Effect of surface modification on the synthesis of pore-filling polymeric monoliths in microfiltration membranes made from poly(propylene) and poly(ethylene terephthalate).
The effect of pre-modification on the interaction of macroporous substrates (membranes) with mainly micro- and mesoporous polymer monoliths was studied. Bulk, porous polymer monoliths were synthesized to optimize the synthesis conditions and their pore morphol., and the data were used as benchmark for this study. Pre-modification of the entire pore surface of PP microfiltration membranes and PET track-etched membranes by UV-initiated grafting with PEGMA was performed using well-established methods, including coating with the photo-initiator, benzophenone. Subsequently, these membranes were functionalized by filling the pores with porous polymer monoliths from MAA and EDMA and compared with membranes that had been functionalized without the pre-modification step. The materials were characterized mainly by the degree of grafting, SEM, and by the gas-adsorption-isotherm method. The DG values, after composite-membrane prepn. under identical conditions, were not influenced by the pre-modification. However, it could be clearly seen from the SEM images that the pre-modification step prevents the formation of voids at the monolith-membrane pore interface. Larger sp. surface area and pore vol. values for composite membranes, prepd. after pre-modification, fully support the SEM results. Esp. large differences in pore structure between the 2 different composite membranes were found in the mesopore range. The results of this study indicate that it is possible to prep. porous, composite membranes where the trans-membrane transport is exclusively controlled by the pore and surface structure of a functional polymeric monolith, for example, made from a molecularly-imprinted polymer.
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