SYNOPSISAromatic polyesters, prepared by the reaction of phthalic or isophthalic acids and a,walkanediols, were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydride. These polyesters were effective as modifiers for toughening of the epoxy resin system. The most suitable composition for modification of the epoxy resins was inclusion of 20 wt % of poly (ethylene phthalate) (MW 7200), which resulted in a 150% increase in the fracture toughness (I&) of the cured resin at no expense of its mechanical properties. The effectiveness of poly (alkylene phthalate) s as modifiers decreased with increasing the chain length of alkylene units. The toughening mechanism was discussed based on the morphological and dynamic mechanical behaviors of the modified epoxy resin system.

SynopsisNew bismaleimides containing ether bonds were prepared. The thermal properties of the bismaleimides were investigated by differential scanning calorimetry (DSC). The effects of structure of the bismaleimides and curing conditions on the thermal and mechanical properties of the cured resins such as initial decomposition temperature (Td), glass transition temperature (T'), and flexural strength were studied. The introduction of ether bonds to bismaleimide resins decreased the brittleness of the resins without reductions in their heat-resistant properties.

The curing reaction of an epoxy resin and acid anhydride with an amine and/or alcohol was studied kinetically. No etherification reaction occurred at 70–140°C. and the initial reaction rate was proportional to the concentration of epoxide, acid anhydride, and catalyst (tertiary amine or alcohol). The apparent activation energies of the reaction in two systems of epoxy resin–hexahydrophthalic anhydride/triethanolamine (0.5 wt. %) were obtained as 14.1 and 14.4 kcal./mole. The effects of the substitution R of the tertiary amine NR3 or alcohol R3COH as catalyst on the curing reaction of the epoxy resin and acid anhydride were studied. The polar reaction constant ρp for amines, obtained negatively, indicates that electron‐repelling substituents of NR3 increase the curing rate; ρp for alcohols, obtained positively, indicates that electron‐withdrawing substituents of R3COH increase the rate of curing reaction. These results supported the proposed curing mechanism better.

The curing reaction of an epoxy resin and acid anhydride with an amine and/or acid, alcohol, and phenol was studied kinetically by using commercial epoxy resins and acid anhydrides. No etherification reaction occurred at 70–140°C., even in the case of epoxide/acid anhydride/HA (acid, alcohol, or phenol) and of epoxide/acid anhydride tertiary amine/HA, and the initial reaction rate was proportional to the concentrations of epoxide, acid anhydride, and catalysts such as tertiary amine, acid, alcohol, and phenol. The apparent activation energy of the reaction system of Epikote 828/methyl‐bicyclo(2,2,1)heptene‐2,3‐dicarboxylic anhydride/triethanol amine/HA was obtained as about 14.7 kcal./mole, and the low frequency factors and large negative entropies of activation for the reaction might confirm that the curing reaction of epoxy resins and anhydrides belongs to the type of nucleophilic bimolecular displacement reaction. The effects of the substituents, R, of acid, alcohol, and phenol as cocatalyst on the curing reaction of epoxy resin/acid anhydride/tertiary amine/HA were studied. The reaction constants, p, obtained positively for HA's, indicate that electron‐withdrawing substituents of HA increase the rate of curing reaction of system of epoxide/acid anhydride/amine/HA. Differences in the catalytic and cocatalytic effects among benzoic acid, benzyl alcohol, and phenol in these reaction systems might be considered to depend on the donating power of hydrogen bond which is the important role rather than a general electrostatic interaction effect as solvent effects in nucleophilic substitution reactions. These results supported the proposed mechanisms reasonably.

Both vinyl methacrylate (VMA) and vinyl acrylate (VA) were homopolymerized by n‐butyllithium catalyst at −78°C. Both of the anionic polymers were soluble in common organic solvents, and only vinyl group was contained in the polymers. Both of the monomers were homopolymerized by free‐radical catalysts under different conditions. The soluble polymers were obtained under low monomer concentrations and at low conversions. It was estimated by NMR and infrared spectroscopy that both the soluble polymers contained mainly a vinyl group, similar to the anionic polymers. The soluble VMA polymers comprised 10–20% cyclic units for monomer concentrations ranging from 1.8 to 0.5 mole/I. The soluble VA polymers comprised 50–60% cyclic units for monomer concentrations ranging from 0.9 to 0.3 mole/l. It was suggested that the cyclic units did not consist of γ‐lactone but of larger‐membered rings than δ‐lactone or of ladder structural units. The difference between the cyclization content of poly‐VMA and that of poly‐VA might be explained by the copolymerization data of the reference monomers.