Polyvinylpyridine complexes

Forster and coworkers have also prepared polyvinylpyridine complexed to a mixture of [Ru(dpp)2Cl]+ and (minority) [Ru(dpp)2]2+ groups, where dpp = 4,7-diphenyl-1,10-phenanthroline. In solution, dual emission from both chromophores is observed, whereas in the solid state, energy transfer to the lowest energy chromophore occurs [25]. The Re(CO)3Cl(diimine) group can also be attached to polyvinylpyridine. The polymer can serve as a template for growing CdS nanoparticles [26],... 

In the presence of palladium catalysts, depending on reaction conditions, the substrate can either be isomerized to propionic aldehyde or be hydrogenated to propanol. Results of allyl alcohol hydrogenation on polyvinylpyridine complexes of palladium and Pd black in water at 293 K are compared in Table 13. 

Table 14. Results of allyl alcohol hydrogenation on polyvinylpyridine complexes of palladium in water at 293 K depending on the catalyst treatment...

The most important characteristic of heterogenized homogeneous catalysts is their stability. The stability of polyvinylpyridine complexes of palladium was studied during the hydrogenation of sequential portions of allyl alcohol. On all the examined samples, the hydrogenation of 10-30 substrate portions occurs without a significant rate decrease (Fig. 25). However with Pd black each subsequent sample is hydrogenated at a lower rate than a previous one. 

However, cross-linked (2swelling ability of the cross-linked polymer matrix and the limited diffusion of the substrate to nickel atoms. 

Organic compounds having labile hydrogen, such as phenols, phenylenedi-amine, disulfides, and acetylene, are oxidatively coupled by metal complex to give polymeric materials as shown in Eqs. (73) and (74). These reactions are called oxidative polymerizations. Tsuchida et al. studied the oxidative polymerization of 2,6-dimethylphenol (XOH) as a redox reaction catalyzed by Cu(II)-polyvinylpyridine complexes, and have proposed a detailed mechanism [93-95]. 

The redox active polymer films might bear the mediator group attached either covalently to the polymer backbone (polyvinylferrocene, Ru(II) complexes of polyvinylpyridine, etc.) or electrostatically within the ion-exchange polymer (e.g. in Nation, cf. Section 2.6). 

It should be pointed out that the addition of substances, which could improve the biocompatibility of sol-gel processing and the functional characteristics of the silica matrix, is practiced rather widely. Polyethylene glycol) is one of such additives [110— 113]. Enzyme stabilization was favored by formation of polyelectrolyte complexes with polymers. For example, an increase in the lactate oxidase and glycolate oxidase activity and lifetime took place when they were combined with poly(N-vinylimida-zole) and poly(ethyleneimine), respectively, prior to their immobilization [87,114]. To improve the functional efficiency of entrapped horseradish peroxidase, a graft copolymer of polyvinylimidazole and polyvinylpyridine was added [115,116]. As shown in Refs. [117,118], the denaturation of calcium-binding proteins, cod III parvalbumin and oncomodulin, in the course of sol-gel processing could be decreased by complexation with calcium cations. 

An alternative strategy for catalyst immobilisation uses ion-pair interactions between ionic catalyst complexes and polymeric ion exchange resins. Since all the rhodium complexes in the catalytic methanol carbonylation cycle are anionic, this is an attractive candidate for ionic attachment. In 1981, Drago et al. described the effective immobilisation of the rhodium catalyst on polymeric supports based on methylated polyvinylpyridines [48]. The activity was reported to be equal to the homogeneous system at 120 °C with minimal leaching of the supported catalyst. The ionically bound complex [Rh(CO)2l2] was identified by infrared spectroscopic analysis of the impregnated resin. 

Once DNA has been condensed by a polycation, it is important for these complexes to retain a certain level of stability in salt solutions to allow sufficient time for cellular uptake of the particles. Izumrudov et al. (1999) studied the stability of a variety of polymers including polyvinylpyridines, linear poly amines, branched polyamines, polymethacrylates, and polyamides in salt solutions at a variety of pHs. They observed that polymers with predominantly primary amines produced the most stable polymer/DNA complexes followed by tertiary then quaternary amines, while higher molecular weight polymers resulted in more stable complexes for all amine types. Thus, it may be possible to specifically control complex stability by adjusting the relative amount of each amine type in the polymer. 

Zinc complexes of several polymeric N-donor ligands have been reported. Poly-(l-vinyl-2-pyrrolidinone) of various molecular weights forms the complex52 [ZnCl2(C6H9NO)]100. Complexes with the polyvinylpyridines poly-(2-pyridylethyl-ene) and poly-(4-pyridylethylene) have also been prepared.53... 

Salen-type complexes have been immobilized by coordinative bonding on polyvinylpyridine-type polymers (97). However, ee values did not exceed 46%. The retention of the complex on the polymer was reported to be excellent. 

The reaction between poly-4-vinylpyridine and PAA in water-ethanol (1 1 by volume) solutions has been investigated by calorimetry,2). This reaction proceeds without the release of H+ or OH- ions. As the heat of dissociation of the polyacid and the heat of formation of ionic bonds between macromolecular components are near zero, the protonation heats of PVPy at different pH both in the presence or absence of PAA have been measured. It has been found that in neutral solutions the heats of polyvinylpyridine protonation in the presence of PAA considerably exceeds the corresponding values in the absence of PAA, i.e. a considerable portion of pyridine rings is protonated in the polyelectrolyte complexes (Fig. 12). This may be caused only by the cooperative trasfer of the proton from the PAA carboxy group to the pyridine ring. Similar reactions cannot occur between low molecular model substances and neither when only one component is a polymer. 

A large number of macromolecules complementary to PMAA, namely polyvinylpyrrolidone, polyvinylpyridine, polyacrylamide, poly(vinyl alcohol), poly(ethylene oxide), oligoethylenimine, poly(sodium styrene sulfonate), polycations of the integral type ionen (2X) were used as P2 and P3. The pH of the media strongly influences the studied reactions of complex formation. For example, in PVPy + PVP + PMAA or OEI + PEO + PMAA systems in the add region, where weak polybases are completely protonized and PMAA does practically not dissodate, complexes with hydrogen bonds (PMAA-PVP or PMAA-PEO) are formed. In neutral medium weak polybases are partially ionizated and polyelectrolyte complexes (PMAA-PVPy, PMAA-OEI) are generated. In the alkaline medium formation of complexes has not been observed. 

Another approach, developed by Chiyoda/UOP, uses a rhodium catalyst heterogenized on a polymeric cation exchange resin. This takes advantage of the fact that the rhodium catalyzed carbonylation involves anionic complexes (see Section 4.2.5 below). The Chiyoda/UOP Acetica process employs a cross-linked polyvinylpyridine which is quaternized by methyl iodide to generate cationic pyridinium sites and which hold the anionic rhodium complexes by electrostatic interactions. The polymer support is tolerant of elevated temperatures and the ionic attachment of the catalyst is quite robust, resulting in only... 

Polyelectrolyte (polyionic) complexes between macromolecular acids and bases or their salts. They are stabilized maiidy by ionic bonds. The complex of poly(meth-acrylic acid) and polyvinylpyridine and complexes of biopolymers with synthetic polyelectrolytes are examples of such complexes. 

The importance of the electron-transfer step is demonstrated, e.g. in the oxidative pol)rmerization of 2,6-dimethylphenol catalyzed by the Cu complex attached to polyvinylpyridine beads. 

A rapid initial drop in molecular weight followed by a slower decrease is observed when polyvinylpyridine is heated at 250°C [85]. This behaviour is qualitatively similar to that of polystyrene. Scission of weak links may be involved in the fast decay of molecular weight, but random scission may also explain the shape of the curve. As in the case of polystyrene, the mechanistic problem is very complex and many more experiments are needed to solve it. Chelation of 2- and 4-polyvinylpyridine makes those polymers less heat-resistant chain scissions already occur at 100°C while the uncomplexed polymer suffers no damage at this temperature. On heating, a change in the absorption spectrum of 2-polyvinylpyridine copper chelate dissolved in 1M HC1 is observed a new peak is formed at... 

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