A kinetic study of the imidization of aromatic polyamido acids

Conclusions An experimental procedure is given for obtaining the kinetic characteristics of the imidization of polyamido acids.A first-order equation has been selected to describe the experimental data; mean values of its coefficients and of their dispersion have been calculated.Recommendations have been formulated on the use of the values of the kinetic model parameters which have been obtained for setting up a technological process with the objective of attaining a required degree of cyclization.Translated from Khimicheskie Volokna, No. 2, pp. 13–14, March–April, 1985.     

Choice of optimum regimes for electric heating of chamotte-polystyrene mixtures on a liquid glass solution

It is shown that introduction of liquid glass affects not only the mechanism of filtration moisture transfer but also the rate of increase of the temperature of the mixture. By increasing the amount and density of the introduced additive it becomes possible to heat a chamotte-polystyrene mixture more rapidly. The parameters of two-stage electric heating with various contents of liquid glass are presented and the optimum density of the solution is shown to be 1.36 g/cm³. Special features of the green and recommendations for removing the mold after electric heating are presented with allowance for the volume stress state of the mixture compacted in the closed volume of the mold. Taking into account the high temperature of the green after demolding, the drying time of the green and the temperature of the heating agent are determined.     

2,6-二甲氧基苯胺的合成与结构表征

研究2,6-二甲氧基硝基苯催化加氢制备2,6-二甲氧基苯胺的工艺。结果表明,室温条件下及乙醇介质中,氢气压强为1．0MPa的条件下,选择Pd/C催化剂（2％,w／w）,可以高活性的催化合成2,6-二甲氧基苯胺,收率可达80％。其结构经过1H NMR鉴定。     

Aging of spinning solutions of PM polyamido acid

Conclusions The aging of concentrated spinning solutions of PM PAA polyamido acid has been investigated with the use of viscosimetry, exclusion liquid chromatography, and rheology.It has been found that the aging of PAA solutions is accompanied by reactions of further polycondensation and of transamidation. These reactions lead to a decrease in the polydispersity index and in structure-formation in the solution, which also causes the observed nonparallel change in intrinsic and effective viscosities of PAA solutions in the initial stages of the process.Translated from Khimicheskie Volokna, No. 3, pp. 15–17, May–June, 1987.     

湿度传感器用聚酰亚胺材料亚胺化工艺研究

利用红外光谱、差热和热失重等分析手段,对聚酰胺酸(PA)的亚胺化工艺过程进行了研究,分析了聚酰亚胺薄膜样品在热演化过程中的分子结构变化,揭示了PA向聚酰亚胺(PI)转化的物理化学过程。实验发现,70～110℃之间各种溶剂挥发比较激烈,PA环化脱水转为PI的亚胺化反应在250℃已经基本完成。如果在150℃以下缓慢升温,使溶剂和化学反应生成物充分挥发,或在真空环境下进行亚胺化,有利于避免敏感膜出现气孔或开裂。     

Thermoanalytical investigation of transformation of polyamido acid into polyimide

The effect of solvent and schedules of treatment of solutions of polyamido acid synthesized from diaminodiphenylic ether and pyromelitic dianhydride on its transformation into polyimide, and the effect on thermal characteristics of the latter, has been investigated by simultaneous thermogravimetric and differential thermal analysis. It was shown that dimethyl-formamide strongly affects the formation and properties of polyimide film. Optimum conditions of preparation of polyimide films were determined with the authors' taking into account the high reactivity of dimethylformamide. A possibility of using a water-acetone mixture as a medium for the preparation of polyimide films was shown.     

聚酰胺酸纤维热酰亚胺化的研究

采用聚酰胺酸纤维热酰亚胺化处理方法制备聚酰亚胺纤维,研究了不同热处理条件对聚酰亚胺纤维性能的影响。结果表明,采用定长处理和持续升温方式,真空氛围,热处理温度420℃,得到的聚酰亚胺纤维性能较好,其断裂强度达5.06 cN/dtex。     

Study on the imidization kinetics of polyether-ester polyamic acid in solid phase by microwave radiation

The polyether-ester polyamic acid imidization process in a solid state was studied by microwave radiation. The imidization content at different radiation times was calculated quantitatively by FTIR and was confirmed by the results of dynamic mechanical analysis (DMA). The microwave radiation imidization may drop the reaction temperature and cut the raction time down in comparison with the thermal imidization. It may be expected theoretically that the microwave radiation may generally be suitable for the condensation polymerization reaction and facilitates the reaction, especially at its later stage. © 1996 John Wiley & Sons, Inc.     

Dry-jet wet spinning of aromatic polyamic acid fiber using chemical imidization

A solution of about 15% polyamic acid (PAA) prepared from 4,4′-oxydianiline and pyromellitic dianhyride in N,N-dimethyl acetamide (DMAc) was used for fiber spinning. To obtain a high draw ratio of the PAA fiber during spinning, acetic anhydride or acetic anhydride and pyridine were added to the PAA solution to make it slightly gelled; such gelling contributed to high drawing of the PAA fibers during spinning. Before spinning the properties of the solution after acetic anhydride or acetic anhydride and pyridine were added, and the diffusion property of DMAc into various coagulants were examined. Even though acetic anhydride was only added to the spinning solution, the diffusion rate became slower and the solution viscosity increased, because PAA was converted to the corresponding polyimide (PI). Pyridine affected the rate dramatically. The mechanical properties of the PAA fibers obtained in this system were examined. Solid PI fibers were also obtained by annealing of the PAA fibers. The ultimate stress and initial modulus of the PAA fiber were around 268 MPa and 4.1 GPa, respectively. After the fiber was annealed at 350°C without tension for 30 min under nitrogen, these values increased to around 399 MPa and 5.2 GPa, respectively.     

Determination of molecular weight and molecular radius of the polyamido carboxylic acid dendrimer using generation numbers

Using of a Molecular equation of a first dendrimer surface and its relation to dendrimer molecular radios, it is possible to suggest the number of generation. Whereas a relative molecular weight is affiliated to the number of molecule formed in structural cells and on the other hand, structural cells have definite and determined dimensions, so by a simple replacement, the dendrimer molecular weight was directly related to its generation number. Data analysis derived from specific equation was shown that the prediction of a dendrimer molecular weight may be applicable by a specific generation.Molecular weight of polyamido carboxylic acid dendrimer with specific number of generation could be theoretically estimated using the following eqs. (4) and (5).

y = log M_w

=2.0703 + 0.0844R_i (4)

=2.6339 + 0.4750G_n (5)

R_i and G_n are molecular radius and number of generation respectively.Such equations would result the molecular radius of the dendrimer. In this invented model there is no need to experiments and it can be key value to evaluate the experimental data.     

Efficient optimum solution for high strength Al alloys matrix composites

This papers describes a search technique to optimize the fabrication process conditions of the high wear resistance Al alloy matrix composites reinforced with different volume percentages of boron carbide particles. An experimental investigation was then carried out on the abrasive wear behavior of the composites in terms of abrasive particle size, weight fraction and applied load in pin-on-disc type of wear machine. Particle swarm optimization suffers from premature convergence problems when applied to high-dimensional problems, which results in a low optimization precision or even failure. In this study, a self-organizing hierarchical particle swarm optimizer based on the shrinking strategy is introduced for high dimensional function processing optimization of Al matrix composites in order to avoid the premature convergence effectively.     

尿素氯化胆碱低共熔溶剂催化聚酰胺酸亚胺化研究

研究了均苯四甲酸二酐（PMDA）和4，4，-二氨基二苯醚（ODA）为单体制取聚酰亚胺（PI）的清洁过程。首先在N,N-二甲基甲酰胺（DMF）中获得聚酰胺酸（PAA）。之后，以尿素-氯化胆碱低共熔溶剂（DES）为化学酰亚胺化催化剂，乙酸酐为脱水剂，协同实现PAA亚胺化。所得产物PI可通过简单过滤分离。用FTIR、TGA-DSC和元素分析等对PAA和PI的结构进行表征。同时考察了反应时间、反应温度、DES催化剂与脱水剂用量等对PAA亚胺化反应的影响。得到亚胺化最佳反应条件为：温度80 ℃，DES与乙酸酐体积比1：2、PAA与DES物质的量比1：2，在该条件下制备的样品，其热重和红外光谱分析结果证实了亚胺键的生成。此外，DES 和DMF可重复使用，过程绿色不使用有毒有害的吡啶、咪唑和喹啉类催化剂。     

Structure and imidization of polyamic acid salt Langmuir–Blodgett films

Polyimide Langmuir‐Blodgett (LB) films were prepared with a Pyromellitic dianhydride‐4, 4′ oxydianiline precursor, and the properties of the polyamic acid salt monolayer characterized by different methods. The π‐A relationship revealed that the precursor monolayer exhibits anisotropy on the water surface, the Wilhelmy plate being more sensitive to pressure when it is perpendicular to the compression direction. FTIR results showed that polyamic acid salt LB films have lower imidization energy than the corresponding painting films and can be imidized at lower temperature. The molecular arrangement in the LB films was studied by X‐ray diffraction and polarized FTIR, showing that the polyamic acid salt LB film is of Y‐type, in which the molecules are highly oriented, with the main chain lying parallel to the substrate and the long fatty acid chains stretching out at a certain angle. © 2002 Society of Chemical Industry     

Spectrophotometric analysis of polymer mixtures based on a copolymer of acrylonitrile and a polyamido acid in dimethylacetamide

Conclusions An instrumental method of analysis of the composition and concentration of polymer compositions from mixtures of a copolymer based on acrylonitrile and a polyamido acid in dimethyl acetamide from their IR spectra has been proposed.The rapidity and selectivity of the method, and the possibility of carrying out the analysis directly on the object without use of auxiliary operations, made it possible to recommend it for serial analyses.Translated from Khimicheskie Volokna, No. 6, pp. 55–56, November–December, 1986.     

Kinetics of imidization of poly(amic acid) in miscible and immiscible polymer blends

Blends of commercial poly(amic acid), LARC-PAA polymer were prepared with thermoplastic polyimide P84. The blends were shown to be miscible over a certain composition range. Chemical imidization of LARC-PAA in the blends leads to phase separation. Thermal imidization of LARC PAA in the blends was carried out in the solid state. Miscible compositions of the blend remained miscible after imidization and showed a single glass transition for each blend. Immiscible compositions after imidization remained immiscible and showed two glass transition temperatures in the DSC scans. The kinetics of thermal imidization of PAA to polyimide (PI) in the solid state were studied using FTIR. In the immiscible blend the kinetics remained unaffected while in the miscible state the rate of imidization became faster than that of the pure PAA.