Moisture Uptake and Thermomechanical Behavior of Epoxy–Amine Networks Derived from Ortho-Substituted Monomers
Michael D. Garrison, Joseph W. Tsang, Matthew C. Davis
Abstract
Ortho-substitution with hydrophobic aliphatic groups has shown reduced moisture uptake in a variety of thermoset networks. In this study, the number and size of ortho-substituents were systematically varied on the epoxy monomers and aniline curing agents to determine network structure–property relationships. Networks were formed from combinations of four epoxies cured with seven aniline curing agents. The cured epoxy–amine networks were exposed to boiling water for 96 h to determine network moisture uptake, as well as wet thermomechanical properties. Ortho-substitution on both the epoxy and aniline monomers showed a reduced moisture uptake of up to 62% over an unsubstituted network. Also, the substituted networks had smaller wet TG knockdowns compared to the unsubstituted network, and networks derived from 2,2′-(((butane-1,1-diylbis(2-(tert-butyl)-5-methyl-4,1-phenylene))bis(oxy)bis(methylene))bis(oxirane) (t-Bu Bisepoxy) had the smallest wet TG knockdowns of only 5 °C or less. These results show the unique advantages of ortho-substituents on epoxy–amine networks in terms of network hydrophobicity and wet thermomechanical behavior. Applications of the ortho-substituted monomers and networks include use in marine environments as composite materials, hydrophobic coatings, or adhesives.