Journal of Macromolecular Science, Part A ( IF 2.1 ) Pub Date : 2021-02-03 Niccolò Braidi, Mirko Buffagni, Franco Ghelfi, Francesca Parenti, Armando Gennaro, Abdirisak A. Isse, Elena Bedogni, Luisa Bonifaci, Gianfranco Cavalca, Angelo Ferrando, Aldo Longo, Ida Morandini
Abstract
“Activator regenerated by electron transfer” “atom transfer radical polymerization” (ARGET ATRP) process catalyzed by CuCl2/tris(2-pyridylmethyl)amine (TPMA) (1/1) in ethyl acetate/ethanol (EtOAc/EtOH) for the polymerization of styrene from ethyl 2,2-dichloropropanoate (EDCP) is described. The (re)generation of the activating CuI complex is accomplished by Na2CO3 without the addition of any explicit reducing agent. Differently from the analogous process operating in the presence of ascorbic acid/carbonate as the reducing system, branching is not present and control over polymerization is improved. The activation mechanism should follow a composite route, where both EtOH and TPMA contribute to the regeneration of the catalyst. The oxidation of TPMA is suggested by the absence of the ligand in the final reaction mixture and by the reduction of CuII even in t-BuOAc/t-BuOH, notwithstanding the very poor ability of t-BuOH as a reducing agent. Oxidative degradation of TPMA causes a progressive malfunctioning of the redox catalyst. Consequently, the polymerization rate, after a prompt start, becomes slower and slower, fixing conversions at around 50% (4.5 h). This means a gradual decrease of the free radical concentration, which develops unfavorable conditions for the reductive coupling (termination) between the bifunctional growing chains, preserving a controlled growth of the polymer.
中文翻译:
仅使用Na2CO3促进苯乙烯在EtOAc / EtOH中的ATRP促进铜催化剂的再生
摘要
CuCl 2 /三(2-吡啶甲基)胺(TPMA)(1/1)在乙酸乙酯/乙醇(EtOAc / EtOH)中催化的“通过电子转移再生的活化剂”“原子转移自由基聚合”(ARGET ATRP)工艺描述了由2,2-二氯丙酸乙酯(EDCP)聚合苯乙烯的方法。活化Cu I配合物的(再生)是通过Na 2 CO 3完成的无需添加任何明确的还原剂。与在抗坏血酸/碳酸酯作为还原体系存在下操作的类似方法不同,不存在支化并且改进了对聚合的控制。活化机理应遵循复合途径,其中EtOH和TPMA均有助于催化剂的再生。最终反应混合物中不存在配体,即使t- BuOAc / t- BuOH中Cu II的还原,尽管t的能力很差,但仍表明TPMA的氧化-BuOH作为还原剂。TPMA的氧化降解会导致氧化还原催化剂逐渐失效。因此,迅速启动后,聚合速率变得越来越慢,转化率固定在50%左右(4.5小时)。这意味着自由基浓度的逐渐降低,从而为双功能生长链之间的还原偶联(终止)产生不利条件,从而保持了聚合物的受控生长。