Processable aromatic polyimides

Two similar polyimide systems were synthesized and characterized. The only structural difference was a sulfide linkage in the anhydride-derived portion of the first system vs. a sulfone linkage in the second. Their physical, mechanical, melt-flow and thermal properties, and their resistance to some of the more common solvents were determined. The flow properties of these polyimides indicate a potential for melt processability.     

Cresylic soluble polyimides

Polyimides are prepared by reaction of dianhydrides with aromatic diamines under dehydrating conditions to insure conversion of the polyamic acids to polyimides. Cresylic acid solubility is observed only for cyclopentane dianhydride and benzophenone dianhydride. Most of the batches are made from BPDA, since it is the preferred dianhydride for thermal stability. Of 19 aromatic diamines only 2,4- and 2,6-diaminotoluene, 2,4-diaminoanisole, 4,5-dimethyl-1,2-phenylene diamine and 1,5-diamino-4,8-dihydroxyanthraquinone contribute a great deal toward making soluble polyimides of BPDA. 2,4-Diamino-acetanilide when used as the only diamine also gives a soluble polyimide with BPDA. The solubility of polyimides can be correlated with their solubility parameters, their symmetry, and their tendency to hydrogen bond.     

Curing of polyimides

The imidization of films of the polyamic acid obtained from reaction of pyromellitic dianhydride (PMDA) with oxydianiline (ODA) was studied by dynamic mechanical thermal analysis (with the Polymer Labs DMTA), Two process regions are observed. The first process is characterized by decomplexation of the NMP/polyamic acid complex, plasticization, and imidization. The heating rate determines the character of the first process. At high temperatures (above 300°C) the second process becomes apparent. It is connected to the increase in chain mobility at these temperatures which allow molecular packing processes (densification, ordering) to occur. The ordering leads to an increase of the storage modulus. The particular transition temperature increases with annealing time.     

PMR聚酰亚胺的发展

本文主要介绍了ＰＭＲ－１５及ＰＭＲ概念，ＰＭＲ聚酰亚胺在热稳定性、工艺性、降低毒性及增韧方面的发展。     

Addition polyimides. I

Crosslinking of 4,4′(bismaleimido)diphenyl ether (BM) was investigated in presence of bis(m-aminophenyl)methylphosphine oxide (BAP), tris(m-aminophenyl)phosphine oxide (TAP), diaminodiphenyl ether (E) and 3,3-bis(p-aminophenyl)phthalide (AP). These crosslinked resins were examined for thermal stability by thermogravimetric analysis. A slight decrease in initial decomposition temperature, the temperature of maximum rate of weight loss, was observed, though the char yield in nitrogen atmosphere at 800°C did not change appreciably. Glass-cloth-reinforced laminates were fabricated from BM and amine mixtures. An improvement in mechanical properties was observed in the presence of phosphorus-containing di- and triamines.     

Multi-scale modeling of polyimides

A coarse-grained model for a set of three polyimide isomers is developed. Each polyimide is comprised of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and one of three APB isomers: 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene or 1,3-bis(3-aminophenoxy)benzene. The coarse-grained model is constructed as a series of linked vectors following the contour of the polymer backbone. Beads located at the midpoint of each vector define centers for long range interaction energies between monomer subunits. A bulk simulation of each coarse-grained polyimide model is performed with a dynamic Monte Carlo procedure. These coarse-grained models are then reverse-mapped to fully atomistic models. The coarse-grained models show the expected trends in decreasing chain dimensions with increasing meta linkage in the APB section of the repeat unit, although these differences were minor due to the relatively short chains simulated here. Considerable differences are seen among the dynamic Monte Carlo properties of the three polyimide isomers. Decreasing relaxation times are seen with increasing meta linkage in the APB section of the repeat unit. The packing behavior of the three isomers is compared with the atomistic and coarse-grained models.     

Aqueous degradation of polyimides

The effect of an aqueous environment on the tensile properties of Kapton polyimide film has been investigated. Immersion of specimens in distilled water at 25° to 100°C for time periods ranging from one hour to several hundred hours resulted in a decrease in the ultimate tensile strength of the polymer from 23 ksi to approximately 14 ksi, and a corresponding decrease in elongation to failure from 38% to approximately 5%. The kinetics of this decrease in mechanical properties are second order and yield an activation energy of approximately 15.6 kcal/mole. The reaction is slightly dependent on pH in the range 2.0 to 12.0, but is highly dependent on the pH in the range 0.4 to 2.0. The decrease in mechanical properties at pH 2.0 to 6.0 appears to be due to hydrolysis of either uncyclized amic acid linkages or diamide functional groups present in the polyimide, whereas that at pH below 2.0 is probably the result of hydrolysis of both imide and amide bonds. Prolonged reflux of the polyimide in water resulted in the extraction of a water-soluble, amide-containing material.     

Aromatic polyimides as carbon precursors

Aromatic polyimides are often employed as carbon precursors to prepare in various morphologies. After a brief explanation on carbonization behavior of aromatic polyimides, structure and functionalities of carbon materials prepared from polyimides are reviewed; highly-crystalline graphite membranes, nanoporous carbon membranes, carbon foams, carbon nanofibers and carbon nanoparticles. The advantages of polyimides as carbon precursors are discussed.     

含氟聚酰亚胺的研究进展

含氟聚酰亚胺是一类重要的高性能聚合物材料,因其突出的物理化学性质、光学和电学性能以及气体选择透过性等被广泛应用于电子工业、光波通讯、航空航天以及气体分离材料等领域。文章着重介绍了含氟聚酰亚胺的研究进展,同时简述含氟聚酰亚胺结构性能及应用。     

Fluorine-containing polyimides with phenylquinoxaline units

A series of new polyimides with phenylquinoxaline units have been synthesized by solution polycondensation of 2,2-bis(1,3-dioxo-1H,3H-isobenzofuran-5-yl)hexafluoropropane (hexafloroisopropylidene-diphthalic anhydride) with aromatic diamines containing preformed phenylquinoxaline units. These polymers are soluble in polar amidic solvents and can be processed into transparent, flexible films, having low dielectric constants and high thermal stability with decomposition temperatures above 400°C.     

聚酰亚胺胶粘剂的研究进展

聚酰亚胺(PI)作为一种特殊的功能材料,可以用作胶粘剂且具有极大的发展空间。按PI胶粘剂的粘接对象进行分类,并依次介绍了其最新的研究进展。     

Azobenzene-functionalized polyimides as wireless actuators

Wireless transduction of light into mechanical work manifested as shape-changing surfaces, adaptive structures, or actuators is a topic of considerable recent interest. In the work reported here, the photomechanical responses of a new series of crosslinked azobenzene-functionalized polyimides prepared with increasing backbone rigidity over a range of crosslinker concentrations are examined. The baseline properties of the materials were characterized with X-ray diffraction, thermal analysis, and photomechanical examination including cantilever bending experiments and tensile tests. Increasing the rigidity of the backbone repeat unit reduces the magnitude of the shape change (observed as cantilever deflection) but increases the magnitude of photogenerated stress (in tensile tests). The promise of these materials as wireless actuators was examined in photoinitiated snap-through experiments.     

Recent advances in thermosetting polyimides

Addition type imide resins are finding increased use as matrix resins for advanced composites. Many different chemical approaches have been used to synthesize imide resins which are easy to process (similar to epoxies) but higher in temperature resistance. This paper outlines recent advances in thermosetting imide resin chemistry; however, only those concepts which have been accepted by the industry and the most promising research concepts are discussed, such as:

• endomethylenetetrahydrophthalimides
• acetylene terminated polyimides
• bismaleimides
• benzocyclobutenes.

Of these, the bismaleimides are easiest to process. When used in combination with comonomers such as bisallylphenyl compounds, bis-o-(propenylphenoxy)-benzophenones, benzocyclobutenes, etc., their toughness can be improved significantly to make them prime candidates as matrices for advanced composites and adhesives.     

High-temperature reactive thermoplastic aromatic polyimides

A series of high molecular weight aromatic enyne polyimides were prepared by the condensation of various aromatic dianhydrides with (E)-1,3-bis(3-aminophenyl)-1-buten-3-yne. The polymers were soluble in common organic solvents and exhibited intrinsic viscosities as high as 0.43 (in DMAC at 30°C) with glass transition temperatures ranging from 200 to 265°C. The new thermoplastic materials have the capability to become lightly crosslinked when thermally treated during a stimulated high-temperature thermoforming process. Thermal treatment diminishes the various solvent-induced problems inherent in linear polymeric materials and advances the glass transition temperature. Copolymers were also prepared using 1,3-bis(3-aminophenoxy)benzene and (E)-1,3-bis(3-aminophenyl)-1-buten-3-yne in an effort to obtain various percentages of enyne along the polymer backbone and, therefore, control the degree of crosslinking. The solvent resistance of selected copolymer compositions both in neat resin and thermoplastic composite form was evaluated.     

XPS analysis of fluorinated polyimides

Five different fluorinated polyimides were characterized using X-ray photoelectron spectroscopy (XPS). Elemental compositions and polyimide stoichiometries as elucidated with XPS are reported. The fluorinated polyimides derived from corresponding poly(amic acid)s were completely imidized after thermal cure at 350°C, giving rise to a single N 1s peak at 400.8 eV. Interestingly, fluorine segregation on the cured polyimide surface was found to be a function of the polyimide backbone stiffness.     

Synthesis and properties of flourine-containing polyimides

A series of new flourine-containing polyimides have been synthesized from the condensation of 2,2,-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-amino-phenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, or 2,2bis[4-(4-amino-2-trifluoro-methylphenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane with various aromatic dianhydrides. The electric constant at 1 KHz in the flourine-containing polyimides decreases from 3.51 to 2.72 as flourine content increases. The poly(amic acid)s had inherit viscosities of 0.52–1.23 dL/g, depending on the diamines and dianhydrides. Most of the resulting polymers showed an amorphous nature and afforded flexible and tough films. The amount of moisture absorption decreases as flourine content in polyimides increases. The glass transition temperatures of these polyimides were in the range of 287–328°C, and the 10% weight loss temperatures were above 542°C in the nitrogen. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 609–617, 1997     

Preparation and fabrication of aromatic polyimides

Aromatic polyimides were prepared from pyromellitic dianhydride and a number of aromatic diamines. The effect of certain variables on the polymerization to, and the degradation of, the intermediate polypyromellitamic acids was studied, and a previously unrecorded reaction intermediate was isolated and identified. From these studies the conditions necessary to obtain high molecular weights were defined. Techniques were developed for the fabrication of satisfactory films and moldings.     

Novel auto-photosensitive polyimides with tailored properties

An overview is given on auto-photosensitive polyimides as introduced for the first time in 1985. It is shown how development proceeded and how the chemical basis of auto-photosensitive polyimides was extended beyond BTDA. Novel “photosensitizer tetracarboxylic dianhydrides” like 2,3,6,7-thioxanthonetetracarboxylic dianhydride (TXDA) were synthesized and copolymerized into preimidized nonphotoactive polyimides containing tetracarboxylic acids like 6FDA or ODPA. Novel photosensitive polyimides were obtained that carry all essential features of BTDA based systems plus higher photospeed. They provide the ability to better tailor material properties to specific applications.     

长链聚酰亚胺的制备与表征

以长链二胺4,4' 二(4 氨基苯氧基)二苯砜(BAPS)为单体,采用两步法分别与二酐PMDA、ODPA、BPADA合成了3种链长的聚酰亚胺。实验利用GPC监测0 05mol/L聚酰胺酸(PAA)的数均聚合度(Xn)及相对分子质量分布随缩聚时间的变化关系,结果表明该反应为一逐步缩聚反应,缩聚速率随二酐电子亲和性(EA)的递增而增加;与预聚体聚酰胺酸相比,热处理环化得到聚酰亚胺其数均分子质量( Mn)和特性粘度[η]均有所下降,而分布指数(D)增大。此外还利用红外光谱(FTIR)、差分扫描量热法(DSC)、热重分析(TGA)等对聚酰亚胺进行了表征,结果表明聚酰亚胺(PI)的玻璃化温度(tg)和热分解温度(td)随着聚合单元长度的增加而降低。