What affects the rate of free radical polymerization of a multifunctional acrylate photoinitiated by cyanine borate salts? Part II. Application of electron transfer theory

Abstract

On the basis of Schuster's investigation, a mechanism of the processes going on during radical polymerization, photoinitiated by cyanine borate salts, has been proposed. As well the possibility of Marcus theory application to describe the kinetics of such polymerization, photoinitiated via electron transfer process, has been presented. It required the determination of the value of free energy of activation of electron transfer process (ΔG e l ), using Rehm-Weller equation. Using cyclic voltammetry the reduction potentials of the dyes and oxidation potentials of borate salts were determined. Parabolic dependence between polymerization rate (Rp) and ΔG value has been obtained for all the salts tested. The lifetimes of excited singlet state of cyanine dye with and without quenching were determined and let calculate the rate constants of primary process of polymerization investigated, i.e. electron transfer from borate anion to excited state of the dye (k e l ). According to the Scheme A, the effect of competitive process, i.e. cyanine and butyl radicals recombination on the photoinitiated polymerization rate was also determined. This process, which does not influence R p value, leads to the dye bleaching what strongly depends on the structure of both dye cation and borate anion. There was stated that initiation rate of polymerization depends on the photoinitiator concentration and R p value - on the co-initiator concentration.