In-situ preparation of poly(2-hydroxyethyl methacrylate)-titania hybrids using γ-radiation

Hybrids of titania and poly(2-hydroxyethyl methacrylate) were prepared using 60Co γ-radiation initiated polymerisation combined with sol-gel chemistry of titanium isopropoxide. Careful control of the rates of the sol-gel reaction was achieved with acetylacetone which ensured that the dispersion of titania nanoparticles remained stable and minimised aggregation during the polymerisation reaction. Essentially quantitative conversion was achieved with extremely few residual volatiles, as indicated by evolved gas FTIR and solid state NMR. The process yielded transparent orange hybrids, with titania loadings ranging from 3 wt.% to 15 wt.% (TGA). The pyrolysis onset temperatures increased by approximately 30 °C for the hybrids compared to the unfilled polymer. DSC indicated higher Tg's compared with other pHEMA data in the literature, with a decrease in magnitude of the Tg occurring with increasing titania content. TEM shows high dispersion of particles in the 10-20 nm range, with modest aggregation. Equilibrium swelling showed that the hybrid hydrogels swelled less than half that of unfilled polymer, indicating that the titania is restricting the mobility of the chains through a cross-linking process.