Effect of stoichiometry and cure prescription on fluid ingress in epoxy networks

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Abstract
Stoichiometry and cure temperature were evaluated for epoxy systems based on the diglycidyl ethers of bisphenol‐A and bisphenol‐F and cured with 3,3′‐ or 4,4′‐diaminodiphenylsulfone. The materials were formulated as stoichiometric benchmarks and with an excess of epoxide and cured in two steps (125°C/200°C) or one step (180°C). Dynamic mechanical analysis and free volume testing indicated decreased crosslink density and increased chain packing in the excess‐epoxy materials, as well as a narrowing gap in properties between 33‐ and 44‐cured networks with excess epoxy. The narrowing gap was less pronounced in materials cured at 180°C. The excess‐epoxy materials were more resistant to water ingress, exhibiting reduced equilibrium water uptake. The excess‐epoxy materials were also more resistant to methyl ethyl ketone ingress, which occurred at a slower rate in most excess‐epoxy materials. The improvement in fluid resistance was attributed to enhanced chain packing in the materials with lower crosslink densities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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