一种含三氟甲基取代不对称芳香二胺及其可溶性透明聚醚酰亚胺 的合成与表征

以2,6-二甲基苯酚和4-硝基苯甲酰氯为起始原料, 经三步有机反应设计合成了一种含氟不对称芳香二胺: (4’-(4’’-胺基-2’’-三氟甲基苯氧基)-3’,5’-二甲基苯)-(4-胺基苯)甲酮(3); 并由该二胺单体和二苯醚四酸二酐经一步法缩聚制备了一种新型含氟聚醚酰亚胺, 其特性粘度为0.68 dL/g. 该聚醚酰亚胺表现出优良的溶解性能和光学性能: 室温下不仅可以溶于N-甲基-2-吡咯烷酮、N,N-二甲基乙酰胺、N,N-二甲基甲酰胺等强极性溶剂中, 还能溶于低沸点的氯仿、四氢呋喃、二氯甲烷等溶剂中; 由该聚合物溶液所制的薄膜无色透明, 截断波长在352, 400 nm后具有高的透明性. 此外该聚醚酰亚胺还表现出良好的热性能和机械性能: 玻璃化转变温度在288 ℃, 氮气中起始分解温度在508 ℃; 该聚合物薄膜的拉伸强度为91 MPa, 断裂伸长率在10%～15%, 起始模量为1.7 GPa.     

On-line measurement of the RMS radius of gyration and molecular weight of polyimide precursor fractions eluting from a size-exclusion chromatograph

The recent introduction of multiangle light-scattering detectors for size-exclusion chromatography has made possible the measurement of the root mean square radius of gyration (R_g) and molecular weight (M) of polymer fractions eluting from a size-exclusion chromatography column. The characterization of the dimensions of a polymer may be accomplished with only a few milligrams. The dimensions of a polyimide precursor prepared by the condensation of the meta-diethyl ester of pyromellitic dianhydride with para-phenylene diamine have been measured with this technique. The dependence of R_g on M across the distribution is compared with that predicted for a freely rotating chain, and with other similar polymers measured with hydrodynamic techniques.     

Stress in polyimide coatings

The effect of film thickness on in-plane molecular orientation and stress in polyimide films prepared from pyromellitic dianhydride with 4,4′-oxydianline was investigated using a prism coupling technique to measure the refractive index. Film thickness was controlled by varying both solution concentration and spinning conditions. Birefringence, the difference between the in-plane and out-of-plane refractive indices, was used to characterize the in-plane molecular orientation. The observed birefringence is a combination of the birefringence resulting from molecular orientation and the birefringence induced by the residual stress present in the films. The birefringence decreases with increasing film thickness over the range of thicknesses studied (3–20 μm) indicating that the molecular orientation decreases with increasing film thickness. The in-plane coefficient of linear thermal expansion (CTE), controlled by the level of orientation in the film, increases from 18 to 32 × 10^?6/°C over the same thickness range. The birefringence of free-standing films was lower than that of adhered films due to the release of residual stress in the film once the film is removed from the substrate. The residual film stress arises primarily from the mismatch in CTEs between the polyimide film and the substrate to which the film is adhered. Thus, since the film anisotropy decreases with increasing thickness, the film stress increases with increasing thickness. Residual stress calculated by integrating the product of the film modulus and the CTE mismatch assuming temperature-dependent properties is comparable to experimentally measured film stress. Ignoring the temperature dependence of the film properties leads to an overestimation of stress. Moisture uptake was used to study the stress dependence of the optical properties. Moisture uptake increases both the in-plane and out-of-plane refractive indices by equal amounts in free-standing films due to an isotropic increase in the polarizability. In adhered films, an increase in moisture uptake leads to a decrease in the birefringence due to a swelling-induced decrease in the residual film stress. © 1994 John Wiley & Sons, Inc.     

共聚结构和分子量对热塑性聚酰亚胺树脂熔融与耐热性能的影响

基于具有刚性主链结构的4,4'-(六氟亚异丙基)双邻苯二甲酸酐/对苯二胺(6FDA/p-PDA)树脂体系, 通过共聚引入间苯二胺(m-PDA)、 4,4'-二氨基-2,2'-双三氟甲基联苯(TFDB)和9,9'-双(4-氨基苯基)芴(BAFL)等主链刚性且兼具大自由体积特性的芳香二胺, 以非反应性封端剂邻苯二甲酸酐(PA)对分子量进行调控, 设计制备了系列分子量可控的热塑性聚酰亚胺(TPI)树脂. 系统研究了共聚结构和分子量对TPI树脂熔融性能和耐热性能的影响, 构建了聚合物的聚集态结构与树脂熔融性能的对应关系, 并对树脂的室温和高温力学性能进行了评价. 研究结果表明, 大自由体积的芳香二胺共聚结构的引入可有效降低分子链堆砌密度, 增大聚合物的自由体积, 从而赋予树脂良好的熔融性能. 降低设计分子量可进一步改善树脂的熔融加工性. 这类具有刚性主链结构的TPI树脂兼具优异的耐热性能和力学性能, 树脂的玻璃化转变温度在308~338 ℃之间, 以TFDB和BAFL共聚制备的TPI-C-25K和TPI-D-25K树脂表现出高强高韧的特性, 拉伸和弯曲强度分别超过120 MPa和190 MPa, 断裂伸长率大于8.2%, 并且在250 ℃高温下表现出良好的耐热稳定性.     

聚酰亚胺粘结MoS2基固体润滑涂层在油介质中的摩擦学性能

为了探讨聚酰亚胺粘结MoS2基固体润滑涂层在油介质中的摩擦学性能及其作用机理,采用MHK-500型摩擦磨损试验机对聚酰亚胺粘结MoS2基固体润滑涂层在4种油介质(RP-3煤油、SG 15W-40机油、0＃柴油和液体石蜡)中的摩擦磨损性能进行了评价,并对其机理进行了初步的探讨.结果表明：与干摩擦相比,涂层在此4种油介质中的摩擦学性能均得到显著提高,其中涂层在柴油介质中的抗磨性能的提高最为突出;同种油介质中,涂层在高速(2.56 m/s)、低载(1 120 N)下的耐磨性明显优于低速(1.54 m/s)、高载(2 120 N)下的耐磨性;在低速(1.54 m/s)、高载(2 120 N)下的煤油介质中,涂层表面的物理状态在摩擦过程中的变化最终导致涂层摩擦系数的起伏和较大的磨损率.     

Preparation and properties of thermally stable polyimides derived from asymmetric trifluoromethylated aromatic diamines and various dianhydrides

A novel method for the preparation of an asymmetric fluorinated aromatic diamine, 3,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone was investigated. This new diamine containing trifluoromethyl side group was synthesized from the nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 3,4′-dihydroxybenzo phenone in the presence of potassium carbonate, followed by catalytic reduction with SnCl₂·6H₂O and concentrated hydrochloric acid. This novel diamine was used to react with different commercially available aromatic tetracarboxylic dianhydrides to prepare polyimides via thermal or chemical imidization. The polyimide properties such as inherent viscosity, solubility, thermal and surface properties were investigated to illustrate the contribution of the trifluoromethyl group and the asymmetry structure of the polyimide. The polyimides obtained had good thermal stability and the glass transition temperature values ranged from 225 to 267 °C. All of these novel polyimides held 10% weight loss at the temperature above 543 °C in air and left more than 47% residue even at 800 °C in nitrogen. The inherent viscosities of the obtained polyimides were above 0.73 dL/g and were easily dissolved in both polar, aprotic solvents and some low-boiling-point solvents. Moreover, these PI films had dielectric constants of 2.94-3.53 (1 kHz), with moisture absorption in the range of 0.07-0.34 wt%. In comparison of the PIs (5) series with the analogous symmetric PIs (6) series based on 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone, the (5) series revealed better solubility, low dielectric constant and moisture absorption.     

Synthesis and characterization of highly soluble aromatic polyimides

Two highly soluble aromatic polyimides were synthesized successfully from a diamine with two tert-butyl groups （MBTBA）and dianhydrides with a thioether or sulfone moiety（DTDA and DSDA）.Both of them showed excellent solubility in common solvents such as chloroform,tetrahydrofuran and dioxane at the room temperature.The number-average molecular weight was 6.0×10⁴ and 8.3×10⁴ according to gel permeation chromatography relative to a polystyrene standard,and the polydispersity index was 1.80 and 1.82 respectively.The glass-transition temperatures of them were 286℃and 314℃（or 315℃and 358℃）respectively,as measured by differential scanning calorimetry（or dynamic mechanical analysis）.The 5%weight loss temperature of both was near 490℃in N₂ by thermogravimetric analysis.These results indicated that the tert-butyl pendent groups reduced the interactions among polymer chains and the thioether or sulfone moiety was flexible which may improve their solubility in conventional organic solvents without the loss of thermal stability. Transparent and flexible films of the two polyimides were obtained via solution casting.The MBTBA-DTDA membrane had higher storage moduli than those of the MBTBA-DSDA membrane.     

Use of block copolymer as compatibilizer in polyimide/zeolite composite membranes

In this work, we introduced a diblock copolymer (dBC), i.e., polystyrene‐b‐poly(hydroxyl ethyl acrylate) (PS‐b‐PHEA) as a compatibilizer to enhance interfacial adhesion between PI and zeolite in PI/Zeolite/dBC (1/0.1/0.05 wt%) membrane for gas separation. FT‐IR spectroscopy showed the formation of hydrogen bonding interactions of the carbonyl and the hydroxyl in dBC with both PI and zeolite. The differential scanning calorimeter (DSC) study showed that the glass transition temperature (T_g) of PI increased upon the introduction of dBC, indicating specific interactions in the mixed matrix membranes. The gas permeabilities of H₂, N₂, O₂, and CO₂ through PI/zeolite 5A/dBC membranes were reduced but the permselectivity were increased compared to neat PI membrane. Copyright © 2009 John Wiley & Sons, Ltd.     

Non‐surfactant template‐directed synthesis of SiO2‐polyimide hybrid self‐standing films with ordered mesoporous structure

The silica‐PI hybrid self‐standing films with ordered mesoporous structure have been prepared by using dibenzoyl‐L ‐tartaric acid (L ‐DBTA) as non‐surfactant template under mild sol–gel route. Polyimide matrix was obtained from polyamic acid (PAA) via thermal imidization process and the template was removed in this process. The PI‐based hybrid film with 20 wt% SiO₂ obtained from DBTA presented the ordered mesoporous channels with average pore size of about 2.0 nm and BET surface area of 1167 m²/g. FTIR and SEM studies indicated that the hydrogen bond interaction between the carboxylic groups of DBTA and benzamide bonds of PAA made the PAA possibly participate in the assembly process of the aggregates of the non‐surfactant template molecules. The mechanical, thermal and some physical properties of these hybrid films materials were also characterized. Copyright © 2010 John Wiley & Sons, Ltd.