Polyurethane–Nanosilica Hybrid Nanocomposites Synthesized by Frontal Polymerization SU CHEN, 1,2 JIANJUN SUI, 2 LI CHEN, 2 JOHN A. POJMAN 3 1 Key Laboratory of Material-Oriented Chemical Engineering, Jiang Su, China 2 School of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, 210009, China 3 Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, Mississippi 39406 Received 28 September 2004; accepted 1 November 2004 DOI: 10.1002/pola.20628 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Polyurethane–nanosilica hybrids were synthesized with frontal polymer- ization. Structurally well-dispersed and stable hybrids were obtained via a two-step functionalization process: First, the silica was encapsulated with 3-aminopropyltri- ethoxysilane (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 con- stant-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 elec- tron 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. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1670 –1680, 2005 Keywords: 3-aminopropyltriethoxysilane; frontal polymerization; nanosilica; poly- urethane hybrids INTRODUCTION The assembly of inorganic– organic nanocompos- ite materials affords unique opportunities to cre- ate revolutionary material combinations. These novel materials can have unexpected properties arising from the synergism between the compo- nents. More and more attention is being paid to the incorporation of an inorganic network such as a silica phase into an organic polymer matrix because of the potential physical and chemical properties. 1–6 There are many methods for at- taching polymer chains onto nanoparticle sur- faces, including chemisorption, 7 the covalent at- tachment of end-functionalized polymers to a re- active surface (grafting-to), 8 and in situ monomer polymerization with the monomer growth of poly- mer chains from immobilized initiators (grafting- from). 9,10 Frontal polymerization (FP) is a mode of con- verting a monomer into a polymer via a localized reaction zone that propagates through the mono- mer. The first FP reactions were discovered in Russia by Chechilo and Enikolopyan in 1972, who studied methyl methacrylate polymerization un- der high pressure. 11–13 The method was later ex- Correspondence to: S. Chen (E-mail: chensu@njut.edu.cn) Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 43, 1670 –1680 (2005) © 2005 Wiley Periodicals, Inc. 1670