Structure and properties of hybrid poly(2-hydroxyethyl methacrylate)/SiO2 monoliths

Abstract: Hybrid poly(2-hydroxyethyl methacrylate) (PHEMA)/SiO2 monoliths were synthesized via a sol-gel process of the precursor tetraethyl orthosilicate (TEOS) and the in situ free-radical polymerization of 2-hydroxyethyl methacrylate (HEMA). The weight ratio of the starting chemicals, TEOS to HEMA, was varied between 100/0 and 0/100. Structural analysis was performed by IR and NMR. The NMR results indicated that the introduction of PHEMA in the silica networks gave rise to a lower degree of condensation of TEOS. The resulting monoliths showed more than 75% transmittance in the visible region, that is, good transparency. Mechanical properties were studied with an Instron tester, and the monoliths exhibited better compressive strength and modulus than did bulk PHEMA. Surprisingly, thermogravimetric analysis (TGA) data showed greater than 50 wt % solid residue up to 700degreesC, possibly related to some degree of chemical crosslinking between the polymer and the silica moiety, which would greatly improve the thermal stability of such hybrid monoliths compared with a pure PHEMA