Penczek Stanislaw, Pretula Julia
Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lodz, Poland.
ACS Macro Lett. 2021 Nov 16;10(11):1377-1397. doi: 10.1021/acsmacrolett.1c00509. Epub 2021 Oct 19.
The origin of the activated monomer mechanism (AMM) in cationic ring-opening polymerization (CROP) is described first. Then, conditions leading to the active chain end (ACE) mechanism and AMM are compared, as well as methods allowing to distinguish between these two mechanisms. These methods are based on the "ion trapping" of the active ionic species using highly basic phosphines or by comparing ACE and AMM kinetics of polymerization. The major factors deciding on the actual mechanism include: basicity of the monomers, ring strain, and the presence of the protic additives in the reaction system. These factors are tabulated for major cyclic ethers and cyclic esters. The historically evolved subsequent steps of AMM in the polymerization of cyclic esters are described: from the first experiments with trialkyloxonium salts, precursors of protonic acids, and added alcohols, via HCl as catalyst, and then CFS(═O)OH (polymerizing lactides) to the most popular derivatives of phosphoric acid, like diphenyl phosphate. Conditions allowing to synthesize poly(ε-caprolactone) (PCL), according to AMM-CROP, with molar mass up to 10 g·mol, are described as well as methods to polymerize CL with a protic initiator and acidic catalyst in one molecule. Then various methods enhancing the activity of the polymerizing systems are compared, based predominantly on hydrogen bonding, either to the polymer active end group (usually the hydroxyl group) or to the acid anion. Finally, kinetic equations for ACE and AMM are compared, and it is shown that the majority of the AMM-CROP systems, mostly studied for CL and lactides, proceed as living/controlled polymerizations. Since polymer end groups are hydroxyl groups, then, as it was shown in several papers, any initiator with one or many hydroxyl groups provides macromolecules with the corresponding architecture. The papers on synthetic methods are not discussed in detail.
首先描述了阳离子开环聚合（CROP）中活化单体机理（AMM）的起源。然后，比较了导致活性链端（ACE）机理和AMM的条件，以及区分这两种机理的方法。这些方法基于使用高碱性膦对活性离子物种进行“离子捕获”，或通过比较ACE和AMM的聚合动力学。决定实际机理的主要因素包括：单体的碱性、环张力以及反应体系中质子添加剂的存在。这些因素以表格形式列出了主要的环醚和环酯。描述了环酯聚合中AMM在历史上演变的后续步骤：从最初使用质子酸的前体三烷基氧鎓盐和添加的醇进行的实验，到以HCl为催化剂，再到CFS(═O)OH（用于聚合丙交酯），直至最常用的磷酸衍生物，如磷酸二苯酯。描述了根据AMM-CROP合成摩尔质量高达10 g·mol的聚（ε-己内酯）（PCL）的条件，以及在一个分子中使用质子引发剂和酸性催化剂聚合CL的方法。然后比较了主要基于氢键作用增强聚合体系活性的各种方法，该氢键作用作用于聚合物活性端基（通常是羟基）或酸阴离子。最后，比较了ACE和AMM的动力学方程，结果表明，大多数主要针对CL和丙交酯研究的AMM-CROP体系以活性/可控聚合的方式进行。由于聚合物端基是羟基，那么，正如在几篇论文中所表明的，任何具有一个或多个羟基的引发剂都能提供具有相应结构的大分子。关于合成方法的论文未作详细讨论。
