Dual cure phenol-epoxy resins: Characterisation and properties

Reactive blends of 2, 2'-diallyl bisphenol A (DABA) and a novolac epoxy resin (EPN) were investigated for their cure behaviour, and their rheological, physical, mechanical and thermal properties. Cure characterisation was by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The system underwent dual curing through a sequential phenol-epoxy reaction and allyl polymerisation. The former reaction was catalysed by triphenyl phosphine (TPP). Whereas the phenol-epoxy reaction was completed, the allyl polymerization was limited to 40% by the regulation of cure conditions. Increase of epoxy concentration in DABA-EPN blends led to an improvement in the tensile strength and flexural strength of the neat castings. The flexural strength and interlaminar shear strength of the glass laminate showed an improvement with an increase in EPN concentration. Although the crosslink density of the neat casting was enhanced by epoxy-concentration, this did not result in any significant variations in the glass transition temperature (T-g) of the cured matrix. The T-g was in the range 78-82degreesC. Complete polymerization of all allyl groups resulted in an increase in the T-g and thermal stability while the mechanical properties of the neat system remained practically unaltered. The dual curing of the matrix system resulted in considerable improvement in the flexural properties of their glass composites.