Cationic epoxy systems

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. 

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

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. 

Materials and additives that are chemically basic in nature have a detrimental effect on the curing of cationic-initiated epoxy systems. These substances can either stop the curing mechanism completely or produce under-cured polymers. Therefore such additives as amines or imides that are known to be adhesion promoters cannot be used in the EB-curable epoxy adhesive formulations. 

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. 

The chemistry involved depends on the oligomer used silicone acrylates cure by radical mechanism epoxy-silicones require cationic curing systems. Silicone... 

The/flc-ClRe(CO)3(4,7-Ph2-phen) complex has been demonstrated to be a useful spectroscopic probe in the curing of photosensitive epoxy-based materials [100], Emission spectra obtained from a 0.05-mm thickness film of a mixed epoxy system of bisphenol-A/novalac resin (Interz, SU8) and diglycidyl ether of bisphenol-A (DGEBA) containing cation-generating triarylsulfonium hexafluo-roantimonate salts as photoinitiators (Union Carbide, Cryacure UVI-6974) and... 

Epoxy acrylates are also commonly used as oligomers in radiation-curing coatings and adhesives. However, their name often leads to confusion. In most cases, these epoxy acrylates have no free epoxy groups left but react through their unsaturation. These resins are formulated with photoinitiators to cure via uv or electron beam (EB) radiation. The reaction mechanism is generally initiated by free radicals or by cations in a cationic photoinitiated system. The uv/EB cured epoxy formulations are discussed in Chap. 14. 

The first coupling of a LINAC with infrared spectroscopy has been performed by Palmese et al. in order to study in situ kinetics of radiation-induced cationic polymerization of epoxy systems. The aim of the study is to understand the curing behavior of polymers under irradiation. A UV light source and an electron beam (10 MeV pulse width of the beam from 2.5 to 10 pm) are coupled to a portable near infrared (NIR) instrument. Briefly, a portable NIR spectrometer (Control Development Incorporated, South Bend, IN, USA) is used,... 

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. 

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 and Z.H. Wang, Cationic photopolymerization of epoxy systems initiated by cyclopentadien-iron-biphenyl hexafluorophosphate ([Cp-Fe-biphenyl]+PF6-). Polym. Bull. 2005, 53(5-6), 323-331. 

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). 

The majority of the currently used coating systems is based on copolymers prepared from epoxy resins, polyfunctional amines, and partially blocked isocyanates (84-87). The resins are generally solubilized by the formation of cationic derivatives of amines by aminolysls of the carbamate in the partially blocked isocyanate. The principal applications of these cationic electrocoating systems are as automotive primers, in appliances, as primers and one-coat system.s, and in various other industrial applications. The main... 

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. 

Figure 7.12 The dynamic modulus versus temperature plots for DETDA-cured epoxy system and the corresponding nanocomposites containing 2.5 wt% and 5 wt% clay (modified with octadecyl ammonium cation). 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 Wiley and Sons Pnhlishers...

Carroy, A.C., Chomienne, F. and Nebout, J.F., Recent progress in the photoinitiated cationic polymerization of cycloaliphatic epoxy systems, Proc. RadTech Europe, 1997, 303-313. 

M.J.M. Abadie, N.K. Chia F.Y.C. Boey - Cure Kinetics for the Ultraviolet Cationic Polymerization of Cycloliphatic and Diglycidyl Ether of Bisphenol-A (DGEBA) Epoxy Systems with Sulfonium Salt Using an Auto Catalytic Model. J. Appl. Pol)rm. Sc. 7, 86-97 (2002)... 

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