Recently in the Bowman research group, we demonstrated a cross-linked polymer that, upon exposure to light, exhibits stress and/or strain relaxation without any concomitant change in material properties (1).  This was achieved by introducing radicals via photocleavage of residual photoinitiator in the polymer matrix, which then diffuse via addition-fragmentation chain transfer of midchain functional groups.  These processes lead to photoinduced plasticity, actuation, and equilibrium shape changes without residual stress.  These polymeric materials that are able to respond "on demand" with control of stress, shape and plasticity are being developed in applications ranging from microdevices to biomaterials and polymeric coatings.

1.    T. F. Scott, A. D. Schneider, W. D. Cook, C. N. Bowman, Science 308, 1615 (2005).