Synthesis and properties of polyurethanes blended with poly(bispropoxyphosphazene)

A two-step polymerization was used to synthesize polyurethanes (PU) with different amount of poly(bispropoxyphosphazene) flame retardant, LFR. Diphenylmethane diisocyanate (MDI) was first reacted with poly(tetramethylene oxide), PTMO 1000, to form an isocyanate-terminated prepolymer. The prepolymer was then reacted with a 1,4-butanediol/LFR homogeneous mixture at 70 degrees C for 100 min, followed by 1 h at 100 degrees C. The structures and properties of these modified PU were investigated using a differential scanning calorimeter (DSC), tensile testing machine, dynamic mechanical analysis instrument, Fourier transform infrared spectrophotometer, nuclear magnetic resonance spectroscopy and scanning electronic microscope (SEM). It was found that the addition of LFR would accelerate the urethane reactions and introduce a formation of micro-crosslinks. Consequently, the glass transition temperature (Tg) of PU was increased and the rubbery plateau region was extended. From SEM observation, LFR additive phase-separated from the PU matrix with good interfacial bonding. The existence of LFR caused a decrease both in ultimate tensile strength and elongation at break of polyurethanes. (C) 1999 Elsevier Science Ltd. All rights reserved.