Structure-property relationships of polyurethanes based on toluene di-isocyanate

Abstract

The thermoplastic polyurethanes are linear segmented copolymers which consist of alternating soft and hard segment units. The soft segment is commonly a low molecular weight polyether or polyester whereas the hard segment generally consists of an aromatic diisocyanate condensed with a low molecular weight diol. It is now generally accepted that the properties of these materials are primarily due to the phase segregation of soft and hard segments leading to the formation of hard segment domains which are dispersed in the rubbery matrix. There are a wide variety of compositional variables which can affect the degree of phase segregation and hard segment organization and, accordingly, the sample properties. In this paper we report the results obtained on an extensive series of polyurethanes based on 2,4-toluene diisocyanate (2,4 TDI) and 2,6-toluene diisocyanate (2,6 TDI). In 2,4 TDI polymers, the asymmetric placement of the isocyanate residues with respect to the methyl group can result in some head-to-tail isomerization in the hard segment. In 2,6 TDI polymers, this problem is absent since the molecule is symmetrical. Other compositional variables examined included polyether vs. polyester soft segment, the molecular weight of the soft segment and the length of hard segment. Extensive physico-chemical techniques such as thermal analysis, wide and low angle x-ray studies and IR spectroscopic analyses have been employed to provide detailed information on the thermal transition behavior, structural organization and the properties.