Catalytically active polymers

In related work a library of 1,458 peptide ligands and various metal salts was tested in hydrolysis reactions of (p-nitrophenyl)phosphates.35 An active substructure composed of polymer-bound histidine in combination with Eu3+ was identified by further dissecting the original hit structure. It needs to be pointed out that catalytically active polymer beads can also be tested for catalytic activity using IR-thermography. In a seminal paper this was demonstrated using 7,000 encoded polymer beads prepared by split-and-pool methods, specifically in the metal-free acylation of alcohols.36... 

Grenz, A., Ceccarelli, S., and Bolm, C. Synthesis and application of novel catalytically active polymers containing 1,4,7-triazacyclononane, Chem. Commun. (2001), 1726-1727. 

Chiral Co(III)-salen complexes can also serve as efficient catalysts for HKR of terminal epoxides. Polymer-supported chiral salen complexes 156 were prepared from chiral Co complex 154 and ethylene glycol dimethacrylate 155, as shown in Scheme 3.45. The chemical reduction of 156, followed by treatment with acetic acid under aerobic conditions, produced the catalytically active polymer 157, which was used in the HKR of propylene oxide [87]. Some other examples of polymeric salen-Co complexes have also been reported for the same reaction [88, 89]. 

Covalent bonding refers to the materials made in which the transition metal is bonded directly to the resin through an organometallic bond. Two different approaches can be used to covalently attach metal complexes to polymer supports (i) synthesis of appropriate functional monomers and their (co)polymerization to form catalytically active polymers (Scheme 11.1) or (ii) attachment of metal complexes to preformed functional polymer supports by chemical reactions. Following these approaches, both soluble and cross-linked chiral polymeric metal complexes can be prepared. An example of an organometallic tin catalyst suitable for transesterification was reported by workers at Rohm and Haas Company [3]. 

As Table 2-3 shows, imprinted polymers have been mainly used as separation media (mostly in chromatography). Of special interest is the enantiomeric resolution of race-mates. Further applications are as immunosorbents and chemosensors. The cavities in the imprinted polymers have also been used as microreactors for selective reactions and, more interestingly, as the active sites of catalytically active polymers. In 1998 nearly 100 papers appeared in the literature on molecular imprinting, together with one book [114] another book is imminent [115]. 

Therefore, 3 has been employed as a binding site functional monomer for imprinted polymers in several application areas like enantioselective separation, sensing layers, and catalytically active polymers mimicking natural enzyme action. 

Briiggemann, O. Catalytically active polymers obtained by molecular imprinting and their application in chemical reaction engineering. Biomol. Eng. 2001, 18, 1-7. 

RTCP involves a reversible chain transfer (RT) process with a catalyst (Scheme 4a) that improves the dispersity control, as well as the mentioned small contribution of DT (Scheme Id). The catalyst can be, e.g., Af-iodosuccinimide (NIS) (Scheme 4a) [31], and works as a deactivator. Polymer (which is originally supplied by the conventional radical initiator) reacts with NIS to produce N-succinimide radical (NS ). NS works as an activator of Polymer-I to generate Polymer and NIS again. This cycle allows for frequent reversible activation of Polymer-I. This process is a reversible chain transfer of NIS that catalytically activates Polymer-I. Therefore, the polymerization was termed reversible chain transfer catalyzed polymerization (RTCP). Regarding the components used, RTCP is similar to initiators for continuous activator regeneration (ICAR)-ATRP [65]. Both systems use a monomer, a dormant species (alkyl iodide or alkyl bromide), a conventional radical initiator, and a deactivator [NIS or copper (II)] to regenerate a highly reactive activator [NS or copper (I)]. 

Bengtson G, Oehring M and Fritsch D (2004), Improved dense catalytically active polymer membranes of different configuration to separate and react organics simultaneously by pervaporation , Chem Eng Process, 43,1159-1170. 

Figure 14 5 outlines a mechanism for ethylene polymerization m the presence of Cp2ZrCl2 Step 1 describes the purpose of the MAO promoter which is to transfer a methyl group to the metallocene to convert it to its catalytically active form This methyl group will be incorporated into the growing polymer chain—indeed it will be the end from which the rest of the chain grows... 

The Zincke reaction has also been adapted for the solid phase. Dupas et al. prepared NADH-model precursors 58, immobilized on silica, by reaction of bound amino functions 57 with Zincke salt 8 (Scheme 8.4.19) for subsequent reduction to the 1,4-dihydropyridines with sodium dithionite. Earlier, Ise and co-workers utilized the Zincke reaction to prepare catalytic polyelectrolytes, starting from poly(4-vinylpyridine). Formation of Zincke salts at pyridine positions within the polymer was achieved by reaction with 2,4-dinitrochlorobenzene, and these sites were then functionalized with various amines. The resulting polymers showed catalytic activity in ester hydrolysis. ... 

Metal deactivators (MD) act, primarily, by retarding metal-catalyzed oxidation of polymers they are, therefore, important under conditions where polymers are in contact with metals, e.g., wires and power cables. Metal deactivators are normally polyfunctional metal chelating compounds (e.g.. Table la, AO 19-22) that can chelate with metals and decrease their catalytic activity [21]. 

Tsuchida, E. and Nishide, H. Polymer-Metal Complexes and Their Catalytic Activity. Vol. 24, pp. 1-87. 

In propylene polymerization by TiCl2 the addition of aluminumorganic compounds results in a fall of the polymerization rale and a concurrent increase of the isotactic fraction content in the polymer (158). A similar effect occurred when triphenylphosphine was added to TiCl2. The content of the isotactic fraction decreased in the series AlEt3 > AlEt2Cl > AlEtCl2. The catalytic activity also decreases in the same row (159). 

D. Tsiplakides, S. Neophytides, O. Enea, M.M. Jaksic, and C.G. Vayenas, Non-faradaic Electrochemical Modification of Catalytic Activity (NEMCA) of Pt Black Electrodes Deposited on Nafion 117 Solid Polymer Electrolyte, /. Electrochem. Soc. 144(6), 2072-2088 (1997). 

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