Effect of novel benzoxazine reactive diluent on processability and thermomechanical characteristics of bi‐functional polybenzoxazine

Effects of a monofunctional benzoxazine diluent (Ph‐a) on properties of a bifunctional benzoxazine resin (BA‐a) have been investigated. The BA‐a/Ph‐a mixtures are miscible in nature rendering the properties highly dependent on their compositions. The viscosity of the BA‐a resin can be reduced to one third using only about 10% by weight the Ph‐a diluent. The addition of the Ph‐a resin into the BA‐a resin can also lower the liquefying temperature of the resin mixtures whereas the gel point is marginally decreased. The gel point, which depends on the BA‐a/Ph‐a mixtures and the cure temperature, was determined by the frequency independence of loss tangent in the vicinity of the sol‐gel transition. The relaxation exponent values of the copolymer were found to be 0.24–0.55, which is dependent on the cure temperature. Gel time of the BA‐a/Ph‐a systems decreases with increasing temperature according to an Arrhenius relation with activation energy of 60.6 ± 1.5 kJ/mol. Flexural moduli of the BA‐a/Ph‐a polymers also increase with the Ph‐a mass fraction, however, with the sacrifice of their flexural strength and glass‐transition temperature.