Abstract
Relationshipbetweenmechanical,physicalpropertiesandinternalstructureofdicyandiamidecuredbisphenol-Aepoxyresinswerestudied.Threekindsofcuredepoxyformulationweremadeusingmixturescomposedofseveralbisphenol-Aepoxyoligomers,whichhavedifferentdistributionofepoxyequivalent(molecularweights)eachother.Thethreecuredresinshadalmostidenticalrubberyplateauvalueofstoragemodulusofelasticityindynamicmechanicalanalyses,whichmeansthecuredresinshadalmostsame"average"crosslinkdensity.However,themechanicalandphysicalpropertiesofthecuredresinswereinlargediversity.Theglasstransitiontemperature(Tg)andthesolventresistancedecreasedwithenhancingthedistributionofepoxyequivalent(molecularweights).Thecompressiveyieldstressofthecuredresinsincreasedwithenhancingthedistributionofepoxyequivalent・Inthemeantime,thecompressivefracturestrainandthefracturetoughness(K,,;)increasedwithdecreasingthedistributionofepoxyequivalentintheepoxyformulation.Thesephenomenasuggestthatthepropertiesofcuredepoxyresinswereunderthecontrolnotonlyofchemicalstructuresofepoxyoligomersandthe"average"crosslinkdensity,butalsoofnon-uniformgelstructurewhichweredeterminedinthecureprocessofeachresinformulation.Scanningprobemicroscopyandelectronmicroscopyrevealedthattheexistenceofnano-sizestructureinthecuredresins.Thedifferenceinthephasestructureconsistingofahard-phaseandasoft-phase,suchasthesizeandtheconnectivityofeachphase,wouldbethekeyfactorswhichexplainthediversityofthepropertiesoftheresins.
