Self-compatibilization effect of phosphonate with cyano group on flame retardancy and mechanical properties of epoxy

Abstract

A phosphonate flame retardant containing cyano group (CPDPO) was synthesized by using diphenylphosphinyl chloride and 4-cyanophenol and used to modify the flame retardancy epoxy (EP). The curing process, flame retardant performance and mechanism of EP/CPDPO were investigated. The cyano is a strong electron-withdrawing group which makes some CPDPO to react with EP via transesterification, thus about 17% diphenyl phosphine oxide (DPO) and 4-cyanophenol group will be grafted onto the chain of EP. Therefore CPDPO plays a self-compatibilization role in the system. The EP with 6 wt% CPDPO achieves the UL-94 V-0 rating and a LOI value of 36.6%. The peak of heat release rate and total heat release of EP with 6 wt% CPDPO are decreased by 47% and 24% compared with EP, respectively. The DPO grafted on the EP network tends to work in the condensed phase, while the free CPDPO is easy to work in the gas phase. The latter is far more than the former. Therefore, the effect of gas phase is obviously greater than that of condensed phase, which matches the structure of EP which has good charring ability itself. Moreover, the EP/CPDPO has better mechanical properties than that of EP and transparency equivalent to itself. This work suggests that the phosphonate containing strong electron-withdrawing group not only has self-compatibilization effect, but also regulates the properties and flame retardant mechanism.