Dynamic Covalent Polymer Networks under Supersonic Micro-Projectile Impact

Dynamic bonding brings new features to polymeric materials, including new modes of energy dissipation and self-healing under quasi-static deformation. The behavior of dynamically bonded materials under high strain rates (HSRs) is relatively unexplored and is of interest for a broad range of applications from body armor to spacecraft protection. The laser-induced micro-projectile impact test (LIPIT) was employed to investigate the energy dissipation characteristics during perforation of ultrathin films of Diels-Alder-based polymer (DAP) dynamic networks. The networks are composed of low-molecular-weight furan-attached prepolymers (7000 g/mol) and bismaleimide crosslinkers. The room temperature Young’s modulus can be tuned nearly three orders of magnitude (MPa to GPa) by varying crosslinking density. Micron-sized silica projectiles were launched at incident velocities of 200-800 m/s toward a DAP thin film, yielding extreme strain rates of ~10⁷ s^-1. Dissociation of the thermally reversible DA bonds was triggered by compressive shock adiabatic heating, followed by viscoelastic, energy-absorbing flow of DAP material. Post-mortem morphology of DAP films shows a volcano shape and partially recovered-healed, smooth surface perforation.