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Synthesis and structure of ordered organic polymer mesoporous materials

Author: MengYan
Tutor: ZhaoDongYuan
School: Fudan University
Course: Inorganic Chemistry
Keywords: nanostructure organic polymer nanomaterials mesoporous polymer mesoporous carbon hard template organic-organic self-assembly
CLC: TB324
Type: PhD thesis
Year: 2006
Downloads: 1727
Quote: 6
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Abstract

Ordered organic nanomaterials, especially ordered mesoporous polymers, is a class of advanced materials and possess enormous potential for many high-tech applications. In Comparison with the ordered mesoporous structures with inorganic framework, however, the development of ordered mesoporous polymers are slower due to the low thermal and chemical stabilities of polymer framework. It remains a challenge to find new methods for the preparation of highly ordered mesoporous polymers, which may enrich the component of ordered mesoporous materials, as well as open an avenue for their applications in catalysis, adsorption, separations, bioreactors and microelectrophoresis.The choice of the organic precursors is a key for fabricating ordered mesoporous polymers. The structures of organic frameworks derived from the polymerization and cross-linking reaction of precursors, directly determine the thermal and chemical stabilities. The characterization of our work is to select resol as organic precursors. The resol is a kind of soluble phenolic resin with low molecular-weight, which are polymerized by phenol and formaldehyde under base-catalyzed condition and have plenty of hydroxyl groups. A simple thermopolymerization without any additives can transform the soluble resol to highly cross-linking phenolic resins which possess 3-D network structures with benzene rings as three or four cross-linking points. This structural feature is analogous to that of microporous zeolites, which are made of four-connected silica tetrahedrons and has a covalently-bonded infinite framework.This thesis divides into two major parts. In the first part, "hard-templating" strategy for ordered nanostrctured polymers is described. Three kinds of nanostructures that are nanoparticles, 2-D and 3-D nanowire arrays are prepared with mesoporous silica as template. In the second part, a family of highly ordered mesoporous polymers and carbons with infinite frameworks are fabricated by use of triblock copolymer PEO-PPO-PEO as template via a solvent evaporation induced organic-organic self-assembly (EISA) strategy.In chapter 2, a one-step synthetic procedure is established for preparing polymer nanostructures. The polypyrrole and poly (methyl methacrylate) nanoparticles with ultra-small sizes were obtained. The spherical nanoparticles are quite uniform with diameters 2 ～ 4 run.In chapter 3, 2-D and 3-D polymer nanowire arrays are prepared by a simple impregnation-solvent evaporation method combined with thermopolymerization byuse of the resoles as polymer precursors and SBA-15 and KIT-6 as hard templates. These nanowire arrays, possessed order stacked-pore structures with uniform mesopore size, are so-called mesoporous polymer materials. They have high surface area (～1600 m~2 /g) and pore volume (1.12 cm~3 /g), as well as narrow pore size distributions of 3 ～ 4 nm. We systematic study the effect of the mass and the temperature of thermopolymerization (300-500℃) of resoles, the interconnectivities of pore channels of mesoporous silica on the mesoscopic order of resultant polymers. It is found that the latter is the key factor. The mesoscopic orders of resultant polymers increase with the augments of interconnectivities of silica templates. Moreover, the high thermopolymerization temperature favor to the ordered mesostructures. In aqueous solution, the resultant mesoporous polymer K2-3-500 exhibits good sorption abilities to organic molecule of aniline and organic dye of Magenta Red.In chapter 4, a family of highly ordered mesoporous polymer and carbon structures with high surface area and uniform pore sizes are fabricated by the organic-organic assembly of triblock copolymers PEO-PPO-PEO with resoles via an EISA strategy. The family numbers includes 2-D hexagonal (p6m), 3-D cubic (Im 3|- m), 3-D bicontinuous (Ia 3|- d) and lamellar mesostructures. Simply increasing the ratio of phenol/template and the PEO/PPO segment in triblock copolymer can generate the mesostructure with a high curvature. Heating the as-made organic materials at 350℃ under argon or nitrogen atmosphere results in decomposition of the templates and formation of ordered mesoporous polymers with various mesostructures. These mesoporous polymers possess highly cross-linking phenolic resin frameworks and can be directly transformed by a careful carbonization process into well-ordered and ultra-stable (> 1400℃) carbon frameworks. Notably, a small amount of oxygen in the feed gas during calcination process facilitates the degradation of templates and organic segments, and thus the formation of large pore sizes (7.1 nm) and high surface areas. Heating the mesoporous polymers causes continuous and distinct framework shrinkage between 350 to 600℃, due to the cross-linking reaction of phenolic resins. Simultaneously, polymer frameworks transform to carbons. The shrinkage is slow once the carbon frameworks form. Accordingly, the unit cell parameters and pore sizes decrease and then reach a platform. However, the BET surface areas and pore volumes increase at a temperature range up to 1200℃, mainly caused by the microporosity. Mesoporous carbons with zeolite-like open frameworks exhibit ultra-highly thermal stability up to 1400℃ and mechanical stability up to 500 MPa.Moreover, a reasonably high reverse electronic capacity is shown in mesoporous carbon materials with well-connected pore structure.In chapter 5, an extraction method with the aid of sulfuric acid is employed to decompose/or remove the templates of triblock copolymer PEO-PPO-PEO from FDU-15. Compared with calcined FDU-15, FDU-15 prepared by extraction method has larger mesopore diameters (～ 8 nm) and smaller framework shrinkage (< 8%). In addition, the frameworks of FDU-15 retain the constitution of phenolic resins after the treatment with sulfuric acid, which is hopeful for the framework functional ization.

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