Mechanical and Thermal Properties of Poly(urethane-urea) Elastomers and their Relations with the Structure of their Chemical Constituent-Monomers

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Abstract
A new series of PoIy(urethane-urea) elastomers was prepared using polydiethyleneadipate (I), 2,6 tolylene diisocyanate (II-A), 1-6 hexamethylene diisocyanate (II-B) and 4-4’ diaminodiphenylsulphone (III) by a modified solution casting technique, to study the relation between the structure and properties of the polymer. Two series of elastomers were prepared by taking (I) and (III) in 1 : 2 molar ratio and by varying the concentration of (II-A) from 3.40 to 2.40 in molar proportions and by varying the concentration of a mixture of the diisocyanates (II-A) and (II-B) in the molar proportion of 70 : 30. The mechanical properties of polymers prepared using only the single diisocyanate (II-A) were found to be superior to those using combinations of (II-A) and (II-B). An interesting feature of the findings was that the % elongation at break of the II-A series increased with decrease of the concentration of (II-A), whereas with mixed diisocyanates the opposite trend resulted. Thermal stability of the first series of polymers was found to be higher than polymers of the second series, a DTA technique being used to measure this property. The presence of 30% of (II-B) in a polyurethane polymer gives a large increase in the glass transition temperature. Thus addition of aliphatic diisocyanate to an aromatic one, reduces the mechanical strength and thermal stability of polyurethane elastomers.

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