Facile metal‐free living cationic polymerization of various vinyl ethers by hydrogen chloride with ether
Facile metal‐free living cationic polymerization of various vinyl ethers by hydrogen chloride with ether
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DOI：
10.1002/pola.22515
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发表时间：
2008-03
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影响因子：
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通讯作者：
S. Sugihara;Yasuaki Tanabe;M. Kitagawa;I. Ikeda
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文献类型：
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作者：
S. Sugihara;Yasuaki Tanabe;M. Kitagawa;I. Ikeda
活性聚合是设计和合成具有可控结构的新型聚合物材料的一种通用工具，如分子量、分子量分布(MWD)和组成重复单元或链段的序列。1乙烯基醚活性阳离子聚合的最新进展使得合成有趣的功能聚合物成为可能，例如急剧变化的刺激响应型共聚物。随着这一发展，人们发现了各种各样的引爆系统。异丁基乙烯基醚(IBVE)等乙烯基醚的活性阳离子聚合大多是由双组分引发体系(阳离子引发剂和活化剂)或三组分引发体系(包括碳阳离子添加剂)催化的。1、3、4在这些例子中，大多数阳离子引发剂是质子酸，其与乙烯基醚的加合物一旦被取出并用作引发剂。阳离子试剂(如IBVE-HCl加合物)的键是共价键，即在低温下对应于休眠状态，不发生聚合反应。通常，键应由路易斯酸如I2、ZnCl2、EtAlCl2和SnCl2亲电活化。如果激活剂很强，应在聚合体系中加入盐或碱。与没有Lewis酸的方法一样，在铵盐存在下用HI聚合IBVE，以及用超强酸或三氟酸聚合也有几个例外。7对于另一种乙烯基单体，存在单独HI的N-乙烯基咔唑8和由AcClO4 9生成的环状不饱和醚。然而，没有使用不含金属路易斯酸的盐酸进行活性阳离子聚合的例子，这是一种比HI更弱的质子酸。因为没有路易斯酸的阳离子试剂不会产生碳阳离子，所以人们认为乙烯基醚不会通过质子酸或单独的盐酸以活的方式聚合到高分子量。Sawamoto和Higashimura用碳正离子的稳定性和反阴离子的亲核性解释了这种NO聚合机理。然而，我们的实验得到了意想不到的结果。不是HCl/Lewis酸体系，而是乙醚(Et2O)中的HCl单独引发了各种乙烯基醚的活性阳离子聚合，如图1所示。在本研究中，我们报道了第一个仅用HCl进行乙烯基醚活性阳离子聚合的例子，严格地说，它的酸是组合催化剂“HClαEt2O”。对于干燥的HCl气体，可以通过鼓泡生成Et2O来很容易地制备HClαEt2O，或者也可以商业获得。乙二醇醚中的HClαEt2O对碳正离子具有引发剂、活化剂和稳定剂三重作用。此外，聚合条件最简单；使用的试剂是HCl、单体和Et2O(或Et2O)，其中溶剂如下
Living polymerization is a versatile tool to design and synthesize new polymeric materials with controlled architecture such as molecular weight, molecular weight distribution (MWD), and sequence of constitutional repeating units or segments. 1 Recent development of living cationic polymerization of vinyl ethers has permitted the synthesis of interesting functional polymers such as sharp-changing stimuli-responsive copolymers. 2 Along with this development, a wide variety of initiating systems have been found. Most of the living cationic polymerizations of vinyl ethers such as isobutyl vinyl ether (IBVE) are mediated by two-component initiating system (cationogen and activator) or three-component including in additives of carbocation. 1, 3, 4 In these examples, most of the cationogens are protonic acid, whose adducts with vinyl ethers are once taken out and are used as initiators. The bond of cationogen (eg, CĀĀCl in case of IBVE-HCl adduct) is covalent one, that is, it corresponds to the dormant state at low temperature, and no polymerization occurs as it is. 5 Typically, the bond should be electrophilically activated by Lewis acid such as I2, ZnCl2, EtAlCl2, and SnCl2. If the activator is strong, salts or bases should be added to the polymerization system. As the method without Lewis acid, there are a few exceptions on polymerization of IBVE by HI in the presence of ammonium salts6 and by superstrong acid, or triflic acid. 7 For another vinyl monomer, N-vinylcarbazole with HI alone8 and cyclic unsaturated ethers by AcClO4 9 exist. However, there is no example on living cationic polymerization using HCl without metal-Lewis acid, which is a weaker protonic acid than HI. Because the carbocation is not generated from cationogen without Lewis acid, vinyl ethers are believed not to be polymerized to high molecular weight in living fashion by protonic acid, or HCl alone. This no polymerization mechanism was explained by the stability of carbocation and nucleophilicity of counter anion by Sawamoto and Higashimura. 8, 10 However, the unexpected results were obtained by our experiments. Not HCl/Lewis acid system but HCl alone in diethyl ether (Et2O) was found to initiate living cationic polymerization of various vinyl ethers as shown in Chart 1. In this study, we report the first example of the living cationic polymerization of vinyl ether by HCl alone, strictly speaking, whose acid is the combination catalyst “HClÁEt2O.” The HClÁEt2O can be easily prepared by bubbling to Et2O for dry HCl gas or also commercially obtained. The HClÁEt2O in ethers play triple roles as initiator, activator, and stabilizer by Et2O for carbocation. Furthermore, the polymerization condition is the simplest; the used reagents are HCl, monomer, and Et2O (or Et2O with a solvent such as