Simultaneous Thermal Cross-Linking and Decomposition of Side Groups to Mitigate Physical Aging in Poly(oxyindole biphenylylene) Gas Separation Membranes

Abstract

Physical aging in amorphous polymers causes a decrease in specific volume and thus in the gas transport properties of their membranes. In this work, the effect of simultaneous thermal decomposition of a thermolabile tert-butyl carbonate group, BOC, and cross-linking by a propargyl group (−CH2–CCH) on the gas selectivity–permeability properties of the resulting membranes is studied to learn how membranes with mitigated variations in the gas permeability coefficients with aging time may be produced. The model copolymer is a poly­(oxyindole biphenylylene) that bears BOC and propargyl groups, [(PN-BOC) x -(PN-Pr) y ] n . Systematic studies on the structure/processing/property relationship assessed by TGA, DSC, and permeation measurement using pure gases reveal that a single thermal treatment for 1 h at 240 °C on a neat copolymer membrane, 12–20 μm thickness, is enough to produce chemically robust membranes (insoluble in NMP and DMSO) and that are physically more resistant to aging since the permeability reduction rate approaches zero. The cross-linked membranes possess lower gas permeability coefficients with higher ideal selectivity with respect to the corresponding neat copolymer membranes, i.e., the P(H2) decreases from 60 to 42 Barrers but H2/CH4 selectivity increases by a factor of 2 (21 to 40), and in general the selectivity–permeability properties for the gas pairs H2/CH4, O2/N2, and CO2/CH4 do not present drastic variations with aging time at least from 72 to 2000 h.

One-Step, Room Temperature Synthesis of Well-Defined, Organo-Soluble Multifunctional Aromatic Polyimides

“…Thermal cross-linking of acetylene-terminated oligoimides for fabrication of composite structures using vacuum-assisted resin transfer molding (VARTM) was also described by Connell and co-workers . Controlled thermal cross-linking of poly­(oxyindole biphenylylene) membranes bearing functional propargyl groups has also been reported recently . We have found that the PI D1-ODPA-B containing propargyl groups becomes insoluble after heating at 250 °C for 1 h in vacuum, thus implicating that the trimerization reactions among three acetylene end groups take place (Scheme ) without the evolution of any volatile compounds.…”

“…50 Controlled thermal cross-linking of poly(oxyindole biphenylylene) membranes bearing functional propargyl groups has also been reported recently. 51 We have found that the PI D1-ODPA-B containing propargyl groups becomes insoluble after heating at 250 °C for 1 h in vacuum, thus implicating that the trimerization reactions among three acetylene end groups take place (Scheme 5) without the evolution of any volatile compounds.…”

Ionic self-assembled organogel polyelectrolytes for energy storage applications

“…In cases where lower degrees of functionalization were achieved, the observed signal around 9 ppm, corresponds to the amide proton associated with the isatin, corroborating the partial modication. 24 The organogel polyelectrolytes were obtained by dissolving the cationic bbers 10% w/ v in DMSO, the high molecular weight and phase segregation allow a three-dimensional arrangement tentatively due to the strong ionic interactions of the graed fragment and the high hydrophobicity in the polymer backbone, leading to gelation processes without the need of chemical cross-linkers.…”

POXINAR Membrane Family for Gas Separation

“…Indeed, asymmetric polymeric porous membranes with excellent thermal ( T D > 500 °C) and solvent resistance for ultrafiltration in organic solvents were prepared via cross-linking of polymer 2aA (poly­[(2-oxo-2,3-dihydro-1 H -indol-3-ylidene)­([1,1′-biphenyl]-4,4′-diyl)] using reactions with dibromoalkanes and functionalization with alkyne side groups, followed by wet-state cyclotrimerization in hot glycerol . More recently, polymer 2aA was used as a model for incorporating thermolabile and cross-linkable groups to illustrate how different thermal treatments lead to POXINAR membranes that not only possess attractive gas permeability and selectivity properties but also are more resistant to aggressive solvents and aging . An unusual and very interesting example of thermal cross-linking of a 2aA membrane followed by long-term annealing under vacuum (10 –3 Torr) was reported; the resulting polymers were resistant to solvent swelling and CO 2 plasticization up to 18 bar, and the selectivity–permeability combinations for O 2 /N 2 overcome the typical trade-off between permeability and selectivity, falling above Robeson’s 2008 upper-bound limit.…”

“…8 More recently, polymer 2aA was used as a model for incorporating thermolabile and cross-linkable groups to illustrate how different thermal treatments lead to POXINAR membranes that not only possess attractive gas permeability and selectivity properties but also are more resistant to aggressive solvents and aging. 9 An unusual and very interesting example of thermal cross-linking of a 2aA membrane followed by long-term annealing under vacuum (10 −3 Torr) was reported; 10 the resulting polymers were resistant to solvent swelling and CO 2 plasticization up to 18 bar, and the selectivity−permeability combinations for O 2 /N 2 overcome the typical trade-off between permeability and selectivity, falling above Robeson's 2008 upper-bound limit. Thus, the aim of this work is to report the gas separation performances of six POXINARs synthesized by polymerization of isatines (1a or 1b) with various aromatic hydrocarbons (H− Ar−H) to produce polymers 2aA−D, 2bC, 2bE and 2bF according to the reaction scheme shown in Figure 1.…”