光致氧化还原催化的可见光活化可控自由基聚合及其应用研究

Compared to the thermal and UV light induced chemical reactions, the visible/solar light activated photochemical process has been recognized as a much green process due to its energy efficiency and easy operation. Since 2008, it has been witnessed a rapid growth in interest in transition metal complexes, which is called photoredox catalyst, mediated photochemical reactions. This emerging technology is becoming a versatile tool for a growing number of organic transformations and an important complement to the conventional thermal and UV reactions because it enables the synthesis of molecules with structures that would be inaccessible using nonphotochemical synthetic methods alone. The reaction was adapted to the controlled free radical polymerization of methacrylates with Ir(ppy)3 as photoredox catalyst in 2012. However, to our best knowledge, the controlled free radical polymerization of the other monomers, such as styrene and acryaltes has not been achieved yet. In this proposal, we aimed to extend this emerging technology to a wide variety of monomers and to develop a process to prepare functional polymers with unusual molecular architectures that cannot be accessed using existing thermal and UV controlled free radical polymerization pathways.In addition, with the versatile reactions of the photoredox catalysis in organic synthesis, it is also intended to exploit the possibility to develop a "one-pot" process for polymers postpolymerization functionalization with the same photoredox catalyst. The scope of this project including: (1) to investigate the relationship of the structure of the photoredox catalyst and its performance of controlability of polymerization, the main factors impacting on the photoredox catalyst include the transitional metal, the ligand and the subtle substituent groups of the ligand; (2) to study on the effect of the structure of the initiator and the synergistic effect between the photoredox catalyst and initiator; (3) to understand the mechanism and the kinetic of the polymerizations; and (4) to exploit the reaction of the postpolymerization functionalization and its application in preparing functional polymers. With the merits of more compatible with thermal sensitive chemicals, especially for bioactive species, and spatially controllable, the expected results of this project would be of importance for 3D printing, advanced micro-manufacturing, bioactive species immobilizing, tissue engineering and sensor fabricating.

与热和UV光活化的可控自由基聚合相比，可见/太阳光激发的可控自由基聚合是更绿色的反应工艺。结合近年兴起的可见光光致氧化还原（Photoredox）催化的ATRA反应的最新成果，拓展新兴的光致氧化还原催化的可见光可控聚合。开发高效和普遍适用的，特别是不能通过热/UV光聚合工艺制备的功能聚合物的合成新方法。结合其它光致氧化还原催化反应，使用同一催化剂，采用"一锅法"工艺，实现对聚合产物的后官能化。通对研究：(1)光致氧化还原催化剂结构(中心原子和配体)与光聚合反应活性的关系；(2)引发剂结构与光致氧化还原催化剂的匹配；(3)聚合反应机理和聚合反应规律；和(4)聚合物的后官能化反应和功能材料的制备，深化对光致氧化还原催化的可见光自由基可控聚合机理的理解。利用光反应可以快速启动/停止的特性，结合光掩模，为3D打印和微制造技术、生物活性物质的原位固定、组织工程和传感器技术的发展提供新的技术。

从高分子化学的基本问题着手，重点研究了可见光介导的活性自由基聚合催化-引发体系，功能性单体的聚合和特殊结构聚合物的设计合成。取得的主要成果有：(Ⅰ)首次将芳香醛类化合物用于Photoredox催化剂的photo-ATRP，photo-RAFT和Thiol-ene点击聚合反应，开发了一类低成本的无金属有机催化剂。以甲氧基苯甲醛、对氰基苯甲醛和2,4-二甲氧基苯甲醛与N,N-二甲基苯胺组成的可见光氧化还原催化剂，全氟己基碘为引发剂，实现了MMA, PEGMA，以及BnMA等单体的活性自由基聚合，并成功制备了嵌段共聚物。将上述苯甲醛类催化剂用于photo-RAFT，实现了MMA和BnMA的活性聚合。以得到的Mn=17000 g mol-1，PDI=1.50的聚合物为macro-PMMA，实现了与PEGMA和BnMA的嵌段共聚合。以对氰基苯甲醛/2-(十二烷基三硫代碳酸酯基)-2-甲基丙酸为催化/调控体系，苯乙烯和对甲基苯乙烯的可见光聚合反应呈现一级动力学特征，产物的Mn随单体转化率线性增长，PDI<1.5，聚合反应表现出了活性聚合行为。作为芳香醛催化剂的应用拓展，发现2,4-二甲氧基苯甲醛可以催化1,4-苯二甲硫醇与二乙二醇二乙烯基醚的点击聚合反应，产物分子量随聚合反应时间的延长近似成线性关系，PDI<2。而且可以通过单体配比来控制聚合物的端基，得到α,ω-二巯基和二乙烯基齐聚物。(Ⅱ)首先报道了Cu(dap)2Cl为催化剂的photo-ATRP，成功实现了PEGMA以及MMA单体的活性自由基聚合。聚合物Mn随转化率的增长而线性增加，PDI<1.2，而且可以合成嵌段共聚物。(Ⅲ)拓展了以fac-Ir(ppy)3催化剂的可见光介导的活性自由基聚合和Thiole-ene点击聚合。以CF3(CF2)5I引发剂，实现了MMA和PEGMA的活性自由基聚合，并得到了首端基为CF3(CF2)5-的均聚物和嵌段共聚物。将fac-Ir(ppy)3催化剂催化用于二乙烯基醚和二巯基化合物的可见光Thiol-ene的点击聚合，制备了α,ω-二乙烯基和二巯基聚硫醚。对于甲基丙烯酸炔丙酯(PgMA),当单体转化率小于50%时，聚合物的分子量随着单体转化率的增长而线性增加，PDI<1.7。当PgMA与MMA共聚时，单体转化率高达88%时仍未出现凝胶现象，这一体系优于铜催化的PgMA的ATRP体系。