Chain-growth polymerization for poly(3-hexylthiophene) with a defined molecular weight and a low polydispersity
Chain-growth polymerization for poly(3-hexylthiophene) with a defined molecular weight and a low polydispersity
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DOI：
10.1021/ma035396o
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发表时间：
2004-02-24
期刊：
影响因子：
5.5
通讯作者：
Yokozawa, T
中科院分区：
文献类型：
--
作者：
Yokoyama, A;Miyakoshi, R;Yokozawa, T
区域规整聚（3-烷基噻吩）（P3 AT）由于其禁带宽度小、电导率高、发光性能好、场效应迁移率高等优点，近年来受到了广泛的关注。3 McCullough 5，6和Rieke 7，8利用Nicatalyzed脱卤聚合反应，区域控制合成了几乎完全头-尾结构的P3 AT（HT-P3 AT）4，其物理性能上级区域无规结构的P3 AT。它们的合成方法都很有价值，是目前合成HT-P3 AT的主要方法。为了检查和改进HT-P3 AT的性能，具有所需分子量和低多分散性的聚合物的合成是重要和关键的。然而，这种受控聚合尚未报道。由于Ni催化的脱卤聚合形式上是缩聚反应，并得到具有高多分散性和不受控制的分子量的聚合物，因此通常认为该聚合通过逐步增长机制进行。实际上，所报道的通过区域控制聚合获得的粗HT-P3 AT（没有分馏）的多分散性（Mw/Mn’s）是高的，例如1.949和3.63;仅在通过粗产物的索氏萃取分馏之后才可以获得具有低多分散性的8 HT-P3 AT’s。5-10在我们合成具有受控分子量和低多分散性的缩聚物的工作过程中，11我们对在HT-P3 AT的合成中控制分子量和多分散性感兴趣。3-烷基-2-溴-5-金属噻吩衍生物在镍催化下的聚合反应可能是通过单体或聚合物增长端的碳卤键与镍催化剂的氧化加成进行的。正如我们在Pd催化的CO插入缩聚中提出的，单体中的供电子碳-金属键将抑制其氧化加成。这将导致选择性氧化添加的聚合物增长结束的镍催化剂和链增长聚合，在我们以前的工作。11在本通讯中，我们证明了镍催化的2-溴-5-氯镁-3-己基噻吩的聚合，其通过2-溴-3-己基-5-碘噻吩（1）与烷基氯化镁反应获得，通过链生长机制得到HT-聚（3-己基噻吩）（HTP 3 HT）的分子量分布，并且HT-P3 HT的分子量由单体与Ni催化剂的进料比控制。使用2-溴-3-十二烷基-5-碘噻吩和甲基氯化镁的先前聚合在CHCl 3分级分离后得到Mn）21 000和Mw/Mn）1.36的HT-聚（3-十二烷基噻吩），6但该聚合的链增长性质尚未报道。在0 ℃下用1当量的异丙基氯化镁处理2-溴-3-己基-5-碘噻吩（1），通过镁-碘交换得到2（方案1）。向反应混合物中加入0.4摩尔%的Ni（dppp）Cl 2（dppp）1，3-双-（二苯基膦基）丙烷）并在室温下搅拌，得到HT-P3 HT。如图1a所示，聚合在室温下顺利进行，2的转化率在15分钟内为50%，1小时内为75%，24小时内为93%。通过GPC相对于聚苯乙烯标准物分析每次转化时粗HT-P3 HT（未通过沉淀或分馏纯化）的Mn和Mw/Mn值。转化率-Mn和转化率-Mw/Mn图表明，单体2以链增长聚合方式聚合：Mn值…
Regioregular poly (3-alkylthiophene)(P3AT) has received much attention in recent years because of its small band gap, high electrical conductivity, 1 and interesting properties such as light emitting ability2 and high field effect mobility. 3 Regiocontrolled synthesis of almost completely head-to-tail P3AT (HT-P3AT) 4 has been developed by McCullough5, 6 and Rieke7, 8 using Nicatalyzed dehalogenative polymerization, and the physical properties of HT-P3AT are superior to those of the regiorandom one. Their synthetic methods are very valuable and the dominant methods for the synthesis of HT-P3AT. To examine and refine the properties of HT-P3AT, synthesis of the polymer having a desired molecular weight with a low polydispersity is important and crucial. Such a controlled polymerization, however, has not been reported. Because the Ni-catalyzed dehalogenative polymerization is formally a polycondensation and gives polymer with a high polydispersity and an uncontrolled molecular weight, this polymerization is generally believed to proceed via a step-growth mechanism. Indeed, the reported polydispersities (Mw/Mn’s) of crude HT-P3AT (without fractionation) obtained by the regiocontrolled polymerization were high such as 1.949 and 3.63; 8 HT-P3AT’s with low polydispersities can be obtained only after fractionation by Soxhlet extraction of the crude product. 5-10 In the course of our work to synthesize condensation polymers having controlled molecular weights and low polydispersities, 11 we took an interest in controlling the molecular weight and polydispersity in the synthesis of HT-P3AT. The Ni-catalyzed polymerizations of 3-alkyl-2-bromo-5-metalothiophene derivatives for HT-P3AT presumably proceed via oxidative addition of the carbonhalogen linkage of monomer or polymer propagating end to the Ni catalyst. As we proposed in Pd-catalyzed CO-insertion polycondensation, 12 an electron-donating carbon-metal bond in the monomer would suppress its oxidative addition. This should result in selective oxidative addition of the polymer propagating end to the Ni catalyst and a chain-growth polymerization as in our previous work. 11 In this Communication, we demonstrate that the Ni-catalyzed polymerization of 2-bromo-5-chloromagnesio-3-hexylthiophene, which is obtained by reaction of 2-bromo-3-hexyl-5-iodothiophene (1) with alkylmagnesium chloride, proceeds by a chain-growth mechanism to give HT-poly (3-hexylthiophene)(HTP3HT) with a narrow molecular weight distribution and that the molecular weight of HT-P3HT is controlled by the feed ratio of monomer to the Ni catalyst. Previous polymerization using 2-bromo-3-dodecyl-5-iodothiophene and methylmagnesium chloride gave HT-poly (3-dodecylthiophene) with Mn) 21 000 and Mw/Mn) 1.36 after CHCl3 fractionation, 6 but the chain-growth nature of this polymerization has not been reported. 13 Treatment of 2-bromo-3-hexyl-5-iodothiophene (1) with 1 equiv of isopropylmagnesium chloride at 0 C gave 2 via magnesium-iodine exchange (Scheme 1). Addition of 0.4 mol% of Ni (dppp) Cl2 (dppp) 1, 3-bis-(diphenylphosphino) propane) to the reaction mixture and stirring at room temperature led to HT-P3HT. As shown in Figure 1a, the polymerization proceeded smoothly at room temperature, and the conversion of 2 was 50% in 15 min, 75% in 1 h, and 93% in 24 h. The Mn and Mw/Mn values of the crude HT-P3HT (without purification by precipitation or fractionation) at each conversion were analyzed by GPC relative to polystyrene standers. Conversion-Mn and conversion-Mw/Mn plots demonstrate that monomer 2 polymerized in a chain-growth polymerization manner: the Mn values …