Structural design at the polymer surface interface in nanoporous silica polyamine composites

The factors affecting the rate of silica leaching in alkaline aqueous media from surface silanized, nanoporous, amorphous, silica gels and from silanized silica gels that have been modified with polyamines to form the previously reported silica polyamine composites (SPCs), BP-1 and BP-2 have been investigated. Silanization with alkyl trichlorosilanes slows the rate of silica leaching relative to the unmodified silica gels. The use of bulkier aryl silanes somewhat decreases the silica leaching under the same conditions. Interestingly, after modification of the silanized silica with poly(allylamine) (PAA) to make BP-1, the leaching increases, but subsequent modification of the SPC with chloroacetic acid to make BP-2, quenches this increase. A mechanism explaining these results is discussed. Analogous composites have been prepared using sol–gel chemistry. These materials were characterized and their silica leaching properties were compared with the original BP-1. CPMAS 13C and 29Si NMR of the various surfaces have been applied to better understand the nature of the modified surfaces. Significant changes in the nature of the surface siloxanes are observed for the different matrices and on their conversion to the polyamine composite. Scanning electron microscopy and pore size distributions for the composites made from commercial silica gel and from sol–gel chemistry are also reported and compared.

Research highlights▶ Silica leaching rates for silica polyamine composites have been measured. ▶ The surface features of the composites with different silane anchors have been evaluated. ▶ The leaching characteristics of the composites are compared with similar materials made by the sol–gel method. ▶ Solid state NMR techniques, porosimetry and electron microscopy have been used to characterize all the materials discussed.