Dicarboxylic Acids and Acid Anhydrides

Resin Mixture of Maleic anhydrides anhydride Components [mol] Diethylene Propylene glycol glycol Glycerol Xylene 

Similar to the vinyl ester resins, the cured epoxyfumarate resins are distinguished by enhanced chemical resistance (e.g. in aqueous 20% NaOH at 60 °C), heat deflection temperature and flexibility. The chemical composition of the R group (methyl, ethyl, n-butyl, benzyl, cyclohexyl) influences the properties of the crosslinked epoxyfumarate resins [6]. If the R group contains bromine (e.g. tribromoneopentyl or 2,3-dibromopropyl), the cured resins are fire retardant [7]. Moreover, the brominated resins are distinguished by increased Martens heat deformation temperature and low water absorption. 

The synthesis of epoxyfumarate resins by adding an add ester of maleic acid to the commerdal low-molecular weight epoxy resin (Epidian 5) with simultaneous isomerization of maleate groups to fumarate ones was presented [9]. The resins were synthesized in the two-step procedure using the acid ester of maleic add prepared separately with epoxy resin or in the one-step synthesis (Fig. 1). The add ester of maleic acid was obtained in the reaction of maleic anhydride and cyclohexanol, although use of benzyl alcohol [10] and w-hexanol was also reported [llj. 

6-Tris(dimethylaminomethyl)phenol was used as a catalyst for the reaction of carboxyl and epoxy groups. The studied resins were crosslinked using styrene. Next, piperidine was added as the isomerization catalyst of maleate groups to fumarate ones (Table 3). 

The structure of the synthesized resins was ascertained by H-NMR spectroscopy and the content of the trans isomer was determined from the NMR spectra according to the method of Curtis using the areas of the signals due to fumarate at about 6.9 ppm and maleate at about 6.4 ppm. It was found that the isomerization of maleate bonds did not occm without piperidine [10]. Moreover, unsaturated epoxymaleate resins were significantly less reactive than the epoxyfumarate resins. The properties before curing and of the crosslinked resins obtained in one- and two-step procedures are similar (Table 4), although the resins prepared in one-step synthesis were character- 

---