Ordered porous polymers

Chen YY, Ford WT, Materer NF, Teeters D. 2000. Facile conversion of colloidal crystals to ordered porous polymer nets. J Am Chem Soc 122 10472 10473. 

A research group in Lehigh University has extensively studied the synthesis and characterization of uniform macroporous styrene-divinylbenzene copolymer particles [125,126]. In their studies, uniform porous polymer particles were prepared via seeded emulsion polymerization in which linear polymer (polystyrene seed) or a mixture of linear polymer and solvent were used as inert diluents [125]. The average pore diameter was on the order of 1000 A with pore volumes up to... 

In addition to mesostructured metal oxide molecular sieves prepared through supramolecular assembly pathways, clays, carbon molecular sieves, porous polymers, sol-gel and imprinted materials, as well as self-assembled organic and other zeolite-like materials, have captured the attention of materials researchers around the globe. Clays, zeolites and sol-gel materials are still very popular because of their extensive and expanding applications in catalysis and separation science. Novel carbons and polymers of ordered porous structures have been synthesized. There are almost unlimited opportunities in the synthesis of new organic materials of desired structural and surface properties via self-assembly or imprinting procedures. 

Just as wood may be impregnated with additives to improve physical properties, a variety of porous polymers also benefit from polymer impregnation. As more and more specialized applications arise, it is necessary to produce polymeric materials with very specific surface and bulk properties. The correct combination of properties may not be obtainable using a single polymer or copolymer. However, polymeric materials may be impregnated with an additive in order to modify the surface energy, bondability, hydro-philicity, and other important properties. 

Block copolymers, which combine polymer segments with different properties, are presumably the most widely examined system for the study of self-assembly to large-scale structures that have controlled structural and functional features on the nanometer length scale [80, 81]. Phase segregation of block copolymers, followed by selective degradation of one polymer block, leads to highly ordered porous 3D structures [82], The pore dimensions obtainable are in the micro- and mesoporous range (<50 nm), which do not meet the requirements for cellular infiltration. 

Particularly, the nonsolvent immersion, that is, the Loeb-Sourirajan preparation method is an important methodology. In this method, a polymer solution is cast into a film and the polymer precipitated by immersion into water [10,144], The nonsolvent (water) quickly precipitates the polymer on the surface of the cast film, producing an extremely thin, dense-skin layer of the membrane [10,144], The polymer under the skin layer precipitates gradually, ensuing in a more porous polymer sublayer [145], Following polymer precipitation, the membrane is usually annealed in order to improve solute rejection [10,144]. 

C/W emulsions may be used as templates in the formation of porous polymers, as shown in Figure 5 (52). Polymerization takes plaee in the aqueous phase eontinuous channels between the CO2 droplets. The CO2 is vented and the water is removed to form a porous polymer. The median pore diameter on the order of 1 pm reflects the size of the original CO2 droplets. Polymer foams may be used as adsorbents, as substrates for catalysts, and as scaffolds in biomedical engineering. 

The aim of our work is to find a new type of solid catalysts in order to be able to control the selectivity. We present in this paper some results obtained with crosslinked porous polymers. Also, we compare the behaviour of different catalysts, in particular, ion-exchange resins, in the esterification of glycerol with oleic acid. The influence of the nature of the resin as well as its swelling properties are discussed. 

Polymer spheres have also been used for the formation of non-ordered porous systems in inorganic structures and such structures are being tested in applications such as bone tissue implants [32]. Below are examples of casting of discrete entities to form inorganic monoliths or film structures using either sol-gel or nanoparticle infiltration. 

The third type, porous layer open-tubular (PLOT) columns, have solid-phase particles attached to the column wall, for adsorption chromatography. Particles of alumina or porous polymers (molecular sieves) are typically used. These colunms, like packed GSC columns, are useful for separating permanent gases, as well as volatile hydrocarbons. The resolution efficiency of open-tubular colunms is generally in the order WCOT > SCOT > PLOT. Wide-bore (0.5-mm) open-tubular... 

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