Photopolymerization activity

J.P. Fouassier, D. Burr, and J.V. Crivello, Photochemistry and photopolymerization activity of diaryliodonium salts. J. Macromol. Sci. Pure Appl. Chem. 1994, A31(6), 677-701. 

FOU 94] Fouassier J.P., Burr D., Crivello J.V., Photochemistiy and photopolymerization activity of diaiyliodonium salts , Journal of Macromolecular Science, Part A. Pure and Applied Chemistry, vol. A31, pp. 677-701, 1994. 

Photopolymerization. In many cases polymerization is initiated by ittadiation of a sensitizer with ultraviolet or visible light. The excited state of the sensitizer may dissociate directiy to form active free radicals, or it may first undergo a bimoleculat electron-transfer reaction, the products of which initiate polymerization (14). TriphenylaLkylborate salts of polymethines such as (23) ate photoinitiators of free-radical polymerization. The sensitivity of these salts throughout the entire visible spectral region is the result of an intra-ion pair electron-transfer reaction (101). 

Table 2 summarizes the peak times for the photopolymerization of HEMA. Among initiators with structures known, the ranking of more active initiators, in terms of decreasing polymerization rate was ... 

In the second dual photo/thermal initiation strategy, the approach described above is augmented by the inclusion of a thermal initiator. Upon illumination, active centers produced by fragmentation of the photoinitiator start the polymerization reaction. The heat evolved from the exothermic photopolymerization elevates the temperature of the system and results in the production of additional active sites by the thermal initiator. This dual initiating strategy provides both the cure on demand (temporal control) afforded by photopolymerization, and the completeness of cure provided by the thermal initiator. 

Dual Photo/Thermal Initiation Studies. A series of studies were performed using reactive formulations containing both a photoinitiator and a thermal initiator dissolved in the Derakane resin. The objective of these studies was to investigate a dual cure strategy in which the heat liberated by the photo-induced polymerization leads to the production of additional active centers by the dissociation of a thermal initiator. In this way, the dual cure strategy could offer both the temporal control of the start of the reaction afforded by the photopolymerization, as well as enhanced reaction rate and completeness of cure provided by the thermal initiation. 

This volume is based on a four-session symposium presented at the 211th National Meeting of the American Chemical Society, sponsored by the ACS Division of Polymeric Materials Science and Engineering, Inc., in New Orleans, Louisiana, March 24-28, 1996. The general interest in the topic of photopolymerization was illustrated by the excellent attendance and active discussions during the symposium, and we were delighted when most of the speakers agreed to contribute chapters to this book. The volume is well balanced, with contributions from both academia and industry, and should provide the reader with an excellent idea of the current directions of photopolymerization research. 

It was found that conventional equation can be applied for description of the process. The process is the first order with respect to monomer and the order with respect to initiator is 0.25. The energy of activation was estimated at 43 kJ/mol. Moreover, it was found that without initiator, photopolymerization also occurs when the system is illuminated by UV light. 

Comparisons of kinetic quantities for dark and photopolymerizations are summarized in Table 6. The small overall activation energy in photo-polymerization is understandable since the initiation process does not require activation energy. The most striking differences come from the study of molecular weight. In both dark and photopolymerizations, the... 

The results are shown in Table 7 (65). The photospeeds indicate NPG is nearly twice as fast as TBBS as an activator of MB sensitized photopolymerization. The wavelength dependence... 

The patent and open literature were searched for examples of dye sensitized photopolymerization in which a common monomer (acrylamide), and one of several common dyes (thionine, T methylene blue, MB or rose bengal, RB) were used in combination with a stated concentration of an activator. The polymerization conditions (monomer concentration, light intensity absorbed, and extent conversion) were stated in each case chosen for inclusion. The relative photospeed of the system was calculated based on several corrections to the raw data. We here define the relative photospeed of a composition as the inverse of the exposure time t needed to effect some fixed percentage of monomer conversion. 

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