International Collaboration in Chemistry: Improving Livingness by Detailed Kinetic Studies into ATRP

原子转移自由基聚合（ATRP）是学术界和工业界最成功的可控自由基聚合（CRP）工艺之一。然而，ATRP仍然面临着一些挑战。它们包括寻求毒性更小的良性催化剂（例如铁基催化剂），可以在较低浓度下使用，并提高选择性。改善对ATRP的控制可以提高生长链的活性，减少参与自由基转移和终止的链的比例。为了达到这一目标，我们提出了系统和详细的模型反应动力学研究和实际的ATRP系统。我们计划研究一系列具有更高ATRP平衡常数的cu基催化剂，这些催化剂基于含有供电子取代基的配体和带阴离子的配体。由于具有较高的稳定性和较高的ATRP平衡常数，这种催化剂在降低催化剂浓度时应具有更好的性能。它们将与各种还原剂一起使用，并应应用于聚合活性较低的单体，如醋酸乙烯和酸性单体。我们还计划用一系列新的配体来探索铁基催化剂。我们已经成功地在极性溶剂中使用了Fe（II）卤化物，没有额外的配体，达到了中等的聚合速率。然而，需要新的配体来进一步提高聚合速度和控制。我们还计划详细研究介质效应，包括压力、温度和各种溶剂。我们发现cu基催化剂的ATRP在高压下有很强的加速作用，而fe基催化剂的ATRP在高压下的加速作用有所减弱。因此，应该开发新的铁基催化剂，在更高的压力下提供更高的速率，从而大大提高活性。然而，在较高的温度下，副反应，如转移，自引发，去传播开始运作。我们想通过压力和溶剂来抑制这些副反应。ATRP在水中的平衡常数比在乙腈中的平衡常数高10000倍，表明适当的压力、温度和溶剂组合可以显著改善对ATRP的控制。为了将催化剂、单体、生长自由基和休眠物种的介质效应和结构参数与ATRP控制和活性综合起来，需要进行更详细的动力学研究。我们相信，为了达到这些目标，有必要协同结合两个小组的专业知识，Matyjaszewski小组在ATRP方面积累的知识与Buback小组在激光辅助方法与epr光谱定量自由基中间体和自由基聚合系统方面的专业知识。

Atom transfer radical polymerization (ATRP) is among the most successful controlled radical polymerization (CRP) processes in academia and in industry. However, there are still several challenges facing ATRP. They include quest for more benign catalysts that should be less toxic (e.g. iron-based) and could be used at lower concentrations and enhanced selectivity. The improved control over ATRP should increase livingness of growing chains and reduce proportion of chains that participate in radical transfer and termination. In order to reach this goal, we propose systematic and detailed kinetic studies of model reactions and also real ATRP systems. We plan to study a series of Cu-based catalysts with significantly higher ATRP equilibrium constants, based on ligands that contain electron donating substituents and also anionically charged ligands. Such catalysts should perform better at diminished catalyst concentrations due to their higher stabilities and also higher ATRP equilibrium constants. They will be used in conjunction with various reducing agents and should be applied to polymerization of less active monomers such as vinyl acetate and to acidic monomers. We also plan to explore Fe-based catalysts, with a new series of ligands. We have successfully used Fe(II) halides in polar solvents without additional ligands to reach moderate polymerization rates. Nevertheless, new ligands are needed to further enhance polymerization rate and control. We also plan detailed studies of medium effects, including pressure, temperature and various solvents. We found strong acceleration of ATRP at higher pressure with Cu-based catalysts but a decreased rate at higher pressure for Fe-based systems. Thus, new Fe-based catalysts should be developed to provide enhanced rates at higher pressure, thus strongly improving livingness. However, at elevated temperatures, side reactions, such as transfer, self -initiation, depropagation start to operate. We would like to suppress these side reactions by pressure and solvents. ATRP equilibrium constants in water are 10,000 times higher than in acetonitrile, showing that appropriate combination of pressure, temperature, and solvent can significantly improve control over ATRP. More detailed kinetic studies are needed to comprehensively correlate medium effects and structural parameters of catalysts, monomers, growing radicals and dormant species with ATRP control and livingness. We believe that to reach these goals, it is necessary to synergistically combine the expertise of both groups, the accumulated knowledge on ATRP in the Matyjaszewski group with the expertise of the Buback group on laser-assisted methods in conjunction with EPR-spectroscopic quantification of radical intermediates and on radical polymerization systems up to high pressure.