Improving mechanical properties and processability of a very high T g epoxy amine network via anti‐plasticizer fortification

Abstract: In this work, molecular fortifiers are added to a highly aromatic and rigid epoxy monomer bis(2,7 diglycidyl ether naphthalenediol) methane (NNE) possessing a very high glass transition temperature (Tg) when cured with 4,4′‐diaminodiphenyl sulfone (DDS) to explore their impact upon mechanical and thermal properties and reactivity. The molecular fortifiers used are the nonfunctional naphthalene (NAPH), the reactive diluent o‐cresyl glycidyl ether (CGE) and an adduct of dihydroxy naphthalene and CGE (molecular fortifier naphthalene, MFN), a variant on the partially reacted substructures approach. The fortifiers are found to affect NNE/DDS reactivity and increase processability depending upon their propensity to attach to the network either through hydrogen bonding or pi‐pi electron interactions. Thermal analysis shows that the fortifiers increased cure conversion although the Tgs of the networks were generally unaffected until higher levels of addition. The fortifiers reduce moisture ingress and suppress glassy state β relaxations while increasing modulus significantly. Although there is little improvement in toughness overall, some evidence for higher fracture toughness is observed for the MFN and NAPH modified networks. This work highlights the effectiveness of different molecular level fortifiers on improving properties, in particular the rigidity of highly crosslinked networks.