Butyl acrylate, methyl methacrylate, and vinyl acetate solution homo- and copolymerizations were monitored using ATR-FTIR spectroscopy with conduit and diamond-composite sensor technology. Monomer conversion and copolymer composition changes as a function of time were calculated by monitoring the peak height of characteristic absorbances of monomers. Results obtained from the ReactIR (TM) 1000 reaction analysis system agreed well with those determined by traditional gravimetry and H-1-NMR spectroscopy. Improved models developed previously to incorporate solvent effects on solution polymerizations of butyl acrylate and vinyl acetate monomers were applied to predict monomer conversion, copolymer composition and molecular weight averages. Comparisons between experimental data and model predictions are presented in this study.