Thermoresponsive polymer-bound substrates
Thermoresponsive polymer-bound substrates
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DOI：
10.1021/ja954065r
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发表时间：
1996-06-26
影响因子：
15
通讯作者：
Caraway, JW
中科院分区：
文献类型：
--
作者：
Bergbreiter, DE;Caraway, JW
聚合物现在广泛用于合成。1-5这种用途最常见于合成生物有机材料，如肽和核苷酸。1，2在催化4和组合化学5等领域的持续进步也导致了聚合物载体在更传统的有机化学中的使用不断增加。聚合物在这种化学中的主要作用是分离。聚合物将底物或催化剂与其他产物分离，或促进文库成员彼此分离。然而，聚合物和小分子之间的固有差异意味着存在其他重要方式，其中聚合物可用于影响侧基底物基团的反应性。在这里，我们描述了一种聚合物，可用于分离和回收试剂，其逆温度依赖性溶解度以有用的方式影响底物的溶解度。具体而言，我们展示了聚合物如何能够影响结合底物的反应性对多相加氢催化剂在一个可逆的，响应的方式凭借聚合物支持的逆温度依赖性的溶解度。与小分子不同，当溶液被加热时，大多数聚合物从溶液中分离。6在有机溶剂中的烃聚合物的情况下，该效应在溶剂的沸点以上发生（例如，聚（异丁烯）在戊烷中在75 ℃下）。7然而，水溶性聚合物在更容易接近的温度范围内发生相分离。此外，这种相分离发生的温度可以通过以可预测的方式改变聚合物的结构来调节。8最近，我们描述了在水中均相催化的例子，我们利用这种效应来制备所谓的"智能"催化剂。在这些情况下，使用具有逆温度依赖性溶解度的聚合物配体制备可溶性聚合物结合的催化剂。所得催化剂在溶液中时是活性的，而在相分离时是非活性的。本报告扩展和扩大了这种化学，包括其他聚合物和聚合物结合的基板。在"正常"溶剂/温度条件下和在"逆"溶剂/温度条件下，这些可还原的聚合物结合的基板上的温度的非常适度的变化的影响的动力学研究说明了从正常的温度依赖性的动力学行为的差异。我们的研究结果表明，聚（N-异丙基丙烯酰胺）（PNIPAM）的共聚物结合基板应该是最有用的在这方面。此外，PNIPAM结合的底物可以简单地通过加热和从所得聚合物悬浮液中倾析过量的水而与可溶性试剂分离和分离。用于下述化学的主要聚合物基底载体是通过N-异丙基丙烯酰胺和丙烯酸或衍生物的自由基聚合产生的共聚物。最详细的动力学研究使用通过AIBN引发的N-异丙基丙烯酰胺和丙烯酸的间硝基苯胺酰胺的共聚制备的共聚物1（当量1）。用1H、13 C NMR和FT-IR对产物进行了表征。测量1的M ν，其为3.2 × 105 Da，使用27 ℃下THF中K和α的值为9.59 × 10 - 3 mL/g和0.65。已知均聚物聚-（N-异丙基丙烯酰胺）具有反温度依赖性溶解度，其较低临界溶解温度（LCST）为31 - 32 ℃。9.11在700 nm下对1的0.1N水溶液进行的变温UV-可见光谱研究（其中没有初始吸光度）证明了在24 ℃下变得明显的不透明性。溶液在视觉上是不透明的...
Polymers are now widely used in synthesis. 1-5 This use is most commonly seen in the synthesis of bioorganic materials like peptides and nucleotides. 1, 2 Continuing advances in areas like catalysis4 and combinatorial chemistry5 have also led to the ever increasing use of polymer supports in more conventional organic chemistry. The main role of the polymer in much of this chemistry is that of separation. The polymer separates a substrate or catalyst from other products or facilitates separation of library members from one another. However, the intrinsic differences between polymers and small molecules mean that there are other significant ways in which polymers can be used to affect the reactivity of pendant substrate groups. Here we describe a polymer that can be used to separate and recover reagents and whose inverse temperature dependent solubility affects a substrate’s solubility in useful ways. Specifically, we show how a polymer can affect a bound substrate’s reactivity toward a heterogeneous hydrogenation catalyst in a reversible, responsive way by virtue of the polymer support’s inverse temperature dependent solubility. Unlike small molecules, most polymers phase separate from solution when the solution is heated. 6 In the case of a hydrocarbon polymer in organic solvents, this effect occurs above the boiling point of the solvent (eg poly (isobutylene) in pentane at 75 C). 7 Water soluble polymers, however, phase separate in more accessible temperature ranges. Moreover, the temperature at which this phase separation occurs can be tuned by altering the structure of the polymer in predictable ways. 8 Recently we described examples of homogeneous catalysis in water where we used this effect to prepare so-called “smart” catalysts. 9, 10 In these cases, soluble polymer-bound catalysts were prepared using polymeric ligands that possessed inverse temperature dependent solubility. The resulting catalysts were active when in solution and inactive when phase separated. This report extends and expands on this chemistry to include other polymers and polymer-bound substrates. Kinetic studies of the effects of very modest changes in temperature on these reducible polymer-bound substrates under “normal” solvent/temperature conditions and under “inverse” solvent/temperature conditions illustrate the difference from normal temperature dependent kinetic behavior. Our results suggest that poly (N-isopropylacrylamide)(PNIPAM) copolymer-bound substrates should be most useful in this regard. In addition, PNIPAM-bound substrates can be isolated and separated from soluble reagents simply by heating and decantation of excess water from the resulting polymer suspension. The principle polymer substrate support used for the chemistry described below was a copolymer produced by radical polymerization of N-isopropylacrylamide and acrylic acid or derivatives. The most detailed kinetic studies used the copolymer 1 prepared by AIBN-initiated copolymerization of N-isopropylacrylamide and the m-nitroaniline amide of acrylic acid (eq 1). The product copolymer was characterized by 1H and13C NMR and FT-IR spectroscopy. The Mν of 1 was measured and was 3.2× 105 Da using values of 9.59× 10-3 mL/g and 0.65 for K and a in THF at 27 C. 11 The homopolymer poly-(N-isopropylacrylamide) is known to have inverse temperature dependent solubility with a lower critical solution temperature (LCST) of 31-32 C. 9, 11 Variable temperature UV-visible spectroscopy studies of 0.1 N aqueous solutions of 1 at 700 nm (where there was no initial absorbance) demonstrated opacity which became apparent at 24 C. The solution was visually opaque …