is measured on to pyrogenic SiO₂, TiO₂ and Al₂O₃. The level of adsorption depends on the solvent, the adsorbent and the copolymer composition. From chloroform, very few vinylferrocene units are required to increase adsorption markedly above that of polystyrene, and further compositional change has little effect on the level of adsorption. The compositional dependence of adsorption of the copolymers from carbon tetrachloride is more complex. ¹H NMR studies show that a very high proportion of repeating units are held close to the silica surface. With polystyrenes, the fraction of units of restricted mobility decreases with polymer molecular weight and with surface coverage; at partial surface coverage virtually all the phenyl groups of low molecular weight polystyrene (mol. wt. = 4000) are immobilised. The copolymers also show large restricted fractions, which decrease along the adsorption isotherm, but which show no significant dependence on polymer composition. Higher restricted fractions seem to be associated with poorer solvent quality.