Hemicyanine sec-butyltriphenylborate salts as effective initiators of free radical polymerization initiated via photoinduced electron transfer process. Part II. Kinetic studies and application of electron transfer theory

Abstract

Ability of two groups of sec-butyltriphenylborate salts of hemicyanine dyes (HCBo), namely styrylpyridinium borates (ABo group) and styrylbenzoxazole borates (BBo group), to photoinitiation of radical polymerization of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA) was investigated. The effects of a dye structure and free energy of activation of electron transfer between the components of photoinitiator pair (DGel) on the rate of photoinduced radical polymerization of TMPTA (Rp) were determined. The results have been analyzed on the basis of Marcus theory describing the kinetics of photoinduced electron transfer. The values of DGel were previously calculated using Rehm-Weller equation [equation (2)]. Oxidation potential of borate was determined using cyclic voltammetry method. Monomer conversion, quantum yield of the polymerization process (Fpolym) as well as photochemical bleaching yield (Fbl) dependently on chemical structure of HCBo investigated were also determined. It was found that the structure of initiator (dye) influenced Rp value. In case of use of ABo type initiators Rp values were similar - 3.24-4.88 while in case of BBo they were placed in wide range 1.00-5.05. The highest value has been reached for B3 dye. B3Bo initiator showed also the highest values of Fpolym, Fbl and monomer conversion. Linear dependence between Rp and Fbl was observed only for ABo type initiators.