Accelerating the graphitization process of polyimide by addition of graphene

In this article, a composite film from polyimide and thermally exfoliated graphene was prepared through in situ polymerization, and the weight percent of thermally exfoliated graphene with respect to the polyimide monomers was 5 wt %. The film was carbonized at 1000°C for 1 h and then heat‐treated at various temperatures up to 2100°C. For comparison, the corresponding pure polyimide film was also prepared and heat‐treated at the same condition. It was found that the addition of graphene could effectively prevent the polyimide film from shrinking in the direction parallel to the film surface during the heat treatment. Furthermore, the results of density, X‐ray diffraction, shrinkage in the direction perpendicular to the film surface and scanning electron microscopy revealed that the graphitization process of the polyimide could be accelerated by addition of graphene obviously. In view of the above phenomena, a reasonable explanation was presented. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41274.     

In-plane orientation and graphitizability of polyimide films: II. Film thickness dependence

The relation between the in-plane orientation of polyimide film and graphitizability was investigated. The degree of in-plane orientation was estimated by means of optical birefringence and ESR technique. The polyimide film was found to have non-uniform orientation in the thickness direction because the thinner the film was, the greater the orientation. The inhomogeneity of orientation caused multiphase graphitization in a film with a composite profile of the X-ray diffraction peak.     

高温热处理对聚酰亚胺薄膜性能的影响

研究了高温热处理对聚酰亚胺(PI)薄膜拉伸性能和热性能的影响。在薄膜完全环化后,随着热处理温度的升高,薄膜的拉伸强度、弹性模量先增大后基本保持不变,断裂伸长率先保持不变后明显降低,热膨胀系数也显著降低,而薄膜的玻璃化转变温度略有增大。高温热处理工艺可制备高强度和低热膨胀系数的高性能PI薄膜。     

Structure and surface elemental state analysis of polyimide resin film after carbonization and graphitization

The carbon materials prepared from polyimide (PI) resin film were investigated by TG‐DTG, X‐ray powder diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS) analysis. TG‐DTG study revealed that the weight loss of PI resin film during carbonization occurred in three stages, and the most serious changes occurred at 605.5°C. XRD results indicated that a disorder structure occurred after the carbonization at 600°C and graphite crystallite appeared gradually with increasing the temperature. And PI resin film still presented some characteristics of nongraphitizing carbon, after graphitizing at 2600°C. XPS analysis identified that pyrrole type nitrogen was a main component of surface nitrogen atoms after carbonization. When the temperature reached 2600°C, nitrogen atoms disappeared totally; the reason why oxygen atoms still existed in the material at so high temperature was our subject of interesting matter in the later study. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Carbonization and graphitization of polyimide films: Polyamide acid methyl ester of PMDA/PDA as a precursor

Polyamide acid was prepared from pyromellitic dianhydride (PMDA) and p-phenylene-diamine (PDA) and was then reacted with NaH and methyl iodide to transform into methyl ester having various degrees of esterification. Polyamide acid methyl ester was also prepared by the polymerization between PDA and acid chloride of half-ester of PMDA. The cast films were imidized as fixed on glass substrate to give polyimide films having slightly higher tensile moduli than those from polyamide acid, suggesting that higher orientation along the film surface was achieved. It should be noted that the polyimide films prepared by the latter method from the meta-rich configuration had considerably low modulus. The polyimide films were then carbonized by heating to 900°C, and the electrical conductivity of the carbonized films was measured at room temperature. It was shown that the carbonized films from methyl ester have higher electrical conductivity than the films from corresponding polyamide acid. The carbonized films were further heated to 2800°C for graphitization, and their degrees of graphitization and orientation of the graphite crystallite as a function of esterification ratio were studied by x-ray diffraction measurement at room temperature and magnetoresistance measurement at liquid nitrogen temperature. Both measurements clearly indicate that the graphite films prepared from polyamide acid methyl ester have high degrees of graphitization and orientation. © 1996 John Wiley & Sons, Inc.     

Structure and imidization of polyamic acid salt Langmuir–Blodgett films

Polyimide Langmuir‐Blodgett (LB) films were prepared with a Pyromellitic dianhydride‐4, 4′ oxydianiline precursor, and the properties of the polyamic acid salt monolayer characterized by different methods. The π‐A relationship revealed that the precursor monolayer exhibits anisotropy on the water surface, the Wilhelmy plate being more sensitive to pressure when it is perpendicular to the compression direction. FTIR results showed that polyamic acid salt LB films have lower imidization energy than the corresponding painting films and can be imidized at lower temperature. The molecular arrangement in the LB films was studied by X‐ray diffraction and polarized FTIR, showing that the polyamic acid salt LB film is of Y‐type, in which the molecules are highly oriented, with the main chain lying parallel to the substrate and the long fatty acid chains stretching out at a certain angle. © 2002 Society of Chemical Industry     

有机硅改性聚酰亚胺复合膜的抗原子氧性能研究

由端氨丙基聚二甲基硅氧烷（PDMS）、均苯四甲酸二酐（PMDA）和4,4’-二氨基二苯醚（ODA）在N,N’-二甲基乙酰胺（DMAc）中共聚,热亚胺化法制备有机硅改性聚酰亚胺复合膜。通过傅立叶变换红外吸收光谱仪（FTIR）、X射线光电子能谱（XPS）分析材料的化学结构,采用扫描电子显微镜（SEM）观察材料的表观形貌,利用地面原子氧（AO）模拟设备研究了该复合膜的抗原子氧性能。结果表明有机硅改性聚酰亚胺复合膜在AO累积通量达到2.06?020atom/cm2时,复合膜的AO剥蚀率可以达到6.69?0-25 cm3/atom,约是纯聚酰亚胺薄膜抗原子氧性能的4.5倍。     

高能离子注入聚酰亚胺薄膜表面结构研究

应用透射电子显微镜研究了聚酰亚胺薄膜在无外加氮源、氢源参与的条件下，分别经过1．0，2．0，2．5MeV的He^ 注入改性后表面的微观结构变化，通过选区电子衍射和高分辨等手段分析，首次发现在注入He^ 后薄膜表层发生了不同程度的晶化，生成了类金刚石晶体和CNx微晶。经一定能量He^ 轰击后的聚酰亚胺薄膜的硬度、耐磨性及抗环境能力得到了提高。     

Preparation and properties of polyimide/carbon nanotube composite films with electromagnetic wave absorption performance

The polyimide (PI)/carbon nanotube (CNT) films including 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), p-phenylenediamine (p-PDA), and CNTs were prepared, which have prominent electromagnetic (EM) wave absorption performance. Experimental analyses of the mechanical properties, thermal stabilities, coefficient of thermal expansion (CTE), the glass transition temperature (T_g), and EM parameter revealed the beneficial effects of the CNTs on the resulting composite films. In particular, when the content of CNTs is 6 wt%, the film shows the highest EM wave absorption performance, which exhibits the effective absorption bandwidth of 2.72 GHz with the matching thickness of only 2.0 mm. These results indicate that PI-based films have a certain potential application in the area of EM wave-absorbing materials.     

Correlation of pretilt angles and surface chemical structures of polyimide alignment films after direct fluorination

A series of polyimides (PIs) with side chains were fabricated from 6‐(4‐phenylphenoxy)hexyl‐3,5‐diaminobenzoate of various ratios with 4,4′‐oxydianiline and 4,4′‐oxydiphthalic anhydride. After PI alignment, films were directly fluorinated using a 10 vol% fluorine/nitrogen mix. The pretilt angle of liquid crystals on the PI films is much improved to more than 20°, and can be continuously controlled by changing the side‐chain content of the PI films from 20 to 100%. The change of the pretilt angles is ascribed to the fluorinated microstructure of molecules at the surface rather than to the surface energy or surface morphology. Moreover, the improvement of rigidity and the steric repulsion of the fluorinated side chains result in an upright conformation of the side chains that leads to the high pretilt angle. Copyright © 2010 Society of Chemical Industry     

Indentation test for adhesion measurement of polyimide films

An indentation technique was used to determine the adhesion of polyimide films on a ceramic substrate. Experimental results were obtained by indenting 13 μm thick polyimide films with a conical indenter at different indentation loads. Among the process variables investigated were the amount of adhesion promoter added to the polyimide and the exposure to temperature and humidity. The technique provides a measure of the bond strength, based on the analysis of indentation debonding of thin films. For well adhered films, no debonding could be induced, indicating the usefulness of the test only for the poorly bonded films.     

均苯型共聚聚酰亚胺薄膜的制备及其性能

以2,2′-双[3-苯基-4(4-氨基苯氧基)苯基]丙烷(BPAPOPP)、4,4′-二胺基二苯醚和均苯四甲酸酐为原料,采用两步法共缩聚制备了一系列共聚聚酰亚胺薄膜.采用红外光谱仪、差示扫描量热仪等分析了薄膜的结构,利用静态热机械分析仪分析了薄膜的性能.结果表明:制备的聚酰亚胺薄膜具有较低的玻璃化转变温度;随着BPAP...     

The use of peel tests to examine the self adhesion of polyimide films

Peel tests were used to examine the adhesion between two layers of the polyimide pyromellitic dianhydride-oxydianiline (PMDA ODA). The main thrust of this work was to examine these tests with particular emphasis on yielding in bending of the peeled strips. Two peel geometries and a range of sample thicknesses were used to study interfaces whose strength could be varied over a wide range by changing the cure schedule. The peel strength varied with strip thickness and often reached a peak at an intermediate thickness. The results were shown to agree qualitatively with a combination of two theoretical models for the effects of yielding on peel tests. It was also found that a second problem of polyimide adhesion, the effect of solvent swelling, could significantly enhance the adhesion between polyimide layers.     

Dielectric and conduction properties of pure polyimide films

Capacitors with an Al–polyimide–Al sandwich film structure have been fabricated: the top and the bottom aluminium electrodes were deposited by vacuum evaporation and the polyimide film was deposited by an isothermal immersion method. An X‐ray diffractogram of the film indicates the amorphous nature of the polyimide film. Dielectric and ac conduction properties of polyimide capacitors in the frequency range 10 kHz to 10 MHz at various temperatures (303–423 K) are reported; the dc conduction at different voltages and at various temperatures (303–423 K) is given. The capacitance of the film decreases with increasing frequency but increases with increasing temperature. The ac conduction studies suggest that electron hopping is responsible for conduction while the dc conduction studies reveal that Poole–Frenkel conduction is predominant at high fields. The activation and zero field activation energies are also calculated. © 2001 Society of Chemical Industry     

Preparation and characterization of magnetic polyimide hybrid thin films

Magnetic polyimide hybrid thin films were synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and Fe₃O₄ magnetic nanoparticles via thermal imidiazation in nitrogen environments. The magnetic polyimide hybrid thin films were analyzed and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The magnetic properties of magnetic nanoparticles and polymer hybrid thin films were assessed using a vibrating sample magnetometer (VSM), and the physical properties of hybrid thin films were tested. Results revealed that the magnetic polyimide hybrid thin films had superparamagnetic behavior and excellent mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

纳米二氧化锆改性聚酰亚胺薄膜的制备及性能

聚酰亚胺（PI）在工程高分子材料领域广受关注,开发新型耐高温、疏水性良好的PI薄膜材料是推动高性能高分子材料在电动汽车等高新技术领域工程化应用的重要突破口。以间苯二胺（MPD）与4,4’-(4,4’-异丙基二苯氧基)二酞酸酐（BPADA）为原料,采用原位掺杂热亚胺化合成PI薄膜,通过向聚酰胺酸（PAA）前驱液中添加纳米ZrO2粉体对聚酰亚胺薄膜进行改性,制得不同ZrO2添加量（0.77%～1.93%,以MPD、BPADA总质量为基准,下同）的复合型PI薄膜。借助XRD、SEM、EDS、FTIR及TGA对复合薄膜进行了结构和形貌表征。结果表明,与纯PI相比,ZrO2添加量为1.93%的复合薄膜初始分解温度为415℃（提高5%）,水接触角为91.7°（提高61%）,表明ZrO2对改善PI薄膜的性能具有重要作用。     

纳米二氧化锆改性聚酰亚胺薄膜的制备及性能研究

聚酰亚胺在工程高分子材料领域广受关注,开发新型耐高温、疏水性良好的聚酰亚胺薄膜材料是推动高性能高分子材料在电动汽车等高新技术领域工程化应用的重要突破口。本工作采用两步法合成复合型聚酰亚胺薄膜,通过纳米ZrO2粉体对聚酰亚胺薄膜进行改性,借助XRD、SEM、能谱、红外光谱等手段对复合薄膜进行结构和形貌的表征,并测试了复合薄膜的热稳定性、疏水性及抗拉强度,结果表明纳米ZrO2的加入增强了聚酰亚胺分子链之间的相互作用,使其耐热性能得到显著提高,分解温度可以提高20 ℃,复合薄膜的水接触角提高60%,疏水性能得到提高。本工作为开发新型高性能聚酰亚胺高分子材料提供了新的思路。     

Preparation and characterization of polyimide/Al2O3 hybrid films by sol–gel process

A sol–gel process has been developed to prepare polyimide (PI)/Al₂O₃ hybrid films with different contents of Al₂O₃ based on pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA) as monomers. FESEM and TEM images indicated that Al₂O₃ particles are relatively well dispersed in the polyimide matrix after ultrasonic treatment of the sol from aluminum isopropoxide and thermal imidization of the gel film. The dimensional stability, thermal stability, mechanical properties of hybrid PI films were improved obviously by an addition of adequate Al₂O₃ content, whereas, dielectric property and the elongation at break decreased with the increase of Al₂O₃ content. Surprisingly, the corona‐resistance property of hybrid film was improved greatly with increasing Al₂O₃ content within certain range as compared with pure PI film. Especially, the hybrid film with 15 wt % of Al₂O₃ content exhibited obviously enhanced corona‐resistance property, which was explained by the formation of compact Al₂O₃ network in hybrid film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Colorless polyimide nanocomposite films: Thermomechanical properties,morphology, and optical transparency

Polyimide (PI)/organoclay hybrid films were prepared by the solution intercalation method, using dodecyltriphenylphosphonium‐mica (C₁₂PPh‐Mica) as the organoclay. The variations with organoclay content of the thermomechanical properties, morphology, and optical transparency of the hybrids were examined for concentrations from 0 to 1.0 wt %. For low clay contents (≤ 0.5 wt %), the clay particles are better dispersed in the matrix polymer, without the formation of large agglomerates of particles, than they are for high clay contents. However, agglomerated structures form and become denser in the PI matrix for clay contents ≥ 0.75 wt %. This is in agreement with the observed trends in the thermomechanical properties and the optical transparency, which worsen drastically when the clay content of the C₁₂PPh‐Mica/PI hybrids reaches 0.75 wt %. However, when the amount of organoclay in the hybrid is 0.75 wt %, the initial modulus of the hybrid film is at its maximum value. The PI hybrid films were found to exhibit excellent optical transparencies and to be almost colorless. It was found, however, that the transparency decreases slightly with increases in the organoclay content because of agglomeration of the clay particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

聚酰亚胺的合成及其膜的制备

先在四氢呋喃/甲醇(质量比为4:1)混合溶剂体系中合成聚酰胺酸(PAA),后在真空烘箱中(200℃/h)形成聚酰亚胺(PI)膜,并通过IR和TG/DTG对产物进行了表征,结果表明能得到耐高温的Pl膜。