Preparation, characterization, and properties of novel ultraviolet-curable and flame-retardant polyurethane acrylate

A series of flame-retardant polyurethane acrylate oligomer (FRPUA)–nhexa- phenoxy-cyclotriphosphazene (HPCP) (n = 0, 10, 15, and 20, where n is the amount of HPCP added to a 100 g mixture of FRPUA and other additives) ultraviolet (UV)-cured samples have been prepared. FRPUA was synthesized by the reaction of poly(glycidyl methacrylate) (an unsaturated polyether), a derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) (2DOPO–4,4′- dihydroxy-benzophenone (DHBP)), and isophorone diisocyanate. As a control sample, the polyurethane acrylate (PUA) oligomer and cured PUA sample were also prepared. Surface drying of the PUA and FRPUA–nHPCP curable mixtures required a few seconds under UV irradiation (400 W lamp). The effects of 2DOPO–DHBP and HPCP on the flame retardancy and thermal stability of the PUA system were also investigated. For the FRPUA–nHPCP series, as n increases from 0 to 20, the limiting oxygen index (LOI) increases from 21.1% to 23.3% and the total heat release (THR) slowly decreases from 32.4 to 26.4 kJ/g, while the PUA cured sample possesses the LOI and THR values of 19.0% and 29.2 kJ/g, respectively. Besides, the PUA system can achieve better flame retardant properties when using both 2DOPO-DHBP and HPCP. Thermogravimetric analysis indicates that the amount of char residue of the FRPUA–nHPCP (n = 0, 10, 15, and 20) cured samples ranges from 15.1 to 21.9 wt.%, which are much are higher than 10.5 wt.% for the PUA cured sample. Improving the flame retardancy of the PUA system will expand its applications, such as for paper manufacturing and architectural coatings, while simultaneously retaining the feature of fast surface drying.