New three‐component photoinitiating systems consisting of a cyanine dye, borate salt, and a 1,3,5‐triazine derivative were investigated by measuring their photoinitiation activities and through fluorescence quenching experiments. Polymerization kinetic studies based on the microcalorimetric method revealed a significant increase in polymerization rate when the concentration of n‐butyltriphenylborate salt or the 1,3,5‐triazine derivative were increased. The photo‐induced electron transfer process between electron donor and electron acceptor was studied by means of fluorescence quenching and SrEt change of the fluorescence intensity. The experiments performed documented that an increase of the n‐butyltriphenylborate salt concentration dramatically increases the rate of dye fluorescence quenching, whereas the increasing of the 1,3,5‐triazine derivative concentration slows down the consumption of the dye. We conclude that the primary photochemical reaction involves an electron transfer from the n‐butyltriphenylborate anion to the excited singlet state of the dye, followed by the reaction of the 1,3,5‐triazine derivative with the resulting dye radical to regenerate the original dye. This reaction simultaneously produces a triazinyl radical anion derived from the 1,3,5‐triazine, which undergoes the carbon‐halogen bond cleavage yielding radicals active in initiation of a free radical polymerization chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3626–3636, 2007

We present a theoretical description of the kinetics for dye-initiated photopolymerization via an intermolecular electron-transfer process which considers the properties of the organic redox pair forming initiating radicals. An application of the Marcus theory yields a kinetic scheme, which considers both the thermodynamical and kinetic aspects of the electron-transfer process. The intermolecular electron transfer is the limiting step in the polymerization initiation. The theory is supported by experimental data. Two organic redox pairs forming free radicals have been tested, (1) a series of pyrazolone azomethine dyes (PAD) (electron acceptors) and IV-phenylglycine (NPG) (electron donor) and (2) the Rose Bengal

This paper presents a theoretical description of the kinetics of free radical dye initiated photopolymerization via an intermolecular electron transfer process. Analysis considers the properties of organic redox pair forming initiating radicals. An application of the Marcus theory gives the kinetic scheme, which considers both the theromodynamic and kinetic aspects of the electron transfer process. The analysis shows that both the reactivity of free radicals resulting from the photoinduced intermolecular electron transfer (PET) process and the rate of the PET process can limit the rate of the polymerization initiation process. The theory is supported by experimental data. Several organic redox pairs forming free radicals have been tested. As the electron-accepting molecules, xanthene dyes and camphorquinone have been tested. As the electron donors, tertiary aromatic amines (TAAs) and N-phenylglycines (NPGs) were used. Several important conclusions are drawn from the theoretical and experimental data:  (i) For the process with the rate of PET much lower than the rate of the diffusion-controlled process, the Marcus theory can be used for analyzing or predicting the ability of organic redox systems for light-induced free radical polymerization. (ii) For the process controlled by the diffusion, the reactivity of radicals formed as a result of the PET process limits the rate of the polymerization initiation. It is shown that this relationship can also be presented as a function of thermodynamic driving forces of the photoredox reaction (−ΔG°). (iii) Experimental results show that one can describe the rate of photoinitiated polymerization as a function of thermodynamic driving forces of the photoredox reaction (−ΔG°; described by the Rehm−Weller equation) of the organic donor−acceptor pair. For the photoinduced electron transfer occurring much slower than diffusion-controlled processes, the relationship between the rate of polymerization and −ΔG° presents a classical Marcus parabolic relationship. For PET controlled by diffusion, the relationship between the rate of polymerization and −ΔG° is dependent on the reactivity of free radicals resulting from the PET process and gives a linear relationship indicating the “inverted region-like” kinetic behavior.

A series of sulfur-containing carboxylic acids (SCCA) was investigated as electron donors in photoinduced free-radical polymerizations, in conjunction with 4-carboxybenzophenone (CB) as sensitizer. These carboxylic acids included (phenylthio)acetic acid, S-benzylthioglycolic acid, 4-(methylthio)phenylacetic acid, 2-(methylthio)ethanoic acid, 4-(methylthio)benzoic acid, 2,2′-thiodiethanoic acid, and 3,3′-thiodipropionic acid. The results were compared to the simplest thioether, dimethyl sulfide. The mechanism of the radicals' formation was established using nanosecond laser flash photolysis and photochemical steady-state measurements of carbon dioxide formation. Photopolymerizations were carried out in aqueous solutions of acrylamide. Several conclusions follow from the experimental data: (1) The rates of polymerization of the CB/SCCA/acrylamide systems are affected by the yields of secondary processes that follow photoinduced electron transfer, e.g. decarboxylation or deprotonation. This is in addition to the reactivity of the free radicals themselves. (2) The highest initiation yield is observed for the system where there is efficient diffusion apart of the radical-ion pairs, followed by efficient decarboxylation. The resulting radicals are localized on carbons adjacent to the sulfur atom. (3) Free radicals with aromatic moieties are better initiators than are the analogous aliphatic radicals. (4) Radicals that retain the carboxylate moiety are inefficient initiators. (5) Photopolymerization of these systems appears to proceed by the conventional mechanism where termination is bimolecular.

We report a new method which uses fluorescence probe methodology to follow the kinetics of polymerization and postirradiation processes of multifunctional acrylates in real time.