A study of butyl acrylate (BA) and vinyl acetate (VAc) solution homopolymerization and copolymerization in toluene was carried out. The conversion and copolymer composition were monitored using traditional techniques (gravimetry and H-1-NMR spectroscopy) and attenuated total reflectance-Fourier transform IR (ATR-FTIR) spectroscopy with a diamond-composite probe and light conduit technology. The peak height of the characteristic absorbances of the monomer(s) during the course of the reaction was used to calculate the conversion and copolymer composition for the ATR-FTIR monitoring. The data obtained using a ReactIR (TM) 1000 reaction analysis system in the off-line mode showed very good agreement with data obtained using traditional techniques. The solvent effects on BA and VAc solution homopolymerizations and copolymerizations in toluene were also investigated. Improvement to model predictions was obtained by allowing the lumped constant (k(p)/k(t)(0.5)) to vary with the solvent concentration. Experimental data and model predictions of the number- and weight-average molecular weights for the investigated systems are also presented.