New Heterocyclic Polyurethane-ureas based on 4,4′-dibenzyl diisocyanate, Part 1: Influence of Oxadiazole Structure on Mechanical Properties

Abstract

A series of polyurethane-ureas was synthesized by solution polyaddition reaction of the following components: a polyester-diol, such as poly(ethylene adipate) (PEA), a polyetherdiol, such as poly(tetramethylene glycol) (PTMG) and a diisocyanate, such as 4,4′-dibenzyl diisocyanate (DBDI) or 4,4′-methylene-bis(phenyl-isocyanate) (MDI). In addition, 2,5-bis-(4-amino-phenylene)-1,3,4-oxadiazole (DAPO) was used as a chain extender. The hard segment content ranges between 1.384 and 1.819 mol NHCOO/1000 g polymer. For comparative studies, similar polyurethane-ureas were prepared by the same way but using 4,4′-methylene dianiline (MDA) and 4,4′-diamino-dibenzyl (DAB) as chain extenders. The resulting linear polymers were characterized by IR spectra, elemental and thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, inherent viscosity measurements, wideangle X-ray scattering and mechanical properties. The study of the relationships between structure and properties reveals the influence of the nature of starting materials, macrodiols, the heterocyclic diamine and diisocyanates on the mechanical properties of the polymers. The great number of hydrogen bonding that formed between urea and urethane groups and the presence of oxadiazole rings in the polymer chain induced an improved thermal stability and good mechanical properties. The mechanical behavior of these polymers was discussed and compared with that of earlier reported linear polyurethane-ureas based on MDI or with that of related polyurethanes chain-extended with diols.