Epoxy resins polyfunctional

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... 

Adhinarayanan [1201 describes the adhesive properties of epoxy—imide resins obtained through the reaction of epoxy resins, namely, Araldite GY250 (di-glycidylether of bisphenol A and epichlorohydrin difunctional) and Araldite EPN1138 (novolac epoxy resin polyfunctional), both manufactured by Hidustan Ciba-Geigy India Ltd (Calcutta), with bis(carboxyphthalimide)s. The chemical structures of these epoxy resins and bis(carboxyphthalimide) are... 

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... 

Aliphatic Glycidyl Ethers. Aliphatic epoxy resins have been synthesized by glycidylation of difunctional or polyfunctional polyols such as a 1,4-butanediol, 2,2-dimethyl-l,3-propanediol (neopentyl glycol), polypropylene glycols, glycerol, trimethylolpropane, and pentaerythritol. 

Polyfunctional aliphatic resins have exhibited high reactivity and degrees of cure with amines but problems of toxicity have diminished their usehilness and commercial interest. SoHd epoxy resins can be prepared by the taffy process or the advancement process. 

Epoxy resins are usually understood to be products of reaction of polyfunctional hydroxy compounds with l-chloro-2,3-epoxypropane (epichlorohydrin) in basic medium. In the simplest case two mol of epichlorohydrin react, for example, with one mol of bisphenol A, according to the following scheme ... 

A modified BMI-epoxy resin system has been introduced by Shell Chemical Company. The system is a highly reactive blend of a bismaleimide, COM-PIMIDE 1206 (55-60% by weight solution of BMI in DMF), and EPON Resin 1151, a polyfunctional epoxy resin (60). In contrast to many polyimide resins on the market, no free MDA is present in the product. This is an important feature, since MDA has been identified as an animal carcinogen and possibly a human carcinogen. This resin system has been fully evaluated for use in multilayer PCB boards (61). 2-Methylimidazole is recommended as a catalyst. However, if required, the processing window can be widened by using 2-phenylimidazole... 

Epoxy Adducts. The epoxy resin itself may be reacted with di- or polyfunctional reactants containing more than one epoxy group. The number of potential epoxy adducts is very large. Typical are phosphorous-containing epoxy resins prepared by reaction of diepoxies with acid dichlorides of phosphoric acids. This is accomplished at an acid diepoxy ratio of 1 2 in the presence of FeCl3 catalyst. Adducts may also be prepared by the reaction of chain hydroxyls. 

The polyaddition reaction is the most commonly used type of reaction for the cure of epoxy resins. The curing agents used in this type of reaction have an active hydrogen compound, and they include amines, amides, and mercaptans. With this reaction mechanism, the most important curing agents for adhesives are primary and secondary amines containing at least three active hydrogen atoms and various di- or polyfunctional carboxylic acids and their anhydrides. 

Di- or polyfunctional epoxy resins may be considered reactive diluents that provide a degree of resiliency, yet most preserve the inherent properties of the base epoxy resin. When added to an epoxy formulation, they will not reduce functionality, and in some cases an actual increase in crosslink density is noticed. Typical resins of these types are shown in Fig. 8.4. As flexibilizers, these diluents are often blended with the more reactive epoxy resins. They, of course, can also be used as epoxy resins in themselves. 

FIGURE 8.4 Typical di- and polyfunctional epoxy resin diluents.8... 

Table 14.4 presents formulation information for bisphenol A and polyfunctional epoxy resin emulsions that are cured with an aliphatic amidoamine curing agent. Adhesive performance data are also provided for substrates common to the automotive industry. Both formulas are based on a 1 1 epoxy-amine stoichiometry and they are reduced to 45 percent nonvolatiles with water. The working life of each system is several hours at room temperature. 

Finally, the Mannich reaction may be applied to the. synthesis of reactive amines used as crosslinking agents of epoxy resins. The process requires the availability of molecules possessing more than two NH groups, which are obtained by reaction of polyfunctional substrates with polyfunctional primary amines (oligomeric polyalkyle-ncamines, diamino cyclohexane, etc.) - (see also 422, Chap. Ill, C). 

Eor adhesive applications, it is more convenient to have the two components of the epoxy resin system react at a reasonable rate at room temperature. Replacing the anhydride component by a suitable, more reactive polyfunctional amine enables this to occur at room temperature. Several aliphatic and aromatic polyfunctional amines are used for this purpose (Eq. 21.28). 

A research team led by O. Figovsky synthesized aliphatic multifunctional cyclic carbonates from corresponding epoxies and carbon dioxide and NIPUs based on them [17,18], The authors tested some compositions polyfunctional carbonates synthesized in the laboratory, namely trimethylolpropane tricyclocarbonate (TMPTCC) and chlorine-contained aliphatic tricyclocarbonates (on the base of chlorine-contained aliphatic epoxy resins Oxilin ) and various diamines 2-methylpentam-ethylene diamine (MPMD), Dytek A, Invista Co. meta-xylenediamine (MXDA), Mitsubishi Gas Chem. Co. polyetheramineJeffamineEDR-148, Huntsman Co. and diethylenetriamine (DETA), D.E.H. 20, Dow Chemical Co. The properties of these materials are shown in Table 4.1. 

In contrast to the phenolic, urea and furan resinous cements, the liquid epoxy resin in the epoxy cements is cured by a reaction with a polyfunctional amine, such as polyethyleneamine or an active polyamide (Versamid) which is dispersed in the carbon or silica filler as shown in the following equation. ... 

Higher molecular weight epoxy resin hardeners such as fatty polyamides do not have the problems associated with amines and amine adducts. These reaction products of dimer and trlmer acids with polyfunctional amines provide films with fewer surface discontinuities. Polyamide cured epoxy coatings are more forgiving than amine cured epoxy coatings since they require less demanding surface preparation. Also, mix ratios are less critical for poly-amide/epoxy coatings (56). 

Polyfunctional mercaptoester chelators have been synthesized and evaluated as potential coupling agents for the adhesion of epoxy resins to steel. The adhesive systems were evaluated by subjecting torsional joints to shear failure after accelerated immersion testing in distilled water. 

---