可时空编程的超分子形状记忆高分子

Spatio-temporal Programmable Supramolecular Shape Memory Polymer

基于超分子作用的形状记忆高分子具有不同于传统热固性形状记忆高分子的突出特点,包括多重刺激响应性、自修复性、重回收性、固态塑性等.超分子作用的动态可逆特性和丰富的分子设计空间带来的可能性远不仅于此.本文着重介绍了近期报道的基于超分子作用的新型形状记忆高分子,旨在揭示其中的分子设计理念以及独特的宏观行为,拓宽现有超分子形状记忆高分子的应用空间.在此基础上,我们进一步具体介绍一类可自发变形的超分子形状记忆高分子.该类材料通过时间编程可实现无刺激的可控变形行为,打破了常规的刺激响应变形模式.超分子作用所具备的时空编程性为未来智能材料的设计提供全新的思路.

Owing to the dynamic nature and the rich library of supramolecular interactions,supramolecular shape memory polymers have shown unique benefits beyond traditional thermoset shape memory polymers including multi-stimuli response,self-healing,recyclability,and solid-state plasticity.Thanks to extensive research over the last two decades,the above characteristics have become well-established.Despite that,new material design opportunities beyond those continue to emerge in the recent five years.In particular,supramolecular shape memory polymer has been reported to possess unusually high output energy density via strain-induced formation of ordered supramolecular structures,which are beneficial for use as artificial muscles.In addition,the hydrophobic domain in a hydrogel has been demonstrated to be effective in fixing the anisotropy of the poly(N-isopropylacrylamide)chains,giving rise to two-way reversible shape memory behavior in hydrogels.Intriguingly,the change in glassy transition temperature due to photo-isomerization of azobenzene moieties leads to athermal shape memory polymers for which no heating/cooling is required for the entire shape memory cycle.Rational design of a shape memory network with self-complementary hydrogen bonding interactions endows the material with superior toughness and multi-recyclability.Collectively,these recent progresses have expanded the scope of shape memory polymers,which are summarized in the first half of this article.The above developments typically take advantage of the on-off switch offered by supramolecular interactions,but their dynamic reorganization process has been by and large neglected.Several reports in the last three years have shown that this latter characteristic is uniquely useful in designing autonomous shape memory polymers for which no external stimulation is needed to trigger the shape recovery.These supramolecular autonomous shape memory polymers are discussed in the second half of this article.This class of materials utilize the time-and temperature-dependent exchange kinetics of supramolecular interactions to manipulate the entropic energy stored via spatio-temporal programming,as a way to control the shape-shifting.This autonomous shape-shifting mode differs drastically from traditional stimuli-responsive shape memory polymers and its trigger-free nature can open up new device applications in which access to external stimulation is difficult.We believe that the principle of spatio-temporal programming via supramolecular interactions can be potentially expanded to other molecular mechanisms,which will provide a new perspective for smart material design in the future.