剪纸作为中国的传统艺术，已经有一千五百多年的历史，是中国最为流行的传统民间艺术形式之一。剪纸艺术不仅能得到美丽的平面图案，特定的图案经“拉花”步骤后还可获得复杂三维立体结构。最近，浙江大学化学工程与生物工程学院谢涛教授课题组（第一作者：博士生郑宁，共同通讯作者：赵骞副教授）用剪纸拉花技术加工传统的热固性聚氨酯，获得了具有复杂三维结构的形状记忆聚氨酯。该技术有望用于构筑可变形超材料以及轻质高强支撑结构。

热固性聚氨酯是一种用途及广的聚合物材料，一直被认为难以永久变形（即难以重新加工利用）。而谢涛教授课题组发现氨酯键在催化剂作用下能发生可逆交换，导致聚合物网络的拓扑结构重排，而该催化剂同时为材料制备时所需的缩聚反应催化剂。这使得热固性聚氨酯的永久形状能被不断改变，具有本征塑性。在一定温度下，仅当材料受较大弹性形变时，才会产生明显的塑性形变。而剪纸拉花技术恰恰能在材料某些局部产生高形变量，从而在固态时永久改变材料形状。研究者认为这一发现将改变以往教科书对热固性聚氨酯的描述。

该项研究工作题名为《Thermoset Shape-Memory Polyurethane with Intrinsic Plasticity Enabled by Transcarbamoylation》，近期发表于《Angew. Chem. Int. Ed.》（DOI: 10.1002/anie. 201602847），且被选为该期刊的Very Important Paper与当期的内封面导读。

Abstract:

Thermoset polymers are known for their superior thermomechanical properties, but the chemical crosslinking typically leads to intractability. This is reflected in the great differences between thermoset and thermoplastic shape memory polymers; the former exhibit a robust shape memory but are not capable of redefining the permanent shape. Contrary to current knowledge, we reveal here that a classical thermoset shape-memory polyurethane is readily capable of permanent reshaping (plasticity) after a topological network rearrangement that is induced by transcarbamoylation. By employing the Jianzhi technique (also known as kirigami), unexpected shape-shifting versatility was observed for this otherwise classical material. As the essential carbamate moiety in polyurethanes is one of the most common polymer building units, we anticipate that our finding will have significant benefits beyond shape shifting.