Shuangjiang Luo

Highly CO2-Selective Gas Separation Membranes Based on Segmented Copolymers of Poly(Ethylene oxide) Reinforced with Pentiptycene-Containing Polyimide Hard Segments

Poly(ethylene oxide) (PEO)-containing polymer membranes are attractive for CO2-related gas separations due to their high selectivity toward CO2. However, the development of PEO-rich membranes is frequently challenged by weak mechanical properties and a high crystallization tendency of PEO that hinders gas transport. Here we report a new series of highly CO2-selective, amorphous PEO-containing segmented copolymers prepared from commercial Jeffamine polyetheramines and pentiptycene-based polyimide. The copolymers are much more mechanically robust than the nonpentiptycene containing counterparts due to the molecular reinforcement mechanism of supramolecular chain threading and interlocking interactions induced by the pentiptycene structures, which also effectively suppresses PEO crystallization leading to a completely amorphous structure even at 60% PEO weight content. Membrane transport properties are sensitively affected by both PEO weight content and PEO chain length. A nonlinear correlation between CO2 permeability with PEO weight content was observed due to the competition between solubility and diffusivity contributions, whereby the copolymers change from being size-selective to solubility-selective when PEO content reaches 40%. CO2 selectivities over H2 and N2 increase monotonically with both PEO content and chain length, indicating strong CO2-philicity of the copolymers. The copolymer film with the longest PEO sequence (PEO2000) and highest PEO weight content (60%) showed a measured CO2 pure gas permeability of 39 Barrer, and ideal CO2/H2 and CO2/N2 selectivities of 4.1 and 46, respectively, at 35 °C and 3 atm, making them attractive for hydrogen purification and carbon capture.

Preparation and gas transport properties of triptycene-containing polybenzoxazole (PBO)-based polymers derived from thermal rearrangement (TR) and thermal cyclodehydration (TC) processes

Polybenzoxazoles (PBOs), such as thermally rearranged (TR) polymers, have been shown to have excellent gas separation performance. Herein we report the preparation and transport properties of two new series of PBO-based polymers that were thermally derived from triptycene-containing o-hydroxy polyimide and polyamide precursors via a thermal rearrangement (TR) process and a thermal cyclodehydration (TC) process, respectively. Incorporation of triptycene units into poly(hydroxyimide) precursor structures led to a significant increase of fractional free volume and created ultrafine microporosity in the converted PBO-based TR polymers, which enabled both high gas permeabilities and high selectivities. Although the TC process of the poly(hydroxyamide) precursor led to moderate improvement in the separation performance of the resulting triptycene-containing PBO polymers as compared to the TR process, the PBO films converted via the TC process exhibited excellent mechanical properties superior to many other TR polymers previously reported in the literature as well as the triptycene-containing TR polymers in this study. In particular, the PBO film thermally rearranged at 450 °C showed a H2 pure gas permeability of 810 barrer, a CO2 permeability of 270 barrer, and CO2/CH4 and H2/CH4 selectivities of 67 and 200, respectively, at 35 °C and 11 atm, which are far beyond the upper bound limits.

Facile Synthesis of a Pentiptycene-Based Highly Microporous Organic Polymer for Gas Storage and Water Treatment

Rigid H-shaped pentiptycene units, with an intrinsic hierarchical structure, were employed to fabricate a highly microporous organic polymer sorbent via Friedel-Crafts reaction/polymerization. The obtained microporous polymer exhibits good thermal stability, a high Brunauer-Emmett-Teller surface area of 1604 m2 g-1, outstanding CO2, H2, and CH4 storage capacities, as well as good adsorption selectivities for the separation of CO2/N2 and CO2/CH4 gas pairs. The CO2 uptake values reached as high as 5.00 mmol g-1 (1.0 bar and 273 K), which, along with high adsorption selectivity values (e.g., 47.1 for CO2/N2), make the pentiptycene-based microporous organic polymer (PMOP) a promising sorbent material for carbon capture from flue gas and natural gas purification. Moreover, the PMOP material displayed superior absorption capacities for organic solvents and dyes. For example, the maximum adsorption capacities for methylene blue and Congo red were 394 and 932 mg g-1, respectively, promoting the potential of the PMOP as an excellent sorbent for environmental remediation and water treatment.

Highly Proton Conducting Polyelectrolyte Membranes with Unusual Water Swelling Behavior Based on Triptycene-containing Poly(arylene ether sulfone) Multiblock Copolymers

Multiblock poly(arylene ether sulfone) copolymers are attractive for polyelectrolyte membrane fuel cell applications due to their reportedly improved proton conductivity under partially hydrated conditions and better mechanical/thermal stability compared to Nafion. However, the long hydrophilic sequences required to achieve high conductivity usually lead to excessive water uptake and swelling, which degrade membrane dimensional stability. Herein, we report a fundamentally new approach to address this grand challenge by introducing shape-persistent triptycene units into the hydrophobic sequences of multiblock copolymers, which induce strong supramolecular chain-threading and interlocking interactions that effectively suppress water swelling. Consequently, unlike previously reported multiblock copolymer systems, the water swelling of the triptycene-containing multiblock copolymers did not increase proportionally with water uptake. This combination of high water uptake and low swelling behavior of these copolymers resulted in excellent proton conductivity and membrane dimensional stability under fully hydrated conditions. In particular, the triptycene-containing multiblock copolymer film with the longest hydrophilic block length (i.e., BPSH100-TRP0-15k-15k) had a water uptake of 105%, an excellent proton conductivity of 0.150 S/cm, and a volume swelling ratio of just 29% (more than 42% reduction compared to Nafion 212).