Poly(amide-imide)-Silica Gel Hybrids: Synthesis and Characterization

Abstract

Several poly(amide-imide)-silica gel hybrids containing metal salts were prepared by the sol-gel reaction. Poly(amide-imide)s were prepared by low temperature polycondensation reaction of trimellitic anhydride (TMA) and diisocyanates [isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and 4,4′-methylenebis(phenyl isocyanate) (MDI). The inherent viscosities of the poly(amide-imide)s obtained ranged from 0.39–0.69 dL/g in DMAc. The hydrolysis and condensation reaction of tetramethoxysilane (TMOS) to form a silica gel network was affected in DMAc containing 5% LiCl, CaCl2 or ZnCl2 during the formation of poly(amide-imide)s. Films could be cast from DMAc solution and gradual evaporation of the solvent afforded pale yellow to amber colored hybrids in which the salts were dispersed at the molecular level. About 30–60% polymer was incorporated in the hybrids. Pyrolysis of the polymer silica gel hybrid samples at 600°C resulted in the formation of porous silica. Pore size and surface area studies on representative porous silica gels, SiG–4, SiG–5, and SiG–8, obtained upon the pyrolysis of the corresponding hybrids HPAI-4, HPAI-5 and HPAI-8, indicated that the silica gels were mesoporous in nature and had narrow pore size distribution (pore radius = 1.8 nm) with a surface area of 371 m2/g, 335 m2/g and 300 m2/g, respectively. The bottle shaped pores exhibited a pore volume of 0.227 cm3/g, 0.314 cm3/g and 0.280 cm3/g, respectively. Computer simulation modeling studies indicated that the poly(amide-imide) chains were not coiled and there was no agglomeration of the chains.