Effect of carbon nanotubes on mechanical and electrical properties of polyimide/carbon nanotubes nanocomposites

Multi-walled carbon nanotubes (MWNTs) reinforced polyimide nanocomposites were synthesized by in situ polymerization using 4,4′-oxydianilline, MWNTs, and pyromellitic dianhydride followed by casting, evaporation and thermal imidization. A homogeneous dispersion of chemically modified MWNTs was achieved in polyimide matrix as evidenced by scanning electron microscopy and atomic force microscopy. The incorporation of the modified MWNTs enhanced the mechanical properties of the polyimide due to the presence of strong interfacial interaction between the polymer matrix and the nanotubes in polymer composites. The resultant polyimide/MWNTs nanocomposites were electrically conductive with significant conductivity enhancement at 3 wt% MWNTs, which is favorable for many practical uses.     

Structural and dielectric properties of POSS reinforced polyimide nanocomposites

In this study, a series of [3-(2-aminoethyl)amino]propyl-heptaisobutyl substituted polyhedral oligomeric silsesquioxane (AHIP) containing polyimide (PI) nanocomposites were successfully prepared. Structural, thermal and electrical properties of the polyimide nanocomposites were studied. The properties of AHIP containing polyimides were compared with those of the neat polyimide films. The surface morphology of the prepared AHIP containing polyimides were determined by using Scanning Electron Microscopy (SEM). The hydrophilic/hydrophobic nature of AHIP/polyimide composites were analyzed by measuring their water contact angles. It was found that the addition of AHIP into the polyimide slightly increased the contact angle values. The incorporation of 5% AHIP to the PI matrix decreased the dielectric constant value of pure PI from 8.6 to 11.7, respectively. Furthermore he dielectric permittivity was changed from 8.6 (neat polyimide) to 5.5 (PI3).     

Preparation of ultrathin films of aromatic polymides by vapor deposition polymerization from N-silylated aromatic diamines or aromatic tetracarboxylic dithioanhydride

A novel method for the preparation of ultrathin films of aromatic polyimides was developed through vapor deposition polymerization from combinations of monomer pairs of either N,N′-bis (trimethylsilyl)-substituted aromatic diamines and pyromellitic dianhydride or aromatic diamines and pyromellitic dithioanhydride. Both diamine component and tetracarboxylic dianhydride component were evaporated simultaneously at a stoichiometric molar ratio under vacuum, giving a deposited film on a substrate, which consisted of a polyamic acid derivative formed by the ring-opening polyaddition. The deposit was then converted to polyimide by thermal imidization at a relatively lower temperature, compared with a conventional method using the parent diamine and tetracarboxylic dianhydride. The properties of polyimide ultrathin films such as thermal stability, chemical resistance, and dielectric behavior were almost the same as those of the polyimide films prepared by a conventional method.     

高介电常数石墨烯/聚酰亚胺复合材料的制备与性能

在原位聚合制备氧化石墨烯/聚酰亚胺复合材料的过程中,加入季铵盐表面活性剂,抑制氧化石墨烯在高温亚胺化时的聚集,同时将氧化石墨烯原位还原,获得高介电常数的石墨烯/聚酰亚胺复合材料.结果表明,采用四丁基溴化铵和四丁基碘化铵作为还原剂,利用原位化学还原方法所制备的石墨烯/聚酰亚胺复合材料的介电常数超过聚酰亚胺薄膜40倍以上,复合材料的热稳定性和机械性能也优于聚酰亚胺薄膜.热重分析结果表明,在复合材料高温亚胺化过程中,季铵盐发生热分解,未残留在复合材料中.     

Synthesis,morphology, and properties of hydroxyl terminated‐POSS/polyimide low‐k nanocomposite films

Polyhedral oligomeric silsequioxane (POSS), having eight hydroxyl groups for the preparation of nanocomposites with polyimide (PI) was synthesized by the direct hydrosilylation of allyl alcohol with octasilsesquioxane (Q₈M₈^H) with platinum divinyltetramethyl disiloxane Pt(dvs) as a catalyst. The structure of allyl alcohol terminated‐POSS (POSS‐OH) was confirmed by FTIR, NMR, and XRD. A high performance, low‐k PI nanocomposite from pyromellitic dianhydride (PMDA)‐4,4'‐oxydianiline (ODA) polyamic acid cured with POSS‐OH was also successfully synthesized. The incorporation of POSS‐OH into PI matrix reduced dielectric constant of PI without loosing mechanical properties. Furthermore, the effects of POSS‐OH on the morphology and properties of the PI/POSS‐OH nanocomposites were investigated using UV–vis, FTIR, XRD, SEM, AFM, transmission electron microscope (TEM), TGA, and contact angle. The homogeneous dispersion of POSS particles was confirmed by SEM, AFM, and TEM. The nanoindentation showed that the modulus increased upon increasing the concentration of POSS‐OH in PI, whereas the hardness did not increase very much with respect to loading of POSS, due to soft‐interphase around POSS molecules in the resulting nanocomposites. Overall results demonstrated the nanometer‐level integration of the polymer and POSS‐OH. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5887–5896, 2008     

含磷聚酰亚胺纤维的制备及其力学与阻燃性能

采用廉价的三苯基氧膦和混酸合成了一种含磷二胺单体,二（3-氨基苯基）苯基膦氧(DAPPO)。在4,4′-二胺基二苯醚（ODA）、3,3′,4,4′-联苯四酸二酐（BPDA）和均苯四酸二酐（PMDA）聚合体系中引入该单体,制备含磷聚酰亚胺纤维。热失重分析（TGA）结果表明,聚酰亚胺纤维的热稳定性随含磷量的增加而明显提高。当n（DAPPO）：n（ODA）为7：93时,纤维的极限氧指数达到了43,说明纤维的阻燃性能显著提高。     

Octahedral oligomeric silsesquioxane (OAPS and OG) - Polyimide hybrid nanocomposite films: Thermo-mechanical,dielectric and morphology properties

Abstract

The nano-sized SQS based polyimides have been successfully synthesized with different oxide groups such as phosphineoxide, sulfone and siloxane as in the backbone of polymer. The SQS-Polyimide nanocomposites prepared through the condensation process using amine and epoxy functionalized SQS as precursor. The presence of SQS in the resulting polyimide nanocomposites was confirmed by FTIR and XRD analyses. The presence of SQS and greatly enhances the char yield to an extent of 16% when compared to that of neat polyimide. The incorporation of SQS into polyimide lowered the value of dielectric constant from 3.31 to 2.09 at 1?MHz and the value of thermal expansion coefficient from 56.6 to 42.7?ppm/K. The composites sample prepared using 20?wt% SQS possess the lowest value of dielectric constant and CTE value. The hydrophobic nature of SQS contributes to lower the water uptake of composites from a value of 2.76 (neat polyimide) to 2.42 for POS-PI containing 20?wt% SQS. Further, the SQS polyimide composite systems possess the enhanced values of thermal stability and glass transition temperatures according their percentage weight. Data obtained from different studies, it is suggested that these hybrid composites can be used as an effective insulation materials for high performance microelectronics applications.     

含磷聚酰亚胺纤维的制备与性能

合成了一种含磷二胺单体, 二(4-胺基苯氧基)苯基膦氧(DAPOPO). 该单体与4,4'-二胺基二苯醚(ODA)、 均苯四酸二酐(PMDA)和3,3',4,4'-联苯四酸二酐(BPDA)共聚得到聚酰胺酸溶液, 通过干喷湿纺法纺丝得到聚酰胺酸纤维, 聚酰胺酸纤维经过热亚胺化和热牵伸得到含磷的聚酰亚胺纤维. 利用纤维强度仪、 扫描电子显微镜、 热失重分析仪和氧指数测定仪等研究了含磷聚酰亚胺纤维的力学性能、 形貌、 热稳定性能和阻燃性能. 结果表明, 随着含磷量的增加, 纤维的热稳定性明显提高, 而极限氧指数从35上升到了45, 说明纤维的阻燃性能得到很大提高.     

Preparation and characterization of novel polyimide‐silica hybrids

Polyimide‐silica (PI‐SiO₂) hybrids were prepared from a novel polyimide (PI), derived from pyromellitic dianhydride (PMDA), 1,6‐bis(4‐aminophenoxy)hexane (synthesized) and 4,4′‐oxydianiline. SiO₂ networks (5–30 wt%) were generated through sol–gel process using either tetraethylorthosilicate (TEOS) or a mixture of 3‐aminopropyltriethoxysilane‐PMDA‐based coupling oligomers (APA) and TEOS. Thin, free standing hybrid films were obtained from the respective mixtures by casting and curing processes. The hybrid films were characterized using Fourier transform infrared, ²⁹Si nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐ray spectrometry and atomic force microscopy (AFM) techniques. ²⁹Si NMR results provide information about formation of organically modified silicate structures that were further substantiated by FE‐SEM and AFM micrographs. Contact angle measurements and thermogravimetric thermograms reveal that the addition of APA profoundly influences surface energy, interfacial tension, thermal stability and the residual char yield of modified hybrids in comparison to those obtained by mixing only TEOS. It was found that reduced particle size, efficient dispersion and improved interphase interactions were responsible for the eventual property enhancement. Copyright © 2012 John Wiley & Sons, Ltd.     

牵伸倍率对联苯型聚酰亚胺纤维形貌、取向及性能的影响

均苯四甲酸二酐(PMDA)和联苯二酐(BPDA)与3,3′-二甲基联苯二胺(OTOL)共聚得到聚酰亚胺(PI)溶液,通过干喷-湿法纺制成纤维.利用扫描电镜(SEM)、广角X射线衍射(WAXD)、纤维力学性能测试仪、动态力学分析仪(DMA)和热失重分析仪(TGA)等表征手段,研究不同牵伸倍率对联苯型聚酰亚胺纤维形貌结构、...     

Novel synthesis of polyimide–polyhybridsiloxane block copolymers via polyhydrosilylation: Characterization and physical properties

The insertion of soft polysiloxane segments into a polyimide backbone introduces changes in its properties (processability, low surface tension, gas permeability, and lower dielectric constant). Generally, these polyimide–polysiloxane copolymers are synthesized by the condensation of a dianhydride with an aromatic diamine and an amine telechelic polysiloxane, or by transimidization between an aminopyridine‐terminated oligoimide and an amine end‐capped oligosiloxane. This study investigated another route to obtain perfectly alternating polyimide–polyhybridsiloxane (PI–PHSX) block copolymers. The hydrosilylation, widely studied previously, was performed to elaborate copolymers from an allyl telechelic polyimide and a hydrosilane telechelic polyhybridsiloxane. The use of a telechelic polyhybridsiloxane as a soft segment brought better thermostability and better chemical resistance in comparison with an oligosiloxane based on ? Si(CH₃)₂? O? units. Using the same allyl telechelic polyimide moiety but varying the size of the hybrid siloxane part, we obtained different PI–PHSX block copolymers, leading to thermoplastic elastomers (TPE). We investigated the effect of the soft‐segment length on the thermal resistance, activation energy of thermal degradation, mechanical behavior, and surface properties of a series three PI–PHSX block copolymers containing 36, 54, and 75 wt % polyimide. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2414–2425, 2001     

基于多层结构设计的高储能密度氧化石墨烯/聚酰亚胺复合材料

采用逐层涂布、 分层控制固化程度的方法, 利用聚酰胺酸(PAA, 聚酰亚胺前体)溶液和含有氧化石墨烯（GO）的PAA溶液制备了一系列由高绝缘性PI层与GO@PI介电层交替组合而成的界面清晰且紧密衔接的多层复合薄膜. 通过调控介电层中GO含量及分层结构, 使多层复合薄膜兼具高介电常数和高击穿强度特征. 结果表明, 三层复合薄膜PI/1.0GO@PI/PI的击穿强度为261.5 kV/mm, 储能密度达到1.27 J/cm³, 与相同介电层厚度的单层薄膜相比, 击穿强度和储能密度分别提高了97%和144%, 同时, 其介电损耗也保持在较低水平(tanδ=0.0079). 绝缘层和高介电常数层的协同作用提升了氧化石墨烯/聚酰亚胺复合薄膜的储能密度. 这种简单的多层结构设计有利于氧化石墨烯/聚合物复合材料在介质储能领域的应用.     

Photo-induced liquid crystal alignment on polyimide containing fluorinated groups

Polyimides were prepared from pyromellitic dianhydride, 4,4'-bis[2-(4-aminophenyl)hexafluoroprop-2-yl]diphenyl ether and 4,4'-diamodiphenyl ether (PMDA-BDAF-ODA) and used for liquid crystal alignment using linearly polarized UV exposure. The alignment properties of a LC on the polyimide films were found to depend on the fluorine content in the PMDA-BDAF-ODA alignment layer and on the UV exposure time. Pretilt angles were obtained in the range 0° to 90° dependent upon the fluorine content in the polyimide film and the UV exposure time. These effects seem to be closely related to the surface energy of the photo-alignment layer.     

Bio-based polybenzoxazine composites for oil-water separation,sound absorption and corrosion resistance applications

In the present work, an attempt has been made to develop bio-based composites using cardanol and eugenol based benzoxazine matrices with bio-silica as well as natural fibrous materials (coir felt, kapok fabric, jute felt and rice husk) as reinforcements. The bio-composites developed were studied for different applications viz., dielectric, water repellent, oil-water separation, sound-absorption including corrosion resistance use. Among the bio-silica reinforced benzoxazine composites, 7 wt% bio-silica reinforced cardanol composites possesses the highest value of water contact angle (147°) and the lowest value of dielectric constant (2.0) than those of other bio-silica reinforced composites. Further, the cotton fabric was coated with cardanol and eugenol based polybenzoxazines separately, whose values of water contact angles are found to be 159° and 157° with oil-water separation efficiency as 96% and 95% respectively. Furthermore, the cardanol based benzoxazine was separately reinforced with jute felt, coir felt, kapok fabric and rice-husk. The corresponding sound absorption efficiency was found to increase in the following order, Neat polybenzoxazine < rice husk < coir felt < kapok fabric < jute felt. Data resulted from corrosion studies, it was noticed that the mild steel specimen coated with bio-based benzoxazine matrices and bio-silica reinforced benzoxazine composites coated specimens exhibit an excellent resistance to corrosion. Data resulted from different studies, it is suggested that the cardanol and eugenol based bio-composites can be considered as an effective materials for microelectronics insulation, water repellent, oil-water separation, sound absorption and corrosion resistant applications.     

Synthesis of novel hyperbranched polyimide for liquid crystal alignment

A novel hyperbranched polyimide (HPPI) was synthesized from a new four‐functional amine and 1,2,3,4‐cyclobutanetetracarboxylic dianhydride. The polyimide with hyperbranched structure exhibited excellent alignment for nematic liquid crystal (LC) compared with traditional linear polyimides. The solution viscosities of the poly(amic acids) (PAAs) and the surface morphology of PI films were investigated using an Ubbelhode‐type viscometer and atomic force microscopy, respectively. The viscosities of the hyperbranched PAAs were much lower than that of the linear PAA solution at any monomer ratio (amine:dianhydride). Pretilt angles of LCs above 2.8° were achieved with HPPI.     

Preparation, structure and properties of porous polyimide films via PAA/PU alloy

A new route to porous polyimide (PI) films with pore sizes in the nanometer regime was developed. A polyamic acid (PAA)/polyurethane (PU) blend with PU as the disperse phase was first prepared via in situ polymerization of pyromellitic dianhydride and 4,4-oxydianiline in PU solutions. Porous PI films were obtained from PAA/PU films by thermolysis of PU at 360°C and imidization of PAA at 300°C, respectively. Fourier transform infrared spectroscopy and thermal gravimetric analysis were used to detect the imidization and thermolysis processes of PAA/PU blends under thermal treatment. The microporous structure of the PI films was observed by transmission electron microscopy. It was found that the size and content of pores increased with an increase in the PU mass fraction in the PAA/PU blend up to 20%. Because of the existence of nanopores, the dielectric constant of PI films decreased by a wide margin and was less than 2.0 at a PU mass fraction of 20%. It implies that this is an effective means to reduce the dielectric constant of PI, but it also causes the decrease of tensile strength and the rise of water absorption. Translated from Chemistry Journal of Chinese Universities 2006, 27(1): (in Chinese)     

共缩聚型可溶性聚酰亚胺的微波辐射合成

以均苯四甲酸酐(PMDA)、3,3′,4,4′-二苯酮四羧酸二酐(BTDA)和甲苯2,4-二异氰酸酯(TDI)为单体,微波辐射低温溶液聚合生成一种共缩聚聚酰亚胺(PI).通过特性黏度([η])、红外光谱(FT-IR)、热失重分析(TGA)和X衍射分析(XRD)等对聚合物进行了一系列的结构表征和性能测试.结果表明,微波辐射溶液聚合能够提高PI的特性黏数及产率,微波的引入大大缩短了反应时间;FT-IR表明,在1779cm-1和1726cm-1处观察到聚酰亚胺特征峰;TGA表明,PI在氮气中520℃左右开始降解,10%热失重温度为585℃;溶解性测试表明,PI可以溶解在强极性非质子溶剂中,如DMF,DMSO,DMAc及NMP等,甚至部分溶解在THF中.     

Preparation and properties of polyimide/chopped carbon fiber composite foams

In this study, a series of reinforced polyimide (PI)/carbon fiber (CF) composite foams were fabricated through thermal foaming of polyester ammonium salt (PEAS) precursor powders. The PEAS precursor powders containing different contents of chopped CF were synthesized from benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride (BTDA) and 4,4′‐diaminodiphenyl ether (ODA). The effects of different CF loadings on foaming behavior of PEAS/CF composite precursor powders, final cellular morphology, and physical properties of PI composite foams were investigated. The results revealed that the chopped CF acted as nucleation agent in the foaming process. The dispersion of CF can be evaluated using digital microscope. It is interesting to find that the chopped CF were highly oriented along the direction of cell arrises. As a result, the mechanical properties of PI foams were significantly enhanced owing to the incorporation of chopped CF. Furthermore, the thermal stability of PI composite foams were also slightly improved owing to fine dispersion of CF. In addition, the PI/CF composite foam shows uniform cell size distribution and the best comprehensive physical properties as chopped CF loading at around 6 wt%. Copyright © 2016 John Wiley & Sons, Ltd.     

Pretilt angle for BTDA,PMDA and CPDA series polyimides with various side chain lengths

Polyamic acid precursors were prepared by mixing dianhydride of 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA), 1,2,3,4-benzene-tetracarboxylic dianhydride (pyrromellitic dianhydride PMDA), cis-1,2,3,4-cyclopentane-tetracarboxylic dianhydride (CPDA), the diamine (alkyl 3,5-diaminobenzoate) with side chain, and 4,4'-oxydianiline (ODA) without side chain. Copolyimide films with various side chain lengths were prepared by thermal imidization of polyamic acid precursors. The roughness of rubbed polyimide surface increased with increase in the side chain length. The pretilt angle for the BTDA and PMDA series polyimide (PI) increased exponentially with increase in side chain length. Various pretilt angles were obtained on the synthesized polyimides. In the case of CPDA series PI, the pretilt angle was nearly constant at 0 until the alkyl side chain length reached 12 (C12) and then increased markedly at C18. Models of pretilt angle generation were tested.     

Two‐sided comb poly(amic ester)–poly(propylene oxide) graft copolymers as porous polyimide precursors

New step‐growth graft block copolymers were synthesized. These two‐sided comb copolymers consisted of a poly(amic ester) (PAE) backbone and pendant poly(propylene oxide) (PPO) grafts. The copolymers were made via a macromonomer approach, in which the 4,6‐bischlorocarbonyl isophthalic acid bis[poly(propylene oxide)] ester macromonomer was synthesized through the reaction of hydroxyl‐terminated PPO oligomers with pyromellitic dianhydride and oxalyl chloride. This macromonomer was subsequently used in step‐growth polymerization with comonomers 4,6‐bischlorocarbonyl isophthalic acid diethyl ester, 2,5‐bischlorocarbonyl terephthalic acid diethyl ester, and 2,2‐bis[4‐ (4‐aminophenoxy)phenyl] hexafluoropropane, and this yielded PPO‐co‐PAE graft copolymers. Accordingly, we report the synthesis and characterization of the PPO oligomer, the PPO macromonomer, and their corresponding PPO‐co‐PAE graft copolymers. Graft copolymers with PPO concentrations of 3–26 wt % were synthesized. These polymers were thermally cured to produce polyimide/PPO composites. The thermolysis of these polyimide/PPO composites yielded porous polyimide films with porosities ranging of 4–22.5%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2266–2275, 2005