Block architecture influence on the structure and mechanical performance of drawn polyurethane elastomers

The macromolecular orientation of some polyurethane elastomers can led to materials with varied mechanical properties. These properties are dependant on the molecular structure of both hard and soft segmants. Some natural biopolymers such as spider silk exhibit superb mechanical properties, characterised by their great toughness. Synthetic polyurethane (PU) copolymers also endow great toughness but lack silk's stiffness and strength. The aim of this work was to elucidate the role of segment block architectural features that influence PU stiffness and strength after cold drawing. For this purpose PUs with varied soft segment character, crystalline versus rubbery, as well as with different hard segment chemistries, 4,4'-diphenylmethane diisocyanate/1,4-butanediol versus 1,6-hexamethylene diisocyanate/1,4-butanediol, were synthesised by a two-step polymerisation method. We found that the architecture of both block segments has a dramatic influence on drawn PU mechanical performance, in which PUs with crystallisable soft segments and crystalline hard segments are shown to have a greater impact on developing stiffer and stronger materials.