Effect of hydrogen bonding on the glass transition behavior of poly(acrylic acid)/silica hybrid materials prepared by sol–gel process

Poly(acrylic acid) is a water soluble polymer, which has a high glass transition temperature of ca. 102°C. However, when silica (20% of TEOS) was incorporated via sol–gel process, it was found that glass transition temperature of the hybrid material decreased drastically. From the analysis of infrared spectra, this phenomenon can be attributed to the decreasing of hydrogen bonding between carboxyl and carbonyl groups of the poly(acrylic acid). Furthermore, with the TEOS content of 40–60%, silica matrix was formed and resulted in the occurrence of phase separation. With TEOS content further increased to 80%, molecular chains of PAA were aggregated together to form poly(acrylic acid) matrix. Hence, the chain segments of PAA were no more confined by the silica matrix and only single Tg was observed during DSC thermo-scan.