Quantum chemical study of the mechanism of radical polymerization of substituted vinylacetylenes

Semi-empirical SCF MO LCAO methods have been used to investigate the possible paths of formation of the polyconjugated portions during radical polymerization of vinylacetylene derivatives. The active centers responsible for the mechanism of chain growth have been modelled. It is shown that the relative changes in the spin densities of the most probable centres localized on the p_z orbitals of the skeletal atoms C₂ and C₄ explain the influence of the nonpolar substituent on the structure of the polymers formed. Experimental data on the realization of the diene regions correlate with the calculated values of the dipole moments of the monomer radicals, the systems not containing a substituent at the terminal C₄ atom forming a separate series. It is concluded that the electrostatic interactions play a dominant role in the formation of the polyconjugated regions.