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Phase Separation of Functionalized Polyester Polyurethanes

Segmented polyurethanes are one of the most widely investigated classes of synthetic polymers. It is generally agreed that their unique and interesting properties are predominantly the result of a two-phase morphology. One method for tailoring properties of polyurethanes is incorporation of additional functional groups that may provide the change in the degree of phase mixing and domain structure. Polyester polyurethanes based on isophoronediisocyanate, polycaprolactone, and 1, 4-butandiol with different amounts of functional groups introduced into the hard segments via second chain extender, 2, 2¢ -bis-(hydroxymethyl) propionic acid, were prepared. The concentration of carboxylic groups varied from 0 to 0.45 mmol g-1. In order to examine the effect of functional group content on the phase separation, degree of ordering within domains and the motional heterogeneity wide-angle X-ray diffraction, WAXD, optical microscopy, differential scanning calorimetry and electron spin resonance, ESR-spin label method have been employed. Polarized micrographs and the extent of ordering from WAXD measurements reveal the changes of phase morphology with the carboxylic group content. The degree of crystallinity and the separation of spherulitic rings increase with increase of functional group content. However, above a certain concentration of functional groups degree of phase separation decreases. Analysis of composite ESR spectra suggests similar behaviour of motional heterogeneity. The effect of functional groups in PU on the hard and soft segment mixing is discussed in terms of additional noncovalent interactions and chain structure which at critical level of interactions lead to a formation of more open hard segment structure accessible to interaction with the soft segment.

polyurethane; phase separation; functional groups

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