Autonomous Off-Equilibrium Morphing Pathways of a Supramolecular Shape-Memory Polymer

The diverse morphing behaviors of living creatures arise from their unlimited pathways. In contrast, the equilibrium-driven morphing pathways of common synthetic shape-shifting materials are very limited. For a shape-memory polymer (SMP), its recovery from the temporary shape(s) to the permanent shape typically requires external stimulation and follows a single fixed route. Herein, a covalently crosslinked SMP is designed with ample ureidopyrimidinone (UPy) supramolecular moieties in the network. The UPy units endow the SMP with strong time-temperature dependency, which is explored as a mechanism for spatio-temporal programming of autonomous shape-shifting pathways. In particular, the use of digitally controlled photothermal heating provides versatility in control via an off-equilibrium mechanism. In addition, cooling/heating across its glass transition introduces a locking/unlocking mechanism for its temporal morphing. The benefits of these unique features are demonstrated by multi-shape-transformation, an invisible-color-based clock, a time-temperature indicator, and sequence-programmable 4D printing.

Automated summary

The article introduces a covalently crosslinked SMP with strong time-temperature dependency, incorporating UPy supramolecular moieties for spatio-temporal programming of autonomous shape-shifting pathways. Utilizing digitally controlled photothermal heating and cooling/heating across its glass transition, the SMP demonstrates multi-shape-transformation, an invisible-color-based clock, a time-temperature indicator, and sequence-programmable 4D printing.