Effect of Initiator Structure on Thiol-Ene Polymerization: A DFT Study

The performance of commercial initiators on thiol-ene polymerization has been investigated by utilizing the M062X/6-31++G(d,p) level of theory. The reactivity of initiators has been explained by the rate coefficients of addition (k(i)), which is considered side reaction and hydrogen abstraction (k(HA)) reactions. In this respect, radicals generated from azobisisobutyronitrile (AIBN) and 2,2-dimethoxy-2-phenylacetophenone (DMPA) have been modeled. In the case of AIBN and the propene-methyl thiol couple as reactants, it has been illustrated that side reaction is highly possible because the calculated rate coefficients k(i) and k(HA) are close to each other 1.02E+00 and 1.50E+02 l mol(-1) s(-1), respectively. In styrene, methyl methacrylate, and maleimide applications, the discrepancy between these reaction rates is relatively less. The high reactivity of DMPA has been explained by possessing high k(HA) values of formed radicals. The hydrogen abstraction reaction is significantly faster than the addition reactions for generated radicals methyl (CH3 center dot) and benzoyl (C6H5CO center dot). For methyl methacrylate, side reaction is probable even in the application of DMPA since relatively fast addition reactions (the k(i) for CH3 center dot and C6H5CO center dot radicals are 4.71E+04 and 3.42E+04 l mol(-1) s(-1) respectively.). Styrene and maleimide show a similar reactivity tendency with methyl methacrylate.