Palioura D, Armes S P, Anastasiadis S H, Vamvakaki M
Institute of Electronic Structure and Laser, Foundation for Research and Technology--Hellas, P.O. Box 1527, 71110 Heraklion Crete, Greece.
Langmuir. 2007 May 8;23(10):5761-8. doi: 10.1021/la063359v. Epub 2007 Apr 5.
Cross-linked sterically stabilized latexes of approximately 250 nm diameter were synthesized by emulsion polymerization of 2-(diethylamino)ethyl methacrylate using a bifunctional oligo(propylene oxide)-based diacrylate cross-linker and a poly(ethylene oxide)-based macromonomer as the stabilizer at pH 9. These particles exhibit reversible swelling properties in water by adjusting the solution pH. At low pH, they exist as swollen microgels as a result of protonation of the tertiary amine units. Deswelling occurs above pH 7 [the effective pK(a) of poly(2-(diethylamino)ethyl methacrylate)], leading to the formation of the original compact latex particles. The swollen microgels can be used as nanoreactors: efficient impregnation with Pt nanoparticles can be achieved by incorporating precursor platinum compounds, followed by metal reduction. Dynamic light scattering was used to compare two methods of Pt nanoparticle impregnation with respect to the size and stability of the final Pt-loaded microgel particles. In the first method, the H2PtCl6 precursor was added to hydrophobic latex particles at high pH, followed by metal reduction. In the second method, H2PtCl6 was added to hydrophilic swollen microgel particles at low pH, and then this metal salt was reduced in situ using NaBH4 and the pH was raised by the addition of base. Both the Pt salt-loaded (metalated) microgels and the final Pt nanoparticle-loaded microgels had well-defined structures that were independent of the synthesis route. Polymer-metal interactions were investigated by UV-visible absorption spectroscopy, which confirmed that the Pt salt was completely reduced to zero-valent Pt. Transmission electron microscopy and X-ray diffraction studies verified the formation of nanometer-sized Pt nanoparticles within these microgels, which can be used as recoverable colloidal catalyst supports for various organic reactions.
通过在pH为9的条件下，使用双官能团聚环氧丙烷二丙烯酸酯交联剂和聚环氧乙烷大分子单体作为稳定剂，对甲基丙烯酸2 - （二乙氨基）乙酯进行乳液聚合，合成了直径约为250 nm的交联空间稳定乳胶。通过调节溶液pH值，这些颗粒在水中表现出可逆的溶胀特性。在低pH值下，由于叔胺单元的质子化，它们以溶胀的微凝胶形式存在。在pH高于7时（聚甲基丙烯酸2 - （二乙氨基）乙酯的有效pK(a)）发生去溶胀，导致形成原始的致密乳胶颗粒。溶胀的微凝胶可用作纳米反应器：通过加入前体铂化合物，随后进行金属还原，可以实现用Pt纳米颗粒的高效浸渍。使用动态光散射比较了两种Pt纳米颗粒浸渍方法对最终负载Pt的微凝胶颗粒的尺寸和稳定性的影响。在第一种方法中，在高pH值下将H2PtCl6前体添加到疏水性乳胶颗粒中，随后进行金属还原。在第二种方法中，在低pH值下将H2PtCl6添加到亲水性溶胀微凝胶颗粒中，然后使用NaBH4原位还原该金属盐，并通过添加碱提高pH值。负载Pt盐（金属化）的微凝胶和最终负载Pt纳米颗粒的微凝胶都具有明确的结构，且与合成路线无关。通过紫外可见吸收光谱研究了聚合物与金属的相互作用，证实Pt盐完全还原为零价Pt。透射电子显微镜和X射线衍射研究验证了这些微凝胶中形成了纳米尺寸的Pt纳米颗粒，其可用作各种有机反应的可回收胶体催化剂载体。
