Removal of palladium nanoparticles from polymer materials
Removal of palladium nanoparticles from polymer materials
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DOI：
10.1021/ma047635t
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发表时间：
2005-02-08
期刊：
影响因子：
5.5
通讯作者：
Krebs, FC
中科院分区：
文献类型：
--
作者：
Nielsen, KT;Bechgaard, K;Krebs, FC
钯催化在合成有机化学中作为一种通用的工具而受到欢迎，它使具有许多敏感基团的复杂分子成为可能，这些分子只能在钯催化提供的温和条件下合成。钯在合成有机化学中的使用导致了一系列反应类型的发展，这些反应类型没有钯的催化是不可能（或非常困难）的。最著名的偶联反应是Heck， 1 Stille, 2 Suzuki， 3根岸，4和Sonogashira， 5，虽然还有更多的存在，但它们是一般主题的变体。一个经常被忽视的事实是钯纳米粒子的形成在化学反应中，当催化剂降解。当化学反应的产物可以通过蒸馏纯化（或小分子结晶）时，通常有可能获得无钯的产物。然而，对于大分子和聚合物，这些纯化方法是不可用的，并且应该始终假设产品被钯污染。钯纳米颗粒在产品中的保留程度取决于对钯的亲和力有多强。例如，钯纳米颗粒与共轭聚合物结合良好，导致含有钯的产品，使用当前的纯化技术无法完全去除。虽然污染物钯纳米颗粒/催化剂在很大程度上可以被去除，但原油产品通常含有钯纳米颗粒/催化剂。钯污染（0.0001-1% w/w）通常不被注意或未被检测到，因为它不会干扰常见的分析技术（元素分析，核磁共振等）。然而，当产品的电性能很重要时，即使是最小的污染也会对薄膜器件的性能产生不利影响。我们最近发现了用两种不同的方法制备聚（苯乙烯）产品的问题：一种是精心设计的无钯方法，另一种是基于赫克反应的一步制钯方法。聚合物产品在大多数物理化学方面（核磁共振，紫外-可见吸收等）是相同的，但当使用钯路线的聚合物产品制成电致发光器件时，它们没有功能，而非钯产品则具有功能器件。功能的缺乏被观察到作为一个非常低的器件电阻和缺乏电致发光。我们后来证明了在Sonogashira条件下由钯路线制备的聚（苯乙烯）s的相同问题。我们尝试使用n， n -二乙基二硫代氨基甲酸酯(2)去除钯污染，并发现我们能够将钯去除到可以制造设备的水平。7,8然而，2的缺点是，延长的反应时间改变了聚苯乙烯产品的光物理性质，在一定程度上抑制了期望的电致发光。然而，器件电阻仍然很高。如果不影响所期望的有机产物，钯纳米颗粒/催化剂的有效化学去除不是一项微不足道的任务，虽然2提供了部分溶液，并已成功地用于在固相合成过程中去除钯，但一种新的方法是非常可取的。各种方法来去除重金属使用n -酰基半胱氨酸，聚苯乙烯基硫脲盐，或硅颗粒携带悬垂烷基与末端巯基官能团已被报道。虽然它们能有效地结合钯，但它们不能很好地用于聚合物产品，因为…
Palladium catalysis in synthetic organic chemistry has been welcomed as a versatile tool and has made it possible to make complex molecules with many sensitive groups that can be synthesized only under the mild conditions offered by palladium catalysis. The use of palladium in synthetic organic chemistry has led to the development of an arsenal of reaction types that were not possible (or very difficult) without palladium catalysis. The most well-known coupling reactions are Heck, 1 Stille, 2 Suzuki, 3 Negishi, 4 and Sonogashira, 5 and while many more exist they are variations over the general theme. An often neglected fact is the formation of palladium nanoparticles during the chemical reactions when the catalyst degrades. When the product of the chemical reaction can be purified by distillation (or for small molecules crystallized), it is often possible to obtain a palladium-free product. For large molecules and polymers, however, these means of purification are not available, and a contamination of the product with palladium should always be assumed. The extent to which palladium nanoparticles are withheld in the product depends on how strong the affinity for palladium is. As an example, palladium nanoparticles bind well to conjugated polymers, leading to a product with palladium that cannot be completely removed using current purification techniques. While the contaminant palladium nanoparticles/catalyst to a large extent can be removed, the crude product typically contains palladium nanoparticles/catalyst. The palladium contamination (0.0001-1% w/w) often goes by unnoticed or undetected, as it does not interfere with common analytical techniques (elemental analysis, NMR, etc.). When, however, the electrical properties of the product are important, even the smallest contamination has a detrimental effect on thin film device performance. We recently discovered6 the problem for a poly (phenylenevinylene) product prepared by two different routes: an elaborate palladium-free route and a one-step palladium route based on the Heck reaction. The polymer products were identical in most physical-chemical aspects (NMR, UV-vis absorption, etc.), but when electroluminescent devices were made using the polymer product from the palladium route, they were not functional whereas the non-palladium product gave functional devices. The lack of functionality was observed as a very low device resistance and the absence of electroluminescence. We later demonstrated the same problem for poly (phenyleneethynylene) s prepared by a palladium route following Sonogashira conditions. 7 We attempted to remove the palladium contamination usingN, N-diethyldithiocarbamate (2) and found that we were able to remove the palladium to a level where device fabrication was possible. 7, 8 The shortcoming of 2, however, was that prolonged reaction times altered the photophysical properties of the poly (phenyleneethynylene) product to an extent where the desired electroluminescence became suppressed. The device resistance, however, remained high. The efficient chemical removal of palladium nanoparticles/catalyst is not a trivial task if the desired organic product is to be left unaffected, and while 2 provided a partial solution and has been employed successfully for removal of palladium during solid-phase synthesis, 9 a new procedure was highly desirable. Various approaches to the removal of heavy metals using N-acylcysteine, polystyrene-based thiuronium salts, or silica particles bearing pendant alkyl groups with terminal thiol functionalities have been reported. 10 While they bind palladium efficiently, they do not work well for polymer products since a …