The effect of structure, composition, and cure on the water absorption and Tg of amine‐cured epoxies was investigated. Water absorption is considered to depend on the polar group concentration and type, and on the amount of free volume in the polymer network. The contribution of polar groups in terms of their hydrogen bonding capabilities is reflected by the effect of meta (with respect to the diglycidylamino group) chloro, bromo, and methyl substituents on the water absorption of bis[N,N‐bis(2,3‐epoxypropyl)‐4‐aminophenyl]methane cured with 4,4′‐diaminodiphenylsulphone. The observed water absorptions are in line with the expected electronic effects of the substituents on the basicity of the amine group. Substituents in the ortho position adversely affect the hydrogen bonding capability of the amine group and limit the extent of reaction by steric interference. Examination of four O‐glycidyl systems (Epon 825, Epon 1153/114, Epon 1031, and Dow XD‐7342) cured with 4,4′‐diaminodiphenylsulphone has revealed quite a good linear relationship between the equilibrium water absorption and Tg for a particular hardener concentration irrespective of the epoxy compound employed. Networks ranged from those of low Tg (110°C) and water absorption (1.3%) to those of high values (300°C and 6.1%) for these parameters. Differences in slope for low (50‐65%) and high (100%) stoichiometric amounts of hardener are attributed to differences in the relative importance of OH/epoxy and NH2 or NH/epoxy reactions. The theoretical polar group concentrations and polar group type are much the same for these different systems and thus, free volume is considered to be a function of Tg and to play an important part in determining the level of water absorption.
The relative value of the rate constants for the reactions between the secondary and primary amine hydrogen atoms of 3‐trifluoromethylaniline with epichlorohydrin, and of aniline with phenyl glycidyl ether and with some N‐alkyl‐N‐glycidylanilines were determined by HPLC analysis. Values ranged from 0.14 to 0.24 and are in agreement with the findings of earlier workers for the reactions of aromatic amines with O‐glycidyl compounds but in direct conflict with the claim of a recent publication. The value for the reaction between 3‐trifluoromethylaniline and epichlorohydrin was unaffected by the nature of the catalyst, which covered a wide range of strengths and steric requirements.
N,N‐Bis (2, 3‐epoxypropyl) aniline and 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl) aniline] containing bromo, chloro, trifluoromethyl or polyfluoroalkoxy substituents were synthesised and cured with aromatic diamines in order to investigate the effect of substituted halogen on water absorption. Significant improvements were achieved: thus use of 4,4′‐methylenebis‐[N, N‐bis (2, 3‐epoxypropyl)‐3, 5‐dichloroaniline] and 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl)‐3‐(trifluoromethyl) aniline] instead of 4,4′‐methylenebis‐[N,N‐bis (2,3‐epoxypropyl) aniline] reduced the water absorption by about a half. Departures from Fickian behaviour were observed during water immersion ageing at room temperature and were a general feature of the epoxy systems examined. Plots of water absorption against the Fickian parameter (√t/d) usually showed at least mild sigmoid character and were not independent of specimen thickness. Further, slow continued uptake of water occurred during long‐term ageing, and evidence is provided that the associated network distortions are reversible.
The improved thermal, mechanical, and environmental properties of a number of matrix resins are described. Chlorinated epoxy resins were found to adsorb much less water than their non-chlorinated analogues, and showed improved hot-wet properties. Custom synthesised thermoplastic toughening agents were used to improve the fracture toughness of a tetrafunctional epoxy resin system. Substantial increases in K IC and G IC were achieved, with minimal loss of temperature performance.A number of highly functionalised epoxy monomers, with up to eight epoxy groups each, were prepared. The resulting cured matrixes were found to have glass transition temperatures in excess of 300°C.Blends of cyanate ester and bismaleimide were investigated as tough, high temperature performance matrixes. Addition of bismaleimide to cyanate ester resulted in an increase in fracture toughness. Dynamic mechanical analysis showed two distinct glass transitions, suggesting that the material has a two phase morphology such as an interpenetrating network.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.