Polymeric supports covalently

To our knowledge, there have been no previous attempts to develop a broad class of molecular catalysts that have temperature-dependent solubilities. When molecular catalysts are covalently bound to polymeric supports, they generally assume the solubihty properties of the host polymer. In the above fluorous catalysts, we Hke to think that a short segment of polymer is being grafted onto a molecular catalyst, hi other words, the ponytails can be viewed as pieces of Teflon , which impart more and more of the solubility characteristics of the polymer as they are lengthened. 

A very successful example for the use of dendritic polymeric supports in asymmetric synthesis was recently described by Breinbauer and Jacobsen [76]. PA-MAM-dendrimers with [Co(salen)]complexes were used for the hydrolytic kinetic resolution (HKR) of terminal epoxides. For such asymmetric ring opening reactions catalyzed by [Co(salen)]complexes, the proposed mechanism involves cooperative, bimetallic catalysis. For the study of this hypothesis, PAMAM dendrimers of different generation [G1-G3] were derivatized with a covalent salen Hgand through an amide bond (Fig. 7.22). The separation was achieved by precipitation and SEC. The catalytically active [Co "(salen)]dendrimer was subsequently obtained by quantitative oxidation with elemental iodine (Fig. 7.22). 

The most common support is highly pure, spherical, microporous particles of silica that are permeable to solvent and have a surface area of several hundred square meters per gram (Figure 25-5). Most silica should not be used above pH 8, because it dissolves in base. Special grades of silica are stable up to pH 9 or 10. For separation of basic compounds at pH 8-12, polymeric supports such as polystyrene (Figure 26-1) can be used. Stationary phase is covalently attached to the polymer. 

Four methods have been developed for enzyme immobilization (1) physical adsorption onto an inert, insoluble, solid support such as a polymer (2) chemical covalent attachment to an insoluble polymeric support (3) encapsulation within a membranous microsphere such as a liposome and (4) entrapment within a gel matrix. The choice of immobilization method is dependent on several factors, including the enzyme used, the process to be carried out, and the reaction conditions. In this experiment, an enzyme, horseradish peroxidase (donor H202 oxidoreductase EC 1.11.1.7), will be imprisoned within a polyacrylamide gel matrix. This method of entrapment has been chosen because it is rapid, inexpensive, and allows kinetic characterization of the immobilized enzyme. Immobilized peroxidase catalyzes a reaction that has commercial potential and interest, the reductive cleavage of hydrogen peroxide, H202, by an electron donor, AH2 ... 

As this area of polymer supported reagents continues to expand the complexity of the polymeric supported resins has increased [18]. Although electrophilic supported reagents like the isocyanate 5 and acid chloride 12 have been shown to be efficient reagents for the covalent capture for primary and secondary amines (Table 1), they are not without their difficulties. The isocyanate resin is particularly expensive and the loading is rather low (approximately 1 mmol NCO/gram). 

Covalent Linking of Chiral Schiff Bases to Polymeric Supports... 

The use of insoluble polymeric carriers has greatly simplified the synthesis of peptides purification of the growing peptide chain in the repetitive steps is achieved by filtration procedures that simply remove all soluble reagents and byproducts from the reaction medium, whilst the covalently resin-hnked macromolecule is retained on the insoluble polymeric support. In all sohd-phase reactions of this type, the polymeric support represents the medium on or in which the chemical reaction takes place. Correspondingly, this medium is represented by the total amount of insoluble polymer present, which in the case of polymeric beads is divided into small, individual reaction compartments. Resin parameters such as the degree of crosshnking, the polarity of the resin, its sweUing properties, mass-transport, phase transitions, bead size, and the particle size distribution therefore have to be taken into serious consideration. 

The majority of reversed-phase methods have been developed on covalently modified silica gel and the most popular stationary phase is octade-cylsilyl silica (ODS, Cig). Polymeric supports, such as functionalized polystyrene-divinylbenzene copolymers (MacBlane et al., 1987), are particularly useful when mobile phases of higher pH are required because of their resistance to degradation in alkaline solutions. The main drawback of polymeric supports is their reduced column efficiencies and their lower mechanical resistance to high pressures compared with silica gel. 

Reactive Organic Functional Groups Covalently Bound on Polymeric Supports and Solid Surfaces... 

The development of methodologies for the covalent bonding of ligands to polymeric supports is important for the preparation of novel reagents to be used in ionic and molecular separations which are important to the environment and for the preparation of chemical sensors which can be used in the monitoring of environmentally sensitive areas. Our research focuses on identifying the mechanisms by which immobilized ligands... 

One way to use surfactants in synthesis is to immobilize them. For example surfactant moieties can be bound covalently to a solid polymeric support [176]. Alternatively a surfactant or a hydrophobic cation can be supported on a solid support such as an ion-exchange resin [106] or silica gel [177]. 

Additional approaches concern the determination of single diffusion coefficients at various polymerization stages and while using polymeric support for the covalent fixing of the metallocene components. 

Even though most of the supported ionic liquid catalysts prepared thus far have been based on silica or other oxide supports, a few catalysts have been reported where other support materials have been employed. One example involves a polymer-supported ionic liquid catalyst system prepared by covalent anchoring of an imidazolium compound via a linker chain to a polystyrene support [79]. Using a multi-step synthetic strategy the polymeric support (e.g. Merrifield resin among others) was modified with l-hexyl-3-methylimidazolium cations (Scheme 5.6-4) and investigated for nucleophilic substitution reactions including fluorina-tions with alkali-metal fluorides of haloalkanes and sulfonylalkanes (e.g. mesylates, tosylates and triflates). 

There are several ways of attaching homogeneous metal complexes to a polymeric support [24, 26] namely, adsorption, covalent and coordination bonding and ion ex-... 

RPC-5 and other mixed mode chromatographic techniques are based on ionic as well as on hydrophobic interactions. RPC-5 is the earliest of these techniques having been introduced more than 20 years ago [26]. The resin applied originally consists of a charged reversed-phase matrix with a quaternary ammonium derivative (such as methyltrialkyl (Cg-Cjo) ammonium chloride) being adsorbed on a non-porous polymer support such as Plaskon or Teflon. In contrast to other HPLC-resins, the surface-forming groups of RPC-5 are physically adsorbed to the polymeric support and are not covalently bound therefore RPC-5, in principle, can be called a... 

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