Fabrication, flame retardancy and physical properties of phosphorus containing porous organic polymers/epoxy resin composites

Abstract

Two kinds of phosphorus containing porous organic polymers (PPOPs) were synthesized through the Friedel-Crafts reaction between triphenylphosphine oxide and 4,4′-bis(chloromethyl)-1,1′-biphenyl (PPOP1) or α,α′-dibromo-p-xylene (PPOP2), where PPOPs were applied to improve the flame retardancy and physical properties of epoxy resin (EP). The PPOPs show high thermal stability, poor combustion properties, and large BET specific surface areas. The average pore diameter is 3.7 nm and 3.5 nm for PPOP1 and PPOP2, respectively. Monomers of EP can effectively diffuse into the pores of PPOPs, and PPOP/EP composites were further prepared by in situ polymerization. With only 1 wt% PPOP1 loaded into the composites, Tg values increase from 114 °C to 117 °C, while tensile strength and flexural modulus increase by 32% and 21%, respectively, resulting from the rigid skeleton of PPOPs and the interpenetrating polymer network structure in the composites. The dielectric constant and loss also decrease with the addition of PPOPs into the EP matrix. Cone calorimeter experiments show that PPOPs exert excellent flame retardancy on the EP matrix. In comparison with pure EP, when loading 5 wt% PPOP2, peak heat release rate, total heat release and total smoke production decrease by 26%, 48% and 39%, respectively. The PPOP/EP composites show higher tensile strength, Tg and flame retardancy than the samples prepared by simply blending the same amount of PPOPs into the EP matrix. Our research provides a promising strategy to prepare flame retardant EP composites with high performances.