Structure-property relationships and melt rheology of segmented, non-chain extended polyureas: Effect of soft segment molecular weight

Novel, segmented non-chain extended polyureas were synthesized. Soft segments (SS) were based on poly(tetramethylene glycol) (PTMO) (average molecular weight 1000 or 2000 g/mol) and hard segments (HS) were based on a single molecule of a diisocyanate, which was either 1,6-hexamethylene diisocyanate (HDI), 1,4-phenylene diisocyanate (pPDI) or 1,4-trans-cyclohexyl diisocyanate (CHDI). An increase in the SS molecular weight was found to lead to an increased formation of SS crystallites below 0 °C, which increased the low temperature modulus. Both 1K and 2K PTMO-based polyureas showed a microphase separated morphology, where the HS formed thread-like, crystalline structures that were dispersed in the continuous SS matrix. Upon deformation, the HS were found to breakdown into distinctly smaller threads, which oriented along the direction of the strain; this effect was found to be partially reversible and time dependent. Both the 1K and 2K polyureas based on HDI HS were found to be thermally stable and potentially melt-processible.