The preparation of novel silica modified polyimide membranes: synthesis, characterization, and gas separation properties

Abstract

In this study, new monomers having siloxane groups were synthesized as an intermediate for preparation of siloxane modified polyimide polymers. Then with these monomers, the synthesis of uncrosslinked and crosslinked polyimide–siloxane hybrid polymer membranes were achieved. The purposes of the preparation of modified polyimides were to modify the thermal and chemical stability, and mechanical strength of polyimides, and to improve the gas separation properties of polymers. The new diamine monomer having siloxane groups was prepared from 3,5‐diaminobenzoic acid (3,5‐DABA) and 3‐aminopropyltrimethoxysilane (3‐APTMS) in N‐methyl‐2‐pyrollidone (NMP) at 180°C. The modified polyimide membranes having different amount of siloxane groups were synthesized from pyromellitic dianhydride (PMDA), 4,4‐oxydianiline (ODA), and 3,5‐diaminobenzamido‐N‐propyltrimethoxy silane (DABA/PTMS) in NMP using a two‐step thermal imidization process. The synthesis of modified polyimide membranes were characterized by Fourier transform infrared spectroscopy (FTIR). The thermal analysis of the polyimides were carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption and swelling experiments were also carried out for the investigation of structural properties of polymers. FTIR observations confirmed that the polyimide membranes with new diamine intermediate were successfully obtained. Thermal analysis showed that the uncrosslinked copolyimides exhibited two glass transition temperatures, indicating that they were separated microphases and it was found that all the modified copolyimides had showed higher glass transition temperature (Tg) than unmodified polyimides. The separation properties of the prepared polyimide membranes were also characterized by permeability for O2 and N2 gases and ideal selectivity values were calculated. Copyright © 2009 John Wiley & Sons, Ltd.

Structure-gas Transport Property Relationship of Hyperbranched Polyimide-silica Hybrid Membranes

“…With regard to the increase of the diffusion coefficient, Boroglu et al reported that the permeability coefficient of polyimide-siloxane hybrid membranes increased with increasing the siloxane content. And they suggested that the increased gas permeability resulted from the large enhancements of mean size and total amount of free volume holes attributed to the loose Si-O-Si networks and the crosslinked structure of the hybrid membranes [28]. The increased solubilities suggest that the Langmuir sorption site is additionally formed by the incorporation of silica domains.…”

Polyimide-silica sol–gel membranes from a novel alkoxysilane functionalized polyimide: preparation, characterization and gas separation properties

“…Similar polyimides containing siloxane pendant groups, reported previously, showed two transition temperatures being the first one associated to Si-O-Si ligands, and the second one related to the rigid aromatic structure [29]. However, the length of siloxane pendant groups in PI-Si was not enough to allow phase segregation and only one glass transition has been observed.…”

“…The solid state 29 Si-NMR spectrum with cross polarization and magic-angle spinning of PI-Si revealed an unexpected alkoxysiloxane structure in the polymer after hydrosilylation with DMES. The appearance of two signals at -9.62 and -20.59 ppm (Fig.…”

“…29 Si-CP/MAS NMR spectra were recorded on a Bruker Avance 400 (Bruker Analytik) spectrometer operating at 9.4 Tesla. The samples were compacted and put inside of zirconium oxide rotors of 4 mm, and sealed with a Kel-F top.…”

Synthesis and Gas Transport Properties of Hyperbranched Polyimide–Silica Hybrid/Composite Membranes

“…We define the terms of "hybrid" and "composite" as following: "hybrid" materials are those that have strong chemical interaction between organic and inorganic components such as covalent bonds, and "composite" materials are those that show weak or no interactions between the two components. Synthesizing polyimide-silica hybrid and composite materials and investigating their physical and gas transport properties have also received much attention [4][5][6][7]. Polyimide-silica hybrids and composites can be prepared by sol-gel processes or the addition of colloidal silica.…”