Nanoporous polymer materials

TEOS/H.O, NH, HF DVB, EDMA Dissolution of silica from polymer/Si02 nanocomposites yields nanoporous polymer materials (39)... 

The field of co-crystalline and nanoporous polymer materials is expected to be widely expanded. In fact, until now, only materials based on syndiotactic polystyrene have been considered for possible applications. Relevant new cocrystalline and nanoporous materials are expected in the future for other stereoregular polymers. 

Wiesenauer BR, Gin DL. Nanoporous polymer materials based on self-organized, bicontinuous cubic lyotropic liquid crystal assemblies and their apphcations. Polym J 2012 44 461-8. 

Methods of Controlling the Pore Shape, Porosity and Size of Nanoporous Polymer Materials.112... 

This chapter reviews the current state of art polymeric nanomembranes and the concept and development of some mixed-matrix nanomembranes. Methods of controlling the pore shape, porosity, and size of nanoporous polymer materials are also reviewed, together with an analysis of a nano-blend with the nano-phase removed for controlled porosity. Finally, recent progress in mixed-matrix nanomembranes and nanomembrane multi-functionalization of various nanocomposites are discussed. 

METHODS OF CONTROLLING THE PORE SHAPE, POROSITY AND SIZE OF NANOPOROUS POLYMER MATERIALS... 

Porous polymer materials, especially in particulate form, are of interest in a diverse range of applications, including controlled drug delivery, enzyme immobilization, molecular separation technology, and as hosts for chemical synthesis [101-104]. MS materials have been used as hosts for the template synthesis of nanoporous polymer replicas through in situ polymerization of monomers in the mesopores [105-108]. 

M. Alvaro, A. Corma, B. Ferrer, M.S. Galletero, H. Garcia, and E. Peris, Increasing the stability of electroluminescent phenylene vinylene polymers by encapsulation in nanoporous inorganic materials, Chem. Mater., 16 2142-2147, 2004. 

Similar approach has also been taken by Ferain and Legras [133,137,138] and De Pra et al. [139] to produce nanostructured materials based on the template of the membrane with etched pores. Polycarbonate film was also of use as the base membrane of the template, and micro- and nanopores were formed by precise control of the etching procedure. Their most resent report showed the successful formation of ultrasmall pores and electrodeposited materials of which sizes were as much as 20 nm [139]. Another attractive point of these studies is the deposited materials in the etched pores. Electrochemical polymerization of conjugated polymer materials was demonstrated in these studies, and the nanowires based on polypyrrole or polyaniline were formed with a fairly cylindrical shape reflecting the side wall structure of the etched pores. Figure 10 indicates the shape of the polypyrrole microwires with their dimension changes by the limitation of the thickness of the template. 

Less straightforward than the parameterization of conductivity is the one of oxygen diffusivity. The main pathways of O2 supply run through the open pore space, in which they exhibit percolation-type dependence. However, there is also a residual O2 diffusivity through the polymer material, and through nanopores between the carbon/catalyst grains, which are impenetrable for the polymer material. An appropriate parameterization of the diffu-sivity parameter, introduced in Eq. (42) is, therefore, given by... 

Interestingly, the 3 1 complex with the less symmetrical 3,4-substituted benzoic acid shows a more stable mesophase (K 79 M 244 I) than the derivative formed from the 3,4,5 substituted benzoic acid (K 63 M 214 I). A related system has also been reported which uses a benzotri(imidazole) (23) as the trifunctional core unit (Fig. 12b) along with benzoic acid derivatives (24). This 1 3 complex exhibits a hexagonal columnar mesophase between 23 °C and 75 °C. The acrylate moieties on the alkoxyl chains could be photopoly-merized to covalently fix the LC phase. Removal of the supramolecularly bound benzotri(imidazole) core yields a nanoporous polymer film containing hexagonally-ordered channels-opening the door to the potential application of these materials in such areas as separation, nano-composites, and catalysis. 

The ability to design LLC mesogens containing functional units other than catalytic moieties has the potential for extending the use of functionalized LLC phases and LLC polymer materials beyond catalysis. For example, the incorporation of other types of functional, task-specific chemical units onto LLC starting materials could lead to NF membranes that could perform molecular level separations using mechanisms other than simple size exclusion. Similarly, such materials could broaden the use of nanoporous LLC systems into as of yet unimagined application areas. 

Ion-track etching is a unique technique for the production of polymer membranes with statistically distributed nanopores. The size, shape, and density of these pores can be varied in a controllable manner by achieving the required transport and retention membrane characteristics (Apel 2001). The widely used polymer materials for ion-track membranes production are polyethylene terephthalate (PET) and polycarbonate (PC) thin films. The commercially available polymer membranes contain... 

Hydrogen bonds (H-bonds) are ideal noncovalent interactions to construct supramolecular nanoporous architectures since they are highly selective and directional [16]. H-bonds are formed when a donor with an available acidic hydrogen atom interacts with an acceptor that carries available nonbonding electron lone pairs. The strength of the H-bond depends mainly on the solvent and number and sequence of the H-bond donors and acceptors. Various supramolecular polymer materials have been developed which use H-bonds as structural element to position molecules. After removal of these molecular templates, a porous material is obtained to fabricate molecule specific systems. 

This chapter provides an overview of the use of H-bonds for the constmction of nanoporous materials. Systems are discussed where the formation of H-bonds directly induces porosity and approaches are presented where the mpture of H-bonds leads to porous materials. First, we describe the use of small molecules capable of forming H-bonds, which directly induces porosity in 2D and 3D H-bonded networks. Next, block copolymers are discussed which self-assemble in nanostructured materials. The removal of H-bonded template molecules leads to porous polymer materials. Finally, H-bonded polymerizable liquid crystals having even smaller pores are discussed. Molecular imprinted polymers that do not contain pores are beyond the scope of this chapter. 

Mesophases can be locked into a polymer network by making use of polymerizable LCs [59]. These molecules contain moieties such as acryloyl, diacety-lenic, and diene. Self-organization and in situ photopolymerization under UV irradiation will provide ordered nanostmctured polymers maintaining the stable LC order over a wide temperature range. A number of thermotropic liquid crystalline phases, including the nematic and smectic mesophases, have been successfully applied to synthesize polymer networks. Polymerization of reactive lyotropic liquid crystals also have been employed for preparation of nanoporous polymeric materials [58, 60]. For the constmction of nanoporous membranes, lyotropics hexagonal or columnar, lamellar or smectic, and bicontinuous cubic phases have been used, polymerized, and utilized demonstrated in a variety of applications (Fig. 2.11). 

The products prepared by reduction of metal ions in nanoporous polymers as nanoreactors, e.g. ion-exchange resins, are also heterogeneous materials. The... 

Block polymers containing an etchable block have been used as precursors for nanoporous polymers [109]. Because nanoporous polymers have large internal surface areas, large pore volumes, and uniform pore dimensions, these materials were studied as separation/pmilication media, batteiy separators, templates for nanostructured materials, low dielectric materials, and low refractive index materials. Both pore wall functionality and robustness of the matrix are important for the practical use of nanoporous polymers. As shown in Eig. 5.16, PLA was selectively etched horn a blend with reactive block co-polymers to form a nanoporous material. 

The types of nanostructured polymers used to date in the production of micro- and nanoporous foamed materials, the resulting porous structures, the experimental evidence between the pore structure and the nanostructure template, and the properties of this kind of materials are further described in the following sections. 

Next, it was demonstrated that the CNT presents limitations when the nuclei size falls into the nanometric range [81]. However, the alternative nucleation models present a significant complexity therefore CNT is commonly used to provide a qualitative estimation of nncleation in nanoporous foams the feamres proposed by Spitael et al. currently are stiU widely accepted. In addition, it is well known that nanoporous polymer requires nuclei densities greater than 10 " nuclei per cubic centimeter of the precursor materials. Therefore initial micelle densities should be higher than this value to produce nanoporous polymers from polymer blends presenting a nucellar nanostructuration, but hopefully these values can be expected even when BCP precursors are blended at low copolymer concentration (eg, <10 wt%). 

Properties and applications of nanoporous foamed materials obtained from nanostructured polymer blends... 

Modification of the foaming processes, polymer precursors, or inclusion or an additional production step that allows connecting the inner open porous structures of some of these materials with the exterior of the sample. By this way a wide set of apphcations could be fulfilled by these nanoporous polymer foams. 

D.A. Olson, L. Chen, M.A. Hillmyer, Templating nanoporous polymers with ordered block copolymers. Chemistry of Materials 20 (2008) 869-890. 

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