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Unraveling the high strain-rate dynamic stiffening in select model polyurethanes – the role of intermolecular hydrogen bonding

Wu, You-Chi Mason; Hu, Weiguo; Sun, Yuchen; Veysset, David; Kooi, Steven E.; Nelson, Keith A.; Swager, Timothy M.; Hsieh, Alex J.

By 27 January 2020No Comments

Polymer, 2019, vol 168pp. 218-227



This study elucidates the influence of molecular attributes on the observed dynamic stiffening in select two-component polyurethanes upon high strain-rate impact. Unlike typical segmented elastomers, polyurethanes consisting of poly(tetramethylene oxide), PTMO, and a diisocyanate, but without a chain extender, are investigated. The hexamethylenediisocyanate (HDI)-based polyurethane, HDI-PU, exhibits crystallinity and a much higher ambient storage modulus, as determined by dynamic mechanical analysis at 1Hz, than that of 4,4′-methylenediphenyldiisocyanate (MDI)-based polyurethane, MDI-PU. In contrast, MDI-PU exhibits a higher glass transition temperature than that of HDI-PU, and a greater dynamic stiffening against silica micro-particle impacts at strain rates between 107 and 108 s-1. The variation in dynamic stiffening corroborates well the observed dynamics at the molecular level, as determined via solid-state nuclear magnetic resonance (ssNMR) spectroscopy. The presence of a slower-dynamics component in MDI-PU, as evidenced in the 13C ssNMR dipolar dephasing time, is used to explain the observed enhanced dynamic stiffening response.

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