电化学调制表面引发原子转移自由基聚合的现场SPR研究

Atom transfer radical polymerization (ATRP) is a controlled/living polymerization technique by activating a dormant alkyl halide initiator to form an active radical capable of chain propagation with a certain transition-metal complex activator, which is then reversibly oxidized to a deactivator. Using the activator/deactivator redox pair to build a dynamic equilibrium between the active radical and the dormant species and to minimize the irreversible bimolecular termination, ATRP allows for precise control over the polymer molecular weights, molecular weight distributions, and complex architectures, and has been extensively employed for polymer synthesis in a wide variety of applications. Electrochemical reduction of the deactivor to the activator is proved to be a feasible route to trigger and regulate the bulk ATRP (Science 2011, 332, 81). However, so far few is known concerning the exact process of electrochemically modulated ATRP due to the absence of both fast electrochemical modulation method and real-time study technique. In this project, we propose an in situ electrochemical surface plasmon resonance (SPR) technique, based on our previous work, to study this interesting phenomenon and further deepen our understanding on it. In details, the ATRP initiator is attached on the surface of SPR gold chip, and the local activator/deactivator ratio at the gold surface will be electrochemically modulated in the oxygen-stable deactivator solution and thus, the surface-initiated polymerization could be controllably triggered, regulated and terminated with the electrochemical modulation. By monitoring the simultaneous in situ SPR response towards the electrochemical modulation, we will study some fundamental issues including the influence of electrochemical modulation on the growth kinetics of polymer chains, the electrochemical stability of the active radicals, and the relation between the electrochemical behaviors of the activator/deactivator pair and their catalytic ability in ATRP. In this project a novel real-time electrochemical-SPR platform for ATRP study will be bulit and an electrochemical method for facile growth of polymer brush on arbitrary conducting surfaces will be developed. Most importantly, this project will help to get more scientific insights into the surface-initiated ATRP process and pave the intriguing way to study polymer science with an electrochemical view.

原子转移自由基聚合（ATRP）通过过渡金属络合物激活剂/钝化剂这一氧化还原电对调控引发剂在活性自由基与休眠态之间的快速转化和可逆平衡，实现活性/可控自由基聚合。采用电化学方法控制该氧化还原电对的相互转化是调控ATRP的可行方法（science 2011, 332, 81），但由于缺乏实时在线的研究手段，对这一过程的研究还不深入。本项目在前期工作的基础上，拟采用电化学－SPR联用技术，对电化学调制表面引发ATRP进行现场研究。具体来说：在金电极表面固定引发剂，采用电化学手段对电极表面的激活剂/钝化剂进行快速氧化还原调制，从而控制表面引发ATRP的进行；采用实时在线SPR技术现场监控表面引发ATRP对电化学调制的响应，深入研究电化学调制表面引发ATRP的基本规律。本项目有望建立一个全新的ATRP实时研究平台，开发一种制备聚合物刷的电化学方法，亦将加深对电化学调制ATRP过程的科学认识。

采用电化学方法控制原子转移自由基聚合（ATRP）的激活剂/钝化剂氧化还原电对的相互转化是调控ATRP 的可行方法，但由于缺乏实时在线的研究手段。本项目采用电化学-表面等离子体共振（SPR）联用技术，对电化学调制表面引发ATRP（即SI-ATRP）进行现场研究。主要考虑有两方面： 1）SI-ATRP聚合速率只与固体表面的激活剂/钝化剂浓度比相关，不受本体溶液的影响；而采用电化学技术控制电极表面的氧化还原电对的浓度比是非常快速准确的。2）SPR技术是一项免标记的光学技术，能实时检测金属/溶液界面上的局域介电常数的改变，其灵敏度和检测频率都满足SI-ATRP研究的需要，更重要的是SPR技术天然的能和电化学技术联用。.本项目研究内容是：在金电极表面固定ATRP引发剂，采用电化学手段对电极表面的激活剂/钝化剂进行快速氧化还原调制，从而控制SI-ATRP 的进行；采用实时在线SPR 技术现场监控SI-ATRP 对电化学调制的响应，深入研究电化学调制SI-ATRP 的基本规律。.经过4年的研究，本项目取得了如下主要结果：.1.建立了一套适合电化学SPR平台研究的SI-ATRP体系，其中包括：SPR流通池/电化学池的设计、引发剂在金膜的固定方案、催化剂、溶剂、配体种类及浓度。这一套方案一方面满足ATRP进行的条件，同时能方便电化学调制，更重要的是溶液折射率在SPR平台可测试区间。.2.发现溶解氧在ATRP中的干扰作用并初步揭示了其可能机理：溶解氧氧化溶液中的低价态金属配合物激活剂，产生中间产物过氧化氢，而过氧化氢又和过渡金属发生类芬顿反应，产生自由基，引发无序的自由基聚合，严重时会干扰ATRP的进行。.3.研究了三种单体的电化学调制SI-ATRP行为。研究结果表明：通过电化学SPR平台进行SI-ATRP的研究是可行的，通过电化学引发SI-ATRP是可行的，不同单体在电化学－SPR体系中的聚合规律并不相同。在此基础上进一步研究了SI-ATRP的反应特点和规律，探讨了其可能的机理.