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Abstract:
To investigate the application of non-covalently imprinted polymers as adsorption material in a continous enantioseparation process we are going to develop a diffusion cell for polymeric membranes. The first step we are currently working on is the development of a material which can recognize one of the two enantiomers of madelic acid. For this compound our institute has much experience in enantioseparation by cristallization. This process don't work with a racemic feed but gives enantiopure cristalls when an enriched solution is used. The preparation of chiral membranes made of Molecularly Imprinted Polymers (MIP's) is done by radical polymerization of a solution of the template (i.e. one of the enantiomers of mandelic acid), cross-linker and functional monomers which build non-covalent complexes with the template. These complexes are freezed in during the polymerization to give recognition sites after the extraction of template. To induce a porous structure inside the MIP a porogen is added. In the polymerization step the growing chains precipitate when their solubility is reached. The porous structure depends on both the ratio of porogenic to monomeric mixture and the polarity of the solvent. Different mixtures of polar and apolar solvents are used to achieve a surface of the monoliths as large as possible. Finally, after an extraction step in which the template, the porogen and unreacted monomers are washed out, one obtain a porous monolith which can separate one enantiomer from the other. These membranes will be integrated into a membrane module which should resolve a racemic mixture. As a prestep we have molded this porous, monolithic MIP in HPLC-columns to optimize their properties (porosity, surface, selectivity) and the fluid phase. Parallel the modeling of the membrane process should support the finding of the best properties for the membrane material and suitable operation parameters. The mass transport through porous chiral membranes follows mainly three independent mechanisms. The viscous flow and the diffusion occur in the pore phase while surface diffusion occurs on the solid phase. Only the surface diffusion is enantioselective therefore the other two transport mechanisms should be suppressed.
