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

原子转移自由基聚合（ATRP）是在学术界和工业上最成功的可控自由基聚合（CRP）方法之一。然而，ATRP仍然面临着一些挑战。它们包括寻求毒性更低的更良性的催化剂（例如铁基），并且可以在较低浓度下使用并提高选择性。对ATRP的改进控制应增加增长链的活性，并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动力学研究模型反应，也真实的ATRP系统。我们计划研究一系列的铜基催化剂具有显着较高的ATRP平衡常数，基于配体，含有供电子取代基和阴离子带电配体。这种催化剂在降低的催化剂浓度下应表现得更好，因为它们具有更高的稳定性和更高的ATRP平衡常数。它们将与各种还原剂结合使用，并应应用于活性较低的单体如乙酸乙烯酯的聚合和酸性单体的聚合。我们还计划开发具有一系列新配体的铁基催化剂。我们已经成功地使用铁（II）卤化物在极性溶剂中没有额外的配体，以达到适度的聚合速率。然而，需要新的配体来进一步提高聚合速率和控制。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，在较高的压力下，铜基催化剂的ATRP的强烈加速，但在较高的压力下，铁基系统的速率下降。因此，应该开发新的铁基催化剂以在更高的压力下提供增强的速率，从而强烈地改善活性。然而，在升高的温度下，副反应，如转移、自引发、解增长开始起作用。我们希望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高10，000倍，表明压力、温度和溶剂的适当组合可以显著改善对ATRP的控制。需要更详细的动力学研究，以全面关联的介质效应和结构参数的催化剂，单体，生长自由基和休眠物种与ATRP控制和活性。我们认为，为了实现这些目标，有必要协同联合收割机的专业知识，ATRP在Matyjaszewski组与专业知识的Buback组的激光辅助方法结合EPR光谱定量的自由基中间体和自由基聚合系统的高压力下积累的知识。

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.