A type of bistriethoxysilane endcapped polyurethane/ureas (SPU) with well-defined structure was synthesized from bis(triethoxysiylpropyl) amine and purified prepolymers, which were obtained from the reaction of 2,4-toluene diisocyanate (TDI) and polyoxyethylene glycol (PEG) with different molecular weight. Then, fourier transform infrared spectroscopy (FTIR), hydrogen nuclearmagnetic resonance ((1)H-NMR) and standard dibutylamine back-titration method were used to confirm the structures of prepolymers and SPUs. Moreover, the properties of SPU were investigated by wide angle X-ray diffraction (WAXD), differential scan-ning calorimetry (DSC), thermogravimetric analyses (TGA), and percentage of water uptake. Results indicated that these polyurethanes were amorphous, and the percentage of water uptake and thermal stability of these polyurethanes went up with the increase of (M) over bar (n) of SPU, accompanying with the glass transition temperature (T(g)) values decreased with the increase of (M) over bar (n). This study provides us with a method to synthesize well-defined end-functionalized polyurethane. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 798-803, 2011