  The relaxation of polymers around and below their glass transition
temperature is governed by a range of correlated unit processes with a wide
range of timescales. The fast deformation rates of shock loading can negate a
significant fraction of these processes resulting in the dynamical glass
transition in rubbers. In this letter we report the inverse, a transient
melting of glassy polymer under shock loading. The large deviatoric stresses
near the shock front induce fast transitions in backbone dihedral angles and a
stress relaxation characteristic of polymer melts. This is followed by the
slower relaxation expected for glasses.
