Comparative dielectric studies of segmental mobility in novel polyurethanes

Abstract

Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4′- diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethyl-hydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the a relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hard-segment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the micro-phase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the a band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II