Macroporous polymer monoliths using

The synthesis of macroporous polymer monoliths using SCCO2 as the porogenic solvent. 

Synthesis of Macroporous Polymer Monoliths using scCOz as the Porogenic Solvent... 

Digestion can also be achieved using a trypsin IMER, where trypsin is immobilized to a solid support, e.g, macroporous silica [38], on POROS material (Porozyme IMER) [39-40], a PVDF membrane in a microreactor [41], or silica-based [42] or porous polymer monoliths [43-45]. 

Frechet and coworkers have reported the development of a functionalized polymer monolith for use in parallel solution phase synthesis in continuous flow applications [10]. In this report, the authors outline the preparation of an azalac-tone-functionalized monolith for scavenging nucleophiles. This method involves the preparation of a macroporous polyfchloromethylstyrene co-divinylbenzene) monolith via the polymerization of the relevant mixture of monomer, initiator and porogen. These are allowed to react with a free radical initiator (4-cyanovaleric acid), followed by reaction with the monomer of choice, to synthesize the functionalized monolith. The authors have thus prepared monoliths functionalized with VAZ to provide an azalactone-functionalized monolith. These monoliths were then demonstrated to completely remove amines after flowing a solution of amine in THF through the monolith for 30 min. They have also reported the reaction of these monoliths with alcohols as well. A small demonstration library of ureas was prepared and after 8 min of residence time up to 76% of the alkyl amines were found to be scavenged (Scheme 8.6). 

Mini-columns for analyte separation/concentration can also behave as reactors, resembling the packed bed reactor. In this context, organic polymer monoliths, largely used in the medical and biological fields [73], should be highlighted. Monolithic mini-columns consist of continuous beds with macropores and mesopores which are characterised by low back-pressure effects. These columns offer several other advantages [74], as emphasised in Chapter 8. In the context of flow analysis, monolithic mini-columns were implemented in a sequential injection analyser in 2003 [75] and the potential and limitations of the approach, called Sequential Injection Chromatography, were recently reviewed [76]. 

Finally, w/c and c/w PFPE based emulsions have been used for the synthesis of porous materials, which are the skeletal replica of the emulsions after removal of the internal phase. W/c microemulsions allowed for macroporous polyacrylate monoliths to be produced (80-82). Conversely, c/w emulsions may be used for the preparation of well-defined porous hydrophilic polymers (83). 

In the early 1990s, yet another category was developed. These rigid macroporous organic polymer monoliths were formed by a very simple in situ molding process in which a liquid mixture of monomers and solvents was polymerized under carefully controlled conditions and immediately used within a closed tube or similar container. Many review artieles describing various aspects of these materials have been published during the years since their inception. ... 

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... 

Commercially available monolithic columns are based either on silica or organic polymer and are generally characterized as a polymeric skeleton with macropores, with a diameter of approximately 2 pm, and mesopores, with a diameter of approximately 13 nm. The role of the macropores (through-pores) is to provide channels with high compounds permeability, which permits the use of higher flow rates with respect to columns based on conventional particle size, and an extended surface area, which is comparable to conventional columns packed with 3 pm particles. 

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