Random Copolyimides Research Articles

Enhancing performance of nonvolatile transistor memories via electron‐accepting composition in triphenylamine‐based random copolymers

ABSTRACTWith the rapid advances in organic memory, organic field‐effect transistor (OFET) memory has been recognition of the value over the past few years. Although the functional polymer with the Donor‐Acceptor (D‐A) structure has been widely investigated, little research has been carried out to clarify the relationships among D‐A structure of the polymer, capability of charge‐transfer, and memory performance. Here, we report the nonvolatile memory characteristics of pentacene‐based OFET memory using random copolyimides, poly[4,4′‐diaminotriphenylamine‐hexafluoroisopropylidenediphthalimide‐co‐4‐(N,N‐bis(p‐aminophenyl)amino)‐4′‐nitroazobenzene‐hexafluoroisopropylidenediphthalimide) (PI(TPA‐6FDA‐DACx)), with feeding ratios of DAC to TPA set as x (where x = 0,10, 30,50,70,100). The OFET memory performance based on the molar ratio of DAC to TPA equal to 30:70 represents the best results with the proper charge mobility, on/off current ratio, and memory window. Intriguingly, the memory performance can be enhanced by introducing more D‐A monomer in polymer electrets, yet the concomitant inferior growth of pentacene decreases the charge mobility, attributed to the intrinsically destructive arrangement of polymer backbone. Our conclusion points out the importance of polymer arrangement and capability of charge‐transfer to the OFET performance and memory characteristics. The comparable results can also be applied for advanced OFET memory devices. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1113–1121

Pure - and sour mixed-gas transport properties of 4,4′-methylenebis(2,6-diethylaniline)-based copolyimide membranes

Three aromatic 6FDA-Durene/MDEA random copolyimides with different Durene:MDEA molar ratios (3:1; 1:1 and 1:3) were synthesized, and pure gas permeation properties through their dense films were investigated. Compared to their corresponding homopolymers (6FDA-MDEA and 6FDA-Durene), the copolymers exhibit significant improvement in gas separation performance, as the membranes display improved gas transport properties. For example, for pure gas, the CO2 permeability for 6FDA-Durene/MDEA (3:1) is around 234 Barrer and CO2/CH4 selectivity equal to 17.8 obtained at 22 °C and feed pressure of 100 psi. In addition, for sweet gas mixture consisting of 10, 59, 30 and 1 vol% CO2, CH4, N2 and C2H6, respectively, the 6FDA-Durene/MDEA (1:3) copolyimide membrane shows CO2 permeability of 73 Barrer and CO2/CH4 selectivity of about 24 at an elevated pressure of 800 psi. For a sour gas mixture with high H2S content (20 vol % H2S in the feed gas), the membrane exhibits H2S/CH4 selectivity of 21; and H2S permeability of 112 Barrer. The transport properties of the herein reported membrane are similar to or even better than the performance exhibited by some polymeric membranes reported in the literature.

Structural relationship between random copolyimides and their carbon fibers

A series of polyimide (PI) fibers synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) were prepared by a two-step wet-spinning process. The prepared PI fibers were then carbonized with the increasing temperatures up to 1500 °C under a high-purity nitrogen atmosphere. The effects of ODA/p-PDA molar ratios on the chemical structure, microstructure, chain orientation, and structural evolutions of the PI fibers were systematically investigated. The elemental composition, morphology, and aggregation structure after carbonization were also analyzed. The results showed that different chemical compositions have greatly influenced the aggregation structures of the resulting PI and carbon fibers. The PI fibers showed increased crystallinity and orientation degree with the decreased ODA moieties, while the corresponding PI-based carbon fibers (CFs) exhibited perfect graphitic structures. The CFs derived from PMDA/p-PDA PI backbone with flat chains exhibited a well-defined graphite structure with d 002 of 0.349 nm and I D/I G of 1.442. In addition, the carbon yield of the prepared PI-based carbon fibers reached more than 95 %.

Influence of conformational parameters on physical properties of copolyimides containing pendant diphenylphosphine oxide units

Modification or designing new molecular architectures are the key strategies to obtain materials with improved/tunable properties able to address environmental restrictions and public needs. Herein, a series of copolyimides containing bulky diphenylphosphine oxide pendant units was synthesized and the physical properties were studied and correlated with the conformational parameters, such as Kuhn segments, Van der Waals and free volumes. It is shown that conformational rigidity determines the packing of macromolecules in glass state, and therefore the free volume, glass transition and dielectric permittivity. The Kuhn segment of the synthesized random copolyimides calculated by Monte Carlo method exhibited a nonlinear dependence on chemical composition. The use of correlations between the chemical structure and conformational parameters is the key to achieve polymers with tailored physicochemical characteristics by varying the comonomers’ ratio.

Gas permeation and mechanical properties of thermally rearranged (TR) copolyimides

Gas transport and mechanical properties are reported for a series of copolyimides and their corresponding thermally rearranged (TR) analogs. Random copolyimides of APAF/HAB-6FDA with various compositions were synthesized via chemical imidization from 2,2′-bis (3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF), 3,3′-dihydroxy-4,4′-diaminobiphenyl (HAB), and 2,2′-bis-(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA). These copolyimides were thermally treated at temperatures between 350 °C and 450 °C to prepare TR polybenzoxazoles (PBOs). Pure gas permeabilities of H2, CH4, N2, O2, and CO2 were measured at 35 °C with upstream pressures ranging from 3 to 17 atm. In general, gas permeability increased and selectivity decreased as TR conversion increased. Gas permeability also increased with increasing APAF content in the polyimides as a result of higher fractional free volume (FFV) imparted by the extra hexafluoroisopropylidene group in APAF. Stress–strain relationships were recorded for the polyimides and their TR analogs. As polyimides underwent thermal rearrangement, samples became more rigid, and tensile stress and elongation at break decreased. A similar trend in mechanical properties was also observed as APAF content increased, which was attributed to the lower molecular weight of APAF-containing polymers, resulting from the lower reactivity of APAF relative to that of HAB.

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

Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides

AbstractResistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX, with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine (AMTPA), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide (NTCDI) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide (BTCDI) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI. The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX. At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI. Combining these results and our previous study on perylenebisimide (PBI), we concluded that memory characteristics could be tailored by changing the conjugation length (PBI > NTCDI > BTCDI) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Synthesis of room temperature ionic liquids based random copolyimides for gas separation applications

Random copolyimides were synthesized using diamino functional room temperature ionic liquid (RTIL) and were characterized. Specifically, a diamino functional RTIL, 1,12-di[3-(3-aminopropyl) imidazolium] dodecane bis[(trifluoromethyl)sulfonyl] imide ([C12(DAPIM)2][Tf2N]2), was reacted with 2,2-bis(3,4-carboxylyphenyl) hexafluoropropane dianhydride (6FDA) and m-phenylenediamine (MDA) to form random cooplyimides with a [C12(DAPIM)2][NTf2]2 concentration varying from 10 to 30mol%. Incorporation of [C12(DAPIM)2][NTf2]2 within the 6FDA–MDA backbone resulted in decreases in the polymer thermal stability, glass transition temperature, d-spacing, fractional free volume and increments in density. The gas permeability, solubility and diffusivity of the random copolyimides decreased and the permeability selectivities increased compared with the pure 6FDA–MDA polyimide.

Pervaporative Separation of Aromatic/Aliphatic Mixtures with Poly(Siloxane-co-Imide) and Poly(Ether-co-Imide) Membranes

Aromatic random copolyimides were synthesized and tested as membrane materials for the separation of a mixture of aromatic and aliphatic hydrocarbons by pervaporation. The polymers were synthesized by a two-step polycondensation route with a total of 4 aromatic dianhydrides, 4 aromatic diamines, and 3 diamino-terminated aliphatic oligomers containing either ether or siloxane units. Pervaporation experiments were conducted at two temperatures with toluene/n-heptane and benzene/n-heptane mixtures as feed streams. All polymers were selective toward the aromatic hydrocarbon. Introduction of siloxane units in the polymer generally led to very high hydrocarbon permeability coefficients, but caused a reduction in selectivity relative to that of the aromatic homopolyimide. Incorporation of ether units, on the other hand, did not generally cause such large increases in permeability, nor large decreases in selectivity. The performance of these materials was compared with previous results reported in the literature for other polymers.

Tuning the Electrical Memory Characteristics from Volatile to Nonvolatile by Perylene Imide Composition in Random Copolyimides

Random copolyimides, PI–PBIX, with different compositions of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), N,N′-bis(4-aminophenyl)-3,4,9,10-perylenebis(dicarboximide) (PBI), and 4,4′-diamino-4″-methyltriphenylamine (AMTPA) were designed and synthesized for resistive-switching memory device applications. By varying the feeding ratio of monomers, PI–PBIX (where X = 0, 1, 2.5, 5, and 10 for molar composition of repeating units containing PBI) showed tunable optical and electronic properties through the charge transfer between AMTPA and PBI. Also, the memory devices prepared from PI–PBIX sandwiched between ITO and Al electrodes exhibited the tunable electrical bistability from the volatile to nonvolatile write once read many-times (WORM) memory characteristics as the PBI composition increased. The OFF/ON electrical switching transition was mainly attributed to the charge-transfer mechanism for charge-separated high conductance, based on the analysis of density function theory. Also, the volatility of PI–PBIX device depended on the stability of charge-transfer complex and charge trapping sites. The deep LUMO energy level of the PBI moiety increased the back-charge-transfer energy barrier and prevented recombination of segregated charges even through applying the high negative and positive voltage. The study revealed that the memory characteristics could be tailored from the donor–acceptor composition in the random copolyimides.

Aromatic polyimide and polybenzoxazole membranes for the fractionation of aromatic/aliphatic hydrocarbons by pervaporation

A series of aromatic polyimides and polybenzoxazoles was synthesized and tested as membrane materials for separation of aromatic/aliphatic mixtures by pervaporation. Homo- and random copolyimides were synthesized by a two-step polycondensation of a total of 6 diamines and 4 dianhydrides. Polybenzoxazoles and poly(benzoxazole- co-imide)s were prepared by the thermal rearrangement of ortho-functionalized polyimide films. Pervaporation experiments were conducted at 80 °C with either toluene/ n-heptane or benzene/ n-heptane mixtures as feed streams. All polymers were selective towards the aromatic hydrocarbon, whose permeability could be changed by approximately 4 orders of magnitude depending on the chemical structure of the diamine. Pure-liquid sorption experiments at 25 °C revealed that these large changes in hydrocarbon permeability were mainly caused by changes in the diffusion coefficient. The performance of the polymers was compared with previous results reported for other polymers, as well as with the performance of a commercial polyimide (Matrimid ®).

Nanoaggregate Formation of Amphiphilic Alternating and Random Copolyimides in Water

Abstract Amphiphilic alternating/random copolyimides (coPIs) formed nanoaggregates in water. The diameter of the aggregates were ca. 90 nm for the alternating coPIs and 35 nm for the random coPI. The difference in the aggregate-forming behavior was attributed to the difference in the mode of association of hydrophobic units.

Effect of conformational adaptation of 4,4′-(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) on the structural features of a perylene-containing copolyimide

A series of perylene-containing random copolyimides with different ratios of diaminododecyl perylene tetracarboxylic dianhydride (PPI-12) and 4,4′-(hexafluoro-isopropylidene) diphthalic anhydride (6FDA) have been studied. Copolymerization improves the solubility and the copolyimide with a low percentage (less than 20% of total dianhydrides) of perylene becomes highly soluble in conventional solvents, such as, CHCl 3, CH 2Cl 2, or THF etc. The positions of the absorption maxima in the UV–visible spectra do not change with 6FDA concentration, but the relative intensities do. Although the homopolymer PPI-12 does not show a distinct glass transition, its T g was derived by extrapolation of the DSC results with the copolymers. The copolymers are semi-crystalline up to a concentration of 60% (mol) 6FDA. It is of interest that the spacings of X-ray reflections also do not change with the addition of 6FDA. This is rationalized on the basis that the conformation of the 6FDA segment does not cause any significant difference in the preferred conformational shapes of the homopolymer of PPI-12. Due to this “conformational isomorphism” 6FDA is not a significant chain “kinker” in this case.

Mechanically stable copolyimide for low level stress buffer

Copolyimide thin films, which has the low level stress and stress relaxation induced by water sorption, were characterized for potential application as encapsulant, stress-relief buffer, and interlayer dielectrics. The polyimides studied are poly(p-phenylene pyromellitimide) (PMDA-PDA), poly(p-phenylene 4,4′-hexafluoroisopropylidene diphthalimide) (6FDA-PDA) and their random copolyimides with various composition. These copolyimide films exhibited good combinations of physical and mechanical properties with low thermal expansion coefficient (TEC) and residual stress behavior by appropriately selecting the ratios of the acid dianhydride component. For these copolyimides, residual stress increased in the range of −5 to 50MPa, whereas stress relaxation induced by water uptake decreased in the range of 20.5–4.5MPa at 30°C, 100% relative humidity with increasing 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) composition, respectively. The degree of in-plane chain orientation was directly correlated to the residual stress and stress relaxation coefficient (S) in the film, which is an in-plane characteristic. However, the stress relaxation caused by the water uptake was significantly influenced by packing order induced by chain mobility, which might occur during thermal imidization. Overall, the candidate for the low level stress buffer application from the PMDA/6FDA-PDA copolyimide was both the 90/10 (=PMDA/6FDA in molar ratio) and 70/30 copolyimides.

Analysis of dimensionally stable copolyimide with a low-level residual stress

Copolyimide thin film, which has low-level stress and stress relaxation induced by water sorption, was characterized for potential applications as an encapsulant, a stress-relief buffer, and in interlayer dielectrics. The polyimides examined were poly(p-phenylene pyromellitimide) (PMDA-PDA) and poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) as well as their random copolyimides with various compositions. These copolyimide films exhibited good combinations of physical and mechanical properties with low thermal expansion coefficients, residual stress, and moisture-induced stress–relaxation behavior by appropriately selecting the ratios of the dianhydride component. For these polyimides, the residual stress increased in the range of −8.1–7.5 MPa, whereas stress relaxation induced by water uptake decreased in the range of 10.3–4.7 MPa with increasing BPDA contents, respectively. The major factor in determining the magnitude of the stress behavior induced by both the thermal mismatch and water uptake in films should be the morphological factors such as chain rigidity, chain orientation, crystallinity, and microvoids. Their morphological structures were examined by wide angle X-ray diffraction and a prism coupler, and the thermal properties were measured using a dynamic mechanical thermal analyzer as well as thermomechanical analysis. Overall, the candidate for the low level stress buffer application from the PMDA/BPDA-PDA copolyimide was the 30/70 (= PMDA/BPDA in molar ratio) copolyimide. This copolyimide showed no residual stress after curing at 400 °C and relatively insensitive stress relaxation to ambient humidity. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 796–810, 2001

Synthesis and characterization of soluble random copolyimides

Synthesis and characterization of soluble random copolyimides

Synthesis and characterization of soluble random copolyimides

Random copolyimides with different proportions of a diamine component were prepared by polymerizing different compositions of diamines with various dianhydrides and imidized thermally to 260°C. The imidization percent of poly(amic acid) was characterized at various temperatures by infrared spectroscopy. The homopolyimide based on bis[4-(3-aminophenoxy)phenyl]sulfone and pyromellitic dianhydride was the only one soluble. By changing the compositions of bis[4-(3-aminophenoxy)phenyl]sulfone and other diamines with pyromellitic dianhydride in N-methyl-2-pyrrolidone, soluble random copolyimides could be prepared. By random copolymerization, the thermal properties and viscosities of homopolyimide could be controlled. All the soluble polyimides prepared in this work were amorphous because of the lack of stereoregularity. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 272–277, 1999

Dimensionally stable polyimide copolymers for microelectronics applications

Polyimides are finding increased applications in microelectronics due to their high thermal stability, good chemical resistance, good adhesion, low moisture absorption, good mechanical properties, and low coefficient of thermal expansion (CTE). Four series of random copolyimides were synthesized and characterized for potential application as encapsulants, stress-relief layers, and interlevel dielectrics. Several candidates exhibited good combinations of physical and mechanical properties with inherent viscosities from 1.21 to 1.42 dL/g, Tg's ranging from 251 to 277°C, 10% weight loss temperatures between 503 and 527°C, and CTEs ranging from 33 to 39 ppm/°C. Mechanical properties at room temperature for the best candidates included tensile strengths of 17.8–21.3 ksi, moduli between 388 and 506 ksi, and elongations of 11–43%. Moisture absorption for these copolyimides ranged between 0.85 and 1.38 wt %. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2383–2393, 1998

Synthesis and characterization of polyimide derivatives prepared by different one-step methods

Homo- and copolyimides with high molecular weight could be synthesized from three dianhydrides and three diamines following two different one-step methods. Solubility behavior with structural effect, viscosity, kinetics of solution imidization, synthesized method, mechanical and thermal properties, and effect of azeotroping agent are discussed. Results indicate that homo-and random copolyimides were only prepared from a one-step method; on the other hand, copolyimide with different arrangement, such as random, block, and alternating, could be synthesized by a modified one. © 1996 John Wiley & Sons, Inc.

Synthesis and characterization of polyimide derivatives prepared by different one‐step methods

Homo- and copolyimides with high molecular weight could be synthesized from three dianhydrides and three diamines following two different one-step methods. Solubility behavior with structural effect, viscosity, kinetics of solution imidization, synthesized method, mechanical and thermal properties, and effect of azeotroping agent are discussed. Results indicate that homo-and random copolyimides were only prepared from a one-step method; on the other hand, copolyimide with different arrangement, such as random, block, and alternating, could be synthesized by a modified one. © 1996 John Wiley & Sons, Inc.