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The thermooxidative stability of cured epoxy resins. I
Author(s) -
Burton Bruce L.
Publication year - 1993
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1993.070471013
Subject(s) - epoxy , polymer chemistry , amine gas treating , degradation (telecommunications) , electrophile , materials science , oxide , chemistry , organic chemistry , composite material , catalysis , telecommunications , computer science
Prior studies have shown that for many epoxy resin systems significant oxidative degradation occurs in air at temperatures as low as 100°C and that thin oxidized surface layers serve as crack initiators in flexural samples at low strains and can reduce flexural strengths to less than 25% of the original values. This study was undertaken in an attempt to identify predominant degradation pathways and cured resin systems that are thermooxidatively stable in 125°C air. Based on flexural property retention and IR spectral data, the thermooxidative resistance ranking of D.E.R.*332 epoxy resin polymerized with the following is p ‐toluenesulfonamide > 4,4′‐diaminodiphenyl sulfone or sulfanilamide > methylene dianiline ≫ triethylenetetraamine > 2,5‐dimethyl‐2,5‐diaminohexane. Oxidation of aliphatic amine‐cured D.E.R. 332 epoxy resin is initiated by electrophilic attack of oxygen on the lone‐pair electrons of the nitrogen to form an amine oxide. Polymer chain cleavage then occurs via Cope reactions. A newly proposed oxidative degradation pathway is described wherein the hydroxylamine products of Cope reactions are further oxidized to nitrones, which then decompose to amides via oxaziridine intermediates. Commercial antioxidants added to an aliphatic amine‐cured epoxy resin were ineffective, supporting the conclusion that the predominant degradation mechanism is not free radical in nature. © 1993 John Wiley & Sons, Inc.