Effect of symmetry and H-bond strength of hard segments on the structure-property relationships of segmented, nonchain extended polyurethanes and polyureas

Segmented, nonchain extended polyurethanes and polyureas based on PTMO soft segments (SS) anti hard segments (HSs) based on only single molecules of a diisocyanate were synthesized. Type and nature of the diisocyanate was systematically varied in order to analyze the effect of HS symmetry and type of linkage between the HS and SS on the structure-property relationship of these segmented copolymers. Results showed that the increased symmetry of the diisocyanates allows a more efficient packing of the HSs which leads to a microphase-separated structure with the crystalline hard ribbon or thread-like domains percolated throughout the SS matrix, even with a low HS content (ca. 13 wt.%). The service window of these segmented copolymers was significantly influenced by the symmetry and type of linkage between the HS and SS. Most copolymers also showed evidence of strain hardening accented by the strain induced crystallization of the PTMO SS.