Dilute solution behaviour of hexamethylene diisocyanate-based carboxylatedpolyurethanes and related ionomers in tetrahydrofuran

The mechanisms controlling the elution of carboxylated polyurethanes (CPUs) and polyurethane ionomers (PUIs) during the size exclusion chromatography (SEC) separation process in tetrahydrofuran (THF) were investigated. In ord er to elucidate the elution process, their dilute solution viscosity behavi our was studied as well. Sample molar mass averages were determined by SEC using polystyrene calibration (SEC-PS) and in the case of CPUs also by SEC coupled with a multi-angle light scattering detector (SEC-MALS). The molar mass averages and intrinsic viscosities of CPUs decrease with increasing de gree of carboxylation as a consequence of side-reactions. The large differe nce in reduced viscosity between non-carboxylated PU and CPUs can be attrib uted to different macromolecular conformations in THF solution. The molar m ass averages of PUIs determined by SEC-PS were much lower than those of the parent CPU and showed a slight dependence on the type of counterion used. In the selected series, the molar mass averages and intrinsic viscosities i ncreased in the order Ca2+ < Li+ < Na+ < K+. The addition of CF3COONa had n o influence on the solution viscosity of CPUs, while it prevented the assoc iation of PUIs. (C) 1999 Elsevier Science Ltd. All rights reserved.