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 Cu^I 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 Cu^II 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.

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的情况下进行的类似方法不同，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路线，其中EtOH和TPMA均有助于催化剂的再生。尽管t的能力很差，但最终反应混合物中不存在配体，即使在t -BuOAc / t -BuOH中，Cu ^II的还原也表明了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，将转化率固定在50％（4.5小时）左右。这意味着自由基浓度的逐渐降低，这为双功能生长链之间的还原偶联（终止）产生了不利的条件，从而保持了聚合物的受控生长。