Bisphenol-A-bis(2-hydroxypropyl methacrylate) (BisGMA) was copolymerized with methyl derivatives of styrene initiated by di-tert-butyl peroxide in the presence of 76 wt% of silica filler at 150 degrees-200 degrees C. The Raman bands of the C=C stretching vibrations at 1630 and 1637 cm(-1) were found to be suitable for determining the conversion of C=C double bonds of the styrene and the methacrylate monomer simultaneously in dependence on the copolymerization time. The C=O Raman band of the BisGMA monomer at 1702 cm(-1) vanishes during the copolymerization, whereas the intensity of the C=O band at 1718 cm(-1) decreases.