Mechanically Tough, Thermally Rearranged (TR) Random/Block Poly(benzoxazole-co-imide) Gas Separation Membranes

Abstract

Insufficient mechanical properties are one of the major obstacles for the commercialization of ultrahigh permeability thermally rearranged (TR) membranes in largescale gas separation applications. The incorporation of preformed benzoxazole/benzimidazole units into o-hydroxy copolyimide precursors, which themselves subsequently thermally rearrange to form additional benzoxazole units, were prepared for the first time. Using commercially available monomers, mechanically tough membranes prepared from random and block TR poly(benzoxazole-co-imide) copolymers (TR-PBOI) were investigated for gas separation. The effects of the chemical structures, copolymerization modes, and thermal holding time of o-hydroxy copolyimides on the molecular packing and properties, including gas transport, for the resulting TR-PBOI membranes have been examined in detail. After treatment at 400°C, tough TR-PBOI membranes exhibited tensile strengths of 71.4−113.9 MPa and elongation at break of 5.1−16.1%. Moreover, they presented higher or comparable gas transport performance as compared to those tough/robust TR membranes reported previously. Reported for the first time is a comparative investigation of the copolymerization mode (random or block) on membrane properties. The novel polymer architecture and systematic property studies promote a better understanding of the materials and process development of commercial TR membranes for gas separation applications.

Shape memory induced structural evolution of high performance copolyimides

“…The shape memory copolyimides exhibit high tensile strength of 177–266 MPa, elongation of breaking of 41%–56%, and elastic modulus of 2.5–2.7 GPa. Compared with the common PIs, introducing rigid benzoxazole or benzimidazole moieties into PI's main chain skeleton obviously improves its mechanical properties, which is consistent with literature reports . However, tensile strength and elastic modulus of PI1 are higher than those of PI2.…”

“…In addition, multiple‐shape memory behaviors of PIs are first demonstrated. Previous literatures show that polymer containing benzimidazole moieties also could possess very high glass transition temperatures and exceptional thermal stability . To our best knowledge, polyimide representing the most typical HTSMPs is expected to be applied in harsh circumstances.…”

Tunable Triple‐Shape Memory Binary Mixtures with High Transition Temperature and Robust Mechanical Properties

“…The mixture films also showed two diffraction peaks in the corresponding regions similar to PIB without any new peaks emerging, although they were relatively broad in comparison with those from typical crystalline polymers. These indicated some ordered chain packing together with a primarily amorphous morphology of domains in the films existed, which is similar to other reported polyimides containing benzoxazole in the main chain backbone . In a previous study, the peak at 2θ = 14.5° corresponded to the interchain ordered packing in the direction of the film thickness, whereas the peak at 2θ = 23.8° could be assigned to the π–π stacking of aromatic heterocyclic rings .…”

Understanding the effects of backbone chemistry and anion type on the structure and thermal behaviors of imidazolium polyimide‐ionenes

“…Recently, we have developed new, broadly applicable approaches that can yield more thermally robust imidazolium ionenes, through the synthesis of bis(imidazole) monomers containing aromatic imide or amide linkages . Developing a rational understanding of the properties and behaviors of polyimide‐ionenes is of particular interest to our research in gas separation membranes as conventional polyimides built from species such as 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) have emerged as among the most promising polymers for separations involving CO 2 from N 2 or CH 4 . Furthermore, utilizing the largely aromatic structures of these imides should yield enhanced thermal stability compared to analogous ionenes linked by n ‐alkyl groups and lacking aromatic imide or amide functionalities.…”