Synthesis and properties of polyurethanes blended with poly(bispropoxyphosphazene)

A two-step polymerization was used to synthesize polyurethanes (PU) with di fferent amount of poly(bispropoxyphosphazene) flame retardant, LFR. Dipheny lmethane diisocyanate (MDI) was first reacted with poly(tetramethylene oxid e), PTMO 1000, to form an isocyanate-terminated prepolymer. The prepolymer was then reacted with a 1,4-butanediol/LFR homogeneous mixture at 70 degree s C for 100 min, followed by 1 h at 100 degrees C. The structures and prope rties of these modified PU were investigated using a differential scanning calorimeter (DSC), tensile testing machine, dynamic mechanical analysis ins trument, Fourier transform infrared spectrophotometer, nuclear magnetic res onance spectroscopy and scanning electronic microscope (SEM). It was found that the addition of LFR would accelerate the urethane reactions and introd uce a formation of micro-crosslinks. Consequently, the glass transition tem perature (Tg) of PU was increased and the rubbery plateau region was extend ed. From SEM observation, LFR additive phase-separated from the PU matrix w ith good interfacial bonding. The existence of LFR caused a decrease both i n ultimate tensile strength and elongation at break of polyurethanes. (C) 1 999 Elsevier Science Ltd. All rights reserved.