Cationic epoxies

Janke, C.J., Dorsey, G.F., Havens, S.J. and Lopata, V.J., Toughened epoxy resins eured by eleetron beam radiation. 28th International SAMPE Technical Conference, S71, 1996. Janke, C.J., Electron beam curable cationic epoxy resin systems and composites. 1st Annual Electron Beam Curing of Composites Workshop, September 18-19, Oak Ridge, TN, Ref. ID, 1996. 

Photopolymer systems are photocurable resins incorporating reactive liquid monomers, photoinitiators, chemical modihers and hhers. Typically stereolithography utilizes UV radiation, so UV-curable systems are used. Free-radical-photopolymerizable acrylate systems were originally used however, newer cationic epoxy-resin and vinyl ether systems (based on iodinium- or sulfonium-salt cationic initiators) are now being utilized. 

Note that there is generally excellent agreement between the experimental data of Figure 4 and shapes of the calculated curves shown in Figure 3. Consequently, this model does afford a reliable predictive tool for this particular photoinitiated cationic epoxy system. The general applicability of the model to other cationic epoxy formulations has not yet been verified. 

As expected, the reaction exothems from our experiments with polyfunctional urethane acrylate systems are much more complex than those found with the cationic epoxy polymerizations. Figure 5 shows results from our aliphatic triacrylate DSC runs at three temperatures under continuous illumination. 

T. Wang, et al., Several ferrocenium salts as efficient photoinitiators and thermal initiators for cationic epoxy polymerization. J. Photochem. Photobiol. A Chem. 2007, 187(2-3), 389-394. 

Cationic epoxy resin based systems can be prepared by reacting quaternary amine salts with epoxy resins to introduce the cationic functions. The polymers can then be cross-linked with blocked isocyanates at reasonable baking temperatures (34. 35). 

Polyols act as chain transfer agents which assist UX cure of cationic epoxy systems. Our results with EHDO and did not... 

Oxman et al., smdied controlled, sequentially curable cationic/free radical hybrid photopolymerization of diepoxide/acrylate hybrid material with the aid of photodifferential scanning calorimetry. The polymerizations were carried out in the presence of various concentrations of either ethyl-4-dimethylamino benzoate or 4-tert-butyl-N,N,-dimethylaniline as electron donors and camphoquinone/diphenyliodonium hexafluoroantimonate as the sensitizing system. The results showed that the free-radical acrylate reactions always precede the cationic epoxy polymerizations. 

Radiation UV-acrylics, cationic epoxies, dual-curing adhesives Liquids UV-curing adhesives have shorter curing times than conventional adhesives and can therefore increase production speed and productivity... 

Cationic epoxies can be used to bond substrates that are not transparent. Unlike radically curing acrylic adhesives, cationic products can be sufficiently pre-activated by UV fight they will then continue to cure once the light has been removed. Cationic epoxies can be equally as effective for applications where one or more components are transparent, or none at all. 

Figure 7.7 XRD plots of organoclay (modified with octadecyl ammonium cation), epoxy/DDS/clay (intercalated) and epoxy/DETDA/clay (exfoliated) nanocomposites. Reprinted from D.Ratna, N.R. Manoj, R.K. Singh Raman, R. Varley and G.R Simon, Polymer International, 2003, 52, 9,1403 2003 John...

The last class of dielectric coatings to be mentioned here is formed by the UV cationic epoxy systems. In most cases photoinitiators as invented by Crivello are used to initiate the chain crosslinking polymerization of di-epoxides or mixtures thereof with monoepoxides. 

Since electrodeposition of sol-gel films is driven by the local pH change on the electrode surfe.ce, it allows codeposition with other pH-responsive materials such as chitosan [61,62,67,70] and cationic epoxy resin [71]. The works... 

The features and detail of the IPN kinetics were also studied in other works [274-276]. The kinetics of thermally initiated cationic epoxy polymerization and free radical acrylate photopolymerization were investigated in [277]. It was found that the preexistence of one polymer has a significant effect on the polymerization of the second monomer. The reaction kinetics and phase separations were studied for sequential IPNs in [278]. The kinetics of IPN formation was studied for IPNs based on PDMS-cellulose acetate butyrate [279]. All these and other works [280-282] confirm the general regularities of the reaction kinetics and its connection with phase separation in forming systems. 

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