Epoxy resins photopolymerization

Using a QCM, Josse et al. [27] have determined the storage and loss modulus of a commercially available UV-curable epoxy resin (SU-8-2002). An in-line monitor of the UV photopolymerization of 2-hydroxyethyl methacrylate with a photoinitiator of 1-chloroanthraquinone was demonstrated by Kim et al. [39]. 

Photopolymerizable epoxies using onium salt photoinitiators also show considerable promise for use in high performance composite applications. Traditional thermally cured epoxy resins are already well entrenched in these applications however, the use of the recently developed photocurable epoxy materials offers considerable potential for rapid fabrication of fiber-reinforced composites without the need for cumbersome ovens and long cure times. Photopolymerized epoxy laminates and filament wound pipe have already been demonstrated in our laboratory. 

Epoxides are widely used in thermally activated reactions but their photopolymerizations are generally slow. This has restricted their use in these processes somewhat. The photocrosslinking of epoxy resins has recently been reviewed by Lohse and Zweifel and their use in dielectric coatings will be discussed in Sect. 6.5. 

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Vinyl ester resins are related to UPRs. They consist of a styrene monomer and the addition products of epoxy resins with methacrylic acid. The vinyl esters are usually cured using a peroxide initiator at elevated temperature [62] or at ambient temperature using a peroxide initiator with a cobalt promoter. Vinyl ester resin can also be photopolymerized [63]. Photocurable vinyl ester systems with methacrylic acid/phenyl glycidyl ether addition product as a diluent were used with ( )-camphorquinone photoinitiator and N,N,3,5-tetramethylaniline photoreducer [64]. The effect of the monomethacrylate... 

Gregory patented Ultraviolet Curable Resin Compositions Having Enhanced Shadow Curing Properties in 2001. This patent has the same idea as Dixon s patent, that is, use photopolymerization at the surface of a filled resin to trigger a thermal front. Gregory went beyond using peroxide-cured vinyl resins. He used dialkyl iodonium salts, sensitized by a-hydroxy ketones, that produced Lewis acids upon UV irradiation. The Lewis acid triggered cationic polymerization of epoxy resins and vinyl ethers. The heat from the photoinitiated process decomposes peroxides into radicals that react with the iodonium salts to produce Lewis acids. 

Figure 8. Kinetics of the photopolymerization of an epoxy diacrylate resin with and without UV absorber CO.5 % of Tinuvin 900)...

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. 

The kinetic of photopolymerization of a typical epoxy monomer (CE) is reported in Figure 2. Notwithstanding its high reactivity CE resin gives rise to photocured films containing around 55% of unreacted epoxy groups after one minute of irradiation. 

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