Research Institute for Physical Chemical Problems of the Belarusian State University, Leningradskaya St. 14, 220030 Minsk, Belarus.
Acc Chem Res. 2010 Mar 16;43(3):357-67. doi: 10.1021/ar900198q.
Polymer latexes are easily prepared on a multimillion ton scale in industry using free radical initiated emulsion and suspension polymerizations in water, a cheap, nonviscous, heat-controlling, and environmentally benign solvent. Until recently, researchers had done little investigation into ionic polymerization because even a small amount of water would easily deactivate the conventional catalysts used in these processes. In the last decade, however, cationic polymerization in aqueous media has emerged as a new and attractive method for controlling the polymerization reactions using mild experimental conditions. This Account reviews the current science of and future outlook for cationic polymerization of vinyl monomers in aqueous media. We particularly emphasize the design and evolution of catalytic systems and the precision synthesis of functional polymers. Early work to tailor the suspension and emulsion cationic polymerizations of reactive monomers such as p-methoxystyrene and vinyl ethers used long-chain strong acids, called INISURF for their dual roles as initiators and surfactants, and lanthanide triflates. These polymerization processes shared two main features: (i) all reactions (initiation, propagation, and termination) occurred at the particle interface; (ii) synthesized polymers have limits on their molecular weight, attributed to the "critical DP" effect, related to the entry of oligomers inside the particles as they become increasingly hydrophobic. The next generation of catalysts, named "Lewis acid-surfactant combined catalysts" (LASC), shifted the polymerization locus from the interface to the inside of the monomer droplets, allowing for the production of long polymer chains. Recently, catalytic systems based on boranes, (BF(3)OEt(2), B(C(6)F(5))(3), (C(6)F(4)-1,2-[B(C(6)F(5))(2)]), and (C(6)F(4)-1,2-B(C(12)F(8)))), have shown great potential in controlling the cationic polymerization in "wet" solution, containing an excess of water relative to Lewis acid, or aqueous media of such industrially important monomers as styrene, cyclopentadiene, and even isobutylene.
聚合物胶乳在工业上很容易通过自由基引发的乳液聚合和悬浮聚合在水中制备，水是一种廉价、非粘性、控温、环境友好的溶剂。直到最近，研究人员对离子聚合的研究还很少，因为即使是少量的水也会很容易使这些过程中使用的常规催化剂失活。然而，在过去的十年中，水相中的阳离子聚合已经成为一种新的、有吸引力的方法，可以在温和的实验条件下控制聚合反应。本综述回顾了目前水相中的乙烯基单体阳离子聚合的科学现状和未来展望。我们特别强调了催化体系的设计和演变以及功能聚合物的精确合成。早期的工作是为了定制反应性单体如对甲氧基苯乙烯和乙烯基醚的悬浮和乳液阳离子聚合，使用长链强酸，因其双重作用作为引发剂和表面活性剂，被称为 INISURF，并使用镧系元素三氟甲磺酸酯。这些聚合过程有两个主要特点：（i）所有反应（引发、增长和终止）都发生在颗粒界面上；（ii）合成聚合物的分子量有限，这归因于“临界 DP”效应，与低聚物进入颗粒内部的情况有关，因为它们变得越来越疏水。下一代催化剂，命名为“路易斯酸-表面活性剂组合催化剂”（LASC），将聚合位置从界面转移到单体液滴内部，从而可以生产长链聚合物。最近，基于硼烷的催化体系，（BF(3)OEt(2)、B(C(6)F(5))(3)、(C(6)F(4)-1,2-[B(C(6)F(5))(2)]）和（C(6)F(4)-1,2-B(C(12)F(8)))），在控制“湿”溶液中的阳离子聚合方面显示出巨大的潜力，“湿”溶液含有相对于路易斯酸过量的水，或者含有工业上重要单体如苯乙烯、环戊二烯，甚至异丁烯的水相。
