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In this work, a new diamine was designed by connecting flexible structures such as ether bond and aliphatic carbon chain between benzene rings, and was synthesized and purified through simple reactions such as Suzuki reaction. Finally, a series of polyimide (PI) films were synthesized by copolymerization with 4.4'-diaminodiphenyl ether (ODA)\pyromellitic dianhydride (PMDA) in different proportions. We prepared polyimide films with new monomer copolymerization ratios of 1% (PI-1), 5% (PI-2), 10% (PI-3), and 20% (PI-4). The polyimide films showed excellent glass transition temperatures, which were attributed to their unique bent architectures. The mechanical and thermal properties of the thermosets were studied using tensile testing, static thermomechanical analysis (TMA), and thermogravimetric analysis (TGA). As the results, the films exhibited the optimal glass transition temperatures (317.56°C–381.91°C), and the component with the highest copolymerization ratio has a 15% decrease in glass transition temperature compared to the component without copolymerization. Moreover, PI-1-PI-4 showed good heat resistance in the N2 atmosphere. The temperatures corresponding to a 5% heat loss in the films (T5%) were 458.12 °C–548.75°C, respectively. [ABSTRACT FROM AUTHOR]

Recently, there has been a rising tendency for the fabrication of membranes using the electrospinning method because it can control the properties of the fibrous mats by changing the parameters of the process. For this reason, in the current research, polyimide (PI) membranes were fabricated by the electrospinning method. The effect of electrospinning parameters on the content of porosity and tensile properties of the electrospun PI mats were investigated. Solution concentration, device voltage, and feed rate were considered the process parameters. Response surface methodology was adopted to design the electrospinning experiments. The results showed that the feed rate had the most contribution to the content of porosity of electrospun PI membranes which increased by decreasing the feed rate. On the other hand, the polymer concentration had a remarkable effect on the tensile strength. Indeed, the tensile strength improved as the solution concentration increased. The optimized electrospinning parameters to achieve both the highest porosity (97.66%) and the highest tensile strength (2.25 MPa) in the PI membrane were as follows: solution concentration 16.78%wt, device voltage 17 kV, and feed rate 1.4 mL h−1. The experimental results were in good agreement with the predicted values. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films with excellent mechanical and electrical properties were produced at a low temperature assisted by microwave. Depending on the reciprocating movement of dipole molecules excited by microwave, even though under a low temperature, the rotation and conformational changes of functional groups could also be promoted. Thus, reaction between N-H bond and -OH in carboxyl which could realize dehydration and cyclization of polyamic acid proceeded normally. Results revealed that the combination between ambient temperature only at 70°C and microwave power at 2000 W or higher could also produce PI films with imidization degree of 100%. For PI-2000W, compared with traditional PI film (PI-300°C) that generated only at temperature of 300°C, even though on the basis of no any change in molecular structure and addition of filler, the tensile strength, elastic modulus, crystallinity, and apparent density increased by about 21%, 51%, 37%, and 5%, respectively. For electrical properties, conductivity enhanced by one to two orders of magnitude comparing with PI-300°C. Results indicated that while keeping the original molecular structure of PI films unchanged, this work provided a new and effective method to assist the enhancement in mechanical and electrical properties of PI films. [ABSTRACT FROM AUTHOR]

Novel fluorine-containing polyimides were synthesized through copolymerization by using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (α-BPDA) and 4,4′-(4,4′-isopropydenediphenox-y) bis-(phthalic anhydride) (BPADA) as dianhydrides and 4,4′-oxydianiline (ODA) and 2,2 - Bis [4-(4-aminophenoxy)phenyl]-hexafluoropropanane (HFBAPP) as diamines. Noncoplanar structure, flexible ether bond, and trifluoromethyl give the polyimide good thermoplastic, solubility, and heat resistance. The glass transition temperatures of polyimide films are 232.5°C∼262.2°C, the 5% weight loss temperatures are 521.5°C∼531.0°C, and the residual mass is more than 50% as heating to 800°C. With the increase of HFBAPP content in diamine, the dielectric constant of the material decreases from 3.21 to 2.78, and the dielectric loss decreases from 0.00962 to 0.00687 at 1 MHz, which greatly improves the dielectric properties of the material. [ABSTRACT FROM AUTHOR]

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2′-bis (trifluoromethyl) −4.4′-diaminobiphenyl (TFMB) or trans-1.4′-cyclohexanediamine (t -CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T550 nm> 88%), great heat stability (CTE <4.4 ppm/K; Tg >314°C; Td5% >478°C) and good mechanical strength (σ > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion. [ABSTRACT FROM AUTHOR]

The set of important properties of polymers necessary for their use as fuel cell membranes, such as film-forming properties, stability in acidic aqueous media, thermal stability, proton conductivity, is determined by their chemical structure, which provides not only basic and fragmentary mobility of the polymer chain but also complex supramolecular structural features (in particular, phase separation). The effect of the chemical structure of aromatic polyimide sulfonic acids, containing a fragment of 4,4′-diamino[1,1′-biphenyl]-2,2′-disulfonic acid (BDSA), on their membrane-forming properties is discussed, as well as the membrane stability under the conditions of a hydrogen-air fuel cell. The research is aimed at investigating sulfonated polyimides based on the commercially available rigid monomer - BDSA and flexible dianhydrides with an electron donor in their structure. As a model for this study, two aromatic anhydrides with flexible -O- bonds were chosen for investigating the potential of corresponding polyimide films in application to proton exchange membranes. The synthesized sulfonic acid polyimide BDSA-SPI-4(H) is of interest as a proton-conducting membrane polymer for direct energy conversion electrochemical devices and has shown to be a promising material for this group of devices. It is suggested that the presence of the flexible electron donor bonds in the structure of dianhydride should increase the stability of the membranes prepared from BDSA. The properties of polyimide sulfonic acids from the aforementioned diamine and dianhydrides of different fragmentary flexibility implemented in this work could help the understanding of the connection between chemical structure and properties of the material in application to proton exchange membranes development. [ABSTRACT FROM AUTHOR]

A series of adenine-containing polyimides (APIs) with intramolecular hydrogen bonding (HB) were prepared from N 1 -(9-(4-aminophenyl)- 9H -purin-6-yl)-2-methoxybenzene-1,4-diamine (b-H-MeO-APA) and commercial dianhydrides. And a systematic comparison between intramolecular and intermolecular HB effects was made using APIs with (b-H-MeO-APIs) and without (b-H-H-API) methoxy group. FTIR indicated that the occurrence of intramolecular HB originated from the side MeO group ortho to -NH-. XRD indicated that the introduction of side group MeO and corresponding intramolecular HB could destroy the orderly stacking of b-H-H-APIs. Birefringence and polarized ATR FTIR studies showed that the groups and chains in b-H-MeO-APIs films could also be simultaneously self-arranged in the in-plane direction. In contrast, the orientation degree in the in-plane direction is generally lower than that of b-H-H-APIs. The b-H-MeO-APIs films showed lower water absorption, higher Tg, and lower CTE compared to b-H-H-APIs films, which indicates that the introduction of intramolecular HB may have some positive influence in controlling water absorption, Tg, and CTE. [ABSTRACT FROM AUTHOR]

In this study, KMnO4 was applied as an etchant to partially decompose the silica microspheres into mesoporous structures. 1H,1H,2H,2H-perfluorodecyltriethoxysilane was grafted onto the surface of the hollow silica. A fluorinated silica/polyimide hybrid material was prepared. Meanwhile, the influence of fluorinated silica on the dielectric property and moisture absorption property of the hybrid material was discussed. It is found that the fluorinated silica can lower the dielectric constant and hygroscopicity of the hybrid film. The fluorinated silica is characterized by strong hydrophobicity, good dispersibility, and good thermal stability. Even at a very low filling level of only 2 wt%, the dielectric constant of the polyimide hybrid is significantly reduced to 2.61 without sacrificing thermal stability. The water absorption rate of the polyimide hybrid film is reduced from approximately 3.1% to 2.1 wt%. Moreover, this provides a new idea for reducing the dielectric and water absorption properties of materials. [ABSTRACT FROM AUTHOR]

Several polyimides were prepared via two-step polycondensation from novel 2,5-furandicarboxylic acid–based diamine, 2,5-bis[4-(4-aminophenoxy)benzoyl]furan, with commercial dianhydrides. The chemical structures of the monomers and polymers were characterized by FT-IR and NMR in detail, respectively. The polyimides exhibited high performances with 5 wt% weight loss temperatures of over 410 oC, glass transition temperatures of over 214 oC, and tensile strengths and Young's moduli of up to 130 MPa and 3.2 GPa, respectively. The thermal crosslinking mechanism was studied by FT-IR, Raman spectroscopy, and model reaction analysis, which showed the Diels–Alder reaction between the furan group and diphenylethylene group was the main reaction. The crosslinked polyimide films showed improved solvent resistance, and thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

To prepare soluble polyimides with high temperature resistance, two new diamine monomers, namely, 2,2′-(4,4′-oxybisphenylene)-bis(1-phenyl-5-aminobenzimidazole) (5a), and 2,2′-(4,4′-hexafluoroisopropylidene)-bis(1-phenyl-5- aminobenzimidazole) (5b), were synthesized and exploited to prepare three series of poly(benzimidazole imides)s (PBIIs) by a conventional two-stage synthesis. The resulting PI films were flexible and tough, possessing high glass-transition temperatures (Tgs = 311°C–390°C), improved optical transparency, and excellent solubility. Moreover, the effect of different configuration on performance was revealed, and these data provided a feasible method to enhance both Tg and solubility of PIs by incorporating N-phenyl benzimidazole and corresponding functional moieties. [ABSTRACT FROM AUTHOR]

A series of three-phase composite films with different filler contents were prepared by in-situ polymerization. The composite films comprise polyimide (PI), poly (vinylidene fluoride) (PVDF), and titanium dioxide (TiO2). Compared with PI/TiO2 composite films, the PI/TiO2-PVDF composite films not only get a significant increase in dielectric constant, but also own better mechanical properties. Our results show that with the loading of 50wt% PVDF particles, the dielectric constant of PI/TiO2-PVDF composite films increased from 6.5 to 18.14 at 1 MHz and room temperature, while the tensile strength of PI/TiO2-PVDF composite films increased from 45 to 72 MPa. In addition, the films maintain a low loss tangent of about 0.02. PI/PVDF composite films were also prepared. It was found that dielectric constant of PI/PVDF composite was significantly lower than that of PI/TiO2-PVDF composite films when the loading of PVDF is 50wt%. [ABSTRACT FROM AUTHOR]

In this article, the polyimide (PI) composite films with synergistically improving thermal conductivity were prepared by adding a few graphene nanoplatelets (GNP) and various hexagonal boron nitride (h-BN) contents into the PI matrix. The thermal conductivity of PI composite film with 1 wt% GNP and 30 wt% h-BN content was 1.21 W(m·k)−1, which was higher than that of the PI composite film with 30 wt% h-BN content (0.45 W(m·k)−1), the synergistic efficiency of GNP under various h-BN content (10 wt%, 20 wt%, and 30 wt%) were 1.70, 2.71, and 3.09, respectively. And it was found that the increased h-BN content can suppress the dielectric properties caused by GNP in the matrix. The dielectric permittivity and dielectric loss tangent of 1 wt% GNP/PI composite film were 10.69, 0.661 at 103 Hz, respectively, and that of the 30 wt% h-BN + GNP/PI composite film were 4.29 and 0.1367, respectively. Moreover, the mechanical properties of the PI composite film were suitable for practical applications. And the heat resistance index and the residual rate at 700°C of PI composite film increased to 326.8°C, 74.43%, respectively, and these of PI film were 292.6°C and 59.26%. Thus, it may provide a reference value for applying the filler hybridization/PI film in the electronic packaging materials. [ABSTRACT FROM AUTHOR]

Mechanically robust optical homogeneous polyimide (PI) films with desirable atomic oxygen (AO) erosion duration were fabricated by initially synthesizing amine-functionalized hyperbranched polysiloxane (NH2-HBPSi), then reinforcing the pristine polyimide skeleton with it via copolycondensation reactions. NH2-HBPSi macromolecule imparts desirable AO survivability to the resulting hybrids. The mass loss per unit area of hybrid films had a downward trend with rising NH2-HBPSi content and AO dose before the complete silica protective layer was formed. It has been proven by the experiments in an underground simulated AO environment. It decreased to 1% of that of pristine polyimide when NH2-HBPSi accounted for 30% of the solid content after 24 h AO attack. The stable thickness uniformity that can meet the Rayleigh criterion was achieved in a 30 wt% HBPSi PI film, mainly due to the selection of the best process parameters. Meanwhile, 30 wt% HBPSi PI demonstrates satisfactory mechanical properties, with a tensile strength of 228.9 MPa and elongation at break of 7.3%. The characterization of scanning electron microscopy confirmed that pristine polyimide was substantially eroded after AO exposure while the surface morphology of 30 wt% HBPSi polyimide showed no evident change. The low AO erosion yield and prominent film thickness uniformity may find extensive usage in ultra-lightweight space diffractive optical elements (DOE) working in low earth orbit (LEO). [ABSTRACT FROM AUTHOR]

Fluorinated polyimide films are widely used in the field of flexible display because of their excellent optical transmittance. Based on previous studies, the adhesion to other substrates of fluorinated polyimide films have been improved by incorporating GAPD into the macromolecular chains, but their heat resistance is not yet very clear. In this study, thermal behaviors of fluorinated polyimide films (PIs) with and without GAPD were studied in N2 ambient and atmosphere by TG-DTG analysis under non-isothermal conditions. Activation energies (Eas) of PIs were calculated by Flynn-Wall-Ozawa method, Kissinger-Akahira-Sunose method and Kissinger method. In addition, mechanisms of thermal decomposition reaction were determined by Coats-Redfern method. By comparison, the Eas of PIs in the same atmosphere were similar and the thermal reaction mechanisms were essentially the same, indicating that adhesion of fluorinated polyimide can be improved by adding appropriate amount of GAPD, while the excellent optical permeability and heat resistance of fluorinated polyimide can be maintained, further expanding its application in flexible display and other fields. [ABSTRACT FROM AUTHOR]

In this study, silver–polydopamine–hexagonal boron nitride (h-BN@Ag) particles were prepared using mussel chemistry and reducibility of catechol. The modified method was simple and eco-friendly. In addition, we prepared h-BN@Ag/polyimide (PI) composite films via in situ polymerization, the scraper method, and thermal imidization. Owing to the good dispersion of the h-BN@Ag filler particles in the PI matrix and the bridging role of the Ag nanoparticles, the thermal conductivities of the h-BN@Ag/PI composite films were higher than that of the pure PI film. The thermal conductivity of the h-BN@Ag/PI film with the filler content of 10 wt% was 0.382 W (m·K)−1, which was 108% higher than that of pure PI films (0.184 W (m·K) −1). Furthermore, the composite films presented extremely low dielectric permittivity and loss tangent. Moreover, the heat resistance index of the composite films (304.6°C) was higher than that of pure PI (294.3°C). Thus, h-BN@Ag/PI composite films could be promising electronic packaging materials. [ABSTRACT FROM AUTHOR]

Intrinsically heat-sealable polyimides with atomic oxygen (AO) resistance (ARPIs) were synthesized from 2,3,3′,4′-oxydiphthalic anhydride (aODPA), 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO), and para -phenylenediamine (PDA). The effects of the molecular structure and diamine ratio were investigated on the properties of the ARPI, including mechanical property, thermal property, heat sealability, and AO resistance. Heat sealability and AO resistance were realized for the ARPI film by combining the asymmetry of the aODPA moiety and the passivated layer forming characteristic of diphenylphosphine phosphine oxide group. Meanwhile, the deficiency of low mechanical strength and thermal resistance, commonly existing in a completely BADPO-derived polyimide system, was remedied effectively by the higher reactivity and rigidity of PDA. [ABSTRACT FROM AUTHOR]

We have successfully prepared reduced graphene oxide/polyimide (RGO/PI) composite films by solution blending method and thermal annealing. The effects of contents of graphene oxides (GOs) and different anneal temperatures were mainly investigated. The oxygen-containing groups on GOs' surface can lead to the formation of hydrogen bonds between GO and PI, which are benefit for GO to disperse in PI uniformly and improve PI properties. The coefficient of thermal expansion decreased drastically from 15.46 μm/(m·°C) to 3.94 μm/(m·°C) within the range of 100–300°C, and the glass transition temperature increased. These improvements can help RGO/PI films resist the high temperature when preparing photoelectric devices and get high-performance flexible photoelectric devices. The elastic modulus of RGO/PI films increased slightly, and tensile strength of RGO/PI films remained the same, while the elongation at break decreased. [ABSTRACT FROM AUTHOR]

A series of polyimide (PI) composite films were prepared using PI as matrix and boron nitride (BN) and aluminum nitride (AlN) as the doped phases. The modification of the thermal conductive filler particles was characterized by Fourier transform infrared (FTIR). The results showed that the silane coupling agent KH550 was successfully coated on the surface of BN and AlN. X-ray photoelectron spectrometer characterization was used to further prove that silane coupling agents were successfully attached to BN and AlN surfaces, forming a new chemical bond. Scanning electron microscope (SEM) was used to analyze the dispersion of filler particles in the matrix. It was found that agglomeration phenomenon occurred when the content of BN particles were high, but this problem was improved after the surface modification of BN. The breakdown field strength and volume resistivity of PI/BN composite film increased first and then decreased with the increase of BN content and reached the maximum when the volume fraction of BN was 5%, which was 191.53 kV/mm and 8.832 × 1013 Ω·m, respectively. When the BN content was 9 vol%, the thermal conductivity of the PI/BN composite film was 0.496 W/(m·K), which was 1.4 times larger than that of the pure PI film. The thermal conductivity of the PI/BN/AlN composite film at the BN and AlN contents of 5 vol% and 1 vol%, respectively, is 0.144 W/(m·K) higher than that of 7 vol% PI/BN. It indicated that the synergistic effect of the composite fillers played a significant role, and at the same time, under the premise of ensuring higher thermal conductivity, the amount of thermally conductive particles could be reduced to some extent. After the surface modification of the filler particles, the properties of the composite film showed the same trend compared with the unmodified one, while the only difference was that there was a certain increase in the numerical value. [ABSTRACT FROM AUTHOR]

In order to obtain colorless and soluble polyimide films, a dianhydride containing 1,4:3,6-dianhydro-D-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And a series of copolyimides were prepared from IMDA, 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), and 4,4′-oxydianiline by adjusting the mole fraction (between IMDA and PMDA) of IMDA from 0% to 100%. It was found that the solubility as well as the transmittance of the copolyimide films enhanced with the increased content of IMDA. Especially, when the content of IMDA was 60% or more, the copolyimides were readily soluble in common polar solvents and could afford flexible, tough, and colorless films with transparency up to 84% at 450 nm, which may be ascribed to the incorporation of the relatively twisted and flexible 1,4:3,6-dianhydro-D-mannitol units into the backbone of copolyimides. Additionally, the influence of IMDA on the thermal, mechanical, and morphological properties of copolyimides was investigated. [ABSTRACT FROM AUTHOR]

A series of polyimide/silica (PI–S) and polyimide/organosilica (PI–OS) hybrid films were prepared via a sol–gel process from mixtures of poly(amic acid) (PAA) and tetraethoxysilane or a silane coupling agent in solution. The PAA was synthesized from bis-(3-phthalyl anhydride) ether and 1,4-bis (4-aminophenoxy) benzene. The hybrid films were produced via an imidization reaction to form silica particles or a silica network in a polymer matrix through a programmed heating process. The derived films were characterized and compared by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, tensile testing, contact angle measurements, moisture absorption measurements, and dielectric property analysis. Both the PI–S and PI–OS hybrid matrixes showed strong regularity with the increasing silica content and greatly improved thermal stability and mechanical properties. Among them, the PI–OS hybrid films possessed superior interphase interactions and were found to have better physicochemical properties. [ABSTRACT FROM AUTHOR]

In this study, a series of porous polyimide films containing benzimidazole units were prepared through a phase separation process. The dibutyl phthalate was selected as porogen. The copolyimides were prepared by the reaction of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride with two diamines of 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) and 4,4′-diaminodiphenyl ether with various molar ratios. The resultant porous polyimide films exhibit optimum cell-size distributions. The effects of BIA on morphology, mechanical, and thermal properties of the porous films were explored. It was found that as the BIA content reached up to 30 mol%, the porous copolyimide film demonstrates remarkable thermal stability and admirable mechanical properties with the glass transition temperature of 294°C, 5% weight loss temperature in argon flow up to 545°C, and a tensile strength of 48 MPa. The incorporation of BIA into the polyimide chains brought the highly rigid structures and strong intermolecular interactions, resulting in the enhancement in the thermal stability and the mechanical properties. [ABSTRACT FROM AUTHOR]

A novel fluorinated ester-bridged aromatic diamine, bis(2-trifluoromethyl-4-aminophenyl)terephthalate (CF3-BPTP) was synthesized, which was employed to prepare a series of fluorinated ester-bridged polyimide (PFEI) films with controlled ester-bridged segments and fluorine contents in the polymer backbone. The PFEI films were prepared by copolymerization of biphenyl tetracarboxylic dianhydride as aromatic dianhydride monomer and the aromatic diamine monomer mixture consisting of p-phenylenediamine and different amounts of CF3-BPTP. Experimental results indicated that the films’ water uptakes (Wus) reduced with increasing of the CF3 groups loadings in the ester-bridged polyimide backbones while keeping the films with low enough coefficient of thermal expansion (CTE). By controlling CF3 group loadings, polyimide films with desirable combination of thermal, mechanical, and dielectric properties for application in high density and thinner flexible printed circuits (FPCs) have been obtained. Thus, polyimide films with CTE of ≤20 × 10−6 1/K (ppm/K) at 50–200°C, glass transition temperature of ≥310°C, Young’s modulus of ≥6.0 GPa, Wu of as low as 0.7 wt%, dielectric constant (ε) of 3.3 have been obtained. The two-layer flexible copper clad laminate prepared by coating the polyimide precursor resin poly(amid acid) solution on the surface of copper foil followed by thermal imidization at elevated temperature did not show apparent curling due to its closed CTE value. [ABSTRACT FROM AUTHOR]

In this research, a novel method for fabricating flexible polyimide foams was developed. The foam was derived from the precursor synthesized via esterification of 3,3′,4,4′-oxydiphthalic anhydride and 4,4′-oxydianiline. After drying process, the remaining solvent acted as blowing agent. By adjusting the synthesis condition, low-molecular weight precursor was obtained and can be foamed under environment temperature. With this novel type of precursor and vacuum-assisted foaming process, we could easily obtain any shape of foams, which was easy to process under relatively low temperature. The foam could be imidized later in order to improve mechanical strength. During the imidization process, in situ Fourier transform infrared (FTIR) analysis was applied to analyze the variation of the imidization percentage with time. The density of the foams could be adjusted from 12 to 30 kg m−3 with uniform cell structure. Other properties of foams were also investigated. The glass transition temperature of the precursor was 70°C, which is obviously lower than that of the usual previously reported. The 5% and 10% weight loss temperatures of the finally imidized foam can reach up to 567°C and 593°C, respectively. The foams belong to open cell structure with 98% open cell content. The limiting oxygen index of the foams varied from 38.6 to 41.9, depending on foam densities. The compressive strength of the foam ranged from 30.6 to 90.6 kPa when the density changed from 15 to 28 kg m−3. In addition, the in situ FTIR analysis was applied to analyze the imidization percentage of the foam during imidization process. [ABSTRACT FROM AUTHOR]

To investigate the effect of terminal groups on the properties of hyperbranched polyimides (HBPIs) for potential optical applications, a series of HBPIs bearing different terminal groups have been synthesized through a novel aromatic CF3-containing tetra-amine, 4,4′-di[3,5-di(2-trifluoromethyl-4-aminophenoxy)phenoxy] sulfone, and a long chain dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane, via a two-step polycondensation procedure. The synthesized HBPIs could form flexible and tough polyimide (PI) films, which exhibit good thermal stability with the glass transition temperatures of 191–234°C for differential scanning calorimetry measurement, the 5% weight loss temperatures of 533–610°C, and residual weights of 45.8–58.6% at 800°C under nitrogen atmosphere. The PI films have favorable mechanical properties with tensile strengths of 77–92 MPa, elongation at break of 3.55–7.99%, and initial modulus of 2.05–2.86 GPa. The films also exhibit the good transmittance of higher than 80% at 800 nm. The average refractive indices (nav) and in-plane/out-of-plane birefringence (Δn) measured at 632.8 nm are in the range of 1.5539–1.6022 and 0.0065–0.0077, respectively. The good transmittance in the visible region, tunable nav, and low Δn are very suitable for optical applications. [ABSTRACT FROM AUTHOR]

To effectively utilize the one-step solvent–thermal route to prepare iron (Fe)–nitrophthalocyanine/magnetite (Fe3O4) hybrid microspheres, we have developed a novel series of flexible Fe3O4/Fe-phthalocyanine (FePc)/polyimide (PI) composite films with various Fe3O4/FePc nanoparticle loadings (15, 27, and 40 wt%) and imidized at different temperatures (200°C and 300°C). The morphology and structure of the composite films were monitored using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the hybrid microspheres were found uniformly dispersed in the polymer matrices without any agglomeration. Mechanical and thermal properties of the composites were also investigated. The observed results indicated enhanced thermal stabilities, dramatically increased tensile modulus, and increased glass transition temperatures of the composite films, with the increment in the content of inorganic nanoparticles. Besides that, the Fe3O4/FePc/PI magnetic films showed higher saturation magnetization (24.33 emu g−1, 27 wt% Fe3O4/FePc loading) with high-temperature treatment compared with that of the Fe3O4/PI film (18.79 emu g−1, 27 wt% Fe3O4 loading). It proved to be an effective way to prevent Fe3O4 nanoparticles from oxidizing by coating the nanoparticles with organic layer. The flexible composite films can easily be moved under a relatively low magnetic field, indicating them to be the high-performance absorbing materials in potential applications. [ABSTRACT FROM AUTHOR]

Glucose has been covalently linked to multiwalled carbon nanotubes (MWCNTs). After that, the modified MWCNTs were added to a poly(amide–imide) (PAI) matrix. PAI-based composites were fabricated by an ex situ blending technique with 5, 10, and 15% of loading by weight. The composite hybrid films were prepared by a solvent-casting method. The structural properties of all hybrids have been characterized using a large variety of spectroscopic and microscopic techniques. It was found that the functionalization of MWCNTs could improve their dispersion and interfacial adhesion to the PAI matrix. The thermal stability of the MWCNT/PAI composite films was improved due to excellent dispersion of MWCNT in the polymer matrix. Tensile tests on the composites showed an increase in the elastic modulus and the yield strength and a decrease in the failure strain. [ABSTRACT FROM AUTHOR]

A series of new polyimides were synthesized by condensation of pyridine-bridged novel diamine monomers, bis(4-aminobenzoyloxy-3,5-dimethyl phenyl)-3′-pyridyl methane and 2,6-bis(2-amino-3-pyridyloxy)pyridine, with various aromatic anhydrides. The monomers and precursors were characterized by elemental analysis, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and carbon-13 nuclear magnetic resonance (13C NMR) spectroscopic techniques. The structure of the polymers were characterized by FTIR and 1H-NMR spectroscopy, and the physical properties of the polymers, including the glass transition temperature (in the range of 199–319°C), thermal and thermo-oxidative stability (10% weight loss temperature is in the range of 375–539°C in air and 403–542°C in nitrogen atmospheres), the char yield in the range of 37.91–56.65% at 800°C, solubility, solution viscosity (0.81–1.81), molecular weight data, optical properties, crystallinity, mechanical properties like tensile strength (86–102 MPa), elongation at break (12.5–16.5%), tensile modulus (1.2–1.8 GPa), and moisture absorption were also studied. [ABSTRACT FROM AUTHOR]

In the past decades, 4-phenylethynyl phthalic anhydride has been the most commonly used endcapper for polyimide (PI). A series of different groups of terminated hyperbranched PIs (HBPIs) were synthesized from 1,3,5-tris(2-trifluoromethyl-4-aminophenoxy)benzene, bis[4-(3,4-dicarboxyphenoxy)phenyl]ether dianhydride, and 4-phenylethynylphthalic anhydride or 4-(1-naphthylethynyl)phthalic anhydride. The glass transition temperatures (Tgs) of the polymers varied from 166°C to 193°C. The 5% weight loss temperatures of polymers were in the range of 548 to 571°C and those of the endcapped HBPIs increased to the range of 600 to 601°C after curing. The PIs exhibited rather low melt viscosity at processing temperature and the complex viscosity increased continuously with the temperature increase. Because there is a large temperature difference between the Tg and cross-linking exothermic temperature, HBPIs provided a wide processing window. [ABSTRACT FROM AUTHOR]

In this article, polyimide (PI) composite films reinforced by graphitic carbon nitride (g-C3N4) have been synthesized using the in situ polymerization process via thermal imidization. Poly (amic acid) (PAA) solutions were prepared from pyromellitic dianhydride (PMDA) and 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy) dianiline (BAPP) in N,N-dimethylacetamide (DMAc) solvent. The different amounts of g-C3N4 obtained from the direct pyrolysis of dicyandiamide (DCDA) at 600°C were incorporated into PAA matrix, which formed g-C3N4/PI composite films by thermal imidization. The morphological structures of the synthesized g-C3N4 and g-C3N4/PI composite films were characterized using fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy and transmission electron microscopy. With 2 wt% g-C3N4 incorporated, the tensile strength and elongation at break of g-C3N4/PI composites were increased by about 23% and 21%, respectively, due to the strong interaction between the g-C3N4 particles and PI. Thermogravimetric analysis indicated that the incorporation of g-C3N4 improved the thermal stability of the PI at low g-C3N4 content. Besides, the dielectric and optical properties of these composites were also studied in this article. [ABSTRACT FROM AUTHOR]

The physicochemical properties of highly fluorinated polyimide blends were studied in order to highlight the advantages of employing a high content of fluorine atoms to tailor the properties of polyimide materials. Thus, dynamo-mechanical analysis was used to evidence the physical phenomena taking place during heating. The trend of storage modulus, loss modulus and loss factor tangent with temperature during and after the α relaxation was explored. The dielectric spectroscopy was carried out to investigate the dielectric behaviour at different temperatures and frequencies and to evaluate the values of dielectric constant, dielectric loss and electrical resistance. The dielectric spectroscopy data were corroborated with the dynamo-mechanical analysis to highlight the sub-glass transitions encountered in these blend films. Dielectric loss diagrams showed sub-glass transitions in the form of γ and β relaxations mainly due to the segmental mobility of the polymer chain components. The gas separation performance of some of the investigated blends was assesed, and their ability to achieve simultaneously higher gas permeability and higher selectivity was demonstrated. [ABSTRACT FROM AUTHOR]

Thermal expansion behavior of polyimide (PI) films based on benzoxazole containing diamine, 5,4′-diamino-2-phenyl benzoxazole (DAPBO), was investigated systematically. Effects of preparation parameters on the values of in-plane coefficient of thermal expansion (in-plane CTE) were studied from the viewpoint of film thicknesses, curing rates, and substrates. It was found that the in-plane CTE values increased as a function of film thicknesses and curing rates, this pattern was also applicable to PI based on DAPBO and pyromellitic dianhydride (PMDA), which showed negative in-plane CTE value. The influence of preparation parameters on in-plane CTEs was interpreted by the effect of residual solvent. Thermogravimetric and dynamic mechanical analyses were used to study the curing process of poly(amic) acid films with various amounts of residual solvent and further to illustrate the effect of residual solvent on in-plane CTE values. In-plane and out-of-plane CTE of PI film based on DAPBO and 3,3′,4,4′-oxydiphthalic dianhydride (ODPA) were directly measured using thermomechanical analysis instrument, and the values were 22.5 and 62.3 ppm K-1, respectively, indicating the orientation character of PI chains along the film plane direction. [ABSTRACT FROM AUTHOR]

New polyimide (PI) films containing zeolite L and/or silica, having a thickness of tens of micrometers, were prepared using a PI matrix with pendant carboxylic groups. The influence of various ratios of inorganic filler on thermal stability, dielectric behavior, and gas transport properties of the films was studied with respect to their structure. The surface morphology was investigated by scanning electron microscopy. The films were flexible, tough, and showed good thermal properties with a glass transition temperature in the range of 187–218°C. The dielectric spectroscopy revealed γ and β subglass transitions having the corresponding relaxation activation energy in the range of 44.7–51.4 kJ mol−1 and 65.1–121.6 kJ mol−1, respectively. At temperatures above 200°C, a conductivity relaxation process was evidenced. Gas permeation tests using small molecules (O2, N2 and CO2), at 6 atm and 30°C, indicated that the PI films containing higher amount of zeolite showed the highest permeability for all gases. [ABSTRACT FROM AUTHOR]

A series of polyimide (PI) films were prepared from a diamine-containing benzoxazole unit (5,4′-diamino-2-phenyl benzoxazole) and five dianhydrides via two-step polymerization process. The PI films showed outstanding mechanical properties with tensile modulus up to 7.3 GPa without preorientation process. According to the results of thermal analysis, the glass transition temperature of the films was up to 412°C, and the films showed good thermodimensional stability. Thermal analysis and wide-angle x-ray diffraction analysis revealed that the PIs were semicrystalline. Excellent properties of these PIs were attributed to the benzoxazole group in the main chain and accordingly to the rigid-rod structure and high level of linearity of the polymer backbones. These results correlate with each other and contribute to our overall understanding of the effects of benzoxazole moiety on the properties of the PI films. [ABSTRACT FROM PUBLISHER]

A series of porous polyimide (PI) films were prepared by decomposing PI/poly(methyl methacrylate) (PMMA)-blended films at appropriate high temperature for a certain period of time in air. The pore-forming agent, PMMA, was blended with poly(amic acid) (PAA) by in situ blending method. As a thermally labile polymer, PMMA was decomposed first to generate substances with low molecular weight, leaving holes in the original location. Fourier transform infrared (FT-IR) spectra were used to characterize the changes in the chemical structure during the process of preparation of porous PI films. The porous morphology was investigated using field emission scanning electron microscopy. Using FT-IR and thermogravimetric analysis, it was confirmed that PMMA disappeared completely after 4 h at 330°C in air. Thus, porous PI films with major differences between surface and bottom morphologies were prepared successfully. The average pore size of the porous films increased with increasing content of PMMA but was not larger than 1 μm. [ABSTRACT FROM AUTHOR]