聚氨酯薄膜材料损伤光可逆自修复的研究

This proposal aims at imparting repeated photochemical remendability to polyurethane film. The polyurethane consists of isocyanate, polyethylene glycol and photo-reversible coumarin moieties that are attached to the main chian as side groups or parts of main chain. Consequently, photo-reversibly crosslinked polyurethane can be yielded. In case of damage, the cracked faces can be covalently reconnected through photocleavage and photodimerization of the coumarin moieties. No catalyst is required and the haeling can be conducted for many times. Additionally, due to the mobility of soft segments and phase separation, the photochemical groups possess possibility of moving, aggregating, and reacting with each other in polyurethane film at ambient condition. On the other hand, the hard segments and crosslink network contribute the materials with sufficient mechanical strength. With this idea of molecular design, photo-induced reversible self-healing can be realized in solid polymer, and performance of the material itself can be conveniently adjusted by changing the ratio of soft and hard segments as well as the content of coumarin derivatives. We will focus on synthesis of the polyurethane, photo-reversible reaction, self-healing mechanism, etc. It is believed that the effects of coumarin derivatives and their position in the macromolecules, the soft segment length, degree of phase separation, and modification of aromatic tertiary amine on self-healing behavior will be revealed. Meanwhile, repeated reversibility of coumarin derivatives with cycles of photodimerization and photocleavage will be illuminated. On the whole, this project will provide deeper understanding about photo-stimulated self-healing of solid polymers, which is believed to be beneficial to various industrial applications of self-healing polyurethane at room temperature under sunlight.

本项目拟发展一种具备高效光可逆自修复能力的聚氨酯薄膜材料。在聚氨酯的侧链或主链中引入光学活性基团香豆素衍生物，构筑光可逆交联网络，当材料遭受损伤后，通过香豆素基团间的光解聚/二聚反应，实现断面的共价键链接，恢复原有的承载能力，整个修复过程无需催化剂，可多次重复。将利用聚氨酯分子结构中软段的运动性及其微相分离过程，辅助所含光活性基团的聚集、排列和光化学反应，并利用聚氨酯分子链的硬段和交联结构，赋予材料在实际应用中所需的力学性能，突破以往光可逆修复往往只能在液相中进行才能获得较高效率的难题。本项目将深入研究这类聚氨酯薄膜材料的合成、光可逆反应特性以及化学、物理机械性能等，阐明香豆素衍生物的含量、位置、软段链长、相分离、芳叔胺修饰等对光可逆反应及自修复性能的影响，揭示香豆素基团间光可逆反应逐渐衰减的规律和减缓或抑制这种衰减的原理，为制备具有光可逆反复自修复能力的聚合物固体材料提供科学依据。

目前对光可逆自修复材料的研究面临着一个难题，即光可逆反应需要聚合物分子链具有足够的运动性，显然硬性的固体材料难以满足这一要求。为此，本项目采用光学活性高的香豆素衍生物作为光可逆官能团，将其引入聚氨酯分子链的侧链或主链上，经350nm紫外光二聚反应形成具有相分离结构的光可逆交联聚氨酯体系。聚氨酯材料中产生裂纹后，利用254nm的紫外光照先诱导断面的香豆素衍生物二聚体开环，然后再用350nm紫外光致使香豆素衍生物再次二聚，修复裂纹。大分子链中的软段因具有柔顺性，导致硬段聚集，使香豆素基团可以互相靠近和排列，有利于它们之间发生光二聚和解聚反应，而分子链中的硬段以及交联结构则为材料提供足够的强度。本项目深入研究了这类聚氨酯薄膜材料的合成、光可逆反应特性以及化学、物理机械性能等，阐明香豆素衍生物的结构、位置、软段链长、相分离等对光可逆反应及自修复性能的影响，揭示香豆素基团间光可逆反应逐渐衰减的规律和减缓或抑制这种衰减的原理，为制备具有光可逆反复自修复能力的聚合物固体材料提供科学依据。.首先，合成了两种含单和双羟基的香豆素衍生物HEOMC及DHEOMC。将六亚甲基二异氰酸酯三聚体（tri-HDI）、HEOMC分别与PEG200、PEG400及PEG800反应，制备了侧链含光可逆基团的聚氨酯THHPEG200，THHPEG400及THHPEG800。研究表明THHPEG400具有更好的光可逆性。通过普通光学显微镜观察和电化学表征证实了三种聚氨酯均具有光致可逆裂纹多次自修复功能以及拉伸断裂-自修复性能。最佳修复条件为254-1min- 350-90min；在该修复条件下，THHPEG400具有更高的修复效率，其连续三次拉伸断裂修复的平均修复效率分别为70.2%、62.9%及56.5%。另一方面，将IPDI、DHEOMC分别与PEG400及PEG800反应，制备了主链含有光可逆基团的聚氨酯。采用拉伸断裂-修复试验测得IDHPEG800-0.25体系三次光可逆自修复的平均修复效率分别为100.66%、76.12%及61.90%。