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The effect of hard segment structure on rheological properties of solutions of segmented polyurethanes

✍ Scribed by Zoran S. Petrović; James Ferguson; Nick Hudson; Ivan Javni; Marija Vraneš

Publisher
Elsevier Science
Year
1992
Tongue
English
Weight
485 KB
Volume
28
Category
Article
ISSN
0014-3057

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✦ Synopsis

Almtract--Segmented polyurethanes based on polypropylene glycol, butane diol and a mixture of (diphenylmethane diisocyanate)/(toluene diisocyanate) (MDI/TDI) were prepared and characterized. Soft segment concentration was kept constant at 50% in all polymers but the structure of the hard segment was varied by using MDI/TDI ratios from zero to pure MDI. The aim of the work was to examine solution properties as a function of the polymer composition and also the stability of polyurethane solutions in dimethylformamide. Polyurethane solutions exhibited Newtonian behaviour up to rather high concentrations of 30%. No structure formation, due to association of polyurethane molecules through hydrogen bonding, was observed in DMF up to concentrations >70%. Ageing of polyurethane solutions, manifested as decrease of viscosity with time, was observed only with two high molecular samples. Solubility of the polymer increased and rigidity decreased with increasing TDI/MDI ratio. Activation energy for viscous flow increased with solution concentration and rigidity of the hard segment.

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