A novel phosphorus-containing semi-aromatic polyester toward flame retardancy and enhanced mechanical properties of epoxy resin

Abstract Aiming to develop high performance flame-retardant epoxy resin (EP), a novel phosphorus-containing semi-aromatic polyester named poly[4,4′-bis(6-hydroxyhexyloxy)biphenyl 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-phosphaphenanthrene-10-oxide] (PBHDDP) was synthesized and employed as a multi-functional additive for EP with simultaneously flame retardation and mechanical enhancement. Appropriate thermodynamic compatibility between PBHDDP and the EP network made no phase separation occurred in the process of curing reaction. Compared with neat EP, the resultant EP thermoset containing barely 2.5 phr (2.44 wt%) of PBHDDP exhibited superior mechanical properties with 20.3% and 149% increase in tensile and impact strengths, respectively. Simultaneously, as increasing the content of PBHDDP, flame retardancy of the thermosets enhanced obviously as evidenced by the elevated anti-ignition and self-extinguishing performance, along with the reduced combustion rate and heat release. Whereas, obvious sacrifice of either transparency, glass transition temperature or thermal stability was absent. The exploration of this novel state-of-art that simultaneously improved the mechanical properties and flame retardancy of EP thermosets at a relatively low content of a single-component multi-functional additive provided a powerful basis for the technologies and potential industrial applications.