Facile preparation of core-shell type molecularly imprinted particles: Molecular imprinting into aromatic polyimide coated on silica spheres

Core-shell type imprinted spherical particles were prepared by using a conventional polymer solution coating method. A poly(amic acid) was synthesized by step-reaction polymerization of the diamines (1:19 mole ratio of the diamine monomer-template complex:4,4'-oxydianiline) and the pyromellitic dianhydride in Ni,N-dimethylacetamide at ambient temperature. The diamine monomer-template complex was synthesized by the reaction of the diamine having an isocyanato group and estrone (template) having a phenol moiety, in which the template was connected to the monomer by means of a thermally reversible urethane bond. The poly(amic acid) containing the template (estrone) molecule was used for the coating of a silica sphere, of which surface was functionalized with amino groups to increase the adhesion property of the poly(amic acid) film on the silica. The thermal imidization resulted in a spherical silica particle coated with a polyimide (thickness of polyimide: about 100 nm). The template molecules were removed from the polyimide layer by heating the particles in 1,4-dioxane in the presence of water or aniline. In the process, the isocyanato groups, which were generated by dissociation of thermally reversible urethane bonds, were converted to amino or phenyl urea groups by the reaction with water or aniline, respectively. The imprinted silica particles were used as a stationary phase in HPLC mode and their specific recognition ability for estrone and its structural analogues were evaluated.