UV-induced photopolymerization

Studies of the solid state photopolymerization of deposited multilayer films reveal that uv induced photopo1ymerizati0n of disubstituted diacetylenes... 

Most of the work reported so far on laser-induced photopolymerization deals with near UV and visible radiation ranging from blue (—400 nm) (3,12) to red light (—700 nm) (4). We present here a kinetic investigation on the... 

It is important to note that values are of the same order of magnitude whether conventional UV or laser radiation were used (Table I). This result is in contrast with the recent work of Sadhir et al. (7) on the photopolymerization of maleic anhydride and styrene, induced by the 363.8 nm emission of an argon ion laser. That work showed to be the laser initiation 1000 times more energy efficient than the UV-induced polymerization. This discrepancy may arise from two factors (i) the lower light-intensity used in the laser irradiation that should favor chain propagation and (ii) differences in the way of comparing the... 

We have also used the Eosin-triethanolamine system to design a two-photon system based on visible laser-induced photopolymerization followed by UV-induced crosslinking as a means of building a three-dimensional network structure aimed at three-dimensional imaging. The key to our design, shown in Scheme 4 below, is incorporation of an acrylate monomer... 

FTIR spectra are also benehcial in establishing the optimum conditions for curing acrylic adhesives by exposure to UV radiation. The degree of UV polymerization of acrylic adhesives can be followed by the decay of the ethylenic ( CH=CH2) absorption band at 810 cm. Scherzer et al. studied the UV-induced crossUnking of a pressure-sensitive acrylic resin with copolymerized benzophenone groups using variable UV doses and intensities. Real time FTIR spectroscopy was also used to study the effect of various photoinitiators in accelerating the photopolymerization of acrylate resins. ... 

Novel polymer systems with much enhanced TPA initiators have been synthesized. However, it is still attractive to use well-known systems that were developed for conventional UV polymerization due to their excellent chemical, physical, and mechanical properties. Initiators in these resins generally have small TPA cross-sections, which require very high laser pulse energy for two-photon use. A strategy for circumventing this situation is to induce photopolymerization not by direct TPA of initiators, but by TPA-induced up-conversion fluorescence. An efficient fluorophore that emits at blue or shorter wavelengths was doped into resin. By TPA, the excited fluorescence polymerizes the resin by a single photon process. Since the fluorescence was three-dimensionally confined at the focal spot, the polymerization was also restrained to occur at this volume. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

Figure 24.9 (a) Time-conversion relationship for the thermally-induced polymerization of (Z,Z)-4CI in the dark at 80-120°C, (b) photopolymerization under UV irradiation, and the effect of crystal size. 

Fig. 18 Schematic cross-section of PEG-liposomes composed of domains of bis-SorbPC and stearoyl lipids. The photopolymerization-induced reduction in the surface area of the bis-SorbPC domains (black areas) during UV irradiation is shown on the right. Reprinted with permission from [108]. Copyright 2003, Elsevier...

In this paper we report some of the progress recently made in these various areas, concentrating on the light-induced polymerization of multiacrylic monomers which are today the most widely used UV-curable systems. We also describe here a new analytical method, based on IR spectroscopy, that permits the kinetics of photopolymerizations, which develop extensively in a fraction of a second, to be followed quantitatively and in real time. 

---