Polyurethane anionomers. I. Structure-property relationships

Abstract

Polyether polyurethane anionomers are prepared using poly(tetramethylene oxide) of molecular weight 2000 as soft segments, 4,4'-diphenylmethane diisocyanate (MDI) as diisocyanate, dimethylolpropionic acid (DMPA) as chain extender, and two ionization agents, triethylamine (TEA) and N-ethyl diethanolamine (EDEA). Properties of the films cast from solution are studied by infra-red spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, wide-angle X-ray diffraction, tensile-elongation testing, transmission electron microscopy and gel-permeation chromatography. In the unionized film, soft segment crystallites are not present. Ionization creates soft segment crystallites and produces increased cohesion in the hard domains, which leads to an increase in both tensile strength and elongation at break. The tensile strength of the two systems studied increases with increasing the ionic potential. The morphology of the films shows that the hard domains are dispersed in the soft domains and that the size of the hard domains increases greatly after ionization. The TEA system has larger hard domains than the EDEA system. After annealing, the unionized film has improved ordering in the soft domains and enhanced tensile strength, but annealing provides no appreciable effect on the ordering of soft and hard domains and mechanical properties for the ionized films.