Microscopic studies of segmented urethanes with different hard segment content

Abstract

AbstractThe morphology of a series of segmented polyurethanes (PUs) has been characterized by means of optical and electron microscopies. Use of a two step replica from cryogenically fractured surface appeared to be a very useful technique to characterize the morphology of segmented PUs. The materials contain poly(ethylene adipate) glycol (PEA) as a soft segment and a hard segment derived from 4,4′‐diphenylmethane diisocyanate (MDI) and butane diol (BDO). Changes in morphology have been observed as a result of the increase of the hard segment content in the series of polyurethanes. The greater the proportion of the hard segment content, the greater the number of grain aggregates on the fracture surface in the sample under investigation. PUs with the hard segment content of 22% are not crystalline and have no grain aggregates on the fracture surface. PUs with the hard segment content above 50% are anisotropic in the whole volume under polarized light and their fracture surface is grainy over almost the whole area. Two types of grain aggregates dispersed in spherulite‐like matrix have been observed for PUs of 32–50% of hard segment content. Two types of the anisotropic structure in some PUs have been found. The comparison of microscopic and thermal analysis results shows the inhomogeneous distribution of the soft and hard segments in some PUs similar to that found by Chang, et al., in the PU system based on poly(propylene oxide) endcapped with poly(ethylene oxide) as a soft segment.