Chemical Imidization Research Articles

A novel family of optically transparent fluorinated hyperbranched polyimides with long linear backbones and bulky substituents

We demonstrated here for the first time the synthesis of fluorinated hyperbranched polyimide (FHPIs) and an evaluation of their properties. A series of novel fluorinated hyperbranched polyimides were respectively synthesized via a two–step chemical imidization method involving a polycondensation reaction between 1,3,5–tris(2–trifluoromethyl–4–aminophenoxy) benzene (TFAPOB) and four different dianhydride monomers bearing bulky substituents. The properties of the synthesized FHPIs (individually denoted as FHPI I–IV) were characterized by Fourier-transform infrared, nuclear magnetic resonance (NMR), Near-IR, and UV-vis spectroscopy, techniques as well as via, atomic force microscopy (AFM), tensile testing, dielectric constants, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), In addition, the dielectric constants, chromaticity values, refractive indices, and birefringence values of these materials were determined. The obtained FHPIs showed good solubility and film–forming properties. The FHPIs exhibited excellent optical properties which included very light color, outstanding optical transparency (80–85% at 450 nm, 86–88% at 550 nm, 88–89% at 800 nm), birefringence values ranging from 0.0011 to 0.0020, adjustable refractive indices (1.4721–1.5644 at 650 nm), a cut–off wavelength within 353 nm, and a low absorption range in the near–infrared region. These materials would be ideal candidates for use in optical devices.

Heat Resistance and Dynamic Mechanical and Rheological Properties of a Blend of Crystallizing Polymers, Polyimide and Copoly(urethane—imide), at Identical Chemical Structure of the Imide Blocks in the Initial Polymers

A blend of crystallizing polyimide and newly synthesized partially crystalline multiblock (segmented) copoly(urethane—imide), consisting of 75 wt % copoly(urethane—imide) and 25 wt % polyimide, was prepared and studied by thermal gravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and melt rheology. Blend samples were prepared by mixing copoly(urethane—imide) and polyimide prepolymers in an N-methyl-2-pyrrolidone solution, in which the subsequent thermal or chemical imidization of the system components was performed. The properties of the initial polyimide, copoly(urethane—imide), and the blend were compared. The results of studies by differential scanning calorimetry and dynamic mechanical analysis demonstrate the presence of a crystalline soft polyester phase in the copoly(urethane—imide) structure and of the crystalline hard imide phase in the blend structure, which suggests the crystallization suppression in samples of the blend. The dynamic viscosity of the melt of chemically imidized copoly(urethane—imide) and blend samples is lower than that of their thermally imidized analogs. Dynamic mechanical analysis shows that the initial copoly(urethane—imide) behaves as a thermoelastoplastic. The blends consisting of copoly(urethane—imide) and thermoplastic polyimide are similar in properties to polyimide thermoplastics for structural purposes.

Gas transport property of the binaphthyl-based polyimide membranes

There is constant need for improving the performance of gas separation membranes for making the membrane technologies viable for industrial applications. In this work, we introduce an array of novel polyimide (PI) membranes containing binaphthyl moieties for gas separations. Using two different methods, chemical or azeotropic imidization, we have synthesized PIs with hydroxyl (OH) group or acetate (OAc) groups based on binaphthyl diamine and three different di-phthalic anhydride monomers (6FDA, BTDA, and ODPA). Permeabilities of H2, CO2, O2, N2 and CH4 were evaluated on six membranes under 0.2 MPa. The contorted binaphthyl PIs are able to sieve small gas molecules in general. Bulky OAc side groups in PI increase free volume via preventing the polymer chains from packing and cause higher gas permeability. The new binaphthyl-based polyimide architecture is developed for a possible application in gas separation.

Colorless and Organosoluble Fluorinated Poly(ether imide)s Containing A Asymmetry, Bulky Featured 4-tert-Butylcatechol Bis(ether anhydride) and Trifluoromethyl Substituents Aromatic Bis(ether amine)s

A series of fluorinated poly (ether imide)s (PEIs) were prepared from asymmetry, bulky featured of 1,2-bis(3,4-dicarboxyphenoxy)-4-tert-butylbenzene dianhydride and various trifluoromethyl-based bis(ether amine)s via conventional thermal (H) or chemical (C) imidization. All fluorinated PEIs exhibited flexible, good mechanical properties and excellent solubility in a variety of organic solvents. In addition, the chemical imidization based PEI thin films showed cut-off wavelengths of UV-vis absorptions below 380 nm with very low yellowness index (b* < 5.5). They also exhibited high thermal stability with the 10 % weight loss temperature from 486 to 550 °C of in nitrogen or air atmosphere. Compared with the corresponding PEIs based on non-fluorinated bis(ether amine)s, fluorinated PEIs not only showed higher optical transparency, lower dielectric constants and water absorptions but also maintained thermal and mechanical properties.

Development of new polyimide powder for selective laser sintering

Abstract

Colorless PI structure design and evaluation for achieving low CTE target

To obtain the colorless polyimide (PI) film with low coefficient of thermal expansion (CTE) and high thermal stability, the rigid biphenyltetracarboxylic acid dianhydride (BPDA) and 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (FDA) were selected and copolymerized with 2,2'-bis (trifluoromethyl)-[1,1'-biphenyl]-4,4'-diamine (TFDB). The physical properties of PIs were effectively regulated and optimized by adjusting the ratio of BPDA to FDA. When the ratio of BPDA to FDA is 6:4, the thermal imidized film (PI-6) performance is the best. It has a glass transition temperature (Tg) of 363 ℃, a 5% weight loss temperature (Td5) of 533 ℃, a CTE of 18.8 ppm/K, and a tensile strength of 140 MPa. The transmittance of PI-6 at 760 nm and 430 nm are up to 89.6% and 83.2% respectively. Further, the PI-6's precursor, PAA-6 were treated by chemical imidization. The obtained film has a transmittance of 92.6% at 760 nm, a decreased CTE of 15.5 ppm/K, and a tensile strength of 227 MPa, which is expected to be used as flexible display substrates. Finally, the effects of molecular and aggregation structure on the properties of PIs were studied.

Thermally rearranged (TR) HAB-6FDA nanocomposite membranes for hydrogen separation

Thermally rearranged (TR) polymers exhibited a good balance of high permeability and high selectivity. For this purpose HAB-6FDA polyimide was synthesized from 3,3 dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoro propane dianhydride (6FDA) by chemical imidization. Initially, the sample was modified from pure polymer to silica nanofiller doped polymer membrane. Further the modification was done by thermal rearrangement reaction at 350 °C temperature. This modification causes a mass loss in polymer structure and therefore enhances the fractional free volume (FFV). The gases used for the permeation test were H2, CO2, N2 and CH4. Selectivity was calculated for H2/CO2, H2/N2 and H2/CH4 gas pairs and plotted in the Robeson's 2008 upper bound and compared with reported data. The transport properties of these gases have been compared with the unmodified membrane. Permeability of all the gases has increased to that of unmodified polymer membrane. Thermally rearranged polymer nanocomposite exhibits higher gas permeability than that of silica doped and pure polymer. Also the selectivity for H2/CO2 and H2/N2 gas pairs exceeds towards Robeson's upper bound limit. It crosses this limit dramatically for H2/CH4 gas pair. Polymer nanocomposite can be utilized to obtain high purity hydrogen gas for refinery and petrochemical applications.

Amino-functionalized graphene quantum dots (aGQDs)-embedded thin film nanocomposites for solvent resistant nanofiltration (SRNF) membranes based on covalence interactions

Solvent resistant nanofiltration (SRNF) membranes are highly demanded in processing organic solutions especially those contain large molecules with molecular weight between 200 to 2000 Da, yet they have some drawbacks such as relatively poor solvent resistance and low solvent permeance. The current work presented an innovative class of amino-functionalized graphene quantum dots (aGQDs) embedded thin film nanocomposites (TFN) for SRNF membranes which were prepared via interfacial polymerization (IP) and subsequent steps (chemical imidization, crosslinking, and solvent activation). The prepared membranes enabled covalent interactions not only between the IP skin layer and the substrate, but also between the IP layer and the embedded aGQDs. The ethanol permeance and surface porosity increased by 44% and 69%, respectively, with the embedment of aGQDs under the optimal conditions, while the Rhodamine B (RDB, 479 Da) rejection maintained essentially stable above 99%. Furthermore, our novel membranes exhibited excellent long-term stability, with a rejection of over 99% for Rose Bengal (RB, 1017 Da) during the continuous filtration of 100 mg L−1 RB/N,N-dimethyl formamide (DMF) solution at room temperature for more than 768 h. They also exhibited good organic solvent resistance and high-temperature tolerance in both DMF and NMP solvents, with a RDB rejection of over 99% and an ethanol permeance of about 38 L m−2 h−1 MPa−1 after being immersed in DMF at 80 oC for 248 h, and a RDB rejection of over 99% and an ethanol permeance of about 41 L m−2 h−1 MPa−1 after being immersed in NMP at 80 oC for 232 h. The results demonstrated that the aGQDs-embedded TFN OSN membrane has vast potential in SRNF applications.

Aromatic polyimides containing pyridine and spirocyclic units: Preparation, thermal and gas separation properties

Six polyimides, containing pyridine and spirocyclic units, were successfully synthesized by chemical imidization. Structure-dependent properties such as thermal decomposition temperatures and gas permeabilities of the high-performance polymers were explicitly investigated. Results showed that all polyimide films exhibited good solubility in common organic solvents and non-polar solvents such as chloroform and tetrahydrofuran. The polymers exhibited good thermal stability, all demonstrating thermal decomposition temperatures (Td10%) over 496 °C in nitrogen. Important from a commercial viewpoint, the permeability coefficients of these for the acidic gas CO2 showed an increase over other tested gases by virtue of the basic group pyridine (C–N linkages) in their structures.

Optical, thermal and gas separation properties of acetate-containing copoly(ether-imide)s based on 6FDA and fluorenyl diamines

The diamine, 9,9-bis[4-(4-amino-3-hydroxylphenoxy)phenyl]fluorene (BAHPPF) was synthesized by the modified two-step method. Then, a series of acetate-containing copoly(ether-imide)s were prepared by the copolymerization of BAHPPF, 9,9-bis(4-aminophenyl)fluorene (BAF) and 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) followed by chemical imidization. The structures and properties of the BAHPPF and copoly(ether-imide)s were characterized by nuclear magnetic resonance spectrometer (NMR), Fourier transform infrared spectrometer (FTIR), X-ray diffractometer (XRD), differential scanning calorimeter (DSC), thermogravimetric analyzer (TGA), ultraviolet-visible spectrophotometer (UV-VIS), and tensile testing. Single gas permeation performances of these copoly(ether-imide)s were also studied for five representative gases of interest including H2, O2, N2, CO2, and CH4. The experimental results showed that the copoly(ether-imide)s showed excellent optical properties with high light transmittance above 80.2% at 450 nm. The glass transition temperature of these copolymers were higher than 333°C. Their tensile strength and Young’s module also increased, and the elongation decreased with the decrease of BAHPPF. High gas permeabilities of copoly(ether-imide)s were obtained, and the ideal selectivity of CO2/CH4 was improved due to the introduction of acetate group and flexible ether linkage. These copoly(ether-imide)s could be applied to the field of optics and gas separation.

Fully Bio-based Aromatic Polyimide Using 4-Aminocinnamic Acid and Mellophanic Dianhydride as Bio-derived Monomers

Mellophanic dianhydride which is aromatic tetracarboxylic dianhydride monomer for synthesis of polyimide, were derived from maleic anhydride and 2,5-dimethylfuran as the bio-derived monomers with the new approach. The obtained mellophanic dianhydride is used to synthesize the fully bio-based poly(amic acid) using 4-aminocinnamic acid dimer as the bio-based aromatic diamine monomer. For controlling the solubility of polyimide, thermal or chemical imidizations are carried out by using stepwise heating method or acetic anhydride/pyridine treatment, respectively. Thermally imidized polyimides show low solubility for organic solvent, however, chemically-imidized polyimide show good solubility for N-methyl-2-pylloridione, dimethylsulfoxide, and N,N-dimethylformamide. In addition, all the obtained polymers show high heat resistance properties, 10 % decomposed temperature (T d10), of poly(amic acid) is 331 °C, while T d10 of polyimides are 389 °C regardless of imidization processes. Thus, fully bio-based polyimides having high thermostability is developed for the first time.

Organosoluble and transparent cardo polyimides with high Tg derived from 9,9-bis(4-aminophenyl)xanthene

9,9-Bis(4-aminophenyl)xanthene (BAPX) was prepared simply and effectively via one-pot, two-step procedure using xanthenone and aniline as main substrates. The monomer BAPX was reacted with six aromatic dianhydrides in N, N-dimethylacetamide (DMAc) to yield the corresponding polyimides (PIs) via the poly(amic acid) precursors and subsequent thermal or chemical imidization. The resulting PIs exhibited good thermal stability with glass transition temperatures of 308–348°C, initial decomposition temperatures of 470–510°C, 10% weight loss temperatures of 540–565°C, and char yields of 55–59% at 800°C in nitrogen, respectively. All polymers were amorphous and readily soluble in organic solvents such as N-methyl-2-pyrrolidone and DMAc. The PI films had tensile strengths of 71–92 MPa, tensile moduli of 1.91–2.35 GPa, and elongations at break of 5–13%. Meanwhile, these polymer films also had high optical transparency with a cutoff wavelength in the range of 367–415 nm, lower dielectric constants (3.02–3.34 at 10 MHz), and low water uptake of 0.30–0.52%.

The In-plane Orientation and Thermal Mechanical Properties of the Chemically Imidized Polyimide Films

The thermal and mechanical properties of the chemically imidized polyimide (CIPI) films and thermally imidized polyimide (TIPI) films were investigated systematically. Experimental results indicated that the CIPI films show dramatically enhanced tensile strength and modulus with obviously reduced coefficient of thermal expansion (CTE) in comparison with TIPI films. These enhancements results from the high in-plane orientation and close packing of the CIPI backbones. Compared with thermal imidization which starts at about 140 °C, the chemical imidization activated by acetic anhydride and isoquinoline initiates the cyclization even at room temperature. The resulting imide rings restrict the mobility of polymer chains and lead to the in-plane orientation with solvent evaporation. Additionally, fewer small molecules remain in the films after treated at 120 °C by chemical imidization than by thermal imidization. The polymer chain plasticization caused by the evaporation of small molecules at high temperature is obviously restricted. Moreover, the partially imidized polymer inhibits the decomposition of mainchains that occurs at subsequent high temperature process, being beneficial to the formation of high molecular weight PI films. Hence, chemical imidization pathway shows apparent advantage to produce PI films with great combined properties, including high modulus, strength and toughness, as well as high thermal dimension stability etc.

Preparation and Characterization of Electrospun Polyimide Microfibrous Mats with High Whiteness and High Thermal Stability from Organo-soluble Polyimides Containing Rigid-rod Moieties

A series of flexible and tough polyimide (PI) microfibrous mats (PI-1~PI-4) have been prepared via the one-step electrospinning procedure with the organo-soluble PI resins as the starting materials. For this purpose, four PI resins were first synthesized by the chemical imidization reaction from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and four aromatic diamines containing rigid-rod moieties in their molecular skeletons, respectively. The PI resins derived from 6FDA and aromatic diamines, including PI-1 from 2-(4-aminophenyl)-5-aminobenzimidazole (APBI), PI-2 from 2-(4-aminophenyl)-5-aminobenzoxazole (APBO), PI-3 from 4,4′-diaminobenzanilide (DABA), and PI-4 from 2-chloro-4,4-diaminobenzanilide (Cl-DABA) exhibited good solubility in polar aprotic solvents, such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc). Flexible and tough microfibrous mats were successfully prepared by a one-step electrospinning procedure from the PI/DMAc solution (solid content: 15–20 wt%; absolute viscosity: 8000–10000 mPa·s). The derived PI mats exhibited good whiteness according to the CIE Lab measurements with W (whiteness) values as high as 94.31, L (lightness) values higher than 94.00, b* (yellowness) values as low as 2.98 and yellow indices (YI) as low as 4.87. In addition, the prepared PI mats exhibited excellent thermal and dimensional stability with the glass transition temperatures (Tg) higher than 345 °C and linear coefficients of thermal expansion (CTE) as low as 27.8×10-6 /K.

Low shrinkage, mechanically strong polyimide hybrid aerogels containing hollow mesoporous silica nanospheres

Low shrinkage, mechanically-strong polyimide hybrid aerogels were synthesized using a supercritical carbon dioxide (scCO2) drying process. Polyimide hybrid aerogels of biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA) containing surface-modified hollow mesoporous silica (AHMS) nanoparticles were prepared by chemical imidization and scCO2 drying. To avoid the high volume shrinkage of wet gels that occurs mainly during the drying process, AHMS nanoparticles were introduced to the network structure of the PI aerogels as a crosslinker. All aerogels exhibited a highly-interconnected, network-like structure of polyimide nanofibers with an average fiber diameter of approximately 27.6 nm and 92.8% porosity. These hybrid aerogels exhibited an excellent compression modulus, thermal stability, and high surface area, as well as low density, low shrinkage, and low thermal conductivity.

Negatively charged polyimide nanofiltration membranes with high selectivity and performance stability by optimization of synergistic imidization

A simple strategy is proposed for high performance polyimide nanofiltration (PI-NF) membranes by optimization of a synergistic imidization reaction. Soluble poly(amic acid) polymers with partial imidization was successfully controlled and fabricated by chemical imidization. With the product as a matrix, NF membranes with an integrally skinned asymmetric architecture were obtained by phase inversion and subsequent thermal imidization. The brittle and ruptured defects caused by directly high temperature conversion for fabricating PI-NF membranes were effectively avoided. The prepared membrane showed high rejections for dye, PEG and typical salts. The fabricated PI-NF membranes were endowed with a high permeance of isopropyl alcohol [approximately 1 L/(m2 h bar)] and a high rejection of rose Bengal (greater than 92%). The molecular weight cut-off of PI-NF membrane is below 800 Da. The pure water flux of PI-NF membrane prepared under optimized conditions was approximately 20 L/(m2 h) and the rejection for Na2SO4 was 93.91% at 5 bar. The rejection for different salts followed the order: Na2SO4 > MgSO4 > NaCl > MgCl2, revealed that Donnan exclusion theory and steric hindrance effect dominated the rejection mechanism. Furthermore, the NF membranes showed excellent stability over a long-term filtration process.

Influence of different ratios of a-ODPA/a-BPDA on the properties of phenylethynyl terminated polyimide

A series of phenylethynyl-terminated imide oligomers based on 3,4′-oxydianiline (3,4’-ODA), with different content of 2,3,3′,4′-oxydiphthalic dianhydride (a-ODPA) and 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA), have been prepared by chemical imidization process. The effects of different dianhydrides ratios on curing behavior, solubility, melt viscosity of oligomers, glass transition temperature (Tg), coefficient of thermal expansion (CTE), thermal stability, mechanical performance of films, and adhesive properties were evaluated systematically. The prepared oligomers with more content of a-ODPA exhibited sufficient solubility in some solvents, lower melt viscosity and better adhesion. The cured resins with more content of a-BPDA exhibited lower CTE value, higher Tg and thermal stability in N2 and air atmosphere. The Tg value of the cured a-BPDA/3,4’-ODA/PEPA system (Oligo-5) was 338 °C by tan δ. Meanwhile, the obtained polyimide films based on a-ODPA/a-BPDA monomers possessed high tensile strength (> 98.0 MPa) and strain (> 10.3%). These detailed results may provide some help to choice suitable matrix resin for structural adhesive and high-performance resin-based composite materials.

Preparation and gas permeation of crown ether-containing co-polyimide with enhanced CO2 selectivity

In present work, crown ether-containing co-polyimide with improved gas permselectivity was developed for CO2/N2 and CO2/CH4 separation. Crown ether segment grants the co-polyimide material good affinity with CO2 as well as strong rigidity of polymer chain. This co-polyimide was prepared by the condensation polymerization and chemical imidization of 4, 4-hexafluoro-isopropylidene diphthalic anhydride, 4, 4′-diaminodiphenylmethane and trans-di(aminobenze)-18-C-6 (trans-DAB18C6). The synthesized materials were characterized by FT-IR, 1H NMR, XRD, TGA, DSC, GPC and electronic tensile machine. The fractional free volume (FFV) and fractional accessible volume (FAV) were calculated with molecular dynamics simulations. The mixed-gas permeation properties of the co-polyimide membranes were investigated to inspect the influence of trans-DAB18C6 content and feed gas pressure. Effects of testing temperature and humidity, casting solvent on membrane with 25mol% trans-DAB18C6 were investigated. The molecular dynamics simulations results showed that （FAV）CO2 decreased, while the ratios of （FAV）CO2/（FAV）N2 and （FAV）CO2/（FAV）CH4 increased progressively with trans-DAB18C6 content. The CO2 permeability increased firstly, and decreased subsequently with trans-DAB18C6 content. At the same time, both CO2/N2 and CO2/CH4 selectivities increased progressively. The co-polyimide membrane with 25mol% trans-DAB18C6 displayed the maximum CO2 permeability of 109.0 barrer and CO2/CH4 selectivity of 92.7, which surpassed the 2008 Robeson upper bound. The long term operation stability study demonstrated that the membrane had good stability.

Thermally Rearranged Polybenzoxazoles Containing Bulky Adamantyl Groups from Ortho-Substituted Precursor Copolyimides

A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the...

Synthesis and properties of novel organosoluble and light-colored poly(ester-amide)s and poly(ester-imide)s with triptycene moiety

Two series of new triptycene-containing poly(ester-amide)s and poly(ester-imide)s were prepared from 1,4-bis(3-aminobenzoyloxy)triptycene with various aromatic dicarboxylic acids and dianhydrides, respectively. The synthesis of the poly(ester-amide)s was achieved by the phosphorylation polyamidation reaction by means of triphenyl phosphite and pyridine, and the synthesis of the poly(ester-imide)s included ring-opening polyaddition to give poly(amic acid)s followed by thermal imidization and chemical imidization to polyimides. All the poly(ester-amide)s and most of the poly(ester-imide)s presented good solubility in many organic solvents and could be solution-cast into transparent and flexible films. These poly(ester-amide)s and poly(ester-imide)s displayed discernible glass-transition temperatures (Tgs) between 242 and 298 °C in the DSC traces and showed moderate thermal stability with 10 wt% loss temperatures above 464 °C in nitrogen or air. These highly optically transparent polymer films possess an ultraviolet-visible absorption cut-off wavelength (λ0) down to 344 nm. 1,4-Bis(4-aminobenzoyloxy)triptycene was also synthesized and used for polymer synthesis; however, less favorable results were obtained.