Thermal Stability Of Polyimide Research Articles

Effect of chemical structures and environmental factors on the thermal degradation mechanism of polyimide: Experiments and molecular dynamics simulations

The impact of chemical structure and environment on the thermal stability of polyimide (PI) was examined, and the degradation mechanism was determined using a combination of experiments and molecular simulations. Changes in mechanical properties and thermogravimetric analysis (TGA) were used to characterize the thermal stability of PI. Pyrolysis gas chromatography mass spectrometry (Py-GCMS) and thermogravimetric-infrared spectroscopy (TG-IR) were used to analyze the degradation products both qualitatively and quantitatively. Molecular simulation was employed to analyze the primary bond breakage and thermal degradation pathways of PI, as well as to investigate the effects of the chemical structure, atmosphere, and temperature on degradation properties. The findings indicated that p-benzene-structured 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (PDA) has the best thermal stability, whereas weak bonds like C–O–C in 4,4′-oxydianiline (ODA) and C–N in the 2-(4-aminophenyl)-1H-benzimidazol-5-amine (BIA) imidazole group decrease thermal stability. The formation path of low molecular weight products (CO2, CO, HCN, and NH3) and the potential degradation mechanism of PI were proposed. The process of PI thermal degradation accelerated by oxygen and high temperature was observed at the atomic level. Taken together, this work offers the possibility of monitoring the structural evolution of PI degradation process in real-time.

Preparation and characterization of silver self-metallization on polyimide

In this work, silver (Ag) self-metallization on a polyimide (PI) film was prepared through autocatalytic plating. PI films were prepared through the solution casting method, followed by etching with potassium hydroxide (KOH) solution, sensitization with tin chloride (SnCl2), and the use of palladium chloride (PdCl2) to activate the surface of PI. Energy-dispersive X-ray analysis (EDX) showed the highest peak in the (Ag) region and confirmed the presence of AgNPs. The diffraction peaks at 2θ = 38.2°, 44.5°, 64.6°, and 78.2° represented the 111, 200, 220, and 311 planes of Ag, respectively. The FT–IR analysis for Ag-metalized PI showed that the =C-O-C= stretching absorption bands at 1735 cm−1 had no changes in position, only a significant difference in peak size at the deposition time increase. The formation of new bands (N–H stretching absorption band and N–C stretching band) assigned at 2325 and 955 cm−1 indicated strong coordination between N atoms and silver nanoparticles. The C–C stretching and = C–H plane vibration band at 1488 and 1117 cm−1 are shifted to 1413 and 1112 cm−1, indicating the silver nanoparticles' interaction with the polymer backbone. The thermal stability of PI- and Ag-metalized PI films at various deposition times (5, 10, and 15 min) was examined using thermogravimetric analysis (TGA). For PI, T0, T5, T10, and Tmax were observed to be 388°C, 402°C, 414°C, and 515°C, respectively. When the deposition time increased, the thermal stability increased. As a function of the deposition, the thickness and surface morphology of the copper layer on the PI films were characterized using scanning electron microscopy (SEM).

Characterization and thermal degradation kinetics of thermoplastic polyimide based on BAPP

Two kinds of thermoplastic polyimides (PIs) were synthesized via a two-step method with 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4′-oxydianiline (ODA) diamine, and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and their thermal degradation kinetics was studied by thermogravimetric analysis at different heating rates under nitrogen. Derivative thermogravimetric analysis curves indicated a simple, single-stage degradation process in PI BTDA-BAPP and a two-stage degradation process in PI BTDA-ODA-BAPP. The activation energies ( Eas) of the thermal degradation reaction were determined by the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods without a knowledge of the kinetic reaction mechanism. By comparing the values of Ea and weight loss temperatures, it was demonstrated that the thermal stability of PI BTDA-ODA-BAPP was superior to that of PI BTDA-BAPP.

High thermal stable polyimide resins derived from phenylethynyl-endcapped fluorenyl oligoimides with low melt viscosities

To improve the processability and thermal stability of polyimide, a series of novel phenylethynyl-endcapped oligoimides (PEPA-oligoimides) with calculated molecular weights (MnC) were successfully prepared from thermal imidization of 4,4’-(9-fluorenylidene) dianiline (BAFL) as fluorenyl diamine, 4,4′-oxy-diphthalic anhydride (ODPA) as aromatic dianhydride and 4-phenylethynylphthalic anhydride (4-PEPA) acted as reactive end-capping reagent at elevated temperatures. Experiment results indicated that the oligoimides were the mixtures of PEPA-endcapped oligomers with different degrees of polymerization characterized by MALDI-TOF mass spectra. The influence of chemical structures on the melt processabilities of the oligoimides, the thermal, dielectric and mechanical properties of the thermoset resins was studied. The typical oligoimide resin owned minimum melt viscosity of 0.2 Pa·s at around 310 °C and wide melting processing window, suitable for resin transfer molding (RTM). Besides, its corresponding thermal-cured polyimide resin possessed glass transition temperature (Tg) as high as 514 °C. The dielectric constants of polyimide resins decreased from 3.15 to 2.80 by reducing the MnC. The mechanical properties of the polyimide neat resins were improved gradually with increasing MnC. Finally, the carbon fiber/polyimide (Cf/PI) composite laminates showed excellent mechanical strength retention rate at 350 °C, might be long-term served at extremely high temperature in aerospace and aviation field.

Synthesis and characterization of polyimide thin films obtained by thermal evaporation and solid state reaction

AbstractIn this research polyimide films were prepared by physical vapor deposition (PVD), using solid state reaction of pyromellitic dianhydride (PMDA) and p-phenylene diamine (PDA) to form poly(amic acid) (PAA) films. The resultant films were converted to polyimide by thermal treatment, usually below 300 °C. For this study, a FT-IR spectrometer has been used to measure the effect of imidization temperature on the chemical structure of the vapor-deposited thin films of aromatic PI. When temperature increased, an increase in all absorption peaks was observed. This suggests that residual PAA monomers continued to be converted into PI. The surface topology of the PI films obtained at imidization temperatures of 150, 200, 250 °C for 1 hour was further examined by using AFM atomic force microscopy. It can be clearly seen that the surface became rougher with increasing imidization temperature. The thermal stability of polyimide was also studied by using thermogravimetric analysis (TGA).

Preparation and characterization of mechanically and thermally enhanced polyimide/reactive halloysite nanotubes nanocomposites

High modulus and thermal stability of polyimide (PI)/reactive halloysite nanotubes (HNTs) nanocomposites were prepared by in situ polymerization. The pristine HNTs were firstly handled with the tetraethoxysilane (TEOS) and secondly grafted with the silane agent. The fourier transform infrared spectroscopy (FTIR) approved that TEOS was beneficial for the silane agent to modify the HNTs. Scanning electron microscopy (SEM) showed the differences of the morphology between the reactive HNTs and pristine HNTs. PI/reactive HNTs nanocomposites exhibited lower moisture absorption than pure polyimide. The reactive HNTs reduced the transmittance of the nanocomposites. Significant improvements in the thermal stability and glass transition temperature (Tg) of PI/reactive HNTs nanocomposites were achieved by addition of only a small amount of reactive HNTs. It was noteworthy that both the tensile strength and Young' modulus of PI/reactive HNTs nanocomposites were significantly enhanced. A 62.8 % increase in tensile strength and a 63.7 % increase in Young' modulus of the nanocomposites with 3 wt.% of the reactive HNTs were achieved. Finally, the preparation mechanism to obtain PI/reactive HNTs nanocomposites was proposed.

In situ Synthesis and mechanical, thermal properties of polyimide nanocomposite film by addition of functionalized graphene oxide

Polyimide (PI) and chemical modified graphene oxide nanocomposite films are prepared by in situ polymerization from solutions of pyromellitic dianhydride and 4,4′‐oxydianiline with various amount (0.5–2 wt%) of 3‐aminopropyltriethoxysilane (APTS) functionalized graphene oxide (GO) sheets in dimethylacetamide. The APTS functionalized GO (GO‐APTS) is a versatile platform for polymer grafting, improving excellent dispersion of GO in the PI matrix, and forming strong interaction with the PI matrix. The GO‐APTS/PI nanocomposites exhibited improvement in mechanical and thermal properties by addition of a small amount of GO‐APTS. With the addition of a small amount of GO‐APTS (1.5 wt%) to PI matrix, mechanical properties with the tensile strength and Young's modulus improved by 45% and 15%, respectively. The thermal analysis showed that the thermal stability of PI was slightly enhanced by the incorporation of GO‐APTS (1.5 wt%). This approach provides a strategy for developing high performance functionalized GO‐polymer composite materials. POLYM. COMPOS., 37:907–914, 2016. © 2014 Society of Plastics Engineers

Synthesis and characterisation of novel soluble polyimides for the application as liquid crystal vertical alignment layers

A new triphenylamine-based functional diamine monomer named N, N-bis (4-aminophenyl)-4-(nonyloxy-biphenyl)-4′-aminophenyl ether (N9) was successfully synthesised from cesium fluoride-mediated N,N-diarylation of 4-(nonyloxy-biphenyl)-4′-aminophenyl ether with p-fluoronitrobenzene and subsequent reduction of the resultant dinitro compound. A series of polyimides (PIs) with triphenylamine (TPA) moieties were prepared from the newly synthesised diamine monomer, 3,3′-dimethyl-4,4′-methylene-dianiline and 4,4′-oxydiphthalic anhydride through a conventional two-step procedure that included a ring-opening polyaddition to give polyamic acids, followed by chemical cyclodehydration. The PIs were completely amorphous and exhibited good solubility in organic solvents. PI films attained from a casting method showed high transmittance above 90% in the wave length range of 400–700 nm and could align liquid crystals vertically before and after rubbing treatment. The PIs derived from N9 exhibited much higher thermal stability compared with the corresponding PIs from 4-dodecyloxy-biphenyl-3′,5′-diaminobenzoate (D12). The results demonstrated that the introduction of TPA units into the polymer backbone could largely enhance the thermal stability of PIs while sustaining its solubility.

Synthesis and electrochromic properties of polybismaleimides containing triphenylamine units

The bismaleimide (BMI) monomer containing triphenylamine was prepared firstly. Then BMI was reacted with different diamines by Michael addition to obtain prepolymers, respectively. Finally, polyimides (PIs) were obtained through melting procedure. The effects of the structure of BMI moiety and thermal curing condition on thermal stability of PIs were studied by thermogravimetric analysis. PIs have excellent processing properties for film casting. Cyclic voltammetry of PI films was carried out on an indium-doped tin oxide-coated glass substrate. Results which exhibit two reversible oxidations at 0.71–0.78 and 1.06–1.16 V vs Ag/AgCl. The electrochromic performance was investigated by spectroelectrochemical methods. These anodically coloring polymer films not only showed good electrochromic properties but also exhibited high optical contrast ratio of transmittance with a color changing from yellow to green. After 100 cyclic switches, the polymer films still retained excellent redox and electrochromic activity.

Effects of tert-butyl substitutes of fluorinated diamine on the properties of polyimides

To investigate the effect of tert-butyl substitutes on the properties of fluorinated polyimides (PIs), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1), 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2- tert-butylbenzene (2), and 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di- tert-butylbenzene (3), which were synthesized in this study. Three series of organosoluble and light-colored PIs were synthesized from 1, 2, and 3 with four dianhydrides 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), pyromellitic dianhydride, 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, and 4,4′-oxydiphthalic anhydride and prepared through a typical two-step polymerization method. These obtained PIs with tert-butyl substituents were soluble in amide polar solvents and even in less polar solvents. The glass transition temperatures ( Tg) of PIs with two tert-butyl substitutes can be reached at 327.7°C, and the 5% weight loss temperatures of PI derived from CBDA were lowest at 439.7°C. These PI films had cutoff wavelengths between 301.2 and 400.0 nm and the transparency at 450 nm between 43.0 and 86.2%. Compared with diamine 1, we found that the introduction of tert-butyl side group of the diamine improved the solubility and Tg of PIs, but decreased the optical transmittance and thermal stability of PIs.

A study of the stabilization of vertical alignment for liquid crystals by increasing the side-chain rigidity of polyimides

A series of polyimides (PIs) with various side-chain structures were prepared via copolymerization of pyromellitic dianhydride, 3,3′-dimethyl-4,4′-methylenediamine and three functional diamines: 4-(4-octyloxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C8-BPDA), 4-octyloxybiphenyl-3′,5′-diaminobenzoate (C8-PDA) and 4-(4-butoxybenzoyloxy)biphenyl-3′,5′-diaminobenzoate (C4-BPDA). PIs derived from C8-BPDA and C4-BPDA exhibited excellent rubbing resistance in comparison with PI from C8-PDA and the pretilt angle could be controlled over 89° after rubbing. Thermogravimetric analysis showed that the thermal degradation of PIs under nitrogen atmosphere occurred above 320 °C, and PI derived from C8-BPDA showed the best thermal stability. Wide-angle X-ray diffraction patterns indicated an amorphous morphology of the PIs, and the PIs also had outstanding solubility in polar aprotic solvents. The resultant PI films were light colored and maintained high transparency in the visible light region. By increasing the rigidity of side-chains, the rubbing resistance and the thermal stability of PIs could be promoted at the same time. © 2012 Society of Chemical Industry

Fabrication of polyimide/titania nanocomposites containing benzimidazole side groups via sol–gel process

In recent years, polyimide (PI) hybrid materials have received considerable attention owing to the dramatic enhancements over their pristine state in thermal stabilities, mechanical properties and other special features by introducing only a small fraction of inorganic additives. In this investigation, hybrid nanocomposite films of titanium dioxide (TiO2) in PI were successfully fabricated by an in situ sol–gel process starting from tetraethyl orthotitanate in the solution of poly(amic acid) in N,N-dimethylacetamide. Neat PI was prepared from the polymerization of 2-(3,5-diaminophenyl)-benzimidazole and pyromellitic dianhydride. The hybrid films were obtained by the hydrolysis–polycondensation of moisture-sensitive titania precursor in poly(amic acid) solution, followed by the elimination of solvents and imidization process. The chelating agent, acetylacetone, was used to reduce the gelation rate of titanium alkoxide. The complete imidization temperature of the poly(amic acid) was delayed; furthermore, the thermal stability of PI was enhanced through the incorporation of the inorganic moieties in the hybrid materials. The chemical and morphological structures of the hybrid materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy. The results show that the TiO2 particles are well dispersed in the PI matrix with particle size between 15 and 30nm in diameter.

Synthesis and characterization of conductive polyimide/carbon composites with Pt surface deposits

The preparation of free-standing polyimide/carbon (PI/Carbon) substrates and the electrochemical deposition of Pt to produce PI/Carbon/Pt electrodes are demonstrated to provide thermally stable and conductive PI composites. The conductivity of polyimide (PI)/Carbon composites is evaluated as a function of composition of a binary solvent involving DMSO (dimethyl sulfoxide) and highly volatile acetone, which enhances carbon dispersion (PI/Carbon) in the polymer precursor. The solution conditions have been optimized to provide the highest conductivity for the lowest relative carbon loading. The deposition of Pt metal on PI/Carbon composite electrodes is demonstrated using cyclic voltammetry. The conductivity of the PI/Carbon composite is sufficient that the metal precursor PtCl 4 2− is fully reduced and deposited without the need for additional chemical reduction processes. Thermal gravimetric analysis (TGA) shows that the thermal stability of PI is maintained with carbon incorporation and platinum deposition. Scanning electron microscopy (SEM) analysis shows that carbon aggregation at the PI surface is minimized and that Pt deposits are well dispersed. X-ray photoelectron spectroscopy (XPS) results indicate that the electrochemical reduction of PtCl 4 2− produces metallic Pt deposits on the PI/Carbon composite. Four-point probe measurements are utilized to assess the conductivity of the materials and highlight the influence of C and Pt on the electronic properties of modified PI. Finally, the electrochemical reactivity of PI/Carbon/Pt composite is examined using the redox properties for ferricyanide and the catalytic oxidation of methanol in acidic solution. The electrochemical experiments demonstrate that the free-standing PI/Carbon composites are sufficiently conductive to observe the electrodeposition of Pt metal that is stable and reactive on the organic substrate.

Preparation of Polyimide-Clay Nanocomposites and Their Performance

A series of polyimide (PI)-organically modified clay nanocomposites were made to enhance tensile modulus, thermal stability of PI. PI was made from 3, 3', 4, 4'-biphenyl tetracarboxylic dianhydride (BPDA), p-phenylediamine (PDA). Montmorillonite (MMT), one type of layered clay, was treated by dodecylamine salt. XRD indicated that organically modified montmorillonite (OMMT) layers were exfoliated and dispersed into PI-film. Tensile measurements indicated that small amount of OMMT (up to 3%) increased tensile modulus nicely. The glass transition temperatures (Tg) of the nano-composites are higher than those of pristine PI. Thermal gravimetric analysis (TGA) showed that nanocomposites have higher decomposition temperatures in comparison with the original PI. Keywords: Polyimide; Organically modified clay; Nanocomposites; Dodecylamine. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v1i2.2297

Morphology and size control of inorganic particles in polyimide hybrids by using SiO2–TiO2 mixed oxide

Polyimide/inorganic hybrids were prepared by sol–gel reaction starting from tetraethoxysilane (TEOS), and tetrabutyl titanate (TBT) in the solution of polyamic acid in N,N-dimethylformamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS and TBT in polyamic acid solution, followed by the elimination of solvents and imidization process. Binary polyimide/SiO2 and polyimide/TiO2 hybrids, as well as ternary polyimide/SiO2–TiO2 hybrids (with varied ratio of SiO2 to TiO2) were prepared to study the effects of the recipes and inorganic components on the morphologies of the polyimide hybrids. Transparent films with much higher inorganic content can be obtained in ternary polyimide hybrids, while lower inorganic content in binary hybrids. The results also indicate that the inorganic particles are much smaller in the ternary systems than in the binary systems, the shape of the inorganic particles and the compatibility for polyimide and inorganic moieties are varied with the ratio of the inorganic moieties in the hybrids. The completely imidization temperature of the polyamic acid was delayed, and furthermore, the thermal stability of polyimide was enhanced through the incorporation of the inorganic moieties in the hybrid materials.

폴리이미드/TiO2나노복합재의 합성과 물성 연구

Organic/inorganic hybrid materials have rapidly become a fascinating research field. In this study, polyimideITi02 composites were synthesized from nano-sized anatase Ti02 and two types of polyimide, that is, BPDA-PPD and PMDA-ODA. Nano-sized Ti02 particles wen: prepared from TiOE\.: solution by the sol-gel method. The synthesized PIITi02 composites were characterized by using XRD, TGA, FT-IR, TEM, and Atomic Force Microscope(AFM). Ti02 particles were dispersed well in polyimides and the mechanical and thermal stability of polyimide was improved with Ti02 nano particles.<br/>

Preparation and properties of rare earth oxide/polyimide hybrids

A series of Eu 2O 3/polyimide hybrids has been successfully prepared via a solution process. X-ray diffraction and atomic force microscopy were used to characterize the hybrids. Mechanical tests showed that introduction of the rare earth can obviously increase the tensile strength of the polymer. Thermal analysis indicated that the addition of rare earth can increase the glass transition temperature and thermal stability of polyimide. The introduction of rare earth also increased the dimensional stability and refractive index.

Synthesis and characterization of side-chain polyimides for second-order nonlinear optics via a post-azo-coupling reaction

A two-step, generally applicable synthetic approach for nonlinear optical (NLO) side-chain polyimides was developed. This included the preparation of a preimidized, organosoluble polyimide with benzene moiety pendant from main chains, followed by the covalent bonding of the NLO chromophores onto the polyimide backbone via a post-azo-coupling reaction. The degree of functionalization of polyimides was estimated by UV-VIS spectroscopy. The glass transition temperature (Tg) of a polyimide decreased by only 10–20°C after the functionalization, which was much smaller than the decrease in Tg when the chromophores were chemically bonded to the polyimide main chains through an ether linkage using a post-Mitsunobu condensation. The solubility and thermal stability of polyimides were also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 290–295, 2000

Comparative thermal analysis (CTA) of thermally-stable polymers and model compounds. Polyimides and model compounds

The method of comparative thermal analysis has been used to determine the thermal stability of polyimides and their model compounds. The extent of defects in the investigated polyimides was determined by gas chromatography. The dependence of the extent of the defects on the chemical structure of the initial components and the supermolecular structure of the polyimides was established.

Effect of structure on the thermal stability of polyimides

AbstractPolyimides with different proportions of m‐phenylene and p‐phenylene (or p,p′‐biphenylene) were prepared by polymerizing different molar ratios of m‐phenylene diamine and p‐phenylene diamine (or p,p′‐diaminobiphenyl) with pyromellitic dianhydride in dimethylformamide at 0°C. Chemical cyclodehydration of polyamic acids resulted in the corresponding polyimides. Polymers were characterized by infrared (IR), viscosity, and density measurements. Viscosity and density of polymers decreased with an increase on m‐phenylene groups in the backbone. The thermal and thermooxidative stabilities were investigated by dynamic thermogravimetry. Stability decreased when m‐phenylene groups were introduced in the backbone.