Abstract
Abstract A spectroscopic method based on model compounds for measuring and ranking thermoset resin hydrogen bond acceptor and donor strengths is demonstrated. This method involves measurements of complex formation constants between polyfunctional resin model compounds and monofunctional probe compounds. For the epoxy (m-phenylenediamine/bisphenol A diglycidyl ether and 1,3-diaminocyclohexane/bisphenol A diglycidyl ether) and cyanate (bisphenol A dicyanate) resins of this study, the ranking of hydrogen bond basicity is aliphatic amine-epoxy > cyanate > aromatic amine-epoxy, and the ranking of hydrogen bond acidity is aromatic amine-epoxy > aliphatic amine-epoxy » cyanate. For the amine-epoxy resin model compounds, intramolecular interactions between the amine and hydroxyl groups reduce the hydrogen bond acceptor strength and enhance the hydrogen bond donor strength relative to expectations for these individual functional groups acting independently. Measurements of the hydrogen bond basicity of the resin monomer model compounds are also reported. Results of single fiber fragmentation tests of an AS4 carbon fiber with the MPDA-epoxy, DACH-epoxy and cyanate resins are indicative of good adhesion and are in a ranking order parallel to that of the hydrogen bond basicity. There is minimal mechanical property variation among these resins, and a hydrogen bonding mechanism is proposed for the correlation of fiber-resin interfacial shear strength and resin hydrogen bond basicity.
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