A COMPARATIVE HYDROGEN-BONDING AND FIBER INTERFACE STUDY OF EPOXY ANDCYANATE RESINS

A spectroscopic method based on model compounds for measuring and rank ing thermoset resin hydrogen bond acceptor and donor strengths is demo nstrated. This method involves measurements of complex formation const ants between polyfunctional resin model compounds and monofunctional p robe compounds. For the epoxy (m-phenylenediamine/bisphenol A diglycid yl 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 a mine-epoxy, and the ranking of hydrogen bond acidity is aromatic amine -epoxy > aliphatic amine-epoxy >> cyanate. For the amine-epoxy resin m odel compounds, intramolecular interactions between the amine and hydr oxyl groups reduce the hydrogen bond acceptor strength and enhance the hydrogen bond donor strength relative to expectations for these indiv idual functional groups acting independently. Measurements of the hydr ogen bond basicity of the resin monomer model compounds are also repor ted. Results of single fiber fragmentation tests of an AS4 carbon fibe r 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 hydr ogen bond basicity. There is minimal mechanical property variation amo ng these resins, and a hydrogen bonding mechanism is proposed for the correlation of fiber-resin interfacial shear strength and resin hydrog en bond basicity.