Block Copolyimide Research Articles

A Molecular Dynamics Study of Single-Gas and Mixed-Gas N2 and CH4 Transport in Triptycene-Based Polyimide Membranes.

Fluorinated polyimides incorporated with triptycene units have gained growing attention over the last decade since they present potentially interesting selectivities and a higher free volume with respect to their triptycene-free counterparts. This work examines the transport of single-gas and mixed-gas N2 and CH4 in the triptycene-based 6FDA-BAPT homopolyimide and in a block 15,000 g mol-1/15,000 g mol-1 6FDA-mPDA/BAPT copolyimide by using molecular dynamics (MD) simulations. The void-space analyses reveal that, while the free volume consists of small-to-medium holes in the 6FDA-BAPT homopolyimide, there are more medium-to-large holes in the 6FDA-mPDA/BAPT copolyimide. The single-gas sorption isotherms for N2 and CH4 over the 0-70 bar range at 338.5 K show that both gases are more soluble in the block copolyimide, with a higher affinity for methane. CH4 favours sites with the most favourable energetic interactions, while N2 probes more sites in the matrices. The volume swellings remain limited since neither N2 nor CH4 plasticise penetrants. The transport of a binary-gas 2:1 CH4/N2 mixture is also examined in both polyimides under operating conditions similar to those used in current natural gas processing, i.e., at 65.5 bar and 338.5 K. In the mixed-gas simulations, the solubility selectivities in favour of CH4 are enhanced similarly in both matrices. Although diffusion is higher in 6FDA-BAPT/6FDA-mPDA, the diffusion selectivities are also close. Both triptycene-based polyimides under study favour, to a similar extent, the transport of methane over that of nitrogen under the conditions studied.

Preparation and characterization of low CTE thermoplastic copolyimide resins based on the structural design of block sequence

In order to solve the challenge of balancing the thermoplastic processing properties and thermal dimensional stability of polyimide (PI) resin, in this research, 3,3′,4,4′-biphenyl tetracarboxylic diandhydride (BPDA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB) were used as rigid components, 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-diaminodiphenyl sulfone (DDS) as flexible components. A series of random copolyimide resins was prepared by adjusting the molar ratio of rigid and flexible monomers. Determining the molar ratio which could balance the thermoplastic processing properties and thermal dimensional stability, block copolyimide resins with different rigid and flexible block lengths were then prepared in this ratio. The research showed that the molar ratio of monomers and the sequence structure of molecular chains had a strong influence on the performance of PI resins. When the content or block length of rigid component increased, the coefficient of thermal expansion (CTE) decreased but the glass transition temperatures (Tg) and melt viscosity increased. The PI-B343 resin had a CTE value of 40.63 ppm/K and the lowest melt viscosity reached 675 Pa·s, achieved the simultaneous regulation of the thermoplastic processing properties and thermal dimensional stability for PI resin.

Fabrication of controllable and reversible bidirectional shape memory fabric composites based on multiblock copolyimide and their properties

The construction of polymer-based materials with reversible bidirectional shape memory effects and good thermal properties is of paramount importance for the development of the intelligent exploration in high temperature fields. In this work, a series of multiblock shape memory copolyimides were synthesized with the introduction of soft segments containing aliphatic diamines into aromatic polyimide structures to control the mobility of the molecular chains. The number of blocks for copolyimide was finely regulated to optimize the shape memory behaviors with thermal stability and both of the shape fixity ratio and shape recovery ratio could reach higher than 97% with the triggering temperature around 260 °C. Then controllable fabric composites with high temperature and reversible bidirectional shape memory effects were firstly constructed by incorporating of deliberately designed block copolyimide with commercialized polyimide fabric. The flexible fabric composites exhibited variable fixed shapes by regulating the thickness discrepancies between upper and lower layers, which showed good two-way shape memory properties with the shape recovery ratio of 98% during the programming process, providing a new sight of the exploration for high temperature shape-memory materials.

Hydroxyl-functionalized block co-polyimide enables simultaneously improved toughness and strength of tetrafunctional epoxy resin

Tetrafunctional epoxy resins are widely used as matrix of advanced composite materials due to their excellent high temperature performance. However, the highly crosslinking density of tetrafunctional epoxy resins results in an inherent brittleness, which limits its further application. In this work, hydroxyl-functionalized block co-polyimide (BPADA-ODA/HAB) is first synthesized by the condensation of 3,3′-Dihydroxybenzidine and 4,4′-Diaminodiphenyl ether with 4,4'-(4,4′-isopropylidenediphenoxy) di-phthalic anhydride, and used to toughen tetrafunctional epoxy resins. The co-polyimide molecules provide reactive blocks that participate in the curing reaction of epoxy resin and decrease the crosslinking density of epoxy resin; the co-polyimide can form nano-sized separated phase via self-assembly, which could activate additional energy dissipative mechanisms to enhance the resistance of failure for the epoxy resins. With 5% BPADA-ODA/HAB, the resultant epoxy resins exhibit simultaneous enhancements in impact strength and tensile strength, 184% and 150% higher than those of neat epoxy resin. This study provides an efficient method for preparing tough and strong tetrafunctional epoxy resins, which are expected to be applied more broadly in industries.

High pressure pure- and mixed sour gas transport properties of Cardo-type block co-polyimide membranes

Multi-block co-polyimides 6FDA-CARDO/6FDA-Durene with varying segmental lengths were synthesized and pure and mixed sour gas transport properties through dense membranes were investigated as function of feed pressure, temperature and gas composition. Pure gas measurement indicated that block co-polyimide 6FDA-CARDO/6FDA-Durene (2500/2500) membrane exhibits high permeation properties and separation characteristics with CO2 permeability and CO2/CH4 selectivity of up to 239 barrer and 28 respectively. The block co-polyimide also showed excellent performance under harsh sour gas environment (i.e. high H2S content of up to 36 vol% and feed pressure of up to 55 bar for a gas mixture consisting of CO2, CH4, N2, C2H6 and H2S). At 36 vol% H2S, the membrane exhibits H2S permeability and H2S/CH4 selectivity of up to 275 barrer and 24 respectively. These values and separation performance exhibited by the co-polyimide are comparable and very competitive even, as compared to the values obtained in some of the high performance polymeric membranes that have been reported in the literature. The stability of the block co-polyimide 6FDA-CARDO/6FDA-Durene membrane under these aggressive environments is quite impressive.

A comparison of pure and mixed-gas permeation of nitrogen and methane in 6FDA-based polyimides as studied by molecular dynamics simulations

Molecular dynamics simulations (MD) of pure nitrogen, pure methane and mixed nitrogen/methane sorption in two fluorinated homopolyimides, 6FDA-mPDA and 6FDA-durene, as well as in the block copolyimide 6FDA-mPDA/durene were conducted asa complement to a series of experimental studies of the corresponding dense flat membranes. These polyimides are known to vary significantly in their gas separation properties. Gas insertion in the model polymer matrices was carried out in a stepwise procedure in order to avoid pre-swelling and to mimic as close as possible the experimental approach. An iterative technique was used to determine the sorption isotherms for the single-component uptakes up to feed pressures exceeding 60bar. A novel iterative method was also used to determine the mixed-gas uptakes at an elevated pressure in the models and under similar conditions to mixtures in natural gas processing. Volume dilation effects were also examined. Estimating the permselectivity of the polyimides exclusively from the results for pure gases can lead to erroneous conclusions.

Effect of block versus random copolyimide structure on hollow fiber membrane spinnability

Soluble homopolyimides can be made into spinnable dopes; but copolyimides often present challenges. A 6FDA (4,4′-(Hexafluoroisopropylidene)diphthalic anhydride)-based copolyimide was used to illustrate these challenges when forming both defect-free and “nodular” skinned fibers. This copolyimide is soluble in strong solvents; but when combined in proportions with non-solvents to allow forming an asymmetric structure, a gel, rather than a flowable dope solution can occur in some cases, making fiber spinning impossible. Analysis of problems and solution are presented to show how varied copolymer chemical structures affect dope formation. Studies were extended to other 6FDA-based copolyimides to show the generality of the problem and solution to the problem. We found a random copolyimide that forms a soluble spinnable dope becomes problematic when a block copolyimide with sufficient insoluble chain segments is present. Branching in copolyimide, impurity, and excessive molecular weight also affect dope formation, but to a less drastic degree.

Aromatic block co-polyimide membranes for sour gas feed separations

Permeation properties of pure and gas mixture consisting of CO2, H2S, CH4, N2 and C2H6 through dense films of the block co-polyimides (6FDA-mPDA)-(6FDA-durene) are studied at 35–55°C and pressures of 100–500psi for combined separation of CO2, H2S and N2 from acid gas streams. The H2S composition in the gas mixture is up to 20vol%. This rigid block copolymer exhibits relatively constant or slightly decrease in pure gas permeability with increasing feed pressure for most of the penetrants. The pure gas CO2/CH4 and N2/CH4 selectivities are up to 61 and 2.6 respectively. The mixed gas studies also show relatively constant or slightly decrease in permeability coefficients with increase in pressure for most of the penetrants. One significant fact is that, at feed pressure of 500psi and 20vol% H2S in feed gas mixture (consisting of CO2, N2, CH4 and H2S), H2S/CH4 and CO2/CH4 separation factors are 23 and 27 respectively. These values are within the same order of magnitude or even better than those obtained in other state-of-the-art polymeric membranes that have been reported. Another unique feature of this co-polyimide is that, in addition to being selective to acid gas, it is also more selective to N2 as compare to CH4. Moreover, the CO2/CH4 separation factor does not suffer significant loss to the same degree as in the case of cellulose acetate (CA), even under these much more aggressive environments. This stability at moderate pressures and high H2S concentration is quite remarkable, as most reported studies are focused on low H2S concentrations and low pressures.

A comparison of homopolymer and block copolymer structure in 6FDA-based polyimides.

Two homopolyimides and the corresponding block copolyimide, all based on the 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), have been synthesized and fully atomistic models have been studied using molecular dynamics (MD) simulation. The respective diamines were 1,3-phenylenediamine (mPDA) and 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene). These polyimides are potential candidates for gas separation applications. The synthesized polymers were processed as dense flat membranes. The effects of diamine structure were investigated at the molecular level and an attempt to compare the structural features of homo- and block copolyimides was made. Amorphous models were generated using a hybrid pivot Monte Carlo-MD sampling preparation technique. Average model densities were validated against experimental measurements on the dense films. Cohesive energies, Hildebrand solubility parameters, conformational characteristics, intermolecular interactions and available void spaces were analysed for each system. The durene diamine was found to hinder stacking and increase the available space. This is associated with the steric effect of the methyl substituents. In general, 6FDA-mPDA/durene exhibits an intermediate behaviour with respect to its base polyimides. For most of the examined properties, the differences between different size simulated systems were minor with the exception of the free volume distribution.

Synthesis and characterization of benzimidazole‐based low CTE block copolyimides

AbstractA series of block and random copolyimide films were synthesized from various molar ratios of two diamines, rigid 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (APBI) and flexible 4,4′‐oxydianiline (ODA) by polycondensation with dianhydride 3,3′,4,4′‐biphenyltetracarboxylic dianhydride. The contents of APBI ranged from 10 to 60 mol % in copolyimides. The copolyimide films obtained by thermal imidization of poly(amic acid) solutions, were characterized by TMA, DMA, TGA, DSC, wide‐angle X‐ray diffraction, FTIR, tensile testing, water uptake (WU), and dielectric constant measurements. Rigid heterocyclic diamine APBI with interchain hydrogen bonding capability, led to low coefficient of thermal expansion (CTE), high Tg, high thermal stability and better mechanical properties. Increasing the APBI mol % caused a gradual decrease in the CTE and increase in Tg, thermal stability and tensile strength properties of the copolyimides films. Moreover, significantly enhanced thermal and mechanical properties of the block copolyimides were also found as compared to random copolyimides. The block copolyimide with APBI content of 60 mol %, achieved excellent properties, that is, a low CTE (4.7 ppm/K), a high Tg at 377°C, 5% weight loss at 562°C and a tensile strength at 198 MPa. This can be interpreted because of comparatively higher degree of molecular orientation in block copolyimides. These copolyimides also exhibited better dielectric constant and WU. This combination of properties makes them attractive candidates for base film materials in future microelectronics. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Phase Separation and Water Channel Formation in Sulfonated Block Copolyimide

We compared experimental and simulated data to investigate the phase separation and water channel formation of proton exchange membranes (PEMs) for fuel cell. Sulfonated block copolyimides (SPIs) were adopted as model polymers for experiments and simulations, and Nafion was used as a reference. Nafion and SPIs were observed to have different microscopic structures such as constituent atoms, backbone rigidity, and the locations of sulfonic acid groups, all of which significantly affect phenomenological properties at the macroscopic level such as density, water uptake, and proton conductivity. In particular, SPIs show much weaker microphase separation than Nafion, mainly due to the lower mobility of sulfonic acid groups and the existence of acceptable sites for hydrogen bonding even in hydrophobic segments, which impedes water channel formation for proton transport. As a result, the phase separation behavior and the resulting water channel formation are the major factors affecting macroscopic properties of PEMs such as water uptake and proton transport.

Synthesis of copolyimides based on room temperature ionic liquid diamines

AbstractBlock copolyimides based on aromatic dianhydrides and diamines copolymerized with diamino room temperature ionic liquid (RTIL) monomers were synthesized over a range of compositions. Specifically, two diamino RTILs, 1,3‐di(3‐aminopropyl) imidazolium bis[(trifluoromethyl)sulfonyl] imide ([DAPIM] [NTf2]) and 1,12‐di[3‐(3‐aminopropyl) imidazolium] dodecane bis[(trifluoromethyl) sulfonyl] imide ([C12 (DAPIM)2] [NTf2]2) were synthesized using a Boc protection method. The two RTILs were reacted with 2,2‐bis(3,4‐carboxylphenyl) hexafluoropropane dianhydride (6FDA) to produce 6FDA‐RTILs oligomers that formed the RTIL component for the block copolyimides. The oligomers were reacted with 6FDA and m‐phenylenediamine (MDA) at oligomer concentration from 6.5 to 25.8 mol % to form block copolyimides. Increasing the concentration of the 6FDA‐RTIL oligomer in the block copolyimides resulted in a decrease in the thermal degradation temperature, glass transition temperature and an increase in the density. The gas permeability of the RTIL based block copolyimide decreased but the ideal permeability selectivity for CO2/CH4 gas pair increased relative to the pure 6FDA‐MDA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4036–4046, 2010

Proton conductivity and stability of low-IEC sulfonated block copolyimide membrane

The proton conductivity and membrane stability of sulfonated block copolyimide membranes with a low ion exchange capacity (IEC) synthesized by chemical imidization using a two-pot procedure were investigated. The proton conductivity of the low-IEC block copolyimide membrane at 80 °C and 98% relative humidity was 16 times larger than that measured for the low-IEC random copolyimide membrane, while that of the high-IEC block copolyimide membrane at the humidity was 4 times than that of the high-IEC random copolyimide membrane, suggesting that the protons in the low-IEC block copolyimide membrane were effectively transported. In addition, the hydrolytic and oxidative stabilities of the low-IEC sulfonated block copolyimide membranes were estimated in detail from FT-IR and 1H NMR. These stabilities of the low-IEC membranes were significantly enhanced compared to those of the high-IEC membranes. The oxidative stability problem in the low-IEC block copolyimide membranes was found to be primarily caused by a decrease in the sulfonic acid groups rather than by polyimide chain scission. These findings indicate that a sulfonated block copolymer consisted of a small amount of sulfonic acid groups is desirable for the development of proton exchange membranes, when considering the balance between the proton conductivity and membrane stability of the proton exchange membranes.

Gas Transport Properties of Asymmetric Block Copolyimide Membranes

We have synthesized fluorinated block copolyimides with different block chain lengths by chemical imidization in a two-pot procedure and prepared the asymmetric coployimide membranes using the dry-wet phase inversion process. The gas transport properties of the asymmetric membranes were measured using a high vacuum apparatus equipped with a Baratron absolute pressure gauge at 76 cmHg and 35 °C. We demonstrated that the skin layer thicknesses and the gas transport properties of the asymmetric membranes depended on the copolyimide structures. The phase separation in the block copolyimide solution instantaneously occurred so that the skin layer of the asymmetric block copolyimide membrane became thinner than that of the asymmetric random copolyimide membrane and the gas permeance of the asymmetric block copolyimide membrane had a high value. The apparent skin layer thickness of the asymmetric block coployimide membrane was 230 nm. The asymmetric copolyimide membrane indicated an O2 permeance of 2:7 × 10−4 [cm3(STP)/(cm2 sec cmHg)] (270 [GPU]) and an O2/N2 selectivity of 4.3.

Reflective and conductive surface silvered polyimide films prepared via in-situ technique using copolyimide as matrix

Reflective and/or conductive surface silvered polyimide films have been prepared by using random and block copolyimide derived from pyromellitic dianhydride (PMDA), 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-oxydianiline (4,4′-ODA) as matrix and (trifluoroacetylacetonato) silver(I) (AgTFA) freshly synthesized from silver acetate and trifluoroacetylacetone as silver precursor. Influence of copolyimide structure on film metallization process and development of film reflectivity and conductivity during the thermal curing cycle were investigated. The metallized films were characterized by DMTA, X-ray diffraction, XPS, TEM, SEM.

A novel positive‐type photosensitive polyimide based on soluble block copolyimide showing low dielectric constant with a low‐temperature curing process

AbstractA soluble block copolyimide (Bco‐PI) was prepared by direct one‐pot polycondensation of 2,2‐bis‐(3‐amino‐4‐hydroxyphenyl)hexafluoropropane, 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, and cyclohexane‐tetracarboxylic dianhydride in the presence of γ‐valerolactone and a pyridine catalyst system using γ‐butyrolactone as the solvent. The thermal transmission temperature (Tg) of Bco‐PI was 282°C. By having the curing process occur at 250°C, which was below the Tg, colorless and transparent films could be obtained. The film showed excellent optical characteristics. Such properties could not be attained by the conventional high‐temperature thermal imidization process of poly(amic acid). The hydroxy groups in the polyimide backbone gave the Bco‐PI the potential to become alkaline. To the Bco‐PI was added 15 wt % ester of 2,3,4‐trihydroxybenzophenone with 1,2‐naphthoquinone‐(2) diazide‐5‐sulfonic acid (NT200) as the photoreactive compound. The system worked as a positive‐type photosensitive polyimide (PSPI). The sensitivity and contrast of the PSPI system were 220 mJ/cm2 and 1.27, respectively, when exposed to UV light, followed by development with a 5% tetramethylammonium hydroxide (TMAH) aqueous solution at room temperature. After curing at 250°C for 1 h, the average refractive index of Bco‐PI with and without NT200 was 1.5543 and 1.5563, and the optically estimated dielectric constant of the polyimides was 2.66 and 2.67, respectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4240–4246, 2006

Sulfonated block polyimide copolymers as a proton‐conductive membrane

A series of sulfonated block copolyimide (SPI-B) ionomers were synthesized, and the effect of the block length was investigated. The new block SPI-B ionomer membranes showed chemical stability comparable to that of the random sulfonated polyimide equivalent. Among the SPI-B copolymers examined, the block/block copolymer SPI-B150/150 membrane, containing long block segments in both the hydrophilic and hydrophobic components, showed the highest proton conductivity of 2 × 10−2 S cm−1 at 48% relative humidity, which was comparable to that of a conventional perfluorinated ionomer membrane. Widespread and well-connected hydrophilic domains were confirmed by scanning transmission electron microscopy, proving the high proton-transporting properties of the SPI- B150/150 membrane. These results proved its potential availability as an electrolyte for high-temperature polymer electrolyte fuel cells.

Preparation of novel fluorinated block copolyimide membranes for gas separation

AbstractWe synthesized novel fluorinated block copolyimides with various diamine compositions and block chain lengths by chemical imidization in a two‐pod procedure. We describe the gas‐transport properties of the novel block copolyimide membranes. We demonstrate that the gas‐transport properties of the copolyimide membranes strongly depended on the block chain lengths. The gas permeabilities of the copolyimide membranes increased with increasing block chain length, and the gas selectivities increased with decreasing lengths. We clarify that the gas diffusivity of the block copolyimide membrane dominated the gas‐transport properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2436–2442, 2006

スルホン酸基を有する長鎖ブロックコポリイミド膜のプロトン伝導性

We have synthesized a novel sulfonated block copolyimide with long block chains by chemical imidization using a two-pot procedure. The proton conductivity of a block copolyimide film, i.e., NTDA-BDSA-b-6FAP (140/60) was approximately 0.45 S cm-1, which is higher than that of Nafion 117®. Additionally, we demonstrated that the proton conductivity of the block copolyimide film strongly depends on the block chain lengths. The conductivities of the block copolyimide films increased with increasing block chain lengths. This may be due to the formation of ionic channels in the copolyimide films and its dependence on the block chain length. We are currently investigating the effects of the morphology and domain size of the block copolyimide film on the proton conductivity.

A novel positive‐type photosensitive polyimide having excellent transparency based on soluble block copolyimide with hydroxyl group and diazonaphthoquintone

AbstractA novel positive‐type photosensitive polyimide having excellent transparency based on soluble block copolyimide (Bco‐PI) with hydroxyl group and diazonaphthoquinone (DNQ) as a photoreactive compound was developed. The base Bco‐PI A was prepared by a direct one‐pot polycondensation of cyclohexanetetracarboxylic dianhydride (H‐PMDA), 2,2‐bis(3‐amino‐4‐hydroxyphenylhexafluoropropane) (Bis‐AP‐AF), and bis(4‐(3‐aminophenoxy)phenyl)sulfone (m‐BAPS) in the presence of a γ‐valerolactone and pyridine catalyst system by using dipolar aprotic solvent such as N‐methyl‐2‐pyrrolidone (NMP).The wholly aromatic polyimides have strong absorptions in the visible regions, because of their change–transfer complex formation. On the other hand, alicyclic dianhydride, H‐PMDA, contributed to the resulting Bco‐PI film with colorlessness and transparency, which are the important factors for a photosensitive polyimide. Photosensitive Bco‐PI, containing 20 wt % 1,2‐naphthoqiunonediazide‐5‐sulfonic acid p‐cresol ester (PC5), showed a sensitivity of 250 mJ/cm2 and a contrast of 2.56 when it was exposed to UV light, followed by development with 5% tetramethylammonium hydroxide (TMAH) aqueous solution at room temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1619–1624, 2005