Cure Behavior of Epoxy Resins With Different Kinds of Onium Salts as Latent Thermal Catalysts

摘要

Two latent thermal catalysts, Dimethyl phenacylsulfonium hexaflouroan-timonate, (Benzyl-S), and triphenyl benzyl phosphonium hexafluoroantimonate, (Benzyl-P), were synthesized. Both these synthesized catalysts fulfill requirements for a rapid cure at a moderately elevated temperature in curing the epoxy resins of neat 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane-carboxylate, (EPC), neat 2,2-bis(4-glycidyloxyphenyl)propane, (EPA), and their hybrid resin. The cure behavior of these resins cured individually with the synthesized catalysts was studied through correlation of the in situ FTIR (Fourier transform infrared) spectroscopy and DSC (Differential scanning calorimetry) dynamic scanning results. Catalyst Benzyl-S is more effective than Benzyl-P. Resin EPC is significantly more sensitive to the latent thermal catalysts than the EPA resin. Activated chain-end (ACE) and activated monomer (AM) mechanisms are basically adopted. Isomerization occurs in the neat EPA cure system, and transesterification takes place in all systems containing EPC species in teh latter curing stage. Most importantly, ester linkages C=O in the hybrid systems have been destroyed at some time during the curing process, but some reformed at the latter curing stage. It is most likely that the C=O linkage in in the EPC segments was attacked by the activated chain-end of the epoxide group of EPA species to form a five-membered cyclic acetal.