Regulating polyurethane shock-resistance via hard-segment aromaticity and soft-segment flexibility competition

Polyurethane (PU) elastomers are widely used in flexible protective systems due to their high toughness and resilience; however, the molecular origins of their thermo-mechanical response under ultrafast shock loading remain poorly understood. In this work, non-equilibrium molecular dynamics (NEMD) simulations are conducted to investigate the shock-wave propagation behavior of PUs with varying hard-to-soft segment mass ratios subjected to particle velocities of 0.1-4.0 km/s. A competitive shock-dissipation mechanism is revealed. Aromatic-rich hard segments enhance compressive rigidity and load-bearing capacity, while flexible soft segments dissipate shock energy through large conformational deformation and chain rearrangement. Dynamic hydrogen bonding, predominantly mediated by carbamate groups, regulates stress redistribution and structural stabilization during compression and release. Among the investigated formulations, a hard-to-soft ratio of 1:1.5 exhibits optimal shock resistance, characterized by reduced volumetric compression (3.2%), increased bulk modulus (37%), and lower in-situ shear stress near the piston surface (∼31%) and shock front (∼18%), accompanied by enhanced hydrogen-bond density (∼10%). These findings establish a direct structure-mechanics linkage between molecular architecture and macroscopic shock response, providing quantitative guidance for the mechanics-based design of high-performance polyurethane materials under extreme loading conditions.