Hybrid ternary organic–inorganic films based on interpolymer complexes and silica

Homogeneous transparent hybrid films consisting of chitosan (CHI), poly(monomethyl itaconate) (PMMI) and silica were obtained indicating the absence of microphase separation. These ternary hybrid materials are very interesting since materials with high functionality can be obtained presenting different properties from those of the starting materials but with the advantage of preserving the inherent property of each component. The inorganic phase was prepared by sol–gel process of tetraethoxysilane (TEOS). Most of the amine groups from CHI (pKb 7.7) are quaternized in the acidic medium used in the preparations (pH=2), where a physical crosslinking via hydrogen bonding could occur through carboxyl groups from PMMI. Silica gel obtained from TEOS has been intercalated as a very fine dispersion in the polymer complex formed between CHI and PMMI. Transmission electron microscopy and atomic force microscopy was used to examine the homogeneity of the ternary polymer hybrids (CHI/PMMI/SiO2), obtained as self-supported films. The results support the nanometer scale dispersion of the phases. Porous silica films with high BET area were obtained by calcination of the hybrid films. The mean pore diameter of these silica films corresponds to the dimension of the polymer domains observed in the pristine hybrid films. Moreover, it was found that the swelling behavior of the samples was influenced by the organic and inorganic phases, where the inorganic phase tends to diminish the swelling.