聚酰胺酸合成工艺与聚酰亚胺膜制备及表征

聚酰亚胺是一类新型高性能的聚合物材料,是由聚酰胺酸脱水环化而成,因此高分子量的聚酰胺酸是获得高性能PI的前提。探讨了聚酰胺酸合成过程中的影响因素,得出了合成高分子量的聚酰胺酸的最佳工艺条件为:均苯四羧酸二酐与4,4' 二氨基二苯醚摩尔比为1.015～1.020∶1,反应温度20℃,反应时间为3h,聚酰胺酸在N 甲基 2 吡咯烷酮中的特性粘度为0.62dL/g左右。采用热转化法将聚酰胺酸脱水环化制备成均苯型聚酰亚胺膜,通过差示扫描量热法、红外光谱等进行了表征,其玻璃化转变温度为365～385℃,拉伸强度达192.4MPa,表明得到的聚酰亚胺膜具有优良的机械性能。     

Polyimide fibers: Structure and morphology

Polyimide fibers were prepared by wet spinning of poly(p,p′ -diaminodiphenylmethanepyro-mellitamic acid). Density measurements and x-ray diffraction studies were carried out to study the structure of the resultant polyimide fibers. Polyamic acid as well as undrawn polyimide fibers were essentially amorphous with two amorphous haloes. Hot drawing of the fibers at 300°C resulted in increase in crystallinity, and a simultaneous decrease in density also took place. X-ray data revealed that meridional reflections correspond to the repeat unit length in the fiber. Scanning electron micrography studies indicated that polyamic acid fibers prepared by a wet-spinning technique developed voids during spinning which increased on cyclodehydration to the polyimide state. Hot drawing of fibers resulted in enlargement of these voids. However, a highly fibrillated structure was developed during drawing which could account for the strength of the fibers.     

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.     

High thermal conductivity and low absorptivity/ emissivity properties of transparent fluorinated polyimide films

Polyimide film materials are a very promising and high-performance polymer in space application. However, the deep coloration of conventional polyimide films greatly limits the wide use in areas where transparency and low solar absorptance are the essential requirement. Here, we prepared the transparent polyimide from 4,4\(^{\prime }\)-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and different ratios of 2,2\(^{\prime }\)-bis(trifluoromethyl)-benzidine (TFB) and 2,2-bis(4-(4-aminophenoxy)-phenyl) hexafluoropropane (BAPP) with a low solar absorptance. Properties, such glass-transition temperature, thermal decomposition temperature, thermal conductivity and transmittance, were investigated, It is suggested that the introduction of fluorine into polyimide will significantly increase transmittance and in turn decrease solar absorptance, The polyimide film with fluorinated groups exhibited superior optical transparency, low absorptivity/emissivity, high thermal conductivity, and good resistance to ultraviolet radiation. The transparent polyimide exhibits a low solar absorptivity of 0.04 and infrared emissivity of 0.6.     

Physicochemical characterization of alloy of polyimide with varying degree of crosslinking through diisocyanates

Polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend components can be synthesized by the reaction of polyamic acid with the varying concentration of crosslinker [here methylene bis (4-phenyl isocyanate or MDI)] from 1.54 × 10^?2 mol/L (i.e. hypothetically calculated critical crosslinker concentration or CCC) to 1.54 × 10^?6 mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and alloys prepared by varying degrees of crosslinking introduced via isocyanate-amic acid reaction. The polyimides were prepared by thermally imidizing the polyamic acid blends at different curing temperatures from 50°C to 350°C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncrosslinked components and two extreme conditions and at specified temperature-time profiles have been studied. The resultant PI-MDI blends have exhibited synergism on mechanical properties. The improvement in mechanical properties, however, was significantly higher at the lower imidization temperature (i.e. 50°C to 150°C). The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was inferred.     

Simulation of polyimide fibers with trilobal cross section produced by dry‐spinning technology

As one type of high performance fibers, polyimide fibers can be prepared from polyamic acid (PAA) solution by dry‐spinning technology. The transformation from the precursor of polyamic acid to polyimides via thermal cyclization reaction in the dry‐spinning process is a main distinguishing feature, which is very different from other fibers produced by dry‐spinning such as cellulose acetate fiber and polyurethane fiber. In this report, the dry‐spinning formation of polyimide fibers with trilobal cross section from PAA solution in N,N‐dimethylacetamide is simulated via a one‐dimensional model based on a viscoelastic constitutive equation, combined with profile degree equation of cross section and imidization kinetics equation. The glass transition temperature, imidization degree and profile degree of the filament along the spinline are predicted by the model, as well as relative parameters such as solvent mass fraction and temperature. As a simulated result, solidification of polyimide fibers take place about 150 cm from the spinneret which is farther than for cellulose acetate fiber (70 cm). Moreover, the final profile degree of fiber is affected by many spinning parameters, such as spinning temperature, surface tension, spinning solution concentration, major, and minor axis length of the spinneret hole. POLYM. ENG. SCI., 55:2148–2155, 2015. © 2015 Society of Plastics Engineers     

Synthesis and characterization of polyimides by use of metal salts and phosphorous compounds in the presence of solvent

Polyimide precursors and polyamic acid were synthesized by direct polycondensation reaction of the 1,2,3,4-butanetetracarboxylic acid (BTCA) and diamines in the presence of metal salts and phosphorous compounds. The BTCA was reacted with an initiating species, which is the phosphonium salt of metal salts and phosphorous compounds, to form acyloxy phosphonium salt building up at moderated temperatures. The salt reacts with diamine to form polyamic acid. The reaction was markedly affected by several factors: reaction temperature and time, solvent, metal salts phosphorous compounds, and tertiary amine. The polyamic acid was converted into polyimide by chemico-thermal or thermal methods. The polyimide with a high molecular weight can be prepared from BTCA and diamines and was soluble in polar aprotic solvent. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of melt-processable polyimides derived from diaminodiphenylsulfone and benzophenone tetracarboxylic dianhydride with excellent heat resistance and thermoplasticity

Polyimide has excellent heat resistance, dielectric properties, and mechanical properties, and has a wide range of applications in aerospace, electronic packaging, and insulating materials. However, traditional polyimide is difficult to melt and dissolve, and its processing is difficult, which has become an important reason limiting its practical application. Therefore, the development of high temperature-resistant thermoplastic polyimide has become a research hotspot. To prepare high temperature-resistant thermoplastic polyimide materials, a series of thermoplastic polyimides was successfully prepared using 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, 3,3′-diaminodiphenylsulfone, 2,3′,3,4′-benzophenone tetracarboxylic dianhydride, 9,9-bis(4-aminophenyl)fluorene, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane via a two-step method. The effects of non-coplanar structure and bulky groups on the solubility, processability, and thermal properties of polyimide were studied. The structure, heat resistance and thermoplasticity of polyimide were characterized via various methods. The results show that the glass transition temperature of the prepared thermoplastic polyimide is between 292 and 302°C, and has excellent thermal resistance. The processing viscosity of polyimides is as low as 9210 Pa.s, and it has a certain degree of processing properties. It may be designed to be used in high temperature-resistant hot melt adhesives for structural components, high temperature-resistant melt processing resins, or thermoplastic composite materials used in the field of aerospace in the future.     

Preparation of polyimide powder

A polyimide powder was prepared from 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) and 4,4′-oxydianiline (ODA). Polyimide powder having low molecular weight was prepared by imidizing low-molecular-weight polyamic acid. The molecular weight of this polyimide powder increased on heating in a solid state. The molecular weight increased with the decrease of crystallinity of polyimide. © 1996 John Wiley & Sons, Inc.     

Polyimide blend alignment layers for control of liquid crystal pretilt angle through baking

Polyimide films were used for liquid crystal (LC) alignment layers to control LC pretilt angles over the full range (8°-90°). The pretilt angles could be controlled using polyimide films prepared from polyamic acid for vertical LC alignment and using polyimide blend films prepared from two types of polyamic acids, one for vertical LC alignment and the other for planar LC alignment, by changing the baking times ranging from 40 to 180 min at 230 °C. The polyimide blend film could control the pretilt angle better than the polyimide prepared from just one polymer component. The LC alignment behavior was well correlated with the wettability of the polyimide films due to the fragmentation of the long alkyl side group on the polyimide surfaces by the baking process.     

Simulation of dry‐spinning process of polyimide fibers

As one type of high‐performance fibers, the polyimide fibers can be prepared from the precursor polyamic acid via dry‐spinning technology. Unlike the dry‐spinning process of cellulose acetate fiber or polyurethane fiber, thermal cyclization reaction of the precursor in spinline with high temperature results in the relative complex in the dry‐spinning process. However, the spinning process is considered as a steady state due to a slight degree of the imidization reaction from polyamic acid to polyimide, and therefore a one‐dimensional model based on White‐Metzer viscoelastic constitutive equation is adopted to simulate the formation of the fibers. The changes of solvent mass fraction, temperature, axial velocity, tensile stress, imidization degree, and glass transition temperature of the filament along the spinline were predicted. The effects of spinning parameters on glass transition temperature and imidization degree were thus discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

2,2-双(3-氨基苯基)六氟丙烷聚酰亚胺单体的合成及表征

以2,2-双(3-硝基苯基)六氟丙烷为原料,在三氯化铁/炭(FeCl3/C)、水合肼的作用下,还原得到了2,2-双(3-氨基苯基)六氟丙烷聚酰亚胺单体,并对其进行了分析表征。然后,2,2-双(3-氨基苯基)六氟丙烷与4,4’-2-六氟亚异丙基-2-邻苯二甲酸酐(6FDA)在N,N-二甲基甲酰胺(DMF)中缩聚制得聚酰亚胺聚合物。     

Adhesion and interface studies between copper and polyimide

The adhesion and interface structure between copper and polyimide have been studied. Polyimide films were prepared by spinning a polyamic acid solution (Du Pont PMDA-ODA) in an NMP solvent onto a Cu foil, followed by thermal curing up to 400°C. The adhesion strength was measured by a 90° peel test. The peel strength of 25 μm thick Cu foil to 25 μm thick polyimide substrate was about 73 g/mm with the peel strength decreasing with increasing polyimide thickness. Cross-sectional TEM observation revealed very fine Cu-rich particles distributed in the polyimide. Particles were not found closer than 80-200 nm from Cu boundary. These Cu-rich particles were formed as a result of reaction of polyamic acid with Cu during thermal curing. We attribute the high peel strength to interfacial chemical bonding between Cu and polyimide. This behavior is in contrast to vacuum-deposited Cu onto fully cured polyimide.     

Formation of graphite fiber–polyimide prepregs by electrodeposition

Nonaqueous electrodeposition of polyamic acid of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether was carried out from an emulsion containing a solvent, precipitant, emulsifier, and the polyamic acid. The amount of polyamic acid deposited onto the graphite fibers was dependent on electrodeposition parameters such as the applied current, the amount of polyamic acid (solid content), precipitant/solvent (P/S) ratio, and the acid/base (COOH/TEA) mole ratio. The weight gain of fibers increased with increased current density, P/S ratio, solid content, and deposition time. A maximum weight gain of fibers of about 95% was obtained from an emulsion composed of 3 wt % solid content, P/S ratio of 3 : 1, and TEA/COOH ratio of 1 : 1. The electrodeposition of polyamic acid onto graphite fibers proceeded in accordance with the Faraday's law of electrolysis and a Coulombic efficiency of about 62.2 mg/C was attained. Thermal analysis shows that the cured polyimide coatings were thermally stable up to 500°C. © 1996 John Wiley & Sons, Inc.     

Positive photosensitive polyimides using polyamic acid esters with phenol moieties

Polyimide resists developable with basic aqueous solutions were realized by polyamic acid esters with phenol moieties (PPh's) and naphthoquinone diazides. The polyimide precursors (PPh's) were synthesized from diamines and dicarboxylic acids that have phenol moieties through ester linkage. A selective reaction of alcohol groups with acid dianhydride groups made the synthesis of the PPh's possible, even if the phenol groups were in the reaction mixtures. The PPh's were soluble in basic aqueous developer, but their dissolution rates were too low for use as resists. To increase the resist dissolution rate, polyamic acids were added to the PPh's. By adjusting the dissolution rates in basic aqueous developers, fine patterns could be realized. The polyimide resists had high thermal stability and reliable adhesive property to silicon substrate. © 1994 John Wiley & Sons, Inc.     

Synthesis,characterization, and properties of a novel positive photoresist polyimide

An aqueous base-soluble polyimide (BAPAF/6FDA) was obtained from the polycondensation of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BAPAF) and 4,4′-(hexafluoroisopropylidene)–bis(phthalic anhydride (6FDA). It exhibits high thermal stability and high transparency at 365 nm. A novel positive photoresist was prepared by protecting BAPAF/6FDA with a trimethylsilyl group while using diazonaphthoquinone as the photosensitizer. In addition, the silylated polyimide was converted to aqueouse base-soluble polyimide in the presence of an acid and a slight amount of water. This photoresist yields a sensitivity of 110 mJ/cm² and a contrast of 3.24. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1313–1318, 1998     

Improvement in the adhesion of polyimide/epoxy joints using various curing agents

An improvement in the adhesion strength of polyimide/epoxy joints was obtained by (1) introducing a functional group on the polyimide surface, (2) improving the mechanical properties of the epoxy adhesive, (3) increasing the curing temperature, and (4) using polyamic acid as an adhesion‐promoting layer. The functional group on polyimide was introduced via treatment with aqueous KOH. An adhesion‐promoting layer was formed by spin coating polyamic acid onto a modified polyimide surface. The maximum adhesion strength of the polyimide/epoxy joint was obtained using polyamic acid as both the adhesion‐promoting layer and as the curing agent. The surface energy of the modified polyimide was examined using contact angle measurements and Fourier transform infrared spectroscopy, and the peel strength was determined by the T‐peel method. The peeled surfaces were analyzed using scanning electron microscopy and X‐ray photoelectron spectroscopy.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 812–820, 2002     

Organosoluble and light-colored fluorinated semialicyclic polyimide derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride

In this study, the alicyclic dianhydrides 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was polymerized with seven kinds of fluorinated aromatic diamines, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (1), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (2), 1,4-bis(4-amino-2-trifluoromethylphenoxy)diphenyl (3), 1,4-bis(4-amino-2-trifluoromethylphenoxy) diphenyl ether (4), 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane (5), 4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl sulfone (6), and 2,7-bis(4-amino-2-trifluoromethylphenoxy)naphthalene (7), via a two-step polycondensation procedure to prepare seven kinds of fluorinated semialicyclic polyimides (PI) PI-1 ∼ PI-7. The structures of these polyimides were confirmed by infrared spectroscopy (IR). Solubility of the polyimides was tested in various organic solvents and their thermal properties were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Ultraviolet-visible spectra (UV-vis) and near infrared absorption spectra (NIR) were obtained to evaluate the optical properties of these polyimides. The obtained polyimides PI-1 ∼ PI-7 displayed excellent solubility in a variety of organic solvents; they were readily soluble in amide-type polar solvent. These polyimide films exhibited good optical transparency in the visible light region (400–700 nm) with the transmittance higher than 80% at 450 nm, and these polyimide films showed little absorption at the optocommunication wavelengths of 1.30 and 1.55 μm. These polyimides showed good thermal stability with the 10% thermal decomposing temperatures higher than 443°C in nitrogen and the glass transition temperatures higher than 265°C. In addition, the effect of the structure of fluorinated diamines on the properties of polyimide films was also compared. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Development and thermal durability of an interfacial bond between electrolessly deposited metals and a fluorinated polyimide

The oxygen content of a fluorinated polyimide surface can be increased by exposure to an oxidant such as an alkaline permanganate solution. Deposition of an electroless metal layer on this oxidized surface results in the formation of an interfacial bond which is predominantly chemical in nature. The level of adhesion achieved depends both on the surface oxidation conditions and post-plating heating. Adhesion maxima are obtained by heating to 200°C for an electroless Cu deposit and to 300°C, the cure temperature for the polyimide film, for deposited electroless Ni. The fluorinated polyimide used in this study was derived from the reaction of 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane with pyromellitic dianhydride and was obtained from Ethyl Corporation as Eymyd® L30N resin.     

聚酰胺酸纺丝溶液的流变性能研究

由均苯四酸二酐(PMDA)和4,4'-二氨基二苯醚(ODA)在N,N-二甲基乙酰胺(DMAc)中共聚合制得聚酰亚胺前驱体——聚酰胺酸的纺丝溶液,采用哈克流变仪研究了溶液的流变性能。结果表明:聚酰胺酸溶液属于切力变稀的非牛顿流体;溶液的表观黏度随溶液温度的升高而降低,随溶液浓度的升高或聚合物特性黏度的增大而增大。溶液温度的升高、浓度的降低或聚合物特性黏度的减小均使得聚酰胺酸溶液呈现切力变稀行为的临界剪切速率变大,使得溶液的非牛顿指数增大,同时使得溶液的结构黏度指数减小。溶液的黏流活化能随剪切速率的增加或随溶液浓度的增高而下降。