We present a mathematical description of the spatial and temporal evolution of the light intensity gradient, initiator concentration gradient, and initiation rate profiles for photobleaching initiator systems. This article builds on the foundation provided by previous researchers' contributions by generalizing the governing differential equations to include the effects of absorption by the initiator fragments, absorption by the monomer, and diffusion of the initiator. Simulation results have confirmed that, at any given time, the initiation rate profile resembles a wave front that propagates through the sample. The simulation results suggest that there is an optimum initiator concentration for efficient photopolymerization of thick samples. As either the initiator concentration or molar absorptivity is increased, the initiation rate at the peak of the wave front increases, the breadth of the propagating front decreases, and the rate of spatial propagation through the sample decreases. In contrast, the maximum photoinitiation rate and rate of spatial propagation of the initiation front can be simultaneously increased with an increasing initiator quantum yield or a decreasing absorptivity of the monomer or photolysis products. Finally, on the basis of these studies, diffusion is expected to have negligible effects in most photobleaching systems. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 793–808, 2002; DOI 10.1002/pola.10162

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Poly(methacrylic acid-g-ethylene glycol) networks were prepared by the copolymerization of methacrylic acid and polyethylene glycol) methacrylate in the presence of a tetraethylene glycol dimethacrylate cross-linking agent Their swelling characteristics depended on swelling solution pH, swelling temperature, copolymer composition, and network structure. In aqueous swelling solutions at acidic pH, copolymer networks swelled to a much lower extent than homopolymer networks. This behavior was attributed to complex formation between polyethylene glycol) and poly(methacrylic acid) segments. Nuclear Overhauser enhancement measurements revealed that graft copolymers formed complexes under a wider range of concentrations and polyethylene glycol) molecular weights than the two ungrafted homopolymers. This enhancement in complexation was attributed to elimination of the unfavorable translational free energy change of complexation by covalent attachment of the complexing species.

Free‐radical/cationic hybrid photopolymerizations of acrylates and epoxides were initiated using a three‐component initiator system comprised of camphorquinone as the photosensitizer, an amine as the electron donor, and a diaryliodonium salt. Thermodynamic considerations revealed that the oxidation potential of the electron donor must be less than 1.34 V relative to SCE for electron transfer with the photoexcited camphorquinone to take place. This electron transfer leads to the production of the active centers for the hybrid polymerization (two radicals and a cation). Further investigation revealed that only a subset of electron donors that meet the oxidation potential requirement resulted in polymerization of the epoxide monomer; therefore, a second requirement for the electron donor (pKb higher than 8) was established. Experiments performed using a combination of electron donors revealed that the onset of the hybrid system's cationic polymerization can be advanced or delayed by controlling the concentration and composition of the electron donor(s). These studies demonstrate that a single three‐component initiator system can be used to initiate and chemically control the sequential curing properties of a free‐radical/cationic hybrid photopolymerization and is a viable alternative to separate photoinitiators for each type of polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1747–1756, 2005

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Three-component initiators generally include a light-absorbing photosensitizer, an electron donor that is often an amine, and the third component, which is usually an iodonium salt. To characterize the role of diphenyl iodonium chloride (DPI) in three-component photoinitiator systems containing methylene blue (MB) as the photosensitizer, a systematic series of electron donors was used. The Rhem-Weller equation was used to verify the thermodynamic feasibility for photo-induced electron transfer from the electron donors to the MB. Comparison of the photopolymerization rates of each two-component initiator system (containing the photosensitizer and amine) to those of the corresponding three-component system (with the addition of (DPI) allowed fundamental information regarding the role of the DPI to be obtained. It was concluded that the DPI enhances the photopolymerization kinetics in two ways: (1) it consumes an inactive MB neutral radical and produces an active phenyl radical, thereby regenerating the original methylene blue, and (2) it reduces the recombination reaction of the MB neutral radical and amine radical/cation.

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