Tailoring the Morphology and Melting Points of Segmented Thermoplastic Polyurethanes by Self-Nucleation

It is demonstrated that the melting behavior and the morphology of three segmented thermoplastic polyurethane elastomers (TPUs) can be tailored by applying self-nucleation (SN) procedures. The self-nucleating temperature ranges for each of the TPU have been first determined by differential scanning calorimetry (DSC), while their morphology was studied by polarized light optical microscopy (PLOM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). When the samples are cooled at slow to moderate rates after SN, the crystallization temperature of the TPUs increases by up to 45 degrees C, when the samples are ideally self-nucleated. This large reduction in supercooling increases the melting points of the samples by approximately 20 degrees C. At the same time, SAXS and AFM experiments demonstrate the growth of thicker lamellae under these slow to moderate cooling conditions as compared to untreated samples. When ideally self-nucleated samples are rapidly quenched (e.g., at rates of 100 degrees C min(-1) or larger) from their self-nucleation temperature to room temperature, the effects of SN described above on the morphology and melting points of the samples disappear for the TPUs that do not crystallize fast enough.