Effect of an epoxidized novolac resin anhydride structure on the properties of resin

Abstract

The properties of an epoxidized novolac resin cured with two homologous series of substituted succinic anhydrides (alkenyl and alkyl) have been determined and the effects of anhydride structure on properties have been evaluated. Substituted succinic anhydrides yield cured resins with lower strengths, lower heat distortion temperatures, and lower moduli. Use of substituted succinic anhydrides could broaden the range of application of alicyclic anhydrides to include those requiring a more flexible resin. Effects of specific elements of anhydride structure have been consistently interpreted from properties measurements and from aging and solvent resistance studies.

Effects of Catalyst Content, Anhydride Blending, and Nanofiller Addition on Anhydride-Cured Epoxidized Linseed Oil-Based Thermosets

“…This difference in reactivity helps to justify an increasing degree of microphase separation as PA content is increased, but it cannot account for the opposing trends in T α observed in the blended NMA and MTHPA systems. This is once more explained by modulation of the potential for double-bond-mediated cross-linking, which has been shown to impact heat distortion temperature more significantly than stiffness . As in the case of the modulus data, it would appear that the T α values of the NMA-based blends are much less affected by dilution, implying that double-bond-mediated cross-linking may be less important with NMA than with MTHPA in the systems studied here.…”

“…In the case of MTHPA, however, it appears that the modulus of the blended system may actually fall below that of both the pure MTHPA- and pure PA-based networks. This is best explained by the observation that the dilution of unsaturated anhydrides with sufficient quantities of anhydrides that (like PA) are incapable of double-bond-mediated cross-linking tends to result in a modest reduction in modulus . While the same effect may be operative in the NMA/PA blends as well, the results indicate that it is the addition of the higher-performing PA rather than double-bond-mediated cross-linking by the NMA that drives increases in modulus in this system.…”

“…The MTHPA formulation starts at a higher E ′ value than the NMA formulation, and both trend toward the same storage modulus as the PA content is increased. While it was initially posited that PA, being highly compact, would provide increased moduli in both systems, MTHPA’s superior storage modulus may be explained by the combined presence of a methyl group and a double bond, which have been posited to inhibit rotation between conformers and bond distortions in anhydride-cured epoxies and, in the latter case, to provide reactive sites for additional cross-linking reactions . As NMA is diluted with PA, the modulus values observed trend toward those of the pure PA network.…”

“…This may be rationalized in light of the argument that anhydride reactivity in an epoxy/anhydride system should track with the dissociation constant of the diacid derived from the anhydride . Predictions of the dissociation constants of NMA, MTHPA, and PA made using the ARChem SPARC physicochemical properties calculator (see ) indicate that while the diacids formed from NMA and the MTHPA isomers typical of anhydrides used for epoxy curing have very similar p K a1 and p K a2 values (3.88–3.94 and 5.64–5.70, respectively) the analogous values for the diacid of PA are distinctly different (3.05 and 5.57, respectively).…”