Isomeric polyimides

This review deals with polyimides based on isomeric dianhydrides and diamines, and with chiral polyimides. First, however, a summary is presented of recent work on the synthesis of isomeric dianhydrides, the reaction of mellophanic dianhydride with diamines, and the tendency toward cyclization in reactions of some dianhydrides and diamines. Then turning to polymers, the discussion covers solubility, thermal and dielectric properties, permeability and permselectivity for gas separation, and rheology of isomeric polyimides. Several useful general rules have been found: i.e. the glass transition temperature of polyimides based on isomeric dianhydrides with a given diamine decreases in the order 3,3'- > 3,4'- > 4,4-dianhydride if the polymers are of comparable molecular weight, whereas the thermal stability and the T-beta/T-g ratio (in absolute temperatures) increase in the order of 3,3'- < 3,4'- < 4,4'-dianhydride. Polyimides from 3,3'- or 3,4'-dianhydride have higher solubility than those from 4,4'-dianhydride. Polyimides from 3,4'-dianhydrides exhibit much lower melt viscosity than those from the other isomeric anhydrides. The dielectric constants of polyimides derived from m,m'-diamines are lower than those from p,p'-diamines. Polyimides based on 3,3'- or 3,4'-dianhydrides have higher permeability and slightly lower permselectivity than polyimides based on 4,4'-dianhydrides.

One-step synthesis of gold-polyaniline core-shell particles

A one-step method has been developed for synthesizing gold-polyaniline (Au@PANI) core-shell particles by using chlorauric acid (HAuCl4) to oxidize aniline in the presence of acetic acid and Tween 40 at room temperature. SEM images indicated that the resulting core-shell particles were composed of submicrometre-scale Au particles and PANI shells with an average thickness of 25 nm. Furthermore, a possible mechanism concerning the growth of Au@PANI particles was also proposed based on the results of control experiments.

In-situ fabrication of hybrid polyoxometalate nanoparticles composite films

inorganic-organic hybrid nanoparticles multilayer films were fabricated by extending the method of nucleation and growth of particles in polymer assemblies. The polyelectrolyte matrix was constructed by layer-by-layer self-assembly method. Synthesis of polyoxometalate nanoparticles was achieved by alternately dipping the precursor polyelectrolyte matrix into AgNO3 and H4SiW12O40 aqueous solutions. Repeating the above synthesis process, Ag4SiW12O40 nanoparticles with controllable diameters of 20 to 77 nm were synthesized in the multilayer films in-situ. UV-vis absorption spectra indicate that the nanoparticles grew gradually in the synthesis process. Transmission electron microscopy was used to observe the size and morphology of the nanoparticles.

Synthesis and morphology of polyethylene chains grafted onto the surface of crosslinked polystyrene microspheres

The bifunctional comonomer 4-(3-butenyl) styrene was used to synthesize crosslinked polystyrene microspheres (c-PS) with pendant butenyl groups on their surface via suspension copolymerization. Polyethylene chains were grafted onto the surface of c-PS microspheres (PS-g-PE) via ethylene copolymerizing with the pendant butenyl group on the surface of the c-PS microspheres under the catalysis of metallocene catalyst. The composition and morphology of the PS-g-PE microspheres were characterized by means of Fourier transform infrared spectroscopy, Fourier transform Raman spectroscopy, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. It is possible to control the content of PE grafted onto the surface of c-PS microspheres by varying the polymerization time or the initial quantity of pendant butenyl group on the surface of c-PS microspheres. Investigation on the morphology and crystallization behavior of grafted PE chains showed that different surface patterns could be formed under various crystallization conditions. Moreover, the crystallization temperature of PE chains grafted on the surface of c-PS microspheres was 6 degrees C higher than that of pure PE. The c-PS microspheres decorated by PE chains had a better compatibility with PE matrix.

Synthesis and characterization of polyethylene chains grafted onto the sidewalls of single-walled carbon nanotubes via copolymerization

Polyethylene (PE) chains grafted onto the sidewalls of SWCNTs (SWCNT-g-PE) were successfully synthesized via ethylene copolymerization with functionalized single-walled carbon nanotubes (f-SWCNTs) catalyzed by rac-(en)(THInd)(2)ZrCl2/ MAO. Here f-SWCNTs, in which alpha-alkene groups were chemically linked on the sidewalls of SWCNTs, were synthesized by Prato reaction. The composition and microstructure of SWCNT-g-PE were characterized by means of H-1 NMR, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analyses (TGA), field-emission scanning electron microscope (FESEM), and transmission electron microscope (TEM). Nanosized cable-like structure was formed in the SWCNT-g-PE, in which the PE formed a tubular shell and several SWCNTs bundles existed as core. The formation of the above morphology in the SWCNT-g-PE resulted from successfully grafting of PE chains onto the surface of SWCNTs via copolymerization. The grown PE chains grafted onto the sidewall of the f-SWCNTs promoted the exfoliation of the mass nanotubes. Comparing with pure PE, the physical mixture of PE/f-SWCNTs and in situ PE/SWCNTs mixture, thermal stability, and mechanical properties of SWCNT-g-PE were higher because of the chemical bonding between the f-SWCNTs and PE chains.

Synthesis and characterization of photo-cross-linked hydrogels based on biodegradable polyphosphoesters and poly(ethylene glycol) copolymers

Novel biodegradable hydrogels by photo-cross-linking macromers based on polyphosphoesters and poly(ethylene glycol) (PEG) are reported. Photo-cross-linkable macromers were synthesized by ring-opening polymerization of the cyclic phosphoester monomer 2-(2-oxo-1,3,2-dioxaphospholoyloxy) ethyl methacrylate (OPEMA) using PEG as the initiator and stannous octoate as the catalyst. The macrorners were characterized by H-1 NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography measurements. The content of polyphosphoester in the macromer was controlled by varying the feed ratio of OPEMA to PEG. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.05% (w/w) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors were evaluated. The results demonstrated that cross-linking density and pH values strongly affected the degradation rates. The macromers was compatible to osteoblast cells, not exhibiting significant cytotoxicity up to 0.5 mg/mL. "Live/dead" cell staining assay also demonstrated that a large majority of the osteoblast cells remained viable after encapsulation into the hydrogel constructs, showing their potential as tissue engineering scaffolds.

Effects of crystal growth conditions on morphology of crystalline syndiotactic 1,2-polybutadiene

The crystalline syndiotatic 1,2-polybutadiene was synthesized with a catalyst consisting of iron acetylacetonate (Fe(acac)(3))-triisobutylaluminum (Al(i-Bu)(3))-diethyl phosphite (DEP), and the effects of crystal growth conditions on morphology of thin films of the polymer were investigated by transmission electron microscopy (TEM) and electron diffraction (ED) techniques. The polymer with melting point 179 degreesC was found to have 89.3% 1,2-content and 86.5% syndiotacticity by C-13 NMR measurement. The results of electron microscopic studies indicate that the solution-cast thin films of the syndiotatic 1,2-polybutadiene consist of lath-like lamellae with the c-axis perpendicular to the film plane, while a- and b-axes are in the film plane. The morphology of isothermally crystallized thin films of the polymer is temperature dependent. At lower crystallization temperatures (130 degreesC), a spherulitic structure consisting of flat-on lamellae is formed. With an increase in the crystallization temperature (e.g., at 140 degreesC), the spherulites and single faceted crystals coexist. At higher crystallization temperatures (150 degreesC), single crystals with a hexagonal prismatic shape are produced.

Modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using hydrogen bonding monomers

Properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were significantly modified by a hydrogen bonding (H-bond) monomer-bisphenol A (BPA). BPA lowered the T-m of PHBV and widened the heat-processing window of PHBV. At the same time, a dynamic H-bond network in the blends was observed indicating that BPA acted as a physical cross-link agent. BPA enhanced the T, of PHBV and reduced the crystallization rate of PHBV. It resulted in larger crystallites in PHBV/BPA blends showed by WAXD. However, the crystallinity of PHBV was hardly reduced. SAXS results suggested that BPA molecules distributed in the inter-lamellar region of PHBV. Finally, a desired tension property was obtained, which had an elongation at break of 370% and a yield stress of 16 MPa. By comparing the tension properties of PHBV/BPA and PHBV/tert-butyl phenol blends, it was concluded that the H-bond network is essential to the improvement of ductility.

Preparation of a phosphopolyoxomolybdate P2Mo18O626- doped polypyrrole modified electrode and its catalytic properties

A phosphopolyoxomolybdate (P2Mo18) doped polypyrrole (PPy) modified electrode was prepared in aqueous solution by a one-step method. During the polymerization of PPy, P2Mo18 acted as both catalyst and dopant. The electrochemical behavior of the PPy/P2Mo18 modified electrode before and after the overoxidation of PPy was investigated. Both of these showed a catalytic effect toward bromate. The PPy/P2Mo18 composite film was characterized by chronoamperometry, cyclic voltammetry, the rotating disk electrode technique, X-ray photoelectron spectroscopy and Raman spectroscopy.

The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of camphorsulfonic acid

Polyaniline-camphorsulfonic acid (PAN-CSA) composite film on platinum electrode surface has been synthesized via the electrochemical polymerization of aniline in the presence of camphorsulfonic acid (CSA). It was found that the doping of polyaniline (PAN) with CSA extends the electroactivity of PAN in neutral and even in alkaline media. The PAN-CSA composite film coated platinum electrodes are shown to be good electrocatalytic surfaces for the oxidation of ascorbic acid (AA) in phosphate buffer solution (PBS) of pH 7.0. The anodic peak potential of AA shifts from 0.63 V at the bare platinum electrode to 0.34 V at the PAN-CSA composite modified platinum electrode with a greatly enhanced current response. A linear calibration graph is obtained over the AA concentration range of 5-50 mM using cyclic voltammetry. The kinetics of the catalytic reaction are investigated using rotating disk electrode voltammetry and chronoamperometry. The results are explained using the theory of electrocatalytic reactions at chemically modified electrodes. The PAN-CSA composite on the electrode surface shows good reproducibility and stability.

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.

Syntheses and properties of soluble biphenyl-based polyimides from asymmetric bis(chlorophthalimide)s

A novel synthesis of asymmetric bis(chlorophthalimide)s (3,4-BCPIs) has been established. The polymerizations of them produced higher molecular weight (0.38-0.51 dL/g) polyimides containing biphenyl units than those of isomeric polymers derived from symmetric bis(chlorophthalimide)s (4,4'-BCPIs) and 3,3'-BCPIs. The distribution of the formed biphenyl units of head to tail, head to head, and tail to tail in the chain of the polymers was about 58.0:21.0:21.0, determined by C-13 NMR spectra of the polymers. The composition of model compounds, determined by HPLC, was well consistent with the 13C NMR spectrum result. Comparing with polymers derived from 4,4'-BCPIs and 3,3'-BCPIs, the polymers derived from 3,4-BCPIs showed better solubilities in N,N-dimethylacetamide (DMAc), N,N-dimethyl-formamide (DMF), and N-methylpyrrolinone (NMP). Flexible films could be cast from the polymer solution with the inherent viscosities of above 0.35 dL/g. The polymer derived from asymmetric bis(chlorophthimide)s gave the highest T-g among the isomeric polymers.

Thermal mechanical and dynamic mechanical property of biphenyl polyimide fibers

High-performance polyimide fibers possess man), excellent properties, e.g., outstanding thermal stability and mechanical properties and excellent radiation resistant and electrical properties. However, the preparation of fibers with good mechanical properties is very difficult. In this report, a biphenvl polyimide from 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline is synthesized in p-chlorophenol by one-step polymerization. The solution is spun into a coagulation bath of water and alcohol via dry-jet wet-spinning technology. Then, the fibers are drawn in two heating tubes. Thermal gravimetric analysis, thermal mechanical analysis, and dynamic mechanical analysis (DMA) are performed to study the properties of the fibers. The results show that the fibers have a good thermal stability at a temperature of more than 400degreesC. The linear coefficient of thermal expansion is negative in the solid state and the glass transition temperature is about 265degreesC. DMA spectra indicate that the tandelta of the fibers has three transition peaks, namely, alpha, beta, and gamma transition. The alpha and gamma transition temperature, corresponding to the end-group motion and glass transition, respectively, extensively depends on the applied frequency, while the beta transition does not.

Microwave-assisted synthesis of high-molecular-weight poly(ether imide)s by phase-transfer catalysis

A facile and rapid polycondensation reaction of disodium bisphenol A with bis(chlorophthalimide)s was preformed with a domestic microwave oven in o-dichlorobenzene by phase-transfer catalysis. The polymerization reactions, in comparison with conventional heating polycondensation, proceeded rapidly and were completed within 25 min. The polymerizations gave the corresponding poly(ether imide)s with inherent viscosities of 0.55-0.92 dL g(-1). The effects of various factors on the polymerization, such as the amount of the catalyst, the reaction time, and the microwave power were studied. The properties of the polymers were briefly characterized.

Facile syntheses and characterization of hyperbranched poly(ester-amide)s from commercially available aliphatic carboxylic anhydride and multihydroxyl primary amine

A new method for synthesis of novel hyperbranched poly(ester-amide)s from commercially available AA' and CBx type monomers has been developed on the basis of a series of model reactions. The hyperbranched poly(ester-amide)s with multihydroxyl end groups are prepared by thermal polycondensation of carboxyl anhydrides (AA') and multihydroxyl primary amine (CBx) without any catalyst and solvent. The reaction mechanism in the initial stage of polymerization was investigated with in situ H-1 NMR. In the initial stage of the reaction, primary amino groups of 2-amino-2-ethyl-1,3-propanediol (AEPO) or tris(hydroxymethyl)aminomethane (THAM) react rapidly with anhydride, forming an intermediate which can be considered as a new AB(x) type monomer. Further self-polycondensation reactions of the AB. molecules produce hyperbranched polymers. Analysis using H-1 and C-13 NMR spectroscopy revealed the degree of branching of the resulting polymers ranging from 0.36 to 0.55. These hyperbranched poly(ester-amide)s contain configurational isomers observed by C-13 and DEPT C-13 NMR spectroscopy, possess high molecular weights with broad distributions and display glass-transition temperatures (T(g)s) between 7 and 96 degreesC.