A novel coating of hyperbranched poly(urethane-phosphine oxide) for poly(methyl methacrylate) with high fire safety, excellent adhesion and transparency

Abstract

In order to enhance the fire resistance of poly(methyl methacrylate) (PMMA), a new transparent flame-retardant coating was prepared by coating hyperbranched poly(urethane-phosphine oxide) (HPUPO) onto PMMA surface, which was synthesized from 4,4′-diphenylmethane diisocyanate (MDI) and trihydroxymethylphosphine oxide (THPO). The ratio of MDI to THPO was changed to prepare HPUPO with different structures. The HPUPO coatings show a strong adhesion of 5B grade to PMMA and all coated PMMA have a high transparency as pure PMMA. In cone calorimetry test, peak heat release rate (PHRR) of all HPUPO coated PMMA decrease very obviously. The PHRR and total heat release (THR) values of PMMA-0.8 (HPUPO coated PMMA with the ratio of MDI to THPO 1: 0.8) are reduced by 83.6% and 33.0% compared to those of pure PMMA. For PMMA-1.1 and PMMA-1.25, the heat, smoke and toxic gas release are all decreased effectively, which indicates improvement of fire safety of PMMA. The PHRR, THR, total smoke production (TSP) and CO yield (COY) of PMMA-1.1 are decrease by 83.3%, 11.0%, 27.6% and 34.8%, respectively. In the back temperature test, PMMA-0.95 and PMMA-1.1 have the lowest back temperature rise rates in HPUPO coated PMMA, and the back temperature are about 200 °C under the continuous burning of the alcohol lamp for 800 s. In summary, PMMA-1.1 shows excellent transparency, adhesion and fire safety. HPUPO coated PMMA is a promising fire safe PMMA material for practical application and HPUPO can be used as transparent flame retardant coating with tailorable properties.