Polymers as Carriers or Supports

The following protocols make use of the compounds adipic acid dihydrazide and carbohy-drazide to derivatize molecules containing aldehydes, carboxylates, and alkylphosphates. The protocols are applicable for the modification of proteins, including enzymes, soluble polymers such as dextrans and poly-amino acids, and insoluble polymers used as micro-carriers or chromatographic supports. 

As described below, ionic catalyst complexes can be supported to both inorganic and polymer (dendrimer) carriers. The efficiency of the support is determined by the general rules of ion exchange and, for this reason, in order to achieve a successful approach it is important to exclude the formation or presence of other ionic compounds, which might compete for (liberate) the catalyst ion from the support. 

The first successful experiments were reported by Schwab [16] Cu, Ni and Pt on quartz HI were used to dehydrogenate racemic 2-butanol 23. At low conversions, a measurable optical rotation of the reaction solution indicated that one enantiomer of 23 had reacted preferentially (eeright-handed quartz gave the opposite optical rotation it was deduced that the chiral arrangement of the crystal was indeed responsible for this kinetic resolution (for a review see [8]). Later, natural fibres like silk fibroin H5 (Akabori [21]), polysaccharides H8 (Balandin [23]) and cellulose H12 (Harada [29]) were employed as chiral carriers or as protective polymer for several metals. With the exception of Pd/silk fibroin HS, where ee s up to 66% were reported, the optical yields observed for catalysts from natural or synthetic (H8, Hll. H13) chiral supports were very low and it was later found that the results observed with HS were not reproducible [4],... 

In this context, facilitated transport of a specific gas molecule through modified polymeric membranes or liquid membranes containing mobile carriers can be employed to improve single bulk material (polymer) properties. Ceramic material is not traditionally employed as hquid membrane support due to their high cost, use of not aggressive compounds to be separated and mild operating conditions. 

The purpose of this paper is to discuss the third area, viz. the enzyme support. Various carriers that have been used over the years for immobilizing enzymes can be classified into three categories. The first is hard particulate substances such as porous glass/ceramics and polymers. The second category is polymers in membranous form, such as reconstituted collagen or ultrafiltration membranes, where the enzyme is trapped behind or within the membrane barrier. The third category is cellulose-derived materials in the form of fibers or beads. Almost all these materials are used either in the form of packed beds or as membranes. In any case, the diffusional resistances are major restrictions to their use as efficient enzyme supports. We will discuss and demonstrate a new type of microporous carrier that can be used very efficiently as an immobilized enzyme support. 

Palladium species immobilized on various supports have also been applied as catalysts for Suzuki cross-coupling reactions of aryl bromides and chlorides with phenylboronic acids. Polymers, dendrimers, micro- and meso-porous materials, carbon and metal oxides have been used as carriers for Pd particles or complexes for these reactions. Polymers as supports were applied by Lee and Valiyaveettil et al. (using a particular capillary microreactor) [173] and by Bedford et al. (very efficient activation of aryl chlorides by polymer bound palladacycles) [174]. Buch-meiser et al. reported on the use of bispyrimidine-based Pd catalysts which were anchored onto a polymer support for Suzuki couplings of several aryl bromides [171]. Investigations of Corma et al. [130] and Plenio and coworkers [175] focused on the separation and reusability of Pd catalysts supported on soluble polymers. Astruc and Heuze et al. efficiently converted aryl chlorides using diphosphino Pd(II)-complexes on dendrimers [176]. 

In this chapter, attention is focused on a number of polymers that are either themselves characterized by special properties or are modified for special uses. These include high-temperature and fire-resistant polymers, electroactive polymers, polymer electrolytes, liquid crystal polymers (LCPs), polymers in photoresist applications, ionic polymers, and polymers as reagent carriers and catalyst supports. 

---