Chunyan Qu

Preparation and characterization of magnetic polyimide composite films copolymerized with aminophthalocyanine-coated Fe3O4 nanocrystals

Iron-aminophthalocyanine-coated Fe3O4 hybrid nanospheres were synthesized by a one-step solvent-thermal method and followed by a catalyticxa0hydrogenation route. To effectively utilize the excellent magnetic sensitivity of the functional aminophthalocyanine/Fe3O4 hybrid nanospheres, we have developed a novel series of flexible Fe3O4@polyimide (PI) composite films, which was prepared with various Fe3O4/FePc–NH2 nanoparticle loadings (7, 15, 27 and 40 wt%). All of the flexible thin films have uniform morphology without any agglomeration, which had been confirmed by the analysis of scanning electron microscope images. The above composite films, which have the higher saturation magnetization compared with that of the corresponding pure Fe3O4/PI films, illustrate that the excellent compatibility and homogeneous dispersion of the amine-coated Fe3O4 particles in the PI matrix based on the strong chemisorptions of PI onto the Fe3O4 surfaces and polymerization reactions between the amine groups and anhydride groups could significantly affect the magnetic properties of nanocomposite materials. The observed enhanced thermal stabilities, dramatic increased storage modulus and increased glass transfer temperatures (Tgs) of the magnetic films with increasing the particle loadings indicate that the composites could be a candidate to be used as high-performance absorbing materials.

One-step synthesis of PI@Fe3O4 composite microspheres and practical applications in Cu(II) ion adsorption

Polyimide(PI)@magnetite(Fe3O4) composite microspheres have been successfully synthesized from poly(amic acid) triethylamine salts (PAAS) and Fe(III) ions by a facile one-step solvothermal process. Furthermore, the formation mechanism of the PI@Fe3O4 composite microspheres has been investigated. The morphology and structure of the samples were both characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and infrared spectroscopy (IR). The results obtained show that the surface of magnetite could be successfully coated with polyimide and the coating could permeate throughout the crystals via a self-assembly process. The size of the composite microspheres was found to increase upon increasing the concentration of PAAS. The thermal properties of the composite microspheres were studied via thermogravimetric analysis (TGA) and the magnetic properties were determined by a vibrating sample magnetometer (VSM). Even though the saturation magnetization of the PI@Fe3O4 composite microspheres is lower than that of pure Fe3O4, the microspheres coated with PI exhibit an increased stability. In addition, basic hydrolysis of the composite microspheres has been carried out and the Cu(II)-adsorption properties of the composite microspheres before and after hydrolysis have been investigated. In doing so, it could be determined that the adsorption capacity of hydrolyzed composite microspheres increases from 5.84 mg g−1 to 24.63 mg g−1.

High-performance bismaleimide resins with low cure temperature for resin transfer molding process

High-performance bismaleimide resin systems (here coined LBMI resin series) based on 4,4-bismaleimidodiphenylmethane, 2,4-bismaleimidotoluene, bisphenol A bisallyl ether, 4,4′-bis[2-(1-propenyl)phenoxy]benzophenone, 2-allylphenol, and cumene hydroperoxide for resin transfer molding (RTM) process with low cure and post-cure temperatures (≦180°C) have been developed. Considering the optimum formulation conditions, the injection temperature is in the range of 70–160°C, and the pot life at 100°C is determined to be approximately 100 min. After curing at 180°C for 6 h, the resins exhibit high thermal resistances, excellent mechanical properties, and exceptionally low dielectric loss. Among others, these findings render the materials suitable for the use as high-performance resins for the production of advanced composites via RTM technique and with low cure temperatures.

Non-isothermal curing kinetics, chemorheological behaviour, and IR spectral study of two trifunctional phenylethynyl-terminated imide oligomers compared with the corresponding bifunctional structure

Two trifunctional phenylethynyl-terminated imide oligomers, m-TPEPA and p-TPEPA, were systematically compared with the corresponding bifunctional phenylethynyl-terminated imide oligomer, BPEPA. The non-isothermal curing kinetics, Master Plots method, and rheological behaviour of the three high performance oligomers were systematically studied by dynamic DSC, small amplitude oscillatory shear rheometry, and infrared spectroscopy. The results show that the activation energy (Ea) depended on the extent of conversion evaluated with three different methods, and the lower Ea values of the trifunctional oligomers, which may lead to different curing reactions, compared with the sustained growth of Ea values of BPEPA. The chemorheological properties of the oligomers were measured and fit numerically with the dual Arrhenius model and gel model. Moreover, the degree of cure (agel) at the gel time (tgel) was calculated by the value of glass transform temperature at different curing temperature combined with rheological and isothermal DSC results. According to structural changes during the curing reaction characterised using FTIR spectra, it was inferred that the structures of the cured trifunctional imide resins have cis-configurations, which may change the part of the configuration from cis to trimerisation with the lower activation energies found in the later part of the conversion, while the difunctional imide structure is trans.

Thermal and mechanical properties of cyanate ester resin modified with acid-treated multiwalled carbon nanotubes

Multiwalled carbon nanotubes (MWCNTs) that were treated with mixed acids were used to reinforce the cyanate ester resin. Meanwhile, the relationship among structure, morphology, and property of the modified resin was investigated. The treated MWCNTs were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS). The XPS results showed that the oxygen content in the treated MWCNTs was higher than that of untreated MWCNTs and the FTIR results indicated the presence of oxygen-containing functional groups on the treated MWCNTs. The microstructure of the resin was characterized by scanning electron microscopy and transmission electron microscopy. The results showed that the dispersion properties of the treated MWCNTs in the resin matrix were improved and compared with the untreated analogue. Addition of MWCNTs to the resin had little effect on the thermodynamic properties of the resin system. Upon addition of 0.8u2009wt% of MWCNTs to the resin, the glass transition temperature of the cured resin changed from 298°C to 285°C, maintaining a relatively high value. For the resins containing 0.6u2009wt% of treated MWCNTs, the plane strain critical stress intensity factor and plane strain critical strain energy release rate in the system were determined to be 1.39 Pa·m0.5 and 364u2009J m−2, respectively, and the fracture toughness is increased by 45.7 and 76.0%, respectively. Furthermore, the modified resin system exhibits excellent toughness and thermal properties. Therefore, the modified resin may be suitable for future applications involving high performance composites and adhesives.

Preparation and magnetic and thermal properties of flexible polyimide films with iron nitrophthalocyanine-coated magnetite microspheres

To effectively utilize the one-step solvent–thermal route to prepare iron (Fe)–nitrophthalocyanine/magnetite (Fe3O4) hybrid microspheres, we have developed a novel series of flexible Fe3O4/Fe-phthalocyanine (FePc)/polyimide (PI) composite films with various Fe3O4/FePc nanoparticle loadings (15, 27, and 40 wt%) and imidized at different temperatures (200°C and 300°C). The morphology and structure of the composite films were monitored using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the hybrid microspheres were found uniformly dispersed in the polymer matrices without any agglomeration. Mechanical and thermal properties of the composites were also investigated. The observed results indicated enhanced thermal stabilities, dramatically increased tensile modulus, and increased glass transition temperatures of the composite films, with the increment in the content of inorganic nanoparticles. Besides that, the Fe3O4/FePc/PI magnetic films showed higher saturation magnetization (24.33 emu g−1, 27 wt% Fe3O4/FePc loading) with high-temperature treatment compared with that of the Fe3O4/PI film (18.79 emu g−1, 27 wt% Fe3O4 loading). It proved to be an effective way to prevent Fe3O4 nanoparticles from oxidizing by coating the nanoparticles with organic layer. The flexible composite films can easily be moved under a relatively low magnetic field, indicating them to be the high-performance absorbing materials in potential applications.

Preparation of high temperature resistant Ag/PI/Cu composite nano particles inserted with PI insulating layer

Polyimide (PI)@copper (Cu) composite nano particles have been successfully synthesized from poly(amic acid) triethylamine salts (PAAS) and Cu(II) ions via a one-step high-temperature induction/imidization route. The formation of PI@Cu nano particles has been investigated by the stoichiometric ratio of PAAS and Cu ion. The resulting products, formed stable shell-core structures, exhibited the uniform core-size and thick shell layer. Additionally, the multi-layer structure, Ag@PI@Cu, was successfully prepared via a post process of PI@Cu nanoparticles. The morphology of the formed “Sunflower-mode” structure, with the pistil of Cu, the sunflower seed of PI, and the petal of Ag, was also characterized by SEM and TEM. Both electrical resistivity and thermal conductivity of nano particles were measured. The coefficient of heat conduction of Ag@PI@Cu is even 255 times, 754 times, 3081 times, and 1310 times as large as PI@Cu in 50xa0°C, 100xa0°C, 150xa0°C, and 200xa0°C, respectively. The resistance of both nano particles is that the result of RsPI@Cu and RsAg@PI@Cu is 11.0*109xa0Ω and 0.11xa0Ω, respectively, and also the difference between them is more than 1012.

Synthesis and properties of acetylene-terminated isoimide and imide oligomers exhibiting excellent solubility behaviors in low boiling point solvents

A series of acetylene-terminated isoimide and imide oligomers were prepared based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, 3,4′-oxydianiline, and 1,3-bis(3-aminophenoxy)benzene as monomers. 3-Ethynylaniline was used as an end-capping reagent and trifluoroacetic anhydride served as a dehydrating agent. The main oligomer structures were confirmed by Fourier transform infrared spectroscopy, and the thermal imidization was characterized by differential scanning calorimetry. All uncured isoimide and imide oligomers exhibit excellent solubility characteristics in organic solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone, and most of the oligomers can be dissolved in low boiling point solvents such as acetone and ethyl acetate (more than 45 wt%). In comparison with imide analogs, the isoimide oligomers exhibited an increased solubility in low boiling point solvents which can be attributed to their unique asymmetric structures. The properties of the cured films and adhesives were evaluated by dynamic mechanical thermal analysis, thermogravimetric analysis, as well as tensile shear strength tests of the polymer adhesives. The cured films exhibited extremely high glass transition temperatures (T g) of up to 341.6°C and 5% weight loss temperatures (T d5) of up to 518.2°C in a nitrogen atmosphere. Taken in concert, the results obtained indicate that all cured films featured an excellent thermal stability and a particularly high thermal-oxidative stability. One of these oligomers was selected and formulated to form a thermosetting adhesive for further investigation of the adhesion properties. This was done in an effort to improve the high-temperature performance characteristics of composite materials.

Vinyl-terminated butadiene acrylonitrile improves the toughness, processing window, and thermal stability of bismaleimide resin

Structural materials with excellent toughness, a wide processing window, outstanding mechanical performance, and high thermal stability are highly desired in engineering. This work reports a novel bismaleimide (BMI) resin system fabricated using bis[4-(4-maleimidephen-oxy)phenyl)]propane (BMPP), 1-(2-methyl-5-(2,5-dioxo-2H-pyrrol-1(5 H)-yl) phenyl)-1H-pyrrole-2,5-dione (BTM), and diallyl bisphenol A (DABPA) by a melt method. The behaviors of the BTM/BMPP/DABPA resin were modified by adding vinyl-terminated butadiene acrylonitrile (VTBN) in various amounts. The cured BTM/BMPP/DABPA/VTBN resin system exhibited all of the abovementioned desirable properties. Excellent performance was achieved by the post-cured BMI resin containing 6 phr of VTBN (VTBN-6). The glass transition temperature (T g) and the 5% weight loss temperature of VTBN-6 were 278°C and 408°C, respectively. Relative to VTBN-0 (BMI resin without VTBN), the impact strength of cured VTBN-6 (12.32 KJ/m2) improved by 45.6%, and the fracture toughness values, K IC and G IC, increased by 48.7% and 26%, respectively. Moreover, the prepolymer of VTBN-6 exhibited low viscosity over a wide temperature range (70–200°C) under dynamic conditions and for an extended time (70 min; 75% improvement over VTBN-0) in an isothermal test. These results confirm the wide processing window of VTBN-6. The high toughness of the VTBN-containing BMI resin was compatible with other excellent performances of the modified resin.

Synthesis, characterization, and properties of thermoplastic polyimides derived from 4,4’-(hexafluoroisopropylidene)diphthalic anhydride in diethylene glycol dimethyl ether

By regulating the order of monomer addition, four kinds of copolymer polyimides (PIs) were prepared using diethylene glycol dimethyl ether (DEGDE) and N,N-dimethylacetamide (DMAc) as the solvents. The molecular weights of polyamide acids (PAAs) ranged from 3.8 × 105 to 9.2 × 105. All of the films displayed high glass transition temperatures (Tgs) ranging from 313°C to 346°C. The polymer films show excellent thermal stabilities with 5% weight loss at temperatures of 505–524°C and char yields at 800°C were as high as 55% under nitrogen. The peel strengths of flexible copper (Cu) clads were in the range from 0.337 N cm−1 to 0.598 N cm−1. Compared to the molecular weight and peel strength of fresh PAA, those of PAAs prepared using DMAc significantly decreased after storage for 3 months at 0°C. However, when DEGDE was used as the solvent, the molecular weights of the PAAs and the thermal properties of the PIs were maintained after long storage time.