通过Diels-Alder反应和多重氢键构筑具有自修复功能的PCL-PEG可逆交联网络及其三重形状记忆行为研究

Triple-shape polymers (TSP) have the ability to change and recovery between three different shape in a predefined way upon appropriate stimulation, which attract great attention in recent year. However, the traditional polymer networks employed in TSP are almost based on the non-reversible covalent bond, which will limit its application to a certain extent. Recently, a new concept to construct reversible network has been highly concerned, and a series of promising materials, such as recyclable rubber and epoxy resin, have been developed. It enlightens us to apply this concept into the molecular design of triple-shape polymer network. .This project aims to develop a novel thermoreversible triple-shape poly(?-caprolactone)-poly(ethylene glycol) (PCL-PEG) network via Diels-Alder reaction and self-complementary hydrogen bond, and the architecture of polymer networks could be well-defined and thermodynamically controlled. Three molecular switches will be assembled in this novel system. Firstly, the flexible and crystallizable PCL and PEG segments act as two switch domains of TSP which dominant the fixing and recovery of two temporary shapes. The melt temperature of PCL (Tm,PCL) and PEG (Tm,PEG) segments employ as transition temperature (Ttrans,A and Ttrans,B). In addition, the corsslink pionts of PCL-PEG network acts as netpionts of TSP which responds the recovery of permanent shape. More important, it also play an important role to be regard as the third molecular switch, that is the thermally reversible character of the network constructed by Diels-Alder reaction or self-complementary hydrogen bond endue this material with the function of excellent self-healing capability and re-processability, which can be triggered by temperature.This smart material conbines the virture of excellent performance of network on shape memory effect and the re-processability of the thermoplastic polymer, which will broaden the scope of applications of this novel class of TSP. .The effect of molecular structure, architecture, composition and the corsslink mode of the networks on their properties, especially triple-shape perfermance and thermally-reversibility, will be investigated systematically, the relationship between the structure and property is expected to established, which will be a valuable reference for the design of shape-memory polymers.

由于三重形状记忆高分子材料(TSP)在外界刺激下可以实现对三种不同形状的固定和恢复，引起了研究人员的广泛关注。本项目将结晶能力强和链段柔韧性好的PCL和PEG链段通过Diels-Alder反应或氢键自组装两种不同的具有温度可逆性的键(缔)合方式，构造出PCL-PEG可逆交联网络。该体系中具有三个温度响应的分子开关，其中PCL和PEG链段分别充当TSP的两个可逆转变相，通过温度程序启动其结晶和熔融，实现对两种不同临时形状的固定和回复。而由Diels-Alder反应或氢键自组装构筑的交联点则控制其初始形状的记忆和恢复。同时利用其温度可逆性，可触动材料自修复功能和反复成型加工性。研究两种不同交联方式对可逆交联网络形状记忆性能及其可逆性的影响，研制出性能优异的TSP材料。该材料即具备了交联网络在形状记忆性能方面的优异体现，同时又具有热塑性材料可反复加工的优势，有望在更加广泛的领域中得到应用。

化学交联在形状记忆高分子材料设计中应用广泛，然而传统的化学交联方式严重制约了材料的成型加工，而且一旦成型后无法反复加工，极大地限制了材料应用。动态网络以其具有特有的可逆性受到研究者的青睐，将其引入到形状记忆高分子网络结构的设计中，既保证了网络结构在形状记忆效应中的重要作用，同时还将赋予材料良好可反复加工性和自修复性能。本项目分别将动态共价键和非共价键两种不同的键合方式应用到形状记忆聚合物共聚网络的设计与合成中，系统研究了聚合物化学和拓扑结构对材料热行为、力学性能、形状记忆性能和自修复性能的影响，为多功能、多重形状记忆高分子材料的设计提供了新的思路。首先，分别将呋喃环修饰到聚对二氧环己酮（PPDO)和聚四氢呋喃(PTMEG)的链端，然后采用三[（2-马来酰亚胺）乙基]胺做交联剂，利用呋喃环与马来酰亚胺基团之间发生Diels-Alder反应成功构筑PPDO-PTMEG动态交联网络，结构表征和溶胀实验结果证明已获得了目标结构。进一步深入的研究了材料的动态可逆性、结晶行为、力学性能、形状记忆行为以及自修复性能，建立了材料结构与性能之间的关系。然后，利用2-脲基-4-嘧啶酮（Upy）可以自识别形成四重氢键的特点，将其作为端基或侧基修饰在聚己内酯（PCL）和PTMEG或聚乙二醇（PEG）链段上，利用氢键自组装制备出具有三重形状记忆功能的热致型形状记忆动态交联网络，详细探讨了其共聚组成对材料结晶行为、形状记忆行为以及自修复性能的影响。研究结果显示，在PCL-PTMEG动态网络中，提高PTMEG含量有助于提高材料的自修复性能。另外，本项目还利用共价键交联和氢键自组装的不同反应机理，构筑了聚己内酯/聚对二氧环己酮互穿网络（PCU/PPDO IPNs），有效改善了两种聚合物链段的结晶性，获得了优异的三重形状记忆性能。