Preparation of ultra-fine polyimide fibers containing silver nanoparticles via in situ technique

Ultra-fine polyimide fibers containing silver nanoparticles were prepared by electrospinning from poly(amic acid)/(trifluoroacetylacetonoto)silver(I) (PAA/AgTFA) solution. Thermal curing of the silver(I)-containing fibers led to cycloimidization of the poly(amic acid) into polyimide with concomitant silver(I) reduction. The polyimide–silver fibers were characterized by FT-IR, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The average diameters of silver nanoparticles and ultra-fine PI fibers electrospun from solutions with different amounts of AgTFA were studied, and the crystal structure of silver nanoparticles was also presented.     

Preparation of nanoporous polyimide thin films via layer-by-layer self-assembly of cowpea mosaic virus and poly(amic acid)

Low dielectric (low-κ) materials are of key importance for the performance of microchips. In this study, we show that nanosized cowpea mosaic virus (CPMV) particles can be assembled with poly(amic acid) (PAA) in aqueous solutions via the layer-by-layer technique. Then, upon thermal treatment CPMV particles are removed and PAA is converted into polyimide in one step, resulting in a porous low-κ polyimide film. The multilayer self-assembly process was monitored by quartz crystal microbalance and UV-Vis spectroscopy. Imidization and the removal of the CPMV template was confirmed by Fourier transform infrared spectroscopy and atomic force microscopy respectively. The dielectric constant of the nanoporous polyimide film thus prepared was 2.32 compared to 3.40 for the corresponding neat polyimide. This work affords a facile approach to fabrication of low-κ polyimide ultrathin films with tunable thickness and dielectric constant.     

正交设计法研究聚酰胺酸分子量及其影响因素

采用正交试验设计方法,研究了聚酰胺酸固体含量、反应温度、加料间隔时间和反应时间对聚酰胺酸分子量的影响,采用凝胶渗透色谱仪测试了不同反应条件下合成的聚酰胺酸的分子量。正交设计试验结果表明,合成最高分子量聚酰胺酸的反应条件为:反应温度为15℃,固体含量为8%,加料间隔时间为9min,反应时间为3h。在此基础上,使用TGA测试了由不同分子量聚酰胺酸合成的聚酰亚胺薄膜的热稳定性。试验结果显示,聚酰胺酸分子量越大,薄膜的热稳定性越好。     

可重复使用型耐溶剂聚酰亚胺纳滤膜的研制

以芳香二酐和自制的3,3'-二甲基-4,4'-二氨基二苯甲烷(DMMDA)二胺为单体,N-甲基吡咯烷酮(NMP)为溶剂,从分子结构的角度出发,设计合成了聚酰胺酸溶液,经化学亚胺化反应制备了高相对分子质量的可溶性聚酰亚胺材料,进一步通过浸没-沉淀相转化法制备出聚酰亚胺基纳滤膜。通过红外光谱、核磁、热重分析、扫描电镜、原子力显微镜等对合成单体和聚酰亚胺基纳滤膜的结构和性能进行了分析和表征。结果表明,成功地合成了DMMDA二胺单体,以该单体为原料制备的聚酰亚胺基纳滤膜具有较高的分离性能,对酸性红94的截留率高达92%,同时具有良好的耐溶剂性及重复使用性。     

Synthesis of poly[(amic acid)-co-(amic ester)] precursors and studies of their imidization using FT-IR and FT-Raman spectroscopy

A pollyimide precursor, poly[(amic acid)-co-(amic ester)] (PAAE), was prepared by partial esterification of poly(amic acid) (PAA). To investigate the thermal imidization behavior of PAAE, several different PAAEs were synthesized by varying the fraction of the amic ester moiety. They were then imidized using a stepwise heating process. The conversion of PAAE to polyimide was investigated as a function of ester fraction and temperature by monitoring the changes in the imide II (1374 cm^–1) and CH stretching vibrational modes (2935 cm^–1) using FT-IR and FT-Raman spectroscopy, respectively. The degree of imidization for a given temperature was compared with expected values. Electronic Publication     

Preparation of N,N-p-phenylene bismethacryl amide as a novel cross-link agent for synthesis and characterization of the core–shell magnetic molecularly imprinted polymer nanoparticles

Novel magnetic molecularly imprinted nanoparticles (MMIPs) using N,N-p-phenylene bismethacryl amide as a cross linker and super paramagnetic core–shell nanoparticle as a supporter for use in controlled release were prepared by precipitation polymerization. Novel cross-linking agents were synthesized by the reaction of methacryloyl chloride with p-phenylenediamine. Then, the Fe₃O₄ nanoparticles were encapsulated with a SiO₂ shell and functionalized with –CH=CH₂ and MMIPs were further prepared by using methacrylic acid as a functional monomer, N,N-p-phenylene bismethacryl amide as a cross-linking agent and betamethasone as template. Magnetic non-MIPs were also prepared with the same synthesis procedure as with MMIPs only without the presence of the template. The obtained MMIPs were characterized by using transmission electron microscopy, Fourier transform infrared spectrum, X-ray diffraction, energy-dispersive X-ray spectroscopy, and the vibrating sample magnetometer. The performance of the MMIPs for the controlled release of betamethasone was assessed and results indicated that the magnetic MIPs also had potential applications in drug controlled release.     

多孔性聚酰亚胺纳米粒子的制备

介绍了用"再沉淀法"并经亚胺化成功制成PI(BPDA-PDA)多孔性粒子,粒径为几百nm;在此同时,加入与PAA(PI的先驱体)有较好相容性聚丙烯酸PAS为多孔源(porogen),而在其粒子表面生成较深的、较高空穴率的空穴,在20～100nm之间.这种多孔性PI纳米粒子可作为下一代低k值PI膜材料候选者之一.     

High organosolubility and optical transparency of novel polyimides derived from 2′,7′-bis(4-amino-2-trifluoromethylphenoxy)-spiro (fluorene-9,9′-xanthene)

A novel spiro(fluorene-9,9′-xanthene) skeleton bis(ether amine) monomer, 2′,7′-bis(4-amino-2-trifluoromethylphenoxy)-spiro(fluorene-9,9′-xanthene), was prepared through a simple acid-catalyzed condensation reaction of 9-fluorenone with resorcinol to form the spiro framework through an sp³ carbon atom. Subsequent nucleophilic substitution reaction of spiro[fluorene-9,9′-(2′,7′-dihydroxyxanthene)] with 2-chloro-5-nitrobenzotrifluoride in the presence of potassium carbonate in N,N-dimethylacetamide, was followed by catalytic reduction with hydrazine and Pd/C in ethanol. A series of new polyimides were synthesized from the diamine with various commercially available aromatic tetracarboxylic dianhydrides via a conventional two-stage process with the thermal or chemical imidization of the poly(amic acid) precursors. Most of the polyimides obtained from both routes were soluble in many organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide and m-cresol. All the polyimides could afford transparent, flexible, and strong films with low moisture absorptions of 0.35–0.64% and low dielectric constants of 2.63–3.09 at 1 kHz. Thin films of these polyimides showed an UV–vis absorption cutoff wavelength at 356–384 nm, and those of polyimides from 4,4′-oxydiphthalic dianhydride and 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) were essentially colorless. The polyimides exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 540 °C in both air and nitrogen atmospheres and glass transition temperatures (T_g) in the range of 274–323 °C.     

基于离子交换与激光打印技术在含氟聚酰亚胺薄膜表面制备银-铜金属线

以4,4’-六氟亚异丙基-邻苯二甲酸酐(6FDA)和4,4’-二胺基二苯醚(4,4’-ODA)为原料制备了含氟聚酰亚胺薄膜,然后通过水解、激光打印、离子交换、化学还原等技术得到银和铜双金属的图案化聚酰亚胺薄膜。通过X-射线衍射仪、四点探针测试仪、光学显微镜、扫描电子显微镜等仪器系统研究了薄膜表面金属的形成过程及水解时间与导电性的关系。实验结果表明,随着水解时间的增加,金属线条的导电性逐渐增加,电导率最大达到500s/cm。     

接枝聚乙二醇单甲醚侧链制备聚酰亚胺多孔微球

以3,5-二氨基苯甲酸与线性低聚物聚乙二醇单甲醚在催化剂存在的条件下发生酯化反应,得到了接枝单体。以接枝单体、3,5-二氨基苯甲酸以及均苯四甲酸二酐在非水乳液体系中发生聚合反应,经过两步亚胺化及热处理得到了多孔聚酰亚胺微球。通过实验确定了接枝单体的最优反应条件:酸醇摩尔比为1.3,催化剂、携水剂的用量与醇的质量比分别为4%、130%,反应时间为6h。实验结果表明,随着接枝单体在聚酰亚胺中浓度从20%～40%,粒径逐渐增大,粒径范围为9.5～15.7μm;而玻璃化温度从210℃降至178℃;同时在接枝单体浓度为40%时得到了孔结构,比表面积为148cm3/g;通过控制热处理时气体压力可以控制孔结构大小。     

Synthesis and properties of new polyimide/clay nanocomposite films

A series of polymer–clay nanocomposite (PCN) materials consisting of polyimide and typical clay were prepared by solution dispersion. Quaternary alkylammonium modified montmorillonite, Cloisite 20A, was used as organoclay. Poly(amic acid) solution was prepared from the reaction of benzophenone-4,4′,3,3′-tetracarboxylic dianhydride and 2-(5-(3,5-diaminophenyl)-1,3,4-oxadiazole-2-yl) pyridine in dimethylacetamide. Thermal imidization was performed on poly(amic acid)/organoclay dispersion in a regular temperature-programmed circulation oven. The study of interlayer d-spacing with X-ray diffraction pattern indicates that an exfoliated structure may be present in the nanocomposite 1%. Intercalated structures were obtained at higher organoclay loadings. Nanocomposites were studied using thermogravimertic analysis and differential scanning calorimetry. Nanocomposites exhibit higher glass transition temperature and improved thermal properties compared to neat polyimide due to the interaction between polymer matrix and organoclay particles. The results are also compared with data of a similar work. Morphology study with scanning electron microscopy showed that the surface roughness in nanocomposite 1% increased with respect to pristine polyimide. Solvent uptake measurements were also carried out for the prepared materials. Maximum solvent adsorption was observed for dimethyl sulfoxide (DMSO). It was found that the solvent uptake capacity decreased with increasing clay content.     

Photo-induced liquid crystal alignment of poly(vinyl cinnamate) and fluorinated polyimide blends

Liquid crystal(LC) alignment properties were mainly affected by surface properties of alignment layers. In our previous work, we prepared poly(vinyl cinnamate) (PVCi) and polyimide blend alignment layer for thermally stable LC alignment. In this work, we utilized fluorinated polyimide for blend alignment layers in order to modify surface properties of alignment layers. For this purpose, polyimides containing fluorine unit were synthesized and used for the blend alignment layers. Fluorine containing diamine, 4,4′-bis[2-(4-aminophenyl)hexafluoropropyl]-diphenyl ether(BDAF), is used for the polyimide synthesis. We prepared the fluorinated polyimide and PVCi blend alignment layers and investigated the effect of fluorine on the LC alignment properties and pretilt angle of LC.     

Separation and purification of hyaluronic acid by glucuronic acid imprinted microbeads

The purification of hyaluronic acid (HA) is relatively significant to use in biomedical applications. The structure of HA is formed by the repetitive units of glucuronic acid and N-acetyl glucosamine. In this study, glucuronic acid-imprinted microbeads have been supplied for the purification of HA from cell culture (Streptococcus equi). Histidine-functional monomer, methacryloylamidohistidine (MAH) was chosen as the metal-complexing monomer. The glucuronic acid-imprinted poly(ethyleneglycoldimethacrylate-MAH-Copper(II)) [p(EDMA-MAH-Cu²⁺)] microbeads have been synthesized by typical suspension polymerization procedure. The template glucuronic acid has been removed by employing 5 M methanolic KOH solution. p(EDMA-MAH-Cu²⁺) microbeads have been characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) images and swelling studies. Moreover, HA adsorption experiments have been performed in a batch experimental set-up. Purification of HA from cell culture supernatant has been also investigated by determining the hyaluronidase activity using purified HA as substrate. The glucuronic acid imprinted p(EDMA-MAH-Cu²⁺) particles can be used many times with no significant loss in adsorption capacities. Also, the selectivity of prepared molecular imprinted polymers (MIP) has been examined. Results have showed that MIP particles are 19 times more selective for glucuronic acid than N-acetylglucose amine.     

On the synthesis and rebinding properties of [Co(C2H3O2)2(z-Histidine)] imprinted polymers prepared by precipitation polymerization

In the present study, the synthesis via free-radical precipitation polymerization of metal-complexing polymer microparticles capable of specific binding to [Co(C₂H₃O₂)₂(z-Histidine)] complex is reported. Initially, the functional monomer (i.e., 4-vinylpyridine, a vinyl monomer with metal chelate properties) is complexed together with the template [Co(C₂H₃O₂)₂(z-Histidine)] molecule via the mediation of cobalt ions. Evidence of the polymerizable complex formation is obtained through the compleximetric titration of the z-Histidine in the prepolymerization reaction mixture. Subsequent polymerization of the polymerizable complex with a bi-functional or tri-functional cross-linker results in the formation of imprinted polymer microparticles in the size range of 1–5 µm. The effects of agitation, cross-linker type, degree of cross-linking and molar ratio of the template to the functional monomer on the rebinding properties of the imprinted polymers are experimentally assessed. The synthesized imprinted polymers can potentially find application in the purification of his-tagged recombinant proteins.     

Layer-by-layer self-assembly of polyimide precursor/layered double hydroxide ultrathin films

The layer-by-layer (LBL) self-assembly has been extensively used as a simple and effective method for the preparation of polyelectrolyte multilayer films. In this work, we utilized this unique method to prepare polyimide precursor/layered double hydroxide (LDH) ultrathin films. Well-crystallized Co-Al-CO₃ LDH and subsequent anion exchanged Co-Al-NO₃ LDH were prepared and characterized by scanning electron microscopy and X-ray diffraction (XRD). By vigorous shaking of the as-prepared Co-Al-NO₃ LDH, positively charged and exfoliated LDH nanosheets were obtained. Atomic force microscopy and XRD investigations indicated the delamination of LDH nanosheets. The precursor of polyimide, poly(amic acid) tertiary amine salt (PAS) was prepared by the polycondensation of dianhydride and diamine, and subsequent amine salt formation. By using the LBL method, heterogeneous ultrathin films of PAS and LDH were prepared. The formation of the ordered nanostructured assemblies was confirmed by the progressive enhancement of UV absorbance and the XRD results.     

聚酰亚胺/纳米Al_2O_3三层复合薄膜的制备

将掺杂纳米Al2O3的聚酰胺酸与未掺杂聚酰胺酸在玻璃板上逐层涂膜,热亚胺化制备了3层聚酰亚胺/纳米Al2O3复合薄膜.采用扫描电镜(SEM)对该薄膜的微观形貌进行了表征,测试了薄膜的热稳定性、力学性能及电击穿场强.结果表明,复合薄膜的热性能及电击穿场强均高于掺杂薄膜及未掺杂膜,当热失重达到10%时,复合薄膜的热分解温度达到了629.1℃;与掺杂薄膜相比,复合薄膜的力学性能得到明显提高,拉伸强度和断裂伸长率分别为117.4 MPa和18.5%.     

Preparation and properties of the polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposites

The polyimide/multi-walled carbon nanotubes (MWNTs) nanocomposite films were prepared by mixing of poly(amic acid) (PAA) solution and MWNTs/DMAc suspension follow by mixture casting, evaporation and thermal imidization. To increase the chemical compatibility between polyimide matrix and MWNTs, MWNTs were modified with mixed strong acid. The results show that the dispersion of the MWNTs is improved greatly in the polyimide matrix after acid modification. The modified MWNTs are dispersed homogeneously in the polyimide matrix while the structure of the polyimide and MWNTs structures is stable in the preparation process. With the incorporation of MWNTs, the mechanical properties of the resultant nanocomposite films were greatly improved due to the strong interfacial interaction between the modified MWNTs and the polyimide matrix. The thermal stability of the nanocomposites was lower a little than pure polyimide because of the drop of thermostability of MWNTs through acid-treatment. The electrical conductivity and the dielectric constant of the nanocomposites were also having sharp increase, which is favorable for practical use in anti-static materials and embedded capacitors.     

聚酰亚胺薄膜的制备及其摩擦学性能研究

通过浸渍得到了聚酰胺酸薄膜,采用适当的方法对薄膜进行处理之后再进行热亚胺化得到聚酰亚胺薄膜.用DF-PM型动静摩擦系数精密测定装置考察所得到的聚酰亚胺薄膜的摩擦学性能.用SEM考察了聚酰亚胺薄膜的磨痕形貌和对偶Si3N4陶瓷球表面的转移膜的形貌.结果表明,聚酰亚胺薄膜在与Si3N4陶瓷球对磨时,由于在摩擦过程中,聚酰亚胺能够在对偶面上形成均匀的并且低剪切强度的转移薄膜,因此表现出了优异的减摩与抗磨性能.聚酰亚胺薄膜的摩擦和磨损行为主要取决于薄膜的制备条件.     

Formation of Ag nanoparticles within the thermosensitive hairy hybrid particles

Herein we report on the production of composite core-shell particles, which are actually self-assembly of poly (N-isopropylacrylamide)-based amphiphilic block copolymers as a template for metal-block copolymer nanocomposites formation. Organic-inorganic composites were prepared with Ag nanoparticles embedded within colloidal particles of an amphiphilic, thermally responsive polymer. To promote the incorporation of unaggregated Ag nanoparticles, temperature responsive microspheres of poly (N-isopropylacrylamide) (NIPAM) block with polystyrene were synthesized. Polyethyleneimine (PEI) could act as the linker between Ag ions (Ag nanoparticles) and poly (styrene-b-N-isopropylacrylamide) (PS-b-PNIPAM) colloids and the reducing agent in the formation of Ag nanoparticles. Transmission electron microscopy (TEM) measurements confirmed the nanostructures, ¹HNMR and FTIR characterized the components of the resulting nanoobjects. These stimuli-responsive hybrid microspheres will have potential applications in biomedical areas, such as tissue engineering and drug delivery.     

Preparation SnO₂ nanolayer on flexible polyimide substrates via direct ion-exchange and in situ oxidation process

Tin oxide (SnO(2)) nanolayers were formed on flexible polyimide (PI) substrate via direct ion-exchange and in situ oxidation process utilizing pyromellitic dianhydride/4,4'-oxidianiline-based poly(amic acid) films as polyimide precursor. During an ion-exchange process, stannous ions were doped into the precursor by immersion in ethanolic solution of stannous chloride. Subsequent thermal treatment of the tin(II)-containing precursor at a constant heating rate not only imidized poly(amic acid) to PI but also converted stannous ions into SnO(2) clusters, which diffused and aggregated onto the surface of polymer matrix, forming continuous tin oxide layers. Inductively coupled plasma (ICP) was used to investigate the ion-exchange process. Changes in chemical structure of the poly(amic acid) film and the crystal structure of tin oxides were analyzed by attenuated total reflection-Fourier transform infrared (ATR-FTIR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the microstructure of the PI/SnO(2) nanocomposite films. The nanocomposite film maintained essential mechanical property and thermal stability of pristine PI films.