Polyfunctional epoxies

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... 

Perez, R. M., Sandler, J. K. W., Altstacdt, V., Hoffmann, T., Pospiech, D., Artner, J., Ciesielski, M., Doering, M., Balabanovich, A. I., and Schartel, B., Effective halogen-free flame retardancy for a monocomponent polyfunctional epoxy using an oligomeric organophosphorus compound, J. Mater. Sci., 2006, 41, 8347-8351. 

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. 

Celanese Epi-Rez SU-8 was chosen for these studies. This resin is a polyfunctional epoxy novolac resin (Scheme 2) made from bisphenol-A. It is optically... 

Although DGEBA resins provide the backbone of most epoxy formulations, they may be blended with other types to achieve modifications. Epoxy novolacs, having higher functionality, increase the cross-linking density, which improves heat resistance but decreases impact resistance. Incorporation of epoxidized oils increases flexibility at the expense of heat and chemical resistance. Low-viscosity polyfunctional epoxies based on polyols or polyhydric phenols reduce viscosity and can increase functionality without impairing cured properties. Monofunctional reactive diluents will also decrease viscosity and form part of the polymer backbone, to impart a measure of flexibility without the possibility of migration. Properties of commercially available epoxy resins and diluents from various suppliers are listed in Table 1. 

Chem. Descrip. Aliphatic polyfunctional epoxy resin CAS 25928-94-3... 

The required temperature resistance depends on the application conditions. For the lower temperature regions, the classical systems based on diglycidyl ether of Bisphenol A (DGEBA) cured with aromatic diamines like 4,4 -diaminodiphenylmethane (DDM) or 4,4 -diaminodiphenylsulphone (DDS) and systems containing dicyandiamide have been used. To increase the bond density and the temperature resistance, polyfunctional epoxy resins have been introduced.(N,N,N, N -tetraglycidyl-4,4 -diaminodiphenylmethane (TGDDM) is an example.) The glass transition temperature, Tg, of these systems may increase far above 200 C. 

Adhesives for use at 350°F to 450°F contain polyfunctional epoxies and usually a latent curative with an aromatic diamine structure such as methylene dianiline, mcta-phenylenediamine, or diaminodiphenylsulfone. Heat distortion temperatures of up to 325°F can be obtained with these aromatic amine hardeners. Toughness has now been incorporated into these high-temperature adhesives (Table I). 

Recently, because high-performance epoxy resin is strict in its requirements, polyfunctional epoxy has been offered in practical fields. In particular, epoxy novolac resin (ENR) is largely used as electronic encapsulation material because of its well-known thermal resistance properties. Because the strucmres of ENR exert a significant influence on the properties of the cured resins, it is necessary to understand their structure-property relationship. Despite various advantages, epoxy needs modifications to overcome some crucial disadvantages like limited solubility in polar solvents, higher cost of bisphenol A-based epoxy and maximum service temperature of only about 100 °C. 

The reaction with amine derivatives such as 4-hydroxybenzeneamine 20 and 4,4 -methylenebis-benzeneamine 22 is used to produce the tri- and telrafunctional epoxies N,N,0-tris(2,3-epoxypropyl)-4-hydroxybenzeneamine 21 and A,A,iV, iV -telrakis (2,3-epoxypropyl)-4,4 -methylenebisbenzeneamine 23, respectively. However, the polyfunctional epoxies that combine the most attractive properties for electronic applications are the resins produced by epoxi-dation of the phenol novolac 24 and cresol novolac 26. Novolac resins are obtained by the condensation of a phenol with formaldehyde in the presence of acid catalysts in such conditions that the degree of polycondensation is in the range of 3—5. The epoxy novolacs 25 and 26 are produced by the reaction of epichlorhydrin with the corresponding phenol novolac and ortho-cresol novolac resins. Epoxy resins are generally characterized by their dynamic viscosity (77) at 25 °C, expressed in millipascal second (mPa s). 

Figure 12.3 Chemical formulae of di- and polyfunctional epoxies commoniy used to manufacture eiectricaiiy conductive adhesives Dainippon Epicion 830 18, Ciba-Geigy ERE 1359 19, Ciba-Geigy MY 0510 21, Ciba-Geigy MY 720 23, Dow Chemicai DEN 438 25, and Ciba-Geigy ECN 1280 27.

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