The cure and diffusion of water in halogen containing epoxy/amine thermosets

Abstract

Dielectric measurements were performed to determine the effect of chlorine, methyl and trifluoromethyl substituents on the cure of bis[ N,N-bis(2,3-epoxypropyl)-4-aminophenyl]methane with 4,4′-diaminodiphenylsulfone and 4,4′-bis[1,4-phenylenebis(1-methylethylidene)]-bis[2,6-dimethyl]benzamine, and the data were analysed to give gelation and vitrification points. Infra-red measurements were also carried out during the cure process to monitor the consumption of epoxy groups. Dynamic mechanical thermal analysis and density measurements were carried out on the N,N-diglycidylaniline system and a reduction in the glass transition temperature was observed to occur with the incorporation of a trifluoromethyl group into the resin structure. Dielectric and gravimetric studies are reported on the absorption of water by these resins. In agreement with gravimetric data for water absorption, dielectric data obtained at 10 Hz showed that trifluoromethyl substitution increases the diffusion coefficient whereas chlorine substitution decreased it. The chlorinated resin exhibited a higher than expected initial dielectric increment, which has been attributed to the effect of a micro-porous surface structure of the resin. Atomic force microscopy of the resins surfaces indicates that the chlorinated and fluorinated resins have greater surface roughness than the protonated analogues, consistent with the dielectric observations. Analysis of the amount of ‘bound’ and ‘free’ water in the resin systems shows that the halogenated resins have a lower percentage of bound water and more of the water is in the ‘free’ state.