Polyurethane-nanosilica hybrid nanocomposites synthesized by frontal polymerization

Polyurethane-nanosilica hybrids were synthesized with frontal polymerization. Structurally well-dispersed and stable hybrids were obtained via a two-step functionalization process: First, the silica was encapsulated with 3-aminopropyltriethoxysilane (APTS). Second, poly(propylene oxide) glycol, toluene 2,4-diisocyanate, 1,4-butanediol, and a catalyst (stannous caprylate) were dissolved in dimethylbenzene and mixed together at room temperature along with the modified nanosilica. A constant-velocity propagating front was initiated via the heating of the end of the tubular reactor. For the complete encapsulation of the silica with APTS, different weight ratios of APTS to silica were investigated. The polyurethane hybrids were characterized with Fourier transform infrared, differential scanning calorimetry, and transmission electron microscopy. The polyurethane hybrids produced by frontal polymerization had the same properties as those produced by batch polymerization with stirring, but the frontal polymerization method required significantly less time and lower energy input than the batch polymerization method. (c) 2005 Wiley Periodicals, Inc.