Characterization of poly(2-hydroxyethyl methacrylate-silica) hybrid materials with different silica contents

Poly(2-hydroxyethyl methacrylate-silica) hybrid materials with significantly lower volume shrinkage were synthesized by using acid-catalyzed sol-gel reactions of tetraethyl orthosilicate and free radical polymerization of 2-hydroxyethyl methacrylate (HEMA). The mechanical, thermal, and optical properties and internal porosities of the poly(HEMA-silica) hybrids with different silica contents (e.g., 15, 25 and 30 wt%) were evaluated with the use of nanoindentation, microscratch, thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, UV-vis spectrophotometer and N2 adsorption-desorption method. A silica percolation threshold was found at around 20-25 wt%, beyond which a marked increase in the poly(HEMA-silica) hybrid hardness and modulus was observed as compared to pure poly(HEMA). Nanoindentation and scratch testing measurements also for the first time were introduced in characterizing poly(HEMA-silica) hybrid materials.