Molecular orbital calculations have been carried out for dimerization steps in the polymerization process of methyl acrylate, methyl methacrylate, and ethyl acrylate through free radicals and ionic mechanisms. The calculations were performed for monomers, dimers, their positive and negative ions, and free radicals. The minimum energy geometry was achieved in all cases, the geometrical and electronic parameters are analysed, a dimerization reaction pathway is proposed, the heats of polymerization obtained are in excellent agreement with experimental data.