聚酰亚胺/SiO2杂化膜的制备、表征和气体渗透性能

采用溶胶凝胶法,在以TiO2为过渡层的硅藻土-莫来石陶瓷膜管基底上,制备了组分不同的聚酰亚胺/SiO2杂化膜。聚酰亚胺是利用4,4′-六氟亚异丙基邻苯二甲酸酐、2,4,6-三甲基-1,3-苯二胺和3,5-二氨基苯甲酸在溶液中进行亚胺化完成的。采用FT-IR、TG/DTA、DSC、SEM、BET和气体渗透测定对膜进行了表征和测试。结果表明,聚酰亚胺通过支链上的羧酸基和SiO2相键连织构成了具有规则孔道的空间网状结构,并且随着SiO2含量的增加孔径逐渐减小;杂化膜具有较高的热稳定性和有机无机兼容性;相对于聚酰亚胺膜,杂化膜对H2、CO2和H2O与N2相比较具有较高的分离性,SiO2含量为25(wt)%的杂化膜对H2/N2、CO2/N2和H2O/N2的分离因子分别达到55.9、31.1和42.8。     

Low percolation conductive graphite flakes-filled poly(urethane-imide) composites with high thermal stability via imidization self-foaming structure

In the study, the conductive graphite flakes filled poly(urethane-imide) composites (PUI/GFs) with high performance were constructed by the thermal imidization self-foaming reaction. It was found that the foaming action could promote the redistribution of GFs during curing process and the formation of stable linear conductive pathways. The percolation threshold of PUI/GFs composites was lowered from 1.26 wt% (2000 mesh GFs) or 0.86 wt% (1000 mesh GFs) to 0.79 wt% (500 mesh GFs), which were relatively low percolation thresholds for polymer/GFs composites so far. When the content of 500 mesh GFs was 4.0 wt%, the electrical conductivity of the composite was as high as 3.96 × 10^?1 S/m. Also, a poly(urethane-imide) (PUI) matrix with excellent thermal stability (T_d10%: 334.97 °C) and mechanical properties (elongation at break: 324.52%, tensile strength: 15.88 MPa) was obtained by introducing the rigid aromatic heterocycle into the polyurethane (PU) hard segments. Moreover, the zero temperature coefficient of resistivity for the composites was observed at the temperature range from 30 °C to 200 °C. Consequently, PUI/GFs composites may provide the novel strategy for considerable conductive materials with high thermal stability in electrical conductivity.     

Thermal imidization of poly(pyromellitic dianhydride-4,4′-oxydianiline) precursors on fluoropolymers modified by surface graft-copolymerization with glycidyl methacrylate

Composite films of polyimide (PI) and poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) or of PI and poly(tetrafluoroethylene) (PTFE) were prepared by thermal imidization of the poly(amic acid) (PAA) precursors of poly(pyromellitic dianhydride-4,4′-oxydianiline) (PMPA-ODA) on glycidyl methacrylate (GMA) graft-copolymerized FEP and PTFE films. The resulting PI/GMA-g-FEP and PI/GMA-g-PTFE composites exhibited T-peel adhesion strength of approximately 7.0 and 6.5 N/cm, respectively, compared to negligible adhesion strength for the laminates prepared from thermal imidization of the PAA on the pristine and the Ar plasma-treated FEP and PTFE films. X-ray photoelectron spectroscopy (XPS) results revealed that both the PI/GMA-g-FEP and PI/FEP-g-PTFE composite films delaminated by cohesive failure inside the FEP and PTFE films, respectively. The so-delaminated PI films with a covalently tethered FEP or PTFE surface layer were highly hydrophobic, having static water contact angles above 140°. The highly hydrophobic property depends on both the composition and roughness of the delaminated surface.     

Structures and Properties of Supported Polyimide/SnO2 Hybrid Membranes

A series of polyimide/SnO2 hybrid membranes supported on TiO2/kieselguhr-mullite were prepared from polyimide with a large amount of carboxyl and SnO2 sol via a sol-gel process. The SnO2 phase chemically linked with the polyimide through the pendant carboxyl along the polyimide. The hybrid membranes were highly homogeneous, and when the SnO2 contents reached 15wt% the SnO2 phase was observed as particles with a diameter of 5 nm dispersed in the hybrid membranes . The cross-linking between the SnO2 phase and polyimide effectively enhanced the glass temperature of the hybrid films. With the increasing of the SnO2 contents, the pore sizes of the membranes decreased, and their pore sizes were mainly focused on 3.8, 3.1, 2.8 and 2.4 nm. The hybrid membranes showed higher permeability for H2, CO2, CO and H2O when compared to the pure polyimide. The separation factors of the polyimide/SnO2 hybrid membranes with 15wt% SnO2 content for H2/N2, CO2/N2, CO/N2 and H2O/N2 were 54.1, 30.2, 35.9 and 40.1, respectively.     

Comparison of different methods for determining the imidization degree of polyimide fibers

In this study, polyimide fibers at different stages of imidization were characterized by TGA, DSC, and FTIR. The imidization degree(ID) calculated by TGA was based on the weight loss of each sample, which was caused by the imidization of residual amic acid groups. The results of TGA showed good regularity with the thermal treatment temperature of the PI fibers. For DSC, the ID was calculated based on the area of endothermal peak of each sample. Compared with TGA, DSC showed a relatively higher value because the endothermal peak was reduced by the exothermic re-formation of polyamic acid which may be partially degraded during thermal treatment. The IDs obtained by the FTIR spectra generally showed poorer regularities than those obtained by both TGA and DSC, especially for the results calculated using the 730 cm-1 band. Based on the 1350 cm-1 band, the obtained IDs showed better agreement with the TGA or DSC results. The results obtained by these three methods were compared and analyzed. The ID obtained by TGA showed much more reliability among these three methods.     

Synthesis of functionalized tetracene dicarboxylic imides

For the first time, a synthesis of tetracene dicarboxylic imides was established with 1,2,3,4-tetrahydrotetracene (1) instead of tetracene as the starting material. Mono-bromination of 1 by CuBr₂ followed by a Friedel-Crafts reaction, oxidation, and imidization gave the tetrahydrotetracene carboxylic imides 5a-b. Subsequent oxidative dehydrogenation of 5a-b with DDQ afforded the functional tetracene dicarboxylic imide monobromides 6a-b, which can be further functionalized to provide functional materials such as the ‘donor-acceptor’ type compounds 7a-b.     

1,6-Disubstituted perylene bisimides: concise synthesis and characterization as near-infrared fluorescent dyes

Detailed studies on bromination and subsequent imidization of perylene bisanhydride were reported. 1,6,7,12-Tetrabromoperylene bisimide was obtained in an optimized high yield. In addition, 1,6-disubstituted regioisomer was separated for the first time in isomerically pure form, and the structure was confirmed by ¹H NMR, MS, element analysis, and photophysical measurements. By using a mixture of regioisomers 1,6- and 1,7-dibromo-perylene bisimide, 1,6-dipiperidinylperylene bisimides (1,6-Piper-Pery) were synthesized, purified, and their fluorescence were measured with a peak at 760 nm. These compounds can be used as stable near-infrared absorbing and fluorescent dyes.     

聚酰亚胺纤维的研究进展

聚酰亚胺纤维由于分子主链含有刚性的芳杂环结构,赋予其优异的力学、热学、耐辐照、介电以及化学稳定性等性能,从而在航空航天、高温耐热、防火阻燃、电子器件、核能等领域具有广泛应用前景,并成为21世纪最具潜力的高性能纤维之一。近年来,随着单体来源、工艺条件的不断改善,聚酰亚胺纤维的研究得到更大关注和投入,极大促进了聚酰亚胺纤维的规模化制备和应用发展开发。本文综述了近年来高性能聚酰亚胺纤维的国内外研究成果,并针对不同化学结构、纺丝工艺以及亚胺化方法对纤维性能的影响进行阐述,同时也对其发展趋势进行展望。     

原位红外光谱法研究电纺聚酰胺酸纳米纤维膜热亚胺化过程

以均苯二酐和二苯醚二胺为原料合成聚酰胺酸溶液,通过静电纺丝法制得聚酰胺酸纳米纤维膜.利用原位红外技术研究亚胺化进程,并以优化的条件制得聚酰亚胺纳米纤维膜.研究结果表明,当升温速率为2℃/min时,在350℃可实现100%亚胺化;升温速率过快,纳米纤维膜的亚胺化程度较低;采用快速-慢速相结合的升温方法,则可以有效地提高亚胺化效率.     

负载型聚酰亚胺/SnO2杂化膜的结构和性能

通过溶胶凝胶法， 以硅藻土-莫来石陶瓷膜管为支撑体，TiO2为过渡层， 利用具有大量支链的聚酰亚胺和SnO2溶胶制备了系列不同SnO2含量的负载型聚酰亚胺/SnO2杂化膜．采用TEM、FTIR、XPS、TG/DTA、DSC、BET和气体渗透测定对系列膜的微观型态、化学结构、热稳定性、孔结构和气体渗透性能进行了表征和测试． 结果表明，SnO2相与聚酰亚胺支链羧酸基发生化学键连； 杂化膜具有较好的有机无机兼容性， 当SnO2达到15%时，SnO2相在杂化膜中以颗粒状存在， 其粒径约为5 nm；SnO2相与聚酰亚胺间的化学键连有效的提高了杂化膜的玻璃化温度； 随着SnO2含量的增加， 杂化膜的热分解温度逐渐下降； 系列膜具有均匀的孔道结构， 其孔径分别为3.8、3.1、2.8和2.4 nm． 相对于聚酰亚胺膜， 杂化膜对H2、CO2、CO和H2O具有较高的分离性，SnO2为15%的杂化膜对H2/N2、CO2/N2、CO/N2和H2O/N2的分离因子分别达到54.1、30.2、35.9和40.1．