以芳香醛/酮为可见光催化剂的表面引发可控自由基接枝聚合研究

In the past two years, the emerging of metal-free organic photoredox catalysts in visible/solar light induced controlled free radical polymerization has been growing to an attractive topic in polymer chemistry. The reported catalysts are mainly derivatives of 10-phenyl phenothiazine, 5,10-dihydrophenazine, perylene (polynuclear aromatics), chlorophyll and fluorescein, etc. The development of the low cost catalysts for potential commercial applications is still a great challenge. Very recently, we demonstrated that the derivatives of simple aromatic carbonyl compounds, benzaldehyde derivatives, could catalyzed the controlled free radical polymerization of methacrylates under visible light irradiation. Inspired by this unexpected result, we proposed to study the visible-light induced surface initiated controlled free radical grafting polymerization with aromatic carbonyl compounds as photoredox catalysts. The objective of this project is to develop a platform technology of grafting polymerization featured with visible light induced, fast on/off, and benign to the substrates and the bio-active species. Combined the visible light-induced click and group transfer reactions with the photoredox catalysts, a wide range of functional groups could be bonded to the grafted polymer chains or brushes. The scope of the project includes (1) the relationship of the aromatic carbonyl compounds and their performance as photoredox catalysts in grafting polymerization, and the synergic effects with initiating groups; (2) the effects of the electron donor, such as the tertiary amines, on the performance of the grafting polymerization; (3) the groups transfer reactions of the grafted chains with the aromatic carbonyl catalysts under visible light irradiation; and (4) the applications of the grafting polymerization technology in the fabrication the 3D nano-/micro-architecture of the grafted layers. In addition, the expected results of this project would be of importance for applications in bioactive species immobilizing, tissue engineering and sensor fabricating.

新兴的无金属有机催化剂催化的可见光可控自由基聚合，已成为高分子化学的热点。见报导的催化剂有10-苯基吩噻嗪、5,10-二氢吩嗪、苝、荧光素和叶绿素衍生物等，开发低成本和有实用价值的催化剂是核心。最近，我们发现苯甲醛衍生物可以催化甲基丙烯酸酯的可见光可控自由基聚合，基于这一结果，提出了以芳香族醛/酮为Photoredox催化剂的可见光表面接枝聚合思路。研究受限条件下的可见光可控自由基聚合规律，开发一种可见光驱动的，能快速启/停，对基材和底物友好的表面接枝聚合技术。通过研究：(1) 光催化剂的结构与可见光表面接枝聚合性能的关系，以及与引发官能团的匹配；(2)第三组分对接枝聚合反应活性和可控能力的影响；(3) 光催化剂催化的大分子有机官能团转化反应；和(4)基于此类光催化剂的可见光表面接枝层微结构的构建及应用。发展一种基材表面接枝层三维结构可设计，并且多种官能团空间分布可定位的表面接枝聚合方法。

系统研究了芳香醛催化的可见光自由基活性聚合(LCRP)和硫醇-烯的点击聚合，以接改性为应用场景。主要成果有：(Ⅰ) p-(N,N-二苯基胺基)苯甲醛(DPAB)有较高的光催化活性，而且无需添加叔胺助还原剂。聚合温度与DPAB催化的光RAFT有正协同效应，在聚合反应温度分别为33℃,40℃和50℃时，DPAB/4-氰基-4-(苯基硫代甲酸酯基)戊酸调控的MMA聚合的表观速率常数分别为0.019, 0.056和0.102 h-1，并保持高嵌段效率。2-氰基-2-丙基十二烷基三硫代碳酸酯的直接光解可以引发(甲基)丙烯酸酯的CRP，对丙烯酸酯的调控能力更优。热对可见光聚合的协同效应为提高LCRP的反应速率提供了一种解决方案。(Ⅱ) DPAB能催化对苯二甲硫醇和二乙二醇二乙烯基醚的点击聚合，调整两单体的摩尔比，可制备α,ω-二乙烯基和α,ω-二巯基聚硫醚。在此基础上，以三羟甲基丙烷三(巯基乙酸)与季戊四醇三烯丙基醚为单体，DPAB作为催化剂，在硅片表面接枝了交联结构的聚硫醚薄膜，巯基的密度达到了9000 /nm2(厚度层范围内)。利用表面-SH的反应活性，将PMMA接枝在聚硫醚薄膜的表面，接枝层表面杨氏模量由378.7 MPa上升到了2.4 GPa。建立了一种以交联的聚硫醚为柔性的中间阻尼层，刚性的PMMA为表面保护层的复合接枝保护层的方法。(Ⅲ)利用LiOCH3与乙烯基醚的络合作用，实现了其自由基接枝聚合。聚乙二醇单乙烯基醚接枝层在0.1M NaOH和0.1 M HCl中浸泡30天，厚度无明显变化，解决了接枝层耐水解性能差的难题。研究了锂盐结构对乙烯基醚自由基均聚合的影响，发现LiI对烷基乙烯基醚更有效，其机理是Li+与乙烯基醚的CH2=CH-O-络合，降低了乙烯基醚双键的电子云密度。DFT计算和NMR证实了络合作用不仅存在于CH2=CH-，而且也跟CH2=CH-O的O原子相互作用。LiI的加入显著提高了异丁基乙烯基醚自由基聚合的单体转化率和选择性。(Ⅳ) 发展了一种通用的以二甲基氨基苯为合成子的有机材料表面改性技术，利用二甲基氨基苯基在UV光辐照时产生α-氨基甲基自由基这一反应，将各种官能团，如-CHO，-CN，-B-OH，-SO3H和-SH等，以共价键连接到大分子链上。作为应用，制备了HBP-BOPP-HBP复合膜并获得了高的储能密度和充放电效率。