Thermally Rearranged (TR) Polybenzoxazole: Effects of Diverse Imidization Routes on Physical Properties and Gas Transport Behaviors

Abstract

Conversion of hydroxyl-containing polyimides into polybenzoxazole can be achieved by thermal rearrangement of the aromatic polymer chain with decarboxylation at elevated temperature. Synthetic methods to prepare polyimide precursors are important for the resulting thermally rearranged (TR) polymer membranes. Here, we report on the effect of several imidization methods on the properties of TR polymer membranes. Thermal and chemical imidizations are the most common routes to prepare polyimides, and solution thermal imidization using an azeotrope is also widely used, especially to obtain soluble polyimide-containing functional groups. We report here on the syntheses of ortho-functional polyimides from 4,4′-hexafluoroisopropylidene diphthalic anhydrides and 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane by three different imidization methods. Acetate-containing polyimides by chemical imidization and further silylation treatment as well as hydroxyl-containing polyimides by thermal and azeotropic imidization are characterized using thermogravimetric analysis, density, positron annihilation lifetime spectroscopy, and gas permeation property measurements. Comparison between the precursor polyimides and the resulting thermally rearranged polybenzoxazole (TR-PBO) membranes exhibited significant increase in fractional free volumes and cavity sizes followed by enhanced gas permeation properties.

Controlled thermal oxidative crosslinking of polymers of intrinsic microporosity towards tunable molecular sieve membranes

“…The significantly enhanced gas selectivity along with high permeability push the overall gas transport properties to surpass the upper bound that has been limiting the polymer membranes for decades. To the best of our knowledge, the overall separation performance of TOX-PIM-1 membranes is higher than all existing soluble polymers including commercial polymers 40 , soluble PIMs 41 and compares very well against TR polymers 18,31,34,[42][43][44] .…”

Polymers of Intrinsic Microporosity

“…PIMs are now recognized as one member of the third generation of polymer materials for membranes (along with thermally rearranged polymers) [127][128][129][130] following on from the commercially useful but low performance cellulose-based polymers and better performing polymers such as polyimides, which are now becoming commercially exploited. The intense activity on PIMs for gas separations should result in better materials and optimized membrane fabrication.…”

Fabrication of thermally rearranged (TR) polybenzoxazole hollow fiber membranes with superior CO2/N2 separation performance

“…HPAAc as the precursor of TR-PBO [10,33] was synthesized from bis-APAF (diamine) and 6FDA (dianhydride), through a condensation polymerization reaction [34]. Both monomers were kept in an oven at 40 1C (diamine) and 100 1C (dianhydride) for 1 day under vacuum.…”

“…The strategies having been investigated included the effect of various imidization routes [10], the use of different precursors [11], the effect of cross-linking on TR-polymers [12], and the development of novel spirobisindane-containing TR-PBO [13]. Significant improvement in separation performance was observed, and the gas sorption behavior of these membranes was also studied to provide the insight into the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/memsci superior gas transport within the TR-polymers [14][15][16].…”