Understanding the Fundamentals of Aqueous ATRP and Defining Conditions for Better Control
Understanding the Fundamentals of Aqueous ATRP and Defining Conditions for Better Control
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DOI：
10.1021/acs.macromol.5b01454
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发表时间：
2015-10-13
期刊：
影响因子：
5.5
通讯作者：
Matyjaszewski, Krzysztof
中科院分区：
文献类型：
--
作者：
Fantin, Marco;Isse, Abdirisak A.;Matyjaszewski, Krzysztof
在水中进行原子转移自由基聚合（ATRP）提供了几个有趣的挑战。为了更深入地了解水相ATRP反应机理，特别是潜在失控的原因，对三种铜胺催化剂（[（CuL）-L-II]（2+），L = PMDETA，TPMA和Me 6 TREN）进行了系统的研究。测定了[（CuL）-L-II]（2+）和[（CuL）-L-I]（+）与X-和OH-的缔合常数（K-x），以及配合物的相对稳定性和氧化还原性质随[X-]和pH的变化，并测定了三种[（CuL）-L-I]（+）配合物的反硝化反应速率常数和平衡常数。最后，ATRP平衡常数（K-ATRP）估计所有的配合物，使用2-羟乙基2-溴异丁酸酯（HEBiB）作为引发剂。影响水相ATRP控制的主要因素是催化剂在低pH和高pH下的不稳定性、失活剂容易解离（K-x < 15）、非常高的K-ATRP和[（CuL）-L-I]（+）的快速反硝化。该指南被用来进行几个有效的电化学介导的水ATRP实验与寡（环氧乙烷）甲基醚甲基丙烯酸酯作为单体，HEBiB作为引发剂和铜配合物与三个不同的配体。首次报道了在强酸性环境（pH 1.5）中成功的ATRP，与迄今为止所认为的相反，表明ATRP可以在酸性条件下容易地控制，而应避免高pH。
Conducting an atom transfer radical polymerization (ATRP) in water provides several intriguing challenges. In order to attain a deeper understanding of the mechanism of aqueous ATRP, with particular attention to the reasons for the potential loss of control, a systematic investigation was carried out with three copper-amine catalysts([(CuL)-L-II](2+), L = PMDETA, TPMA and Me6TREN). The association constants (K-x) of [(CuL)-L-II](2+) and [(CuL)-L-I](+) with X- and OH-, as well as the relative stabilities and redox properties of the complexes, were determined as a function of both [X-] and pH. In addition, rate constants and equilibrium constants of disproportionation for all three [(CuL)-L-I](+) complexes were measured. Finally, ATRP equilibrium constants (K-ATRP) were estimated for all complexes, using 2-hydroxyethyl 2-bromoisobutyrate (HEBiB) as initiator. The primary factors affecting control in aqueous ATRP were identified as catalyst instability at both low and high pH, easy dissociation of deactivator (K-x < 15), very high K-ATRP and fast disproportionation of [(CuL)-L-I](+) Overall, the results obtained in this study provide a set of guidelines for a well-controlled aqueous ATRP. The guidelines were used to conduct several efficient electrochemically mediated aqueous ATRP experiments with oligo(ethylene oxide) methyl ether methacrylate as monomer, HEBiB as initiator and copper complexes with three different ligands. A successful ATRP in a strongly acidic environment (pH 1.5) is reported for the first time, contrary to what was believed until now, indicating that ATRPs can be easily controlled in acidic conditions, while high pH should be avoided.