Hierarchical Porosity in Self‐Assembled Polymers: Post‐Modification of Block Copolymer–Phenolic Resin Complexes by Pyrolysis Allows the Control of Micro‐ and Mesoporosity

Abstract

It is shown that self‐assembled hierarchical porosity in organic polymers can be obtained in a facile manner based on pyrolyzed block‐copolymer–phenolic resin nanocomposites and that a given starting composition can be post‐modified in a wide range from monomodal mesoporous materials to hierarchical micro‐mesoporous materials with a high density of pores and large surface area per volume unit (up to 500–600 m2 g–1). For that purpose, self‐assembled cured composites are used where phenolic resin is templated by a diblock copolymer poly(4‐vinylpyridine)‐block‐polystyrene (P4VP‐b‐PS). Mild pyrolysis conditions lead only to monomodal mesoscale porosity, as essentially only the PS block is removed (length scale of tens of nanometers), whereas during more severe conditions under prolonged isothermal pyrolysis at 420 °C the P4VP chains within the phenolic matrix are also removed, leading to additional microporosity (sub‐nanometer length scale). The porosity is analyzed using transmission electron microscopy (TEM), small‐angle X‐ray scattering, electron microscopy tomography (3D‐TEM), positron annihilation lifetime spectroscopy (PALS), and surface‐area Brunauer–Emmett–Teller (BET) measurements. Furthermore, the relative amount of micro‐ and mesopores can be tuned in situ by post modification. As controlled pyrolysis leaves phenolic hydroxyl groups at the pore walls and the thermoset resin‐based materials can be easily molded into a desired shape, it is expected that such materials could be useful for sensors, separation materials, filters, and templates for catalysis.

Nanoporous Membranes of Hydrogen‐bridged Smectic Networks with Nanometer Transverse Pore Dimensions

“…When heated further the monomer becomes isotropic at 110 8C. The synthesis of 1,4-phenylene bis(4-(6-(acryloyloxy)hexyloxy) benzoate) (monomer 2) was as reported by Valkama et al [25] In its pure state monomer 2 melts at 76 8C to become SmA. It exhibits a SmA-to-N transition at 138 8C and it becomes isotropic at 150 8C.…”

“…[21,22] A bottom-up approach, using self-organization by the controlled microphase separation of block copolymers and the subsequent removal of one of the blocks, provides a variety of pore shapes and sizes depending on the molecular weight and types of micellar phases. [23][24][25] For smaller dimensions supramolecular dendritic structures can self-assemble into pores with a well-controlled inner chemical nature. [26,27] Bottom-up methods that are especially appealing are based on the self-organization of liquid crystals and their polymers because they decrease the pore sizes down to the order of molecular length scales, for example, around 1 nm and below, while the assemblies themselves can have much larger dimensions.…”

Fabrication and Characterization of Inorganic Silver and Palladium Nanostructures within Hexagonal Cylindrical Channels of Mesoporous Carbon

“…Evaporation-induced self-assembly (EISA) has been developed aggressively as a strategy for the fabrication of mesoporous nanostructures because of its broad applicability to soft templating using various block copolymer templates [1][2][3][4][5][6][7][8][9][10][11][12]. Prior to its development, the pore sizes of mesoporous carbons were limited to approximately 5-10 nm as a result of the need for copolymer templates of low molecular weight [13,14].…”

“…Prior to its development, the pore sizes of mesoporous carbons were limited to approximately 5-10 nm as a result of the need for copolymer templates of low molecular weight [13,14]. The EISA method made it feasible to regulate pore structures and pore sizes and allowed the preparation of various mesoporous materials from water-insoluble systems, including mesoporous silicas [2,7,8,10,[15][16][17][18], mesoporous resins [3,6,9,11], mesoporous TiO 2 [19][20][21], and mesoporous carbons [2,4,12,16,[22][23][24]. The typical procedure used to prepare ordered mesoporous carbons, so-called "template synthesis" [25][26][27][28][29][30], involves the use of mesoporous silicas as hard templates, impregnation of carbon precursors into their mesochannels, carbonization under an inert gas, and finally dissolving the hard template of the "ordered mesoporous silica" through etching in HF (aq) .…”

Mesoporöse Kohlenstoffmaterialien: Synthese und Modifizierung

“…[134] Kohlenstoffmaterialien auf der Basis solcher Blockcopolymersysteme bekannt. [136] In beiden Fällen wurde Hexamethylentetramin als Härter bei der Vernetzung verwendet, weil es eine sehr gleichmäßige Vernetzung ermöglicht.…”