Polyamide-silica gel hybrids containing metal salts: Preparation via the sol-gel reaction

The hydrolysis and condensation of tetramethoxysilane in a DMF solution of polyamides containing LiCl, CaCl₂ or ZnCl₂, both in presence and absence of polyoxazoline, resulted in the facile formation of polyamide-silica gel hybrids. Films were cast from the resulting mixtures and evaporation of the solvent resulted in the formation of clear, transparent hybrids with the salts dispersed at the molecular level. Pyrolysis of hybrids at 600 °C gave porous silica. Pore size and surface characteristics of these silica gel samples indicated a porous nature with a pore radius of 1.1 nm for silica gels obtained from hybrids HPA-6 (containing no salt) and HPA-9 (containing ZnCl₂) and a surface area of 213 m² g⁻¹ and 310 m² g⁻¹, respectively. Silica gel from hybrid HPA-7 (containing LiCl) had a pore radius of 1.9 nm and a surface area of 15 m² g⁻¹. The silica gel samples obtained from hybrids HPA-6, HPA-7 and HPA-9 exhibited narrow slit-like pores with a pore volume of 0.68 cm³ g⁻¹. Received: 7 January 1997/Accepted: 6 March 1997