Abstract:Four aromatic polyimides were prepared using a conventional
two-stage
polymerization reaction of diamine monomers containing different noncoplanar
rigid sites with commercially available dianhydride 6FDA. All polymers
displayed high relative molecular masses, excellent solubilities,
and outstanding thermal properties with T
g values higher than 260 °C, which ensured that they were able
to be casted as dense films for gas permeation measurement. The comprehensive
gas transport properties of four prepared polyim… Show more
“…The good optical properties of the co-polyimide films indicate that the inter- and intra-chain CTCs of the polymer molecules are effectively reduced, causing a lower packing density and higher free volume, thus facilitating the transport of permeating gas molecules. 36,37 Figure 5.UV–vis spectra of co-polyimide membranes.…”
A series of fluorinated co-polyimide films based on the 6FDA-FTPPA/BAFL backbone were prepared from 4-(3-fluoro-4-(trifluoromethyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (FTPPA),commercial 9,9-bis(4-aminophenyl)fluorene (BAFL), and 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), with varying ratios of FTPPA:BAFL units (3:1, 2:1, 1:1, 1:2, and 1:3). Co-polyimides not only exhibit high thermal stability ( Tg > 357°C), good optical properties (λcutoff > 327 nm) and hydrophobicity (contact angle >91.4°), but also favorable solubility properties in both high and low boiling organic solvents. The fractional free volume of the polymers was simulated using molecular mechanics and molecular dynamics and correlated with experimental gas separation data. The presence of bulky groups led to high FFVs (>17.8%) and the formation of large microcavities with diameters ranging from 5.48 to 5.72 Å, which efficiently increased gas permeability. In pure gas permeation experiments, the permeability coefficients of CO2 and He for the 6FDA-FTPPA/BAFL (3:1) film were 41.48 and 79.38 bar, respectively, which were superior to those of commercial Matrimid and Kapton in terms of gas permeability. In especial, the 6FDA-FTPPA/BAFL (1:2) and 6FDA-FTPPA/BAFL (1:3) in co-polyimide membranes exhibited the most attractive separation performance for O2/N2 gas pairs, approaching the 1991 Roberson upper limit.
“…The good optical properties of the co-polyimide films indicate that the inter- and intra-chain CTCs of the polymer molecules are effectively reduced, causing a lower packing density and higher free volume, thus facilitating the transport of permeating gas molecules. 36,37 Figure 5.UV–vis spectra of co-polyimide membranes.…”
A series of fluorinated co-polyimide films based on the 6FDA-FTPPA/BAFL backbone were prepared from 4-(3-fluoro-4-(trifluoromethyl)phenyl)-2,6-bis(4-aminophenyl)pyridine (FTPPA),commercial 9,9-bis(4-aminophenyl)fluorene (BAFL), and 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), with varying ratios of FTPPA:BAFL units (3:1, 2:1, 1:1, 1:2, and 1:3). Co-polyimides not only exhibit high thermal stability ( Tg > 357°C), good optical properties (λcutoff > 327 nm) and hydrophobicity (contact angle >91.4°), but also favorable solubility properties in both high and low boiling organic solvents. The fractional free volume of the polymers was simulated using molecular mechanics and molecular dynamics and correlated with experimental gas separation data. The presence of bulky groups led to high FFVs (>17.8%) and the formation of large microcavities with diameters ranging from 5.48 to 5.72 Å, which efficiently increased gas permeability. In pure gas permeation experiments, the permeability coefficients of CO2 and He for the 6FDA-FTPPA/BAFL (3:1) film were 41.48 and 79.38 bar, respectively, which were superior to those of commercial Matrimid and Kapton in terms of gas permeability. In especial, the 6FDA-FTPPA/BAFL (1:2) and 6FDA-FTPPA/BAFL (1:3) in co-polyimide membranes exhibited the most attractive separation performance for O2/N2 gas pairs, approaching the 1991 Roberson upper limit.
“…The permeability, diffusion, and selectivity of gases such as He, O 2 , N 2 , CH 4 , and CO 2 are generally evaluated. PI materials exhibit extremely high gas selectivity and excellent thermal, mechanical, and chemical stability, rendering them one of the most suitable membrane materials for gas separation [ 158 , 159 ]. This chemical structure of PI-based materials for gas separation membranes should satisfy the following aspects: (1) the backbone can inhibit the flow in the segments of the chain, which should be the rigid chain structure; (2) prevent polymer chain accumulation; and (3) weaken the interaction between the chains.…”
Section: Application Of Pi-based Compositesmentioning
Polyimide (PI) is one of the most dominant engineering plastics with excellent thermal, mechanical, chemical stability and dielectric performance. Further improving the versatility of PIs is of great significance, broadening their application prospects. Thus, integrating functional nanofillers can finely tune the individual characteristic to a certain extent as required by the function. Integrating the two complementary benefits, PI-based composites strongly expand applications, such as aerospace, microelectronic devices, separation membranes, catalysis, and sensors. Here, from the perspective of system science, the recent studies of PI-based composites for molecular design, manufacturing process, combination methods, and the relevant applications are reviewed, more relevantly on the mechanism underlying the phenomena. Additionally, a systematic summary of the current challenges and further directions for PI nanocomposites is presented. Hence, the review will pave the way for future studies.
“…14 Their capability to form mechanically stable membranes with high productivity (i.e., gas permeability) and efficiency (i.e., gas pair selectivity) made them great candidates for such application. An important aspect of polyimides is the multitude of molecular engineering that can be applied to their backbones: design of diamine monomers with different 3D structure and functional groups, 15,16 crosslinking, 17−21 copolymerization, thermal rearrangement, 22,23 and post-synthetic chemical modification. 2,24−26 These different methodologies allow the polymer's structure to be tailored for specific gas separation properties.…”
Section: Introductionmentioning
confidence: 99%
“…An important aspect of polyimides is the multitude of molecular engineering that can be applied to their backbones: design of diamine monomers with different 3D structure and functional groups, , crosslinking, − copolymerization, thermal rearrangement, , and post-synthetic chemical modification. ,− These different methodologies allow the polymer’s structure to be tailored for specific gas separation properties. For example, copolymerization is a polymerization technique that allows the combination of, for example, a permeability-enhancing monomer with a selectivity-enhancing comonomer into a single polymer backbone to produce a polymer with improved permeability and selectivity .…”
Chemical modification is an interesting tool to introduce
functional
groups into polymers’ backbones to tailor their properties
in a desired fashion. Polymers used in membrane-based gas separation
applications need to possess high gas permeability and selectivity
during mixed-gas separation under harsh operational conditions of
pressure and temperature. Herein, we report the modification of three
copolyimides containing the moiety 9,9-bis(4-aminophenyl)fluorine
(CARDO) through Friedel–Crafts alkylation to introduce bulky tert-butyl groups into their backbones. Membranes prepared
from the modified polymers were evaluated using pure- and sweet mixed-gas
under aggressive feed pressures. Based on the promising results obtained,
a selected copolyimide was subjected to sour mixed-gas separation
under feed pressures up to 500 psi. Mixed-gas separation studies,
especially those containing hydrogen sulfide, are of great interest
to develop membranes for use in sour natural gas reserve treatment.
For example, the H2S and CO2 permeability coefficients
of 6FDA-Durene/6FDA-CARDO(t-Bu) at 500 psi were recorded
as 456 and 238 Barrer, respectively, where the H2S/CH4 and CO2/CH4 are 20.4 and 10.6, respectively.
The obtained results are very promising and even superior to many
glassy polymers reported previously. This work represents an example
of the benefit of chemical modification on polymers to tailor their
structure–property relationship. Future works will be focused
on the fabrication and testing of asymmetric or composite hollow fibers
to imitate the membrane modules used industrially.
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