Synthesis of reactive DOPO-based flame retardant and its application in polyurethane elastomers

An inherently flame-retardant polyester diol (FRPE) containing phosphorus was successfully synthesized via condensation polymerization with the commercial reactive flame retardant 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phospha-phenanthrene-10-oxide (DDP), adipic acid (AA), ethylene glycol (EG), and 1,4-butanediol (1,4-BDO). Flame-retardant polyurethane elastomers (FR-PUEs) were subsequently produced by employing FRPE, 4,4-diphenylmethane diisocyanate (MDI) and 1,4-BDO. The mechanical and thermal properties and flame retardancy of the resulting FR-PUEs were characterized by tensile tests, thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) analysis, dynamic mechanical analysis (DMA), limiting oxygen index (LOI) analysis, vertical burning tests (UL-94), and cone calorimeter (CC) analysis. It was suggested that DDP would increase the interaction between the hard and soft segments, resulting in FR-PUEs of unexpected higher tensile strengths of up to 40.0 MPa. In addition, it was found that the introduction of DDP can give rise to an increase of the residual char yield and limiting oxygen index (LOI), whereas reduces the total heat release (THR). Especially, using a low phosphorus content of 0.72 wt.%, the vertical burning level and LOI of the resultant FR-PUE reached V-0 and 24% respectively, and reduced THR of 52.6 MJ/m(2) was obtained. The flame-retardant mechanism of phosphorus in DDP was proposed both in the gas and condensed phases based on cone calorimeter (CC), residual char analyses and TG-IR analysis. (C) 2020 Elsevier Ltd. All rights reserved.