Systems of linear and crosslinked poly(ε-caprolactone) polymers for Shape Memory Assisted Self-Healing (SMASH)

Photocured miscible blends of linear and crosslinked poly(ε- caprolactone) (l-PCL:n-PCL) demonstrate shape recovery for local crack closure and concomitant crack rebonding for recovery of full mechanical strength. We term this functionality shape-memory assisted selfhealing (SMASH). The crosslinked component, n-PCL, exhibits reversible plasticity, a form of shape memory (SM) where plastic deformation is fully recovered due to the entropy elasticity of the network that is liberated upon heating above the network melting temperature (T_m ∼55 °C). The linear component, l-PCL, interpenetrates the SM n-PCL component, yet freely diffuses above T_m to yield a tacky surface capable of rebonding any cracks formed during damage by molecular diffusion. Importantly, a single heating event can tackify crack surfaces while bringing them into molecular contact, resulting in SMASH and recovery of mechanical strength. SM was accomplished at RT by achieving a desired strain percentage before reversible recovery was attained. Studies show initial crack made prior to stretching and the propagated crack created while stretching have healed when the blends are exposed to above its T_m. Near-complete recovery of mechanical properties for damaged samples healed in this manner where minimal crack re-opening and necking at the initial crack regions are evident when samples are stretched. Necking is apparent when the two crack surfaces are fully rebonded together due to the increase l-PCL adhesive component. SMASH materials may be utilized for coatings and films where long-term use and repair are needed and also for pressurized space deployment structures where puncture healing properties are desired.