Gas separation membranes made through thermal rearrangement of ortho-methoxypolyimides

Abstract

SummaryOrtho-methoxypolyimides were prepared by the classical chemical imidization method and also by azeotropic imidization, using 3,3'-dimethoxybenzidine (DMAB) and hexafluoroisopropylidene diphthalic anhydride (6FDA) as monomers. High molecular weights were achieved by both methods, and the physical properties of the materials were investigated by spectroscopic and thermal analytical techniques. Polymers exhibited excellent thermal properties and film-forming ability, which allowed them to be tested as dense membranes for gas separation after a convenient treatment at high temperature (450 °C) to promote thermal rearrangement (TR). Spectroscopic evidences indicated that the final composition of the TR materials seemed not to correspond to TR-polibenzoxazoles, as it is the case when ortho-hydroxypolyimides are exposed to similar thermal treatments. A detailed study was carried out with the purpose of elucidating the actual mechanism of rearrangement, comparing ortho-

Intermediate thermal manipulation of polymers of intrinsic microporous (PIMs) membranes for gas separations

“…Colorful sphere: Data in this work (black for PIM‐1, blue for PIM‐1‐400, and red for PIM‐1‐450, with the thickness of 44 μm, 35 μm, and 33 μm, respectively). Open shapes: Data of TR‐PIM, UV rearranged PIM, thermal oxidative crosslinking PIM, thermal crosslinking PIM, photo oxide PIM, PIM‐based MMMs, and other polymeric TR membranes and CMS membranes, et al, from Reference 32, 34, 37, 38, 40, and 49–59 [Color figure can be viewed at wileyonlinelibrary.com]…”

Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

“…Recently, a parallel mechanism that suggested the formation of rigid aromatic lactams as well as polybenzoxazoles during the TR process was proposed based on experimental and theoretical data. 35,70,72 Kostina et al reported the appearance of bands at 1670 cm −1 (amide I) and 1550 cm −1 (amide II), attributable to lactams, in samples of o-hydroxypolyimides treated at temperatures above 400 °C. 72 Some of the copolymers treated at 450 °C in this study showed a small band at 1675 cm −1 that could be related to amide I of lactam, but in all of the cases, the intensity of this peak was low compared to the imide and benzoxazole bands.…”

“…27,28 These results encouraged research in this area, and new structures were developed. 29−32 In this way, the search for relationships between structure and properties was envisioned, and the feasibility of carrying out the TR process on oacyl- 21,28,29 or o-alkoxypolyimides 35 was realized. Additionally, important efforts on the design and synthesis of new TR polymers have been accomplished by incorporating contorted monomers with high rigidity to produce o-hydroxy polyimides with high FFV, which subsequently produced thermally rearranged polybenzoxazoles (TR-PBOs) with excellent gas separation properties.…”

“…In 2007, a new approach paved the way for obtaining materials with outstanding gas separation properties. − The methodology consisted of thermal rearrangement (TR) of ortho -hydroxy polyimides (HPIs) in the solid state above 400 °C (named the TR process) to generate polybenzoxazole (PBO) groups together with release of CO 2 . − This thermal process led to the formation of an increased number of fine-tuned free volume elements, which yielded materials with very high permeability , and good selectivity. The observed improvement was so high that the gas separation properties clearly surpassed the 2008 Robeson limit for some gas pairs. , Because of the elevated temperature required for this conversion, cross-linked materials were obtained, which improved its plasticization resistance and decreased its physical aging. , These results encouraged research in this area, and new structures were developed. − In this way, the search for relationships between structure and properties was envisioned, and the feasibility of carrying out the TR process on o -acyl- ,, or o -alkoxypolyimides was realized. Additionally, important efforts on the design and synthesis of new TR polymers have been accomplished by incorporating contorted monomers with high rigidity to produce o -hydroxy polyimides with high FFV, which subsequently produced thermally rearranged polybenzoxazoles (TR-PBOs) with excellent gas separation properties. ,, In this way, TR-PBOs derived from polyimides with bulky 9,9-diphenylfluorene moieties have been obtained. , In order to improve the properties of the final TR-PBO materials, classical polymer science approaches, such as copolymerization of well-designed monomers, have been employed, and the results were promising. − Finally, classical technologies employed in the field of gas separation membranes such as the cross-linking of precursor polyimides , or the formation of high-quality hollow fibers have been used to obtain high-productivity TR-PBO materials …”

Synthesis and gas permeation properties of thermally rearranged poly(ether-benzoxazole)s with low rearrangement temperatures

“…[21][22][23][24] Although the imidization methods usually lead to the nal TR polymers with the same chemical structure, the physical and gas separation properties of the TR polymers were very different. [25][26][27][28][29] Therefore, the structure and properties of TR polymers could be easily adjusted by molecular structure design and preparation methods to facilitate specic gas separation applications. [30][31][32][33][34][35] According to the reported literatures, [25][26][27][28][29][30][31][32][33][34][35] HPI is the most commonly used precursor for the preparation of TR polymers, and most of TR polymers are based on HPI precursors made from 4,4 0 -(hexauoroisopropylidene)diphthalic anhydride (6FDA) and 2,2 0 -bis(3-amino-4-hydroxyphenyl)-hexauoropropane (APAF) or 3,3 0 -dihydroxy-4,4 0 -diaminobiphenyl (HAB).…”