Novel Macro and Meso Porous Materials Prepared from Miscible Polysulfone/Polyimide Blends
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Novel Macro and Meso Porous Materials Prepared from Miscible Polysulfone/Polyimide Blends Yong Ding*, Benjamin Bikson Innovative Membrane Systems, Inc., 189 Dean Street, Norwood, MA, 02062, U.S.A.
ABSTRACT: Novel macro and meso porous polysulfone materials were prepared from miscible blends of polysulfones with a phenylindane containing polyimide by chemically decomposing the polyimide phase with a dilute hydrazine solution in methanol. The polyether sulfone meso porous membranes are transparent films, with uniform pore sizes in the range of 30 nm. On the other hand, bisphenol A polysulfone based porous materials are opaque with pore sizes in the range of 200 nm.
INTRODUCTION High specific surface area macro and meso porous materials are increasingly important to understanding, creating, and improving materials for a large number of diverse applications, such as catalytic surfaces and supports, separation and adsorption media, biomaterials, chromatographic materials, etc.1-3 A typical example is the ordered mesoporous inorganic material MCM-41. MCM-41, with pore size in the range of 10 – 100 nm, is formed by blending a silicate source, such as tetraethoxysilane, with an ionic surfactant under appropriate polymerization conditions.4,5 MCM-41 is now widely utilized in removal of ultrafine contaminants.5 Macroporous materials typically contain pores with diameter greater than 50 nm, while mesoporous materials are usually defined as those with pore diameter in the range of 2 – 50 nm.3 Our objective was to develop a simple, reliable and industrially feasible process for the fabrication of macro and meso porous polymeric materials with the following key features: (1)a uniform pore size distribution; (2)a three dimensional interconnected network of channels in the bulk; (3)a high specific surface area. It is well documented that the self-assembly of polymers in polymer blends can provide a co-continuous, nano-phase separated system.6 Such miscible polymer blends offer the potential for the fabrication of porous polymer films by selectively removing one of the components. However, a practical application of this methodology has been limited due to the difficulty of selecting a solvent that removes one of the high molecular weight components quantitatively.7-9 Herein we report our finding that the polyimide in a polymer blend can be decomposed and removed quantitatively. This finding provides a convenient method for the fabrication of macro- and meso- porous polymeric materials.
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EXPERIMENTAL Instruments ATR-FT-IR spectra were recorded on a Nicolet Avatar 360 FT-IR instrument equipped with an Omni-ATR attachment. Differential Scanning Calorimetry (DSC) data were obtained with a Seiko DSC 6200 instrument under nitrogen atmosphere. The pore size distribution and the total surface area of the macro porous films were determined by Porous Materials, Inc., Ithaca, N. Y., using the mercury intrusion porosimetry method. Cumulative pore volumes and the distribution function ∆V/∆log(r) was used to express the pore
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