Exploiting differences in refractivity and ultraviolet absorption between pairs of monomers and their associated polymers, automatic, continuous, online monitoring of polymerization reactions (ACOMP) was extended to copolymerization. ACOMP uses no chromatographic separation columns. Copolymerization of methyl methacrylate and styrene was chosen for developing the method. Both the instantaneous concentrations of comonomers and their incorporation rates into copolymer are obtained, which allows model-independent evolution of the average copolymer composition to be followed. Using the compositional information and simultaneous light-scattering data permits monitoring model-independent M-w (cumulative weight-average molecular weight), without requiring measurements in different solvents. Simultaneous use of a viscometer allows a cross check on the light-scattering data. Molecular weight and composition data are used to obtain the copolymer bivariate mass and composition distribution. Monomer reactivity ratios are found by an errors in variables method. The reactivity ratios and composition distribution allow sequence length distributions to be computed.