In order to overcome the shortcomings of nanofiber membranes such as low mechanical properties and poor acid resistance, amino-rich functionalized polyimide (PI)-polyethyleneimine (PEI) fibers were successfully prepared in the study. The structure and morphology in each functionalization step were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), static contact angle, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS) measurements. The adsorption kinetics analysis showed that the adsorption process followed a pseudo-second-order model, and the adsorption isotherm could be described better by the Langmuir model indicating the adsorption process was mainly chemical and homogeneous monolayer adsorption. Furthermore, the maximum adsorption capacity based on the Langmuir model was about 50 mg g(-1), and the calculated thermodynamic parameters demonstrated an endothermic process. Meantime, the PEI-grafted PI fibers also exhibited good regeneration performance and stable tensile strength during recycling tests process. In the first 3 adsorption-desorption cycles, the removal efficiency and tensile strength of PI-PEI fibers could be maintained up to 60.44% and 89.29% of the initial adsorption, respectively. This work achieved the function of removing Cr (VI) by combining the excellent high temperature resistance, acid resistance, and mechanical properties of PI fibers.

The polyamic acid (PAA) solutions with high solid content and low viscosity derived from 3,3',4,4'-biphe-nyldianhydride (BPDA)/p-phenylene diamine (PDA) were synthesized via heat treatment and partial chemical imidization, and the structure and properties of the corresponding polyimide (PI) fibers were studied. The results show that both heat treatment and partial chemical imidization can destroy the gel network structure without affecting the molecular weight of PAA, and restore the fluidity of PAA gel with high solid content. The PI fibers prepared from the PAA solution with high solid content and low viscosity have better mechanical properties, which is attributed to the high solid content reduces the internal structural defects of the nascent PAA fibers caused by dual-diffusion effect in the coagulation bath stage.

The porous polyimide (PI) composite fibers, which exhibit high-efficiency electromagnetic wave adsorption (EMWA) performance, were successfully fabricated by controlling temperature of the coagulation bath during the wet spinning process. The mechanical properties of composite fiber decreased and average radius of micropores increased gradually with the rise of coagulation bath temperature. In addition, carbon nanotubes (CNTs) and nano-Fe3O4 were introduced into the system by in situ polymerization. CNTs and nano-Fe3O4 contribute to the attenuation of electromagnetic wave (EMW) through microwave absorption and reflection loss (RL), and the porous structure was able to provide multiple reflection paths for incident EMW and achieved higher attenuation. Particularly, when the temperature of coagulation bath was 50 degrees C, the minimum RL (RLmin) value of the PI/CNTs/nano-Fe3O4 (PI/C-Fe) composite fibers was demonstrated to be -54.61 dB with the matching thickness of 2.10 mm. The successful preparation of PI/C-Fe composite fiber in this study pointed out a new direction for the application of PI-based fiber materials in structural EMWA materials.

A series of pyromellitic dianhydride/4,4 '-oxydianiline orientation models are constructed by molecular dynamic simulation, and the effects of drafting rate, drafting temperature, and imidization degree on structure and mechanical properties of polyimide fibers are studied. The high drafting rate is conducive to the orientation of molecular chains along the axis, but it is easy to form defects inside of the fibers, so the tensile modulus of the orientation model at a draft ratio of 6 is decreased from 21.6 to 9.8 GPa with increasing the drafting rate. The high drafting temperature reduced the intermolecular interaction, which is not conducive to the orientation of the molecular chain along the axis, the tensile modulus of orientation models at a draft ratio of 6 decreased from 21.6 to 11.7 GPa with the drafting temperature increasing from 298 to 598 K. Besides, the molecular chains of PI fibers drawn from the high imidization degree are arranged more regularly along the axis due to the PI units have greater rigidity than the polyamic acid units. This work provides guidance for the optimization of PI fibers heat-drafting process from the perspective of molecular chain conformational evolution.

Here, a rapid and efficient strategy was introduced to prepare polyimide/graphene nanosheet (PI/GN) composite fibers by microwave-assisted imidization. The mechanical properties of the PI/GNs (1 wt%) fibers treated by microwave-assisted imidization were apparently improved with the tensile strength of 1.12 GPa at 350 °C, which was approximately 1.7 times as much as those treated with traditional thermal imidization. The PI/GNs (1 wt%) fibers heated by the microwave-assisted imidization method exhibited excellent thermal stabilities of up to 570.3 °C in nitrogen for a 5% weight loss, and a glass transition temperature above 339 °C. The results of the infrared spectrum and thermal properties indicated that the microwave-assisted treatment could promote the imidization degree of the PI/GN fibers prominently. Meanwhile, as a microwave absorber, graphene nanosheets (GNs) could also promote the imidization process by converting microwave energy into thermal energy. The microwave-polyimide/graphene nanosheet (MW-PI/GN) fibers possessed an optimum tensile strength of 1.38 GPa and modulus of 56.82 GPa at the GN content of 0.25 wt%. The 5% weight loss temperature in nitrogen ranged from 520.9 °C to 570.3 °C, and the glass transition temperature was increased from 305.7 °C to 339.1 °C with increasing the GN content.

Polyimide/graphene (PI/G) composite fibers containing p-phenylenediamine ( p-PDA), 3,3′,4,4′-Biphenyl tetracarboxylic diandhydride (BPDA) and graphene (G) were prepared by wet spinning and thermal imidization. The mechanical properties, thermal stability, orientation factor and morphology of PI/G composite fibers were characterized and studied. Within the scope of the study, the tensile strength and tensile modulus of the fibers increased first and then decreased with the increase of the graphene content. Moreover, the glass transition temperature and thermal decomposition temperature of the PI/G composite fibers increased with the increased of the graphene content. X-ray diffraction (XRD) showed that the degree of orientation of the of prepared fibers increase firstly and then decrease with the content of graphene increasing. SEM indicated that graphene was dispersed evenly in the PI/G composite fibers and graphene had satisfactory compatibility with PI matrix.

The polyimide (PI)/carbon nanotube (CNT) films including 3,3 ',4,4 '-biphenyl tetracarboxylic dianhydride (BPDA), p-phenylenediamine (p-PDA), and CNTs were prepared, which have prominent electromagnetic (EM) wave absorption performance. Experimental analyses of the mechanical properties, thermal stabilities, coefficient of thermal expansion (CTE), the glass transition temperature (T-g), and EM parameter revealed the beneficial effects of the CNTs on the resulting composite films. In particular, when the content of CNTs is 6 wt%, the film shows the highest EM wave absorption performance, which exhibits the effective absorption bandwidth of 2.72 GHz with the matching thickness of only 2.0 mm. These results indicate that PI-based films have a certain potential application in the area of EM wave-absorbing materials.

Pyromellitic dianhydride (PMDA)/4,4'-oxidianiline (ODA) polyimide (PI) orientation models with different draft ratios were established to reveal the macromolecular structural evolution of PI chains during large-ratio uniaxial fiber orientation process. The high consistency between experimental data and modelling results, in terms of mechanical properties and XRD patterns, demonstrates the rationality of the orientation models. The simulation results indicated that the PI chains became stretched from entanglement and arranged along the draft direction in the fiber drafting process, and chain orientation observed in PMDA/ODA-based PI fibers during drafting was mainly caused by the change of C-C-O-C torsion distribution in the ODA units.

A new hyperbranched poly (amine-ester)-poly (lactide-co-glycolide) (HPAE-co-PLGA) copolymer was synthesized by ring-opening polymerization of D, L-lactide, glycolide and a fourth generation branched poly (amine-ester) (HPAE-OHs4) with Sn(Oct) 2 as catalyst. The chemical structures of copolymers were determined by FT-IR, 1 H-NMR ( 13 C NMR), TGA and their molecular weights were determined by gel permeation chromatography (GPC). Two methods, double emulsion (DE) and nanoprecipitation (NP), were employed to fabricate the polymeric nanoparticles. Isoniazid (INH) was loaded as a model antitubercular drug. Influence of the preparation conditions on the nanoparticles size, encapsulation efficiency and release profile in vitro was investigated. Their entrapment efficiency (EE) to INH could reach 96% at an available condition. In vitro release behavior of NPs showed a continuous release after a burst release. The results showed that the HPAE-co-PLGA copolymer nanoparticles have a promising potential in hydrophilic drug delivery system.

A series of hyperbranched poly(amine-ester)-co-D,L-lactide (HPAE-co-PLA) copolymer were synthesized by ring-opening polymerization of D,L-lactide with Sn(Oct)(2) as catalyst to a fourth generation branched poly(amine-ester) (HPAE-OHs4). The chemical structures of copolymers were determined by FTIR, H-1-NMR, C-13-NMR, and TGA. Double emulsion (DE) and nanoprecipitation (NP) method were used to fabricate the nanoparticles of these copolymers encapsulating bovine serum albumin (BSA) as a model. DSC thermo-grams indicated that the nanoparticles with BSA kept stable below 40 degrees C. Different factors which influence on particular size and encapsulation efficiency (EE) were investigated. Their EE to BSA could reach 97.8% at an available condition. In vitro release behavior of NPs showed a continuous release after a burst release. The stability maintenance of BSA in the nanoparticle release in vitro was also measured via circular dichroism and fluorescence spectrometry. The results showed that the copolymer nanoparticles have a promising potential in protein delivery system. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 1156-1167, 2010

Novel amphiphilic protein-loaded hyperbranched poly (amine-ester) copolymers nanoparticles were fabricated by double emulsion (DE) and nanoprecipitation (NP) methods. Encapsulation efficiency (EE) of nanoparticles to Bovine serum albumin (BSA) could reach 97.8% at BSA (0.01g/ml), internal phase volume (0.5ml), copolymer weight (50mg), and PVA concentration (4%, w/v) condition.

BACKGROUND: The aim of the work presented was to synthesize a series of amphiphilic hyperbranched poly[(amine-ester)-co-(D,L-lactide)] (HPAE-co-PLA) copolymers and study the formation of copolymeric micelles. These copolymeric micelle systems are expected to be potential candidates for applications in protein drug delivery.RESULTS: The chemical structures of the copolymers were confirmed by Fourier transform infrared spectroscopy, C-13 NMR and thermogravimetric analysis. Fluorescence spectroscopy and dynamic light scattering confirmed the formation of copolymeric micelles of the HPAE-co-PLA copolymers. The maintenance of stability of bovine serum albumin (BSA) during release from micelles in vitro was also measured using circular dichroism and fluorescence spectrometry.CONCLUSION: Novel hyperbranched HPAE-co-PLA copolymers have been synthesized. Conjugation of PLA to HPAE was proved to be an available method for the preparation of micelles for protein delivery. The BSA-loaded micelles showed enhanced encapsulation efficiency and the structural stability of BSA was retained during the release process. The hyperbranched polymeric micelles could be useful as drug carriers for protein drug delivery systems. (C) 2008 Society of Chemical Industry

We report the seed-dependent shape evolution of gold@silver (Au@Ag) core-shell nanostructures with various morphologies through using pre-existing Au nanocrystals as nuclei in a polyvinylpyrrolidone (PVP)-assisted polyol reduction process. Au nanocrystalline seeds with different shapes such as cube, truncated-octahedron, octahedron, twinned hexagon and triangle, five-twinned decahedron and nanorod are firstly synthesized by refluxing a 1,5-pentanediol solution containing Au precursors in the presence of PVP. The Au seeds obtained in this way then serve as the nuclei for further epitaxial growth of Ag shells by using Ag precursors via the same route. Scanning transmission electron microscope (STEM) characterization of the products obtained demonstrates that the morphological evolution of the Ag shells depends completely on the shapes of the Au seeds that are used. We have observed that the Au@Ag core-shell nanostructures formed with various regular shapes such as cube, bi-triangle, and nanorod with five-twinned cross section, are mostly surrounded by {100}-type Ag crystalline facets. Our findings provide new evidence and clear evolution routines from the Au cores with well-defined shapes to the corresponding Ag shells for the Au@Ag core-shell nanostructures by the family of the PVP-assisted polyol reduction methods.