Synthesis and selected properties of polyurethanes with monodisperse hard segments based on hexane diisocyanate and three types of chain extenders

Poly(tetramethylene oxide)-based segmented polyurethanes were synthesized by the chain extension of a poly(tetramethylene oxide) with a length of 1270 g/mol that was end-capped with 1,6-hexane diisocyanate. Three types of uniform chain extenders were used: a diamine diamide, a diol diamide, and a diol diester. The concentration of the monodisperse hard segments was approximately 32 wt %, and the materials were clear and tough. The polyurethanes with monodisperse hard segments were subsequently characterized with differential scanning calorimetry, dynamic mechanical thermal analysis, and compression set measurements and were found to display low glass-transition temperatures, an almost temperature-independent rubbery plateau, and sharp melting temperatures. The rate of crystallization (melting temperature - crystallization temperature) was moderately fast (36-54 degrees C). Moreover, the melting temperature of the polyurethanes increased with the number of hydrogen-bonding groups in the hard segment, whereas the modulus at room temperature was more dependent on the structural regularity of the extender. The best elastic properties were found for the materials extended with the diamine diamide. Finally, an interesting combination of properties was revealed for the polyurethane with a diol diamide extender based on aminopropanol. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012