N-烷基吡啶甲醇酯类可见光裂解型聚合物的合成与功能构筑

The emergence of photocleavable (or photolabile) polymers makes it possible to control the cleavage points and reaction processes of polymer chains in time and space. And it is very useful for the functionalization of polymers and fine-tuning their properties. However, to date, the cleavage processes of such polymers are mainly based on the photochemical reactions that are triggered by the use of UV light, two-photon lasers and near-infrared light. The non-toxic “green” visible light is rarely adopted to realize the cleavage reactions within polymers, and the related study is in its infancy. The bottleneck is how to synthesize the visible light-sensitive units of photocleavable polymers in a facile way. This proposal aims to address this issue and synthesize a series of visible light-sensitive units, where the commercial 4-pyridylmethanol is used as the starting material. 4-pyridylmethanol is an unsymmetrical molecule that is easily functionalized by the esterification and N-alkylation reactions with corresponding acids (or acyl chlorides) and halides, respectively. These 4-pyridylmethanol derivatives, namely N-alkyl-picolinium esters (NAPE), are photolabile that are used as the key building blocks for the synthesis of photocleavable polymers with the assist of typical polymerization methods, such as “click” chemistry, controlled radical polymerization and others. The effect of substituted groups of NAPE on the bond scission of C-O in themselves will be systematically studied by the density-functional theory calculations and experimental methods. Furthermore, we are going to synthesize the multiple light-responsive or branched NAPE-containing photocleavable polymers, and explore the applications of as-synthesized polymers in the fields of drug release and photocleavable films. Based on these investigations, it is expected that the visible light-triggered bond scission of NAPE can be introduced into the system of photocleavable polymers as a kind of typically visible light-degradable building blocks. More than that, it will enrich the study of photocleavable polymers and broaden the application of the “green” visible light in polymer science. Also, it will provide new concepts and strategies for the further study and application of cleavable polymers.

光裂解型聚合物的出现使得我们从时间和空间上精确控制聚合物断裂位置与过程成为可能，也为聚合物功能构筑与调控提供了便利。然而目前研究多集中于以紫外光、双光子技术和近红外光为反应触发源的聚合物光裂解过程，以无光毒性的“绿色”可见光作为触发源的研究还处于萌芽阶段。其瓶颈在于如何简单获得功能化的可见光裂解型聚合物构筑基元。本项目拟以4-吡啶甲醇为起始物，通过酯化和N-烷基化反应合成具有可见光裂解性质的N-烷基吡啶甲醇酯，实现以该类分子为核心的可见光裂解型聚合物制备与功能构筑。利用密度泛函计算和实验方法研究取代基对光裂解过程的影响，并以此为基础开展具有多重光响应性和树枝状结构的裂解聚合物合成，探索在物质装载与释放、光降解聚合物膜等领域的应用。期望通过深入研究，将可见光触发N-烷基吡啶甲醇酯裂解过程作为一类新的裂解体系引入到光裂解型聚合物范畴，拓宽可见光在高分子领域的应用，为裂解型聚合物研究提供新思路。

降解过程可以实现聚合物功能的精确和实时调控。然而，如何从聚合物设计入手来解决当前可降解聚合物研究的不足是高分子材料领域面临的一大挑战。在国家自然基金青年项目支持下，我们在国际上首次开展以吡啶鎓酯为可见光响应聚合物功能基团的系列研究，设计了多种功能性聚合物，对其合成方法、降解机理以及应用进行了系统而深入探索。在项目执行期内，我们以酯化和N-烷基化反应实现了以吡啶鎓酯为骨架的小分子合成，明确了功能化过程对其降解行为的影响、聚合物分子结构与降解之间的直接关系，并实现了可降解聚离子液体、多层薄膜和瞬态柔性电子材料的多功能合成与构筑。利用其降解特性，实现了细胞的可控粘附与增长、昂贵材料的廉价回收及二次利用。通过上述研究，我们成功将吡啶鎓酯作为可见光降解型功能基团引入到聚合物研究领域，丰富了响应聚合物的研究内容。

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