Fabricated polymer-based monolithic

In addition to utilization of monoliths as a column material, two reports describing respectively silicate and synthetic organic polymer based monolithic frits were published recently [85,86], The conventional method of frit fabrication for a particle packed column usually involves thermal sintering of a section of the packing material, such as bare or octadecyl silica, using a heating device. This approach has several weaknesses such as the lack of control of the temperature and porous properties of the frit that decreases reproducibly of the fabrication process. 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

In contrast, polymer-based thin-film electrodes offer the possibility of creating a monolithic device, in which the microelectrodes and the flexible interconnect are fabricated as one structure. 

In addition, the GMA/EDMA copolymer proved to serve as a basic unit for the fabrication of highly permeable bioreactors in capillary format. Trypsin immobilization after epoxide ring opening with diethylamine and attachment of glutaraldehyde is mentioned as the probably most prominent example [64], The immobilization of trypsin was also carried out using another class of reactive monolithic methacrylate polymer, which is based on 2-vinyl-4,4-dimethylazlactone, acrylamide, and ethylene dimethacrylate [65]. In contrast to GMA/EDMA, trypsin can directly be immobilized onto this kind of monolith, as the 2-vinyl-4,4-dimethylazlactone moieties smoothly react with weak nucleophils even at room temperature. 

Polymer pyrolysis to form advanced ceramics allows the production of highly covalent refractory components (fibers, films, membranes, foams, joints, monolithic bodies, ceramic matrix composites) that are difficult to fabricate via the traditional powder processing route [1-4]. Yajima was the first to demonstrate the feasibility of producing high-strength SiC-based fibers from pyrolysis of polycarbosilane [5]. In this process, a thermoplastic pre-ceramic polymer is first shaped into the desired form, cross-linked into a pre-ceramic network and finally converted into a ceramic material by a pyrolysis process in a controlled atmosphere (Fig. 1). A common feature of the polymer route is the formation of intermediates called amorphous covalent ceramics (ACC) [6]. These are formed after removal of the organic components and before crystallization that occurs at higher temperatures. 

All these factors must be taken into account when attempting to fabricate monoliths with not only good flow-through characteristics but also optimized pore distributions for a specific application. The novel work by Frechet and Svec in 1992, which optimized the porosity of a methacrylate-based polymer for chromatography application, was a jumping point for many subsequent studies on macroporous monoliths. As discussed in the following sections, their protocol was absolutely influential on the first attempts at combining monoliths with molecularly imprinted polymers. 

The early attempts at fabricating molecularly imprinted capillary monoliths adapted the procedure set forth by Frechet and Svec [4] for the in situ preparation of non-MIP macroporous polymer rods for FC separation. In this procedure, porogenic solvents cyclohexanol and dodecanol (80 20 v/v) were used with a methacrylate-based polymer system to produce porous monoliths. When this system was applied to the fabrication of molecularly imprinted monoliths for CEC, the polymers obtained were sufficiently porous but resulted in poor enantiomeric separations [36]. It is thought that the polar-protic nature of the porogens used may have inhibited the formation of well-defined imprints. Polar-protic solvents such as these are often poor porogens for the noncovalent imprinting approach because they interfere... 

The strength, resistance to temperature, wear, corrosion and mechanical shock of high density (sintered) silicon carbide combine to make it one of the high performance ceramic materials. These properties have allowed silicon carbide to be used in a variety of applications industry-wide. The current major markets for these applications are based upon relatively simple shapes such as seals and guides (wear parts). Although current estimates have the market growing rapidly the most substantial growth will only occur after improvements in both the fabrication process and the sintered properties of the monoliths are made. These types of needs have hastened the development of preceramic polymer binder systems that aid in the fabrication of sintered silicon carbide monoliths. 

The concept of fabrication of transparent silica gel-PMMA composites in two phases was introduced by Pope et al. in the late 1980s [22] as a procedure to prepare large sol-gel monoliths with desired optical and mechanical properties. The principle of the concept is reinforcing the silica skeleton with organic polymer without influencing the optical quality. This concept is based on the ability to use the sol-gel technology to carry out a chemical preparation of an inorganic oxide, such as silica, under carefully controlled conditions, which produces pores... 

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