Properties Of Polyimides Research Articles

Understanding the Effect of the Dianhydride Structure on the Properties of Semiaromatic Polyimides Containing a Biobased Fatty Diamine.

In this work we report the effect of the hard block dianhydride structure on the overall properties of partially biobased semiaromatic polyimides. For the study, four polyimides were synthesized using aliphatic fatty dimer diamine (DD1) as the soft block and four different commercially available aromatic dianhydrides as the hard block: 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride) (BPADA), 4,4′-oxidiphthalic anhydride (ODPA), 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA). The polymers synthesized were fully organo-soluble thermoplastic branched polyimides with glass transition temperatures close to room temperature. The detailed analysis took into account several aspects of the dianhydrides structure (planarity, rigidity, bridging group between the phtalimides, and electronic properties) and related them to the results obtained by differential scanning calorimetry, rheology, fluorescence and broadband dielectric spectroscopy. Moreover, the effects of physical parameters (crystallization and electronic interactions) on the relaxation behavior are discussed. Despite the presence of the bulky branched soft block given by the dimer diamine, all polyimides showed intermolecular charge transfer complexes, whose extent depends on the electronic properties of the dianhydride hard block. Furthermore, the results showed that polyimides containing flexible and bulky hard blocks turned out fully amorphous while the more rigid dianhydride (BPDA) led to a nanophase separated morphology with low degree of crystallinity resulting in constrained segmental relaxation with high effect on its mechanical response with the annealing time. This work represents the first detailed report on the development and characterization of polyimides based on a biobased fatty dimer diamine. The results highlight the potential of polymer property design by controlled engineering of the aromatic dianhydride blocks.

Synthesis, gas barrier and thermal properties of polyimide containing rigid planar fluorene moieties

ABSTRACTIn order to obtain pristine polyimides with high barrier properties, pyromellitic dianhydride (PMDA) and 9H-fluorene-2,7-diamine (FDA) containing rigid planar fluorene moieties were used to prepare polyimide (FPI) via a conventional two-step polymerization process in this paper. The synthesized polyimide shows good barrier properties, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 1.01 cm3 m−2 day−1 and 2.35 g m−2 day−1, respectively. The effect of rigid planar structure in main chain on the barrier properties of polyimide was studied by means of wide angle X-ray diffractograms (WAXD), molecular dynamics simulations and positron annihilation lifetime spectroscopy (PALS), which was rarely reported before. The results reveal that the good barrier properties of FPI are mainly due to the high crystallinity, high chain rigidity and low free volume, which are resulted from the rigid planar structure. Additionally, the polyimide exhibits excellent thermal and dimensional stability with 5 wt% loss temperature of 519°C, glass transition temperature of 370°C and coefficient of thermal expansion (CTE) of 5.72 ppm/K. The good gas barrier and thermostability endow the polyimide with promising potential in flexible electronics encapsulation applications.

Simulating local mobility and mechanical properties of thermostable polyimides with different dianhydride fragments

ABSTRACTThe dynamic and mechanical properties of the three thermoplastic polyimides—crystallizable polyimide BPDA‐P3 and amorphous polyimides ODPA‐P3 and aBPDA‐P3—have been simulated using the atomistic molecular dynamics technique. The three simulated polyimides differ in the chemical structure of their corresponding dianhydride fragments. Analyzing the local orientational mobility of different phenylene rings, it has been established that the increase of the glass‐transition temperature (Tg) in the ordered set is caused by the slowing down of the phthalimide rings relaxation in the corresponding dianhydride fragments. It has been observed that rather poor mechanical characteristics upon aBPDA‐P3 stretching in the strain‐hardening regime are also due to the low orientational mobility of the phthalimide rings. The correlation between the dynamic fragility and the polyimides strain‐hardening moduli has been observed; the increase of the dynamic fragility leads to the increase of the strain‐hardening modulus. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 375–382

Synthesis, characterization, and properties of thermoplastic polyimides derived from 4,4’-(hexafluoroisopropylidene)diphthalic anhydride in diethylene glycol dimethyl ether

By regulating the order of monomer addition, four kinds of copolymer polyimides (PIs) were prepared using diethylene glycol dimethyl ether (DEGDE) and N, N-dimethylacetamide (DMAc) as the solvents. The molecular weights of polyamide acids (PAAs) ranged from 3.8 × 105 to 9.2 × 105. All of the films displayed high glass transition temperatures ( Tgs) ranging from 313°C to 346°C. The polymer films show excellent thermal stabilities with 5% weight loss at temperatures of 505–524°C and char yields at 800°C were as high as 55% under nitrogen. The peel strengths of flexible copper (Cu) clads were in the range from 0.337 N cm−1 to 0.598 N cm−1. Compared to the molecular weight and peel strength of fresh PAA, those of PAAs prepared using DMAc significantly decreased after storage for 3 months at 0°C. However, when DEGDE was used as the solvent, the molecular weights of the PAAs and the thermal properties of the PIs were maintained after long storage time.

Colorless polyimides derived from isomeric dicyclohexyl-tetracarboxylic dianhydrides for optoelectronic applications

Two isomers of conventional cis-dicyclohexyl-3,3′,4,4′-tetracarboxylic dianhydride (4,4′-HBPDA), i.e. dicyclohexyl-2,3′,3,4′-tetracarboxylic dianhydride (3,4′-HBPDA) and dicyclohexyl-2,2′,3,3′-tetracarboxylic dianhydride (3,3′-HBPDA), were prepared through a four-step procedure. The data from single crystal X-ray diffraction revealed that 3,3′-HBPDA possessed higher structural rigidity/linearity than 4,4′-HBPDA. The one-step polycondensation of isomeric HBPDAs with commercial diamines enabled the synthesis of alicyclic polyimides. The isomer effects of the dianhydrides on the properties of resulting polyimides were studied in detail. For certain diamines, 3,3′-HBPDA-derived polyimides possessed higher glass transition temperatures (Tg) and better dimensional stability compared with those from 4,4′-HBPDA and 3,4′-HBPDA. These phenomena could be attributed to the higher structural rigidity/linearity of 3,3′-dicyclohexyl-tetracarboxydiimide, and restricted rotation of 3-substituted cyclohexylimide. Owing to the asymmetric structures and suppressed rotation of 3-substituted cyclohexylimides, 3,4′-HBPDA-based polymers exhibited higher Tg, improved dimensional stability, and enhanced solubility compared with 4,4′-HBPDA-based ones. Furthermore, all the isomeric HBPDA-derived polyimides were essentially colorless with excellent optical transparency in the UV–Visible region. The excellent overall properties of polyimides from 3,3′-HBPDA and 3,4′-HBPDA made them promising candidate materials for optoelectronic applications.

The effect of N-doped quantum dots on the properties of in situ prepared colorless polyimide nanocomposite films

Conventional polyimide nanocomposites reinforced with graphene-based nanofillers usually possess excellent properties, such as high thermal decomposition temperature, enhanced tensile strength, tensile modulus, etc. However, the elongation at break of the nanocomposites is reduced. Here, we prepared N-doped graphene quantum dots/colorless polyimide nanocomposite (N-GQDs/CPI) films for the first time by in-situ polymerization, whose elongation at break is about 2 times that of the pure film. Meanwhile, the thermal properties and other mechanical properties of the films are improved. Through analyzing FT-IR, XPS, XRD, TAG SEM, etc. of N-GQDs and the films, we consider that the strengthening mechanism of matrix performance is attributed to N-GQDs' well dispersion, its small size effects and strong interface interaction with the matrix. Furthermore, at the indicative wavelength of 550nm, the optical transmittance of the film with 1wt% N-GQDs still maintains 79%, indicating the resulting films have excellent optical transmittance. The hydrophilic properties of the prepared films' surface is reduced, their water surface contact angle are increased from 63±2.7° to 92±1.7° with the content of N-GQDs increasing. This research shows that N-GQDs can enhance the various properties of polyimide and provides a high performance nanocomposite films for potential flexible substrates.

Antifouling polyimide membrane with grafted silver nanoparticles and zwitterion

Abstract In order to improve the antibacterial and antifouling properties of polyimide (PI) membrane, both silver nanoparticles (AgNPs) and zwitterionic sulfobetaine methacrylate (SBMA) are grafted onto PI membrane surface via a two–step modification route. The reaction mechanism involved, as well as changes in the membrane morphology and surface properties are investigated via various characterization techniques. The antibacterial performance is assessed by the zones of inhibition and bacterial suspension immersion tests. The antifouling property of the modified membrane is evaluated via the filtration test using the bovine serum albumin (BSA) and dodecyl trimethyl ammonium bromide (DTAB) aqueous feed solutions. The results show that, the modified PI membrane exhibits significantly improved antibacterial and antifouling performances simultaneously.

Effect of diamond blend on the gas-separation properties of composite membranes

The morphological structure and gas transport properties of polyimide- and polyamide-imidebased rigid-chain polymers containing a fine carbon filler (a diamond blend) are studied. Gas transport properties are measured, and the effect exerted on these properties by intermolecular interaction between the functional groups of polymer chains and the fine filler is analyzed.

Improving mechanical, thermal, and electrical properties of polyimide by incorporating vinyltriethoxysilane functionalized graphene oxide

Functionalized graphene oxide (FGO) nanosheets were produced by reacting graphene oxide with vinyltriethoxysilane (VTES). The vinyltriethoxysilane graphene oxide and polyimide (VGO/PI) composites were prepared by solution blending method. In comparison with the pristine polyimide (PI) and graphene oxide/polyimide (GO/PI) composite, VGO showed better mechanical, electrical and thermal properties. The tensile strength of VGO/PI composite with 0.8 wt% VGO loading was up to 148 MPa, i.e., 105% higher than that of pure PI. The respective electrical and thermal conductivity values of composite were found 2.15 × 10−3 S/m and 0.89 W/mK as compared to 1.21 × 10−12 S/m and 0.13 W/mK for the pure PI. The thermal stability of composite was found to improve with the addition of VGO. Significant improvement in the properties has been explained in terms of homogeneous dispersion of VGO in the matrix and its strong interfacial adhesion with polymer due to surface modification of GO. POLYM. COMPOS., 39:E1635–E1642, 2018. © 2017 Society of Plastics Engineers

Chemical and Electrical Dynamics of Polyimide Film Damaged by Electron Radiation

The processes of electrical charge accumulation and dissipation in dielectric materials are critical to spacecraft construction and operational anomaly resolution. Electrical conductivity, and therefore surface potential, of radiation-damaged materials undergoes unpredicted changes while on orbit. The space environment causes fundamental modifications in the chemical structure of spacecraft materials by breaking intermolecular bonds and creating free radicals that act as space charge traps. Over time, free radicals react with each other and the material recovers. The rates of free radical formation and loss determine the dynamics of the conductivity of spacecraft materials. Lack of knowledge about dynamic aging is a major impediment to accurate modeling of spacecraft behavior over its mission life. This paper presents an investigation of the chemical and physical properties of polyimide (PI) films during and after irradiation with high-energy (90 keV) electrons. The constant voltage method was utilized to monitor material conductivity during the recovery process. To quantify the concentration of free radicals within the irradiated material, the electron paramagnetic resonance technique was used. Changes in the infrared (IR) absorption profile of irradiated materials during the recovery process were identified using the directional-hemispherical reflectance technique coupled with the Fourier transform IR spectroscopy. This physical/chemical collaboration allowed correlation of chemical changes in PI with the dynamic nature of spacecraft material aging.

Electrical, Mechanical, and Thermal Properties of Mg(OH)2/PI Nanocomposite Films

Nano-Mg(OH)2 particles were prepared by reverse precipitation. Nano-Mg(OH)2/PI composite films with varying contents of Mg(OH)2 were successfully prepared by in situ polymerization and thermal imidization. The surface morphology, thermal stability, and the mechanical and dielectric properties of the films were characterized. Results indicated the following: the nanoparticles were homogeneously dispersed in the matrix, thermal stability was reduced, and the Young’s modulus of PI-3% was 2851.6 N/mm2 and increased by 155% relative to that of neat PI. The real and imaginary parts of relative permittivity increased, and electric modulus formalism was introduced to determine the dielectric relaxation behavior of the composites in the study. The result from the Cole–Davidson semicircle showed that the increase in nano-Mg(OH)2 concentration led to an increase in the inhomogeneous distribution of relaxation time. Direct current illustrates that the activation energy of the hopping process exhibits an increasing trend. The aging threshold increased in accordance with the theory of space-charge limited current. Breakdown increased to 323 kV/mm, whereas the pure film was is 292 kV/mm, and the electric property of polyimide improved.

Influence of the Composition and Imidization Route on the Chain Packing and Gas Separation Properties of Fluorinated Copolyimides

A strong effect of the chemical composition and imidization method on physical and especially on gas transport properties of polyimides was demonstrated. Two fluorinated diamines 6FpDA and bisAPAF were polymerized in different ratios, employing the fluorinated dianhydride 6FDA to get polyimides with nine different compositions. For all synthesized materials three imidization methods were used: azeotropic, thermal, and chemical. The 6FDA-6FpDA homopolymers showed significant differences in the gas transport properties, indicating the influence of the imidization route on the final properties of the polyimides. For polyimides containing bisAPAF, the chemical composition played an important role due to the exchange of the hydroxyl groups by acetate groups leading to different interchain interactions. The gas transport was mainly controlled by the chain packing for thermally and azeotropically imidized polymers with bisAPAF contents lower than 30 mol %. For bisAPAF contents above 50 mol % the gas transport wa...

Preparation and Thermal Properties of Silicon-containing Polyimide Composite Films

Aromatic polyimide is a kind of polymer material with high temperature resistance, low temperature resistance, radiation resistance, excellent chemical stability, excellent electrical properties and good mechanical strength. It has been widely used in aerospace, electrical and electronic fields. At present, the synthesis, properties and application of polyimide containing silicon is one of the hot spots in the research field of polyimide. The processing property of polyimide can be greatly improved by introducing silicon group or polysiloxane segment into the main chain structure. And it has been given a good solubility, permeability, impact resistance, UV resistance and anti-degradation in oxygen rich environment. The introduction of siloxane chain segments or silicon containing groups in polyimide framework can enhance the adhesion between polyimide and inorganic materials, including the adhesion of metal materials and other substrates. A variety of polyimide hybrid materials can be prepared by the excellent bonding properties. A series of polyimide / silicon containing polyimide / BaTiO3 nanocomposite films were prepared and their structures and properties were studied in this paper. In addition, the preparation, structure and properties of polyimide / mesoporous silica composite films were studied. Silicon containing polyimide/silane mesoporous silica composite films have low infrared emissivity compared with bulk polyimide. Under the same content of mesoporous silica, the composite films prepared by copolymerization have lower infrared emissivity. Moreover, the infrared emissivity decreases with the increase of the content of silica. In short, silicon containing polyimides and their composite films with excellent performance differ from other traditional polyimides, and it has broad application prospects in the technological field of aerospace, electrical and electronic, gas separation, absorbing material preparation.

Electrical properties of flexible graphene reinforced polyimide composites

ABSTRACTThe electrical properties of polyimide and the composite at different volumes fractions were studied in the frequency range 200–20 kHz and in the temperature range 30–200 °C. Increasing the volume fraction of graphene up to 10%, resulted in an extremely large increase in the dielectric constant, which indicates the composites remarkable ability to store electric potential energy under the effect of alternating electric field. An increase in dielectric constant was also observed with increasing temperature and decreasing frequency. The outstanding dielectric properties of polyimide graphene nanocomposites are attributed to the large volume fraction of interfaces in the bulk of the material. The measured increase in dielectric constant with increasing temperature was attributed to the segmental mobility of the polymer chains. The AC conductivity for polyimide and the composites was calculated from the loss factor and a remarkably high conductivity was obtained for the composites due to the formation of conducting paths in the matrix by the graphene sheets. Also this study showed that the thermal conductivity of the composites increased sharply with increasing graphene concentration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45372.

Effect of imidization process on the performance of PI/nano-Al2O3 three layer composite film

PurposeThe purpose of this paper was to comprehensively understand the effects of imidization process on the structure and properties of polyimide (PI) films through the preparation and characterization of a variety of PI/aluminium oxide (Al2O3) nanocomposite films by using several imidization-based strategies.Design/methodology/approachPoly(amic acid) (PAA) containing different amounts of inorganic materials (namely, 0 Wt.%, 4 Wt.%, 8 Wt.%, 12 Wt.% and 16 Wt.%) was synthesized by using pyromellitic dianhydride and 4,4-diaminodiphenyl ether as raw material and N,N-dimethylacetamide as solvent. Subsequently, the solution obtained was casted on a glass substrate and dried by the means of various curing processes. The micro-structure, Fourier transform–infrared spectral features, breakdown field strength, dielectric properties and the corona-resistant time parameters of films were achieved.FindingsThe imidization process influences substantially the properties of composite films. Therefore, as the imidization rate is increased, the corona-resistant time and the electrical breakdown strength of composite films are also improved, while the dielectric constant faces a+ decreasing.Research limitations/implicationsIn this paper, the impact of imidization process on the performance of PI/nano-Al2O3 three-layered composite film is reported. However, there are multiple factors governing these systems (such as, interlayer thickness ratio and humidity), which are not discussed herein.Originality/valueThe current study expounds the relationship between imidization ratios as well as the effect of imidization ratio on the performance of the film.

Synthesis and properties of chloro-containing polyimides

A number of soluble chloro-containing (co)polyimides are synthesized by the one-step high-temperature polycondensation in m-cresol. The obtained (co)polymers are characterized by high heat resistance and thermal stability: 285–350 and 515–565°C, respectively. It is shown that these (co)polymers containing chlorine atoms in benzene rings and hexafluoropropylidene and cardo groups are soluble in a number of common organic solvents and form with light wavelength up to 440 nm transparent films with high stress–strain characteristics.

An investigation on the graphitic carbon nitride reinforced polyimide composite and evaluation of its tribological properties

ABSTRACTThis article presented a novel application for the graphitic carbon nitride (g‐C3N4), which was used as nanofillers to improve the tribological properties of polyimide (PI). The composite based on PI and g‐C3N4 was prepared by mechanical mixing process and hot compression molding process. The characterizations of g‐C3N4 and PI/g‐C3N4 composites were investigated by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Friction and wear tests were carried out using UMT‐2 reciprocating tribo‐tester against stainless steel ball under dry friction. The results showed that the amount of g‐C3N4 was decisive to the tribological properties of PI/g‐C3N4 composites. The optimal tribological properties occurred when the amount of g‐C3N4 was 10 wt %, which showed the smallest friction coefficient and the lowest wear rate. Furthermore, this work provided an example of application for the g‐C3N4 as the excellent nanofiller in polymer matrix composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45403.

The electrical, mechanical and thermal properties of Mg(OH)2/ZnO/PI nanocomposite films

Nano Mg(OH)2/Zn(OH)2 particles were prepared using a reverse precipitation method, and nano Mg(OH)2/ZnO/PI composite films with different mass contents of Mg(OH)2/ZnO were successfully prepared using in-situ polymerization and thermal imidization. The surface morphology, thermal stability and dielectric properties of the films were characterized and discussed. Several results were obtained: the nanoparticles were homogeneously dispersed in the matrix; the thermal stability was decreased; the relative permittivity and dielectric loss were increased; and the Young’s modulus of PI-4% was 2226 MPa, having increased by 99% compared to the neat PI. This paper introduces the formalism of the electric modulus in order to research the dielectric relaxation behavior of the composites studied, and the result from the Cole–Davidson semicircle show that the increase of nano Mg(OH)2/ZnO concentration led to an increase in the inhomogeneous distribution of the relaxation time. According to the theory of space charge limited current, the aging threshold was increased, the breakdown was increased to 296.6 kV/mm, the pure film was 271.1 kV/mm, and the electric property of polyimide was improved.

Conductive mechanism of carbon black/polyimide composite films

Abstract During the fabrication of black polyimide composite films, it is common to introduce carbon black (CB) into this composite system. The introduction of CB significantly decreases the resistivity of the films and consequently has a great effect on the inherent insulation property of polyimide. Here, the exploration of the conductive mechanism of CB/polyimide composite films is aimed to explain the change on resistivity fundamentally. In this study, two kinds of representative CBs were chosen to prepare CB/polyimide composite films. The rudiment of the conductive mechanism was built up based on the resistivity curves, and scanning electron microscopy (SEM), tensile, thermal gravimetric analysis, Fourier transform infrared (FT-IR) spectroscopy, UV, Raman and X-ray diffraction (XRD) were conducted to confirm it. The experimental results further verified the mechanism and gave us a chance to propose an integrated conductive mechanism including three sections (tunneling effect mechanism, conductive network mechanism and doping mechanism) for CB/polyimide composite films. As the conductive mechanism has been understood, it paves the way for optimization of the fabrication of conductive black polyimide films and insulating black polyimide films, even other colorful polyimide composite films.

Barrier and thermal properties of polyimide derived from a diamine monomer containing a rigid planar moiety

AbstractAn aromatic polyimide (3,6‐CPI) was prepared by the polymerization of pyromellitic dianhydride and diamine (3,6‐CDA) containing a rigid planar carbazole moiety. The synthesized polyimide shows outstanding barrier properties with oxygen permeation rate and water vapor permeation rate low at 7.9 cm3 m−2 day−1 and 9.8 g m−2 day−1, respectively. Wide angle X‐ray diffraction, positron annihilation lifetime spectroscopy and molecular dynamics simulations reveal that the excellent barrier properties of 3,6‐CPI are mainly due to the crystallinity and low free volume of the polymer, which result from the rigid planar backbone structure and strong interchain hydrogen bonding. In addition, the polyimide exhibits excellent thermal stability and favorable mechanical properties with a 5 wt% weight‐loss temperature of 559 °C in nitrogen, a glass transition temperature (Tg) of 397 °C and a tensile strength of 115.4 MPa. The as‐synthesized polyimide shows potential packaging applications in the field of flexible electronics and displays, flexible and thin film photovoltaics, and light‐emitting diodes. © 2017 Society of Chemical Industry