Effect of polystyrene coating on pore, structural and chromatographic properties of silica packings

Abstract

A series of mesoporous and macroporous silicas with a mean pore diameter (PD), between 6 and 200 nm were reacted with a copolymer of styrene and vinyl-methyldiethoxysilane. The mass load of coated silicas corresponded to the monolayer capacity of the polymer calculated on the basis of the molecular cross-sectional area, except for the two mesoporous silcias of PD = 6 and 7.5 nm. Depending on the pore size, changes occurred in the specific surface area, a s, between the native and the coated product. A comparison of the specific pore volume, ν p, of silicas before and after polymer immobilization indicated a major loss of ν p for the two mesoporous silicas whereas this effect was much less pronounced for the macroporous silicas. Surprisingly, the two macroporous silicas of PD = 50 and 100 nm exhibited a decrease in the mean pore diameter after modification, which seems to be caused by the narrowing of the pore entrances owing to polymer immobilization. The change in d p was shown by size-exclusion separations of polystyrenes on the native and coated silica. Tests of the packings in reversed-phase chromatography with amines as solutes showed that silanophilic effects on the coated silicas were absent. it was demonstrated that the immobilization did not change the performance of the silcia columns in terms of plate height and plate number.