Ultraviolet light photopolymerization

Photopolymerization and Plasma Polymerization. The use of ultraviolet light alone (14) as well as the use of electrically excited plasmas or glow discharges to generate monomers capable of undergoing VDP have been explored. The products of these two processes, called plasma polymers, continue to receive considerable scientific attention. Interest in these approaches is enhanced by the fact that the feedstock material from which the monomer capable of VDP is generated is often inexpensive and readily available. In spite of these widespread scientific efforts, however, commercial use of the technologies is quite limited. 

Figure 3 Polymeriztion of 50/50 w/w methecrylic anhydride initiated with 0.5 wt% DMPA and 80 mW/em of ultraviolet light (a) Illustration of the temporal eontrol of the photopolymerization. Initiation is eeased at —30 s and reinitiated at —40 s (dashed line) eompared to eontinuous initiation (solid line), (b) Evaluation of the eompressive modulus as a funetion of exposure time.

Photopolymerization using ultraviolet light-activated initiators... 

Kou et al., reported using a hyperbranched acrylated aromatic polyester as a modifier in UV eurable epoxyacrylate resin. The material is compatible with the epoxy-acrylate resins. They found that the photopolymerization rate of the resin is promoted by this modifier. Also, the shrinkage of the resin was redueed. At the same time, the tensile, flexmal, compressive strength, and thermal properties of the ultraviolet light eured films are greatly improved. 

Photoinitiation n. Initiation of a free radical polymerization by irradiation with ultraviolet light (or other frequency of hght), causing photopolymerization. Odian GC (2004) Principles of polymerization. John Wiley and Sons Inc., New York. 

Photopolymerization by irradiation with ultraviolet light irradiation [2] in particular is known as a method having excellent controllability of polymer dispersion structure. With decreasing monomer concentration, the aggregating morphology from phase separation changes from liquid crystal droplets to bubble-shaped cellular polymer structure and to polymer fiber networks, as shown in Fig. 8.6. 

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). 

Photopolymerizations were initiated with either ultraviolet or visible blue light of varying intensity (1-150 mW/cm2). In general, the high concentration of double bonds in the system and the multifunctional nature of the monomer (two double bonds per monomer molecules) led to the formation of a highly crosslinked polymer system in a period of a few seconds, depending on the initiation rate. 

Sodium chloroaurate (NaAuCl4 2HaO) initiates polymerization of VCZ both thermally and photochemically. When the polymerization is conducted in nitrobenzene, photopolymerization under illumination of near ultraviolet to visible light proceeds with remarkable rapidity, whereas thermal polymerization starts after an induction period as shown in Fig. 8. This is a unique example of photoacceleration of cationic polymerization. Since the initiation mechanism is different from known cationic polymerization, the thermal system will be mentioned briefly before the discussion of the photochemical system. 

Dark Stability. The examples cited have demonstrated that dye sensitized photopolymerization is potentially rapid in solution, but that substantial speed losses result when polymeric binder compositions are used in an imaging fashion. Our work has shown that TBBS activated compositions sensitized by MB can exhibit absolute photospeeds to red light that are comparable to those of commerical photopolymer systems that are sensitive only to ultraviolet wavelengths (65). These systems can offer features not now available in UV-only sensitive systems. The major failure of all such systems, however, is a pronounced lack of stability on dark storage for the lengths of time required by industry standards. 

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