The rate of solution copolymerization of styrene (M1) and 2‐hydroxyethyl methacrylate (M2) was investigated by dilatometry. N,N‐dimethyl formamide, toluene, isopropyl alcohol, and butyl alcohol were used as solvents. Polymerization was initiated by α,α′‐azobisisobutyronitrile at 60°C. The initial copolymerization rate increased nonlinearly with increasing 2‐hydroxyethyl methacrylate (HEMA)/styrene ratio. The copolymerization rate was promoted by solvents containing hydroxyl groups. Two different approaches were used for the prediction of copolymerization rates. The relationships proposed for the copolymerization rates calculation involve the effects of the total monomer concentration, mole fraction of HEMA, and of the solvent type. Different reactivity ratios were found in polar and nonpolar solvents: r1 = 0.53, r2 = 0.59 in N,N‐dimethyl formamide, isopropyl alcohol and n‐butyl alcohol; r1 = 0.50, r2 = 1.65 in toluene. The usability of these reactivity ratios was confirmed by batch experiments.

SynopsisSemicontinuous emulsion copolymerization of ethyl acrylate and butyl acrylate was studied at conversions higher than 0.9. It was found that, in the cases in which the mole fraction of ethyl acrylate in the reaction mixture was over 0.65, the copolymerization diagram differs from the one given by the reactivity ratios. It was suggested that this deviation was caused by the diffusion control of the process. This suggestion was also supported by the differences in the free-monomer composition of the systems with and without seed latex, respectively, at the beginning of the copolymerization.