Cationic epoxy resin

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. 

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). 

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... 

A second type of uv curing chemistry is used, employing cationic curing as opposed to free-radical polymerization. This technology uses vinyl ethers and epoxy resins for the oligomers, reactive resins, and monomers. The initiators form Lewis acids upon absorption of the uv energy and the acid causes cationic polymerization. Although this chemistry has improved adhesion and flexibility and offers lower viscosity compared to the typical acrylate system, the cationic chemistry is very sensitive to humidity conditions and amine contamination. Both chemistries are used commercially. 

For some years, this type of vehicle was used in anionic electro deposition primers. However for automobiles cationic electro deposition primers are now preferred. The vehicles for cationic primers are proprietary but probably consist of the reaction product of epoxy resins and polyfunctional amines solubilized by the conversion of amine groups into salts using an acid such as lactic acid (2-hydroxypropanoic acid) [50-21-5] Alcohol-blocked... 

Of the commercially available EB-curable adhesives [9-12], the resins fall within one of two categories based on their curing mechanisms. The majority of EB-curable resins are based on (meth)acrylate-functionalized oligomers involving a free-radical curing mechanism. The second category is the epoxy resins that cure by a cationic mechanism. 

Crivello, J.V. and Lee, J.L., The synthesis, characterization and photoinitiated cationic polymerization of silicon-containing epoxy resins. J. Polym. Sci. Polym. Chem. Ed., 28, 479-503 (1990). 

Phenol was the 33rd highest-volume chemical. The 1994 U.S. production of phenol was approximately 4 billion pounds. The current world capacity is approximately 15 billion pounds. Many chemicals and polymers derive from phenol. Approximately 50% of production goes to phenolic resins. Phenol and acetone produce bis-phenol A, an important monomer for epoxy resins and polycarbonates. It is produced by condensing acetone and phenol in the presence of HCI, or by using a cation exchange resin. Figure 10-8 shows the Chiyoda Corp. bisphenol A process. 

Epoxy resin (Tufnol, Bakelite, Epophen) Styrene divinylbenzene ion exchange resins Reillex HPQ anion exchange resin Phenol/formaldehyde cation exchange resin Polyurethane Cellulose (as tissues)... 

Resinous adducts, 10 394 Resinous odor, 3 229t Resins. See also Epoxy resins Lacquer resins Novolac resins Phenolic resins Resole resins Thermoplastic resins acidic cation-exchange, 12 191 advanced materials, 1 693 antilipemic agents, 5 141 aromatic glycidyl amine, 10 372—373 chromatographic, 14 383-384 for coatings, 7 95-107 derived from furfuryl alcohol, 12 271— 272... 

Both anionic and cationic initiation are used to cure (polymerize and crosslink) epoxy resins (Sec. 2-12d) by ROP of the oxirane end groups. Photochemical cationic initiation (Sec. 5-2a-4) is important in various coating applications (3-4c) [Decker et al., 2001]. 

An alternative is a cationically initiated epoxy resin system cured by electron beam. The experiments with this process showed the following advantages ... 

For iodides, the order of efficiency is tetrabutyl > tetraethyl > tetramethyl 56 A rise in the catalytic effect of initiator is observed for alkali salts and for ammonium salts with increasing diameter of the cation, hence with growing distance between charge centres. This is in agreement with an increase of the electropositivity of cations and the increasing ability of salts to dissociate 54), Despite of this, the remarkable efficiency of lithium salts in curing of epoxy resins 58) or in copolymerization reactions 411 was confirmed in some papers. 

A rare example of cationic polymerization of emulsified epoxy resins has been reported by Walker et al.973 Polymerization of water emulsion of epoxy resins with a variety of superacids (triflic acid, HCIO4, HBF4, HPF6) results in polyols with two glycidyl units (294) in contrast to commercial epoxy resins with one unit separating the aromatic moieties. The level of residual glycidyl ether and Bisphenol-A units is also much lower than in conventional epoxy resins. 

All of these species (XIV, XV) have been for the most part applied towards function in the olefin polymerization arena use of these novel anions for the stabilization of other electrophilic species remains to be explored. Recently, the imidazolide anion XVI, as well as the perfluorinated tetraaryl borate derived from the diborane IX of Chart 2, have been used to stabilize iodonium cations.222 These cations are used as photoinitiators for cationic polymerization of epoxy resins in photolithography applications. While use of the [B(C6F5)4] led to a breakthrough in this area of research,223 higher activities are observed for more WCAs. 

The generation of a protonic acid (HX) is responsible for the initiation of cationic polymerization. Various monomers are polymerized by sulfonium photoinitiators. Especially this system has been shown to be potentially useful for UV curable coatings of metal and plastics with epoxy resins. 

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