Polystyrene Hybrid Supports

Figure 3.8. An early example of a hybrid support applied in the rhodium catalysed hydroformylation operated in a continuous flow reactor. Polystyrene containing phosphite ligands were grafted on inorganic silica, such that the catalyst will behave as a homogeneous catalyst when using a compatible solvent...

Various novel imprinting techniques have also been presented recently. For instance, latex particles surfaces were imprinted with a cholesterol derivative in a core-shell emulsion polymerization. This was performed in a two-step procedure starting with polymerizing DVB over a polystyrene core followed by a second polymerization with a vinyl surfactant and a surfactant/cholesterol-hybrid molecule as monomer and template, respectively. The submicrometer particles did bind cholesterol in a mixture of 2-propanol (60%) and water [134]. Also new is a technique for the orientated immobilization of templates on silica surfaces [ 135]. Molecular imprinting was performed in this case by generating a polymer covering the silica as well as templates. This step was followed by the dissolution of the silica support with hydrofluoric acid. Theophylline selective MIP were obtained. 

A first example of a polystyrene dendronized with a hyperbranched polymer was recently reported by Stumbe and Haag [36]. They synthesized a polystyrene-polyglycerol hybrid support (61) by coupling a hyperbranched polyglycerol (15)... 

Chromatographic resolution is also dependent on column efficiency (i). Column efficiency is directly dependent on the nature of the support matrix and how well that support is packed in its column. Available chromatographic supports are based on dextran, agarose, polystyrene, acrylic, cellulose, silica gel and a variety of other polymers. Althou cellulosic supports are manufactured in both microcrystalline and leaded forms, most supports are beaded. Newer supports may use hybrid bead construction where the base support is coated with a second materid (e.g., dextran or silica coated with agarose). 

In protein microarrays, capture molecules need to be immobilized in a functional state on a solid support. In principle, the format of the assay system does not limit the choice of appropriate surface chemistry. The same immobilization procedure can be applied for both planar and bead-based systems. Proteins can be immobilized on various surfaces (Fig. 1) (12). Two-dimensional polystyrene, polylysine, aminosilane, or aldehyde, epoxy- or thiol group-coated surfaces can be used to immobilize proteins via noncovalent or covalent attachment (13,14). Three-dimensional supports like nitrocellulose or hydrogel-coated surfaces enable the immobilization of the proteins in a network structure. Larger quantities of proteins can be immobilized and kept in a functional state. Affinity binding reagents such as protein A, G, and L can be used to immobilize antibodies (15), streptavidin is used for biotinylated proteins (16), chelate for His-tagged proteins (17, 18), anti-GST antibodies for GST fusion proteins (19), and oligonucleotides for cDNA or mRNA-protein hybrids (20). 

Solid-Supported Surface Catalysis by Metal Complexes. Hong et al. (1987a, b, in press) have prepared a variety of hybrid catalysts between Co(II) phthalocyanine complexes and the surfaces of silica gel, polystyrene-divinylben-zene, and Ti02 and tested these hybrids for catalytic activity with respect to the autoxidation of hydrogen sulfide, sulfur dioxide, 2-mercaptoethanol, cysteine, and hydrazine ... 

To overcome such limitations, Imura et al. covered the surface of a silica gel with sulfonated cross-linked polystyrene [5]. After adsorption of styrene, divinyl-benzene, and r-butyl peroxide and subsequent free-radical polymerization, the acid groups are introduced via classical sulfonation. Control of the thickness of the crosslinked polymer layer on the surface is essential to prevent pore clogging. This sulfonated polystyrene-Si02 hybrid material preserves a large specific surface area, with a typical ion-exchange capacity of 1.8 meq g. Alternatively, a sulfonated layer can be deposited on silica by copolymerization of silica-supported methacrylate and potassium p-styrene sulfonate [6]. 

Recently, Haag and coworkers reported on the synthesis of polystyrene beads dendronised with a hyperbranched polymer [66, 67]. The polystyrene-polyglycerol hybrid support 5 was obtained by grafting of a hyperbranched polyglycerol directly onto a Merrifield resin [67] or alternatively polymerising glycidol directly onto a polyhydroxylated crosslinked polystyrene... 

Original ELISA plates were polystyrene and were not suitable for hybridization at temperatures much above 50°C due to deformation of the plastic. Plates of polycarbonate, polyvinyl, and other materials and with proprietary surface treatments to reduce nonspecific binding are now available. Novel surfaces, including nonplastic solid supports, are incorporated into commercial products. Polypropylene exhibits very low binding of DNA and is not suitable as a solid phase without surface modification. 

---