可溶性BAPP-MDA-ODPA共聚聚酰亚胺的合成与性能

用2,2-双[4-(4-氨基苯氧基)苯基]丙烷(BAPP)和4,4′-二氨基二苯甲烷(MDA)作为二胺,3,3,′4,4′-二苯醚四羧酸二酐(ODPA)作为二酐,以N,N-二甲基甲酰胺(DMF)为溶剂,通过常规的两步法,分别经热亚胺化和化学亚胺化过程合成了可溶性共聚聚酰亚胺。用FT-IR对聚合物的结构进行了表征,FT-IR测试结果表明在1 780 cm-1、1 720 cm-1和725 cm-1左右出现了聚酰亚胺的特征吸收峰。采用溶解性测试、DSC、TGA、拉伸测试和吸水率测试对产物的性能进行了测试。共聚聚酰亚胺在常见有机溶剂中可溶,并且有很好的热稳定性,在氮气氛中,起始降解温度超过500℃,800℃质量保持率为58.2%。共聚聚酰亚胺膜的拉伸强度、拉伸模量、断裂伸长率分别为103.5 MPa,2.36 GPa和11.7%。同时共聚聚酰亚胺膜还有很低的吸水率,为0.87%。     

The Effect of Asymmetric Heterocyclic Units on the Microstructure and the Improvement of Mechanical Properties of Three Rigid‐Rod co‐PI Fibers

Three kinds of rigid‐rod copolyimide (co‐PI) fibers are prepared by wet‐spinning of their precursor poly(amic acid)s, which are copolymerized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), p‐phenylenediamine (PDA), and the third asymmetric heterocyclic diamines, including 2‐(4‐aminophenyl)‐5‐aminobenzoxazole (BOA), 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ), and 2,5‐bis(4‐aminophenyl)‐pyrimidine (PRM), respectively. The asymmetry is increasing in the order PRM < BOA ≈ PABZ. The introduction of asymmetric heterocyclic units results in mesomorphic order structure and decreases the size of microvoid of PI fiber, which apparently improves the toughness of PI fiber and shows positive effects on mechanical properties. The tensile strength and initial modulus of co‐PI fibers are in the ranges of 2.6–3.2 GPa and 91.8–133.5 GPa, respectively. The lowest asymmetry leads to the highest lateral order, crystal orientation, and initial modulus of BPDA/PDA/PRM co‐PI. Moreover, the introduction of asymmetric heterocyclic units can effectively improve compressive properties. BPDA/PDA/PABZ co‐PI fiber shows the highest loop strength and recoil compressive strength due to hydrogen bonding interactions. The highest orientation leads to the lowest transverse strength of BPDA/PDA/PRM co‐PI fibers, reducing the recoil compressive strength.

     

ODPA/异构ODA共聚酰亚胺的合成及其性能研究

采用3,3′,4,4′-二苯醚四甲酸二酐(3,3′,4,4′-ODPA),4,4′-二氨基二苯醚(4,4′-ODA)和3,4’-二氨基二苯醚(3,4′-ODA)为原料合成了共聚酰亚胺,实验中还以邻苯二甲酸酐(PA)为分子量调节剂,制备了理论分子量为10000的共聚酰亚胺,主要研究了其热性能和结晶性能。结果表明,与均聚型聚酰亚胺(ODPA/4,4′-ODA为原料合成)比较,间位异构体3,4′-ODA的加入使聚酰亚胺的玻璃化转变温度降低。经过等温结晶处理后,能够在DSC测试中出现较明显的熔融峰,而且延长结晶时间或者升高结晶温度有利于晶体的进一步完善。但是当共聚单体3,4′-ODA的加入量增加到10%(摩尔比)时,即使经过较长时间的等温处理,该共聚酰亚胺依然为无定形结构。     

Synthesis of perylene dianhydride-incorporated main chain polyimides and sequential structural transformation through a dipolar cycloaddition

Perylene dianhydride (PDA)-incorporated polyimides were prepared. The perylene unit in the polyimide was thermally converted to the corresponding N-heterocyclic polyarene unit through a Diels–Alder reaction. The monomer, 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (6FAP), was modified via O-alkylation to improve the solubility of the polymer. 2-Ethylhexyl-attached 6FAP yielded a soluble copolyimide that contained ca. 70 mol% PDA using pyromellitic dianhydride. The perylene unit of the copolyimide transformed to a polyarene unit through the dipolar cycloaddition of 4-aryl-1,2,4-triazole-3,5-dione (TAD) and maleic anhydride. The perylene transformation of the polyimide occurred with 50% conversion with maleic anhydride and quantitatively with TAD. The PDA-copolymer exhibited a spectral blue-shift and red-shift by maleic anhydride and TAD, respectively.     

Gas permeability and permselectivity of photochemically crosslinked copolyimides

A series of copolyimides were prepared from 2,4,6-trimethyl-1,3-phenylenediamines (3MPDA), 3,3′,4,4′-benzophenone tetracarboxyl dianhydride (BTDA), and pyromellitic dianhydride (PMDA). Modification of the copolyimides by ultraviolet irradiation were carried out. Gas permeabilities of H₂, O₂, and N₂ through the copolyimides and photochemically crosslinked copolyimides were measured at temperatures from 30 to 90°C. The relationships between gas permeabilities and temperature are in agreement with the Arrhenius equation. The structure of photochemically crosslinked copolyimides were characterized by Fourier transform infrared and gel measurement methods. Linear relationships between both log P and E_p and the volume fraction of PMDA–3MPDA exist. Photochemically crosslinking modification result in a decrease in gas permeability and an increase in E_p and α(H₂/N₂) for all the copolyimides. For H₂/N₂ separation, photochemically crosslinked copolyimides are of higher gas permeabilities and permselectivities simultaneously than normal polyimides. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 521–526, 1999     

Flexible Backbone Aromatic Polyimide Adhesives

Continuing research at Langley Research Center on the synthesis and development of new inexpensive flexible aromatic polyimides as adhesives has resulted in a material identified as LARC-F-SO₂ with similarities to polyimidesulfone (PISO₂) and other flexible backbone polyimides recently reported by Progar and St. Clair. Also prepared and evaluated was an endcapped version of PISO₂. These two polymers were compared with LARC-TPI and LARC-STPI, polyimides researched in our laboratory and reported in the literature.

The adhesive evaluation, primarily based on lap shear strength (LSS) tests, involved preparing adhesive tapes, conducting bonding studies and exposing lap shear specimens to 204°C air for up to 1000 hrs and to a 72-hour water boil. LSS tests at RT, 177°C and 204°C were performed before (controls) and after these exposures. The type of adhesive failure as well as the Tg was determined for the fractured specimens.

The results indicate that LARC-TPI provides the highest LSSs, 33 MPa at RT, 30 MPa at 177°C, and 26 MPa at 204°C. LARC-F-SO₂, LARC-TPI and LARC-STPI all retain their strengths after thermal exposure for 1000 hrs and PISO₂ retains greater than 80% of its control strengths.

Most of the four adhesive systems showed reduced strengths for all test temperatures although they still retained a high percentage of their original strength (<60%) except for one case.

The predominant failure mode was cohesive with no significant change in the Tgs.

Although the LARC-F-SO₂ could not be prepared in diglyme alone as the solvent, the properties of the resulting adhesive were notable. The darkening of the adhesive during bonding was typical of systems which utilize amide solvents.     

Evaluation of a thermoplastic polyimide (422) for bonding GR/PI composite

A hot-melt processable copolyimide designated 422 previously synthesized and characterized as an adhesive at NASA Langley Research Center for bonding Ti-6A1-4V has been used to bond Celion 6000/LARC-160 composite. Comparisons are made for the two adherend systems. A bonding cycle was determined for the composite bonding and lap shear specimens were prepared which were thermally exposed in a forced-air oven for up to 5000 h at 204°C. Lap shear strengths (LSSs) were determined at room temperature, 177°C, and 204°C. After thermal exposure to 5000 h at 204°C, room temperature and 177°C LSSs decreased significantly; however, a slight increase was noted for the 204°C test. Initially the LSS values were higher for the bonded Ti-6AI-4V than for the bonded composite; however, the LSS decreased dramatically between 5000 and 10 000 h of 204°C thermal exposure. Longer periods of thermal exposure up to 20 000 h resulted in further decreases in LSSs. Although the bonded composite retained useful strengths ( > 11.1 MPa) for exposures up to 5000 h, based on the poor results of the bonded Ti-6A1-4V beyond 5000 h, the 422 adhesive bonded composites would most likely also produce poor strengths beyond 5000 h exposure. Adhesive bonded composite lap shear specimens exposed to boiling water for 72 h exhibited greatly reduced strengths at all test temperatures. The percent retained after water boil for each test temperature was essentially the same for both systems.     

PMDA/ODA型聚酰亚胺的共聚改性研究

以1,3-双(4-氨基苯氧基)苯(队PB134)和4,4'-二氨基二苯醚(ODA)为二胺单体,与均苯四甲酸二酐(PM-DA)进行共聚,合成了一系列具有一定溶解性的聚酰亚胺(PI).采用IR、TGA、DSC、XRD和拉伸实验等手段,对其结构和性能进行了研究.结果表明:共聚酰亚胺(CoPI)薄膜为非晶态结构,其热性能和拉伸强度与均聚物相当,模量有所降低,而断裂伸长率显著提高.     

High-performance polymer films. III. Preparation and characterization

A series of polyimide and copolyimide films were prepared by film casting, drying, and thermal imidization from the respective precursor poly(amic acid) (PAA) and copoly(amic acid) solutions derived from two dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and two diamines, 4,4′-oxydianiline (ODA) and a proprietary aromatic diamine (PD) as monomers. Depending on the solution's inherent viscosity value (molecular weight) and the nature of the polymer chains (derived from rigid or flexible monomers), precursor poly(amic acid) and copoly(amic acid) solution concentrations of 8–12% (w/w) were found to be suitable for the preparation of good quality polyimide/copolyimide films. The recovery of film toughness and creasability from the brittleness at the intermediate temperature of the cure cycle depended not only on the molecular weight of the precursor poly(amic acids)/copoly(amic acids) but also on their chain flexibility. The poly(amic acid) derived from both rigid dianhydride and diamine practically gave rise to a brittle film of polyimide even after curing to 360°C. The resulting polyimide and copolyimide films were compared with Du Pont's Kapton H film. The density of the films was in the range 1.39–1.42 g/cm³. The thickness of most of the films was in the range 20–30 μm. The HPF 3 film, based on PMDA–PD, appeared to be highly colored (reddish brown), and the HPF 2 film, based on BTDA–ODA, had the lightest yellow coloring among the films in this investigation, including Kapton H film. HPF 2, HPF 6, and HPF 8 films were more amorphous than the other films. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 976–988, 2001     

Synthesis and characterization of multifunctional copolyimide incorporating triarylamine and NLO chromophore in backbone

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