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Information Sought 2 Workshop Composition 2 Workshop Program 2 Questionnaire 4 WORKSHOP PRESENTATIONS Review of 1987 Workshop Processing Methods Technologies that Complement Processing Scientific and Technical Barriers

The heat of reaction and kinetics of curing of diglycidyl ether of bisphenol-A (DGEBA) type of epoxy resin with catalytic amounts of ethylmethylimidazole (EMI) have been studied by differential power-compensated calorimetry as a part of the program for the study of process monitoring for composite materials. The results were compared with those from 1 : 1 and 1 : 2 molar mixtures of DGEBA and EMI. A method of determination of heat of reaction from dynamic thermoanalytical instruments was given according to basic thermodynamic principles. The complicated mechanism, possibly involving initial ionic formation, has also been observed in other measurements, such as by time-domain dielectric spectroscopy. The behavior of commercially available DGEBA resin versus purified monomeric DGEBA were compared. The melting point of purified monomeric DGEBA crystals is 41.4 ~ with a heat of fusion of 81 J/g. The melt of DGEBA is difficult to crystallize upon cooling. The glass transition of purified DGEBA monomer occurs around -22 ~ with a ACp of 0.60 J/K/g. Epoxy resins are the most widely used polymer matrices for composite materials. Epoxy resins are commonly cured by amines or anhydrides, with or without the use of catalysts and accelerators. Phenolic curing agents are sometimes used. Epoxies may also be cured by means of catalysts alone. The catalytic curing process produces crosslinked epoxy homopolymers composed mainly of ether linkages rather than amide or ester linkages as in amine or anhydride cured epoxies. Epoxies cured by phenolic crosslinking agents will also consist of ether linkages. The resultant polymer from the relatively low temperature catalytic cure possesses superior thermal stability and chemical resistance than most epoxies made from other processes. The chemical stability of the ether linkage is higher than either the amide or ester linkages which may be subject to hydrolysis by strong acidic or alkaline agents. The glass transition temperature of catalytically cured epoxies is generally higher than 150 ~ .2-Ethyl-4(5)-methylimidazole, EMI, has been used widely in the curing of epoxies either as an accelerator for a curing agent in the amounts of below 1 phr (parts per hundred-part of resin) or as a catalyst alone for curing in the amounts between 2 to 10 phr. The curing mechanism of EMI and the most popular epoxy resin, diglycidyl ether of bisphenol-A (DGEBA), has been studied mainly through the use of the model compound phenyl glycidyl ether as well as other imidazoles [1][2][3]. The initial rapid reaction was considered to be the formation of 1 : 1 epoxy-EMI adduct and the subsequent formation of the 2:1 epoxy-EMI adduct in the form ol'imidazolium alkoxide. The alkoxide ion was considered as an effective catalytic center to attack another epoxy group and to continue the polymerization reaction [1] with the EMI incorporated in the polymer. Further investigation [3] indicated that an inherent instability of the imidazolium system led toward the regeneration of imidazoles during the curing process by at ...

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