Other Epoxy Resins

In addition to the DGEB A resins, there are several other types of epoxy resins of commercial significance. The most common of these are epoxy novolacs, glycidyl ether of tetraphe-nolethane, bisphenol F-based resins, and aliphatic and cycloaliphatic resins. 

Epoxy Novolac and Other Phenols. Resins of greater functionality than DGEB A can be produced in several ways. Polyols having more than two hydroxyl groups per molecule (e.g., phenol novolac resins) can be reacted with epichlorohydrin to produce epoxy novolac resins with a structure shown in Fig. 2.5. 

The epoxy novolac resins are synthesized by reaction of phenolic or cresol novolacs with epichlorohydrin in the same fashion as the bisphenol A resins. The number of epoxy groups per molecule is dependent on the number of hydroxyls in the phenol novolac molecule and to the extent to which they are reacted. Complete epoxidation can be accomplished, but this will lead to steric factors, which could limit the useful size of the cured polymer. Thus, selective epoxidation is often practiced.9 

The inherent thermal stability of the phenol formaldehyde chemistry is preserved but with the crosslinking characteristics of the epoxy groups. However, epoxy novolacs also form very rigid and brittle polymers when fully cured because of their high crosslink density. For this reason, they are often used as modifiers in epoxy adhesive systems rather than as the base polymer. 

Glycidyl Ether of Tetraphenolethane. A large number of polyhydric phenols have been used to prepare diglycidyl ethers. The polyphenol, l l,2 2-(p-hydroxyphenol)ethane, is used to prepare a tetrafunctional epoxy resin, tetraglycidyl ether of tetraphenolethane. The functionality of commercial resins (e.g., EPON Resin 1031, Resolution Performance Products, LLC) is about 3.5. This forms a solid resin (melting point of 80°C) with a structure as shown in Fig. 2.6. Commercial products are solid resins and solutions. 

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Several other epoxy resins have been made. Many contain glycidyl ether group while others are cyclic aliphatic epoxies and acrylic aliphatic epoxies. 

Because of their low viscosity, cycloaliphatic epoxies are often used to dilute other epoxy resins. These resins, however, have not achieved general importance in adhesive formulations because of relatively low tensile strength and because they do not cure well at room temperature. One major application for cycloaliphatic epoxies, however, is for adhesives and coatings that can be cationically cured by exposure to uv light. 

The aliphatic epoxy resins formed from reaction with hydrogen peroxide or peracetic acid include epoxidized polybutadiene, epoxidized soya or linseed oil, and epoxidized polyglycols. The resulting products have too low a functionality for use as base polymers. They are almost always used in combination with other epoxy resins to improve properties such as cure rate, flexibility, and heat deflection temperature. Therefore, these resins are often considered to be reactive diluents and flexibilizers. 

These resins are most often characterized by their epoxy equivalent weight (EEW), molecular weight (number of repeating units ri), and viscosity. Table 4.2 shows the relationship between EEW and viscosity. These DGEBA epoxy resins can be used alone or in blends with other DGEBA resins, other epoxy resins, or even other types of polymeric resins. Very often commercial epoxy resin products are actually blends of resins having a broad molecular weight distribution. 

Some curing agents can also be used to form adducts with epoxy resins, and these adducts, in turn, offer unique curing properties with other epoxy resins. Adducts are commonly used in adhesive formulations to reduce the vapor pressure of the system, to modify the reactivity of the system, to improve mix ratios so that they are closer to equal parts of the resin component and of the curing agent component, and to provide a certain degree of flexibility into the end product. 

Solvents. Solvents commonly used in epoxy resin applications present a flammability hazard. These solvents present other special health hazards. Contact with solvents will cause defatting and drying of the skin, which enhances the chance for skin irritation. Some solvents are absorbed directly though the skin, and absorption may be enhanced if the skin is abraded or irritated. They also have the ability to dissolve other epoxy resin system chemicals and carry them through the skin. The inhalation of solvent vapors or mists may cause respirator irritation and depression of the central nervous system. 

Several other epoxy resins have been used in literature fracture studies. Chang et al. used a diglycidyl ether of butane diol resin (DGEB) to prepare... 

Previous work (8) on partially cured thin-films of two other epoxy resins showed much less temperature separation between softening, further reaction, and ultimate glass transition than is the case with Resin 5208. In fact, overlap between the dispersion regions made it impossible to identify the chemical reaction process. 

SAFETY PROFILE Animal experiments have shown disturbed blood formation. The degree of toxicity of uncured epoxy resins varies and is partly dependent on the extent of unreacted curing agents. See also other epoxy resin entries and POLYMERS, INSOLUBLE. When heated to decomposition they emit acrid smoke and fumes. 

Kinetic analysis of other epoxy-resin systems... 

The calculated Tg-value of a linear polymer with this repeating unit is 321 K. The contribution of two crosslinks is 82 K. Hence, the calculated Tg-value for the resin system A/ HHPA system is 321 K + 82 K 403 K. The measured Tg-value was 399 K. The Tg-values of five other epoxy resin systems were calculated (and measured) in the same way, all results are listed in Table 7.5. It is important to realise that the used structures are idealised structures. Every deviation from this ideal network structure will lower the experimental Tg-value. Thus, the calculated Tg-values will in general be equal or higher than the measured Tg-values. This was confirmed for the six systems investigated. 

Other epoxy resins are also being manufactured, but their commercial j utilization is not so far advanced as those based on bisphenol A and i epichlorohydrin. For instance, resorcinol and a mixture of diphenol-poly-(hydroxyphenyl)-pentadecanes, obtained by the addition reaction of phenol with an unsaturated phenol derived from cashew-nut oil (see structure below) can be reacted with epichlorohydrin to produce epoxy resins. ... 

The brominated resins are more effective than the chlorinated resins and have become more predominant commercially. The ability of the resins to retard or extinguish burning is due to the evolution of hydrogen halide at elevated temperatures. Brominated epoxy resins are generally blended with other epoxy resins to impart flame retardance in such applications as laminates and adhesives. 

The measured Jp t) curves of the other epoxy resins studied, Epon 1004, 1002, 1001, and 828/DDS, were successfully reduced at chosen reference temperatures and altogether the results are shown in Figure 5.4 as functions of the reduced time t/ar in a double logarithmic plot. This comparison plot was constructed by requiring all the reduced curves to cross at a compliance level of log 7p(f) = -8.5. The choice of Ibis 100.7,110.7,118.6,130,and205 for the DDS crosslinked 1007,1004, 1002, 1001, and 828 Epons, respectively. 

Other Polynuclear Phenol Glycidyl Ether Derived Resins. In addition to the epoxy novolacs, there are other epoxy resins derived from... 

Most industrial chemicals and polymers are not the 100% pure, single chemicals as described in their general chemical stmctures. In the case of epoxy resins, they often contain isomers, oligomers, and other minor constituents. As a first requirement, one would need to know the epoxy content or EEW of the epoxy resin so the proper stoichiometric amoimt of cross-linker(s) can he calculated. However, a successful thermoset formulation must also have the proper reactivity, flow, and performance. Consequently, other epoxy resin properties are required by the formulators and supplied by the resin producers. 

The cure of epoxidized novolaks, prepared via the reaction of Ph0H/CH2=0 copolymer with epichlorohydrin, in the presence of Nadic methyl anhydride, was studied by differential scanning colorimetry (DSC) [121]. The use of DSC to study other epoxy resin curing systems has been reported in the literature. 

Union Carbide produces a number of epoxyaliphatic resins under the name of ERLA, obtained by homo- or copolymerization of the mixture of esters formed between bis-2,3-epoxychloropentylol with ethylene glycol in the presence of ben-zyldimethylamine. The diepoxide formed is commercialized under the name ERLA-4205. Compared with other epoxy resins, ERLA epoxies show a higher resistance by 25 to 110% to bending, compression, and tension. 

Analogous to the above, the diglycidyl ether of bisphenol-A and other epoxy resins have been condensed with to obtain electron-... 

Figure 4 shows the chemical formulae of other epoxy resins commonly used to prepare conductive adhesive compositions. Representative of approximately difunctional compounds are the diglycidyl ether of bisphenol-F (DGEBF) 18 and the diglycidyl ether of 1,3-dihydroxybenzene 19. Epoxy resins with a functionality higher than two are prepared by the reaction of l-chloro-2,3-epoxypropane 7 with polyfunctional starting materials. 

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