Influence of microstructure on micro-/nano-mechanical measurements of select model transparent poly(urethane urea) elastomers

Morphology of 4,4′-dicyclohexylmethane diisocyanate–poly(tetramethylene oxide) (PTMO)–diethyltoluenediamine based poly(urethane urea) (PUU) elastomers is investigated by atomic force microscopy (AFM) and compared with elastic modulus data measured from AFM-enabled indentation, dynamic nanoindentation (nanoDMA), and dynamic mechanical analysis (DMA). These measurements highlight the effect of altering the molecular weight (Mw) of PTMO, which is used as a soft segment (SS), on the microstructure. In particular, at SS Mw 2000 g/mol, a strong microphase-separated morphology is observed, whereas a phase-mixed dominated microstructure is noted in PUU with SS Mw of 1000 and 650 g/mol. These observations are also consistent with DMA tan δ results. Furthermore, instrumented impact indentation is also utilized for elucidation of dynamic damping characteristics in these PUUs.