Inverting polyurethanes synthesis: Effects on nano/micro-structure and mechanical properties

Two sets of new thermoplastic elastomeric polyurethanes were prepared by different routes. One route was the common two shoot polymerization, in which a short diol is added at the last step in order to link prepolymer chains. The new rout that is described here consisted in preparing firstly the hard segments upon 1,6-hexamethylene diisocyanate (HDI) and 1,4-butanediol (BD), used in the previous case as chain extender, and adding finally the polydiol in the second step, in a chain extender fashion, in order to form the grown polyurethane. The differences between these two sets of materials were considerable due to the more ordered and crystalline hard segments formed and the subsequent nano-domain distribution that aroused when inverting the common synthesis. Inter-domain distances and domains sizes are measured and also compared with those of the literature. The structure/properties relationships of synthesized polyurethanes with different hard segment content were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), atomic force microscopy (AFM), and performing tensile and Shore D hardness tests.