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

Abstract

A new nucleophilic monomer (2,2-bis(3amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of orthoacetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization.Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the TR process was evaluated by directly synthesizing PBOs, which were made from the reaction, and ulterior thermal cyclization, of 2,2-bis(4-chlorocarbonylphenyl)-hexafluoropropane with ADHAB/APAF. TR-PBO membranes made through a thermal treatment at 450 °C for 30 min showed excellent gas separation properties for the CO 2 /CH 4 gas pair with values close to the 2008 Robeson limit.

Enhanced gas separation and mechanical properties of fluorene-based thermal rearrangement copolymers

“…Therefore, many HPI precursors with novel chemical structures have been designed to improve the separation performance of membrane materials. [31][32][33][34][35][36] As we have known that the rigid and bulky structures easily destroy the regular arrangement of molecular chains, reduce the interaction between molecular chains, and increase the free volume fraction, leading to high gas permeabilities and moderate selectivities. [37][38][39][40][41][42] For example, Fahd et al introduced the triptycene structures into the main chain of TR polymer, so the permeability of O 2 was 311 Barrer, and the O 2 /N 2 selectivity was 5.4, which was close to the 2008 upper bound.…”

Recent progress in microporous polymers from thermally rearranged polymers and polymers of intrinsic microporosity for membrane gas separation: Pushing performance limits and revisiting trade‐off lines

“…Preformed nucleophilic adamantane‐containing hydroxyl diamines were designed for this study. [ 87 ] The precursors showed good thermal stability capable of TR processing, and all adamantane‐based TR polymers exhibited increases in FFV and gas permeability at the thermal rearrangement temperature. In particular, AD (0.5), which is a copolymer containing 50 mol% of adamantane moiety, presented a ~15‐fold increase in CO 2 permeability after being thermally treated at 450°C.…”

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).…”