Synthesis and characterisation of novel flame retardant polyurethanes containing designed phosphorus units

In this study, 2-carboxyethyl(phenyl)phosphinic acid (CEPPA) and trimethylolpropane (TMP) are used to synthesise a novel flame retardant containing phosphorus units: 5-hydroxy-3-(2-hydroxyethyl)-3-methylpentyl-3-[2-carboxyethylphenylphosphine]propanoate (HMCPP). Then, 4,4′-diphenylmethane diisocyanate (MDI) is taken as a hard segment, with HMCPP and polycaprolactone diol (PCL) as soft segments, and 1,4-butanediol (BD) is used as a chain extender to prepare a novel polyurethane (HMCPP/PUs). The results of ¹H NMR and FT-IR reveal the successful synthesis of the HMCPP flame retardant. The gel permeation chromatography analysis demonstrates that an increase in the HMCPP content is accompanied by a decrease in the molecular weight of PU. The FT-IR analysis reveals the complete NCO group exhaustion of PU and HMCPP/PUs. The thermal analysis shows that the initial decomposition temperature of PU is higher than that of HMCPP/PUs by 19 °C. Both DMA and DSC analyses show that the Tg and the dynamic Tg of PU are higher than those of HMCPP/PU. Stress-strain tests indicate that the HMCPP content is increased, the maximum stress and Young’s modulus of HMCPP/PUs are decreased, and the elongation at break is increased. All of the HMCPP/PUs exhibit excellent flame retardancy, obtaining higher than 27.7 in limiting oxygen indices and a V-0 rating in the UL-94 test.