Synthesis and characterization of hyperbranched aromatic poly(ester-imide)s

The synthesis and characterization of hyperbranched aromatic poly(ester-imide)s are described. A variety of AB(2) monomers, N-[3- or 4-bis(4-acetoxyphenyl)toluoyl]-4-carboxyl-phthalimide and N-{3- or 4-[1,1-bis(4-acetooxyphenyl)]ethylphenyl}-4-carboxy phthalimides were prepared starting from condensation of nitrobenzaldehydes or nitroacetophenones with phenol and used for synthesis of hyperbranched poly(ester-imide)s containing terminal acetyl groups by transesterification reaction. These hyperbranched poly(ester-imide)s were produced with weight-average molecular weight of up to 6.87 g/mol. Analysis of H-1 NMR and C-13 NMR spectroscopy revealed the structure of the four hyperbranched poly(ester-imide)s. These hyperbranched poly(ester-imide)s exhibited excellent solubility in a variety of solvents such as N,N-dimethylacetamide, dimethyl sulfoxide, and tetrahydrofuran and showed glass-transition temperatures between 217 and 255 degreesC. The thermogravimetric analytic measurement revealed the decomposition temperature at 10% weight-loss temperature (T-d(10)) ranging from 365 to 416 degreesC in nitrogen.

Morphology and structures of self-assembled symmetric poly(di-n-alkylsilanes)

The self-assembly of poly(di-n-butylsilane) (PDBS) and poly(di-n-hexylsilane) (PDHS) on the surfaces of amorphous carbon and highly oriented pyrolytic graphite (HOPG) have been investigated, respectively. The morphology and structures of these self-assembled thin films were studied by using atomic force microscopy, transmission electronic microscopy, and wide-angle X-ray diffraction. In the case of weak van der Waals interactions between absorbed molecules and substrate, i.e., on amorphous carbon, the self-assembly process was driven by absorbate-absorbate intermolecular interactions. For PDBS with weak absorbate-absorbate intermolecular interactions, the thin film showed organization lacking any measurable preferred orientation on the surface of amorphous carbon. While for PDHS with rigid backbone and strong intermolecular interactions, flat-on lamellae with silicon backbones perpendicular to the surface of amorphous carbon were formed. However, in the case of strong van der Waals interactions between absorbed molecules and substrate, i.e., on HOPG, the self-assembly process was tailored by the balance of absorbate-absorbate intermolecular interactions and molecule-substrate interactions. Both PDHS and PDBS thin films grew into edge-on lamellae on the surface of HOPG, which aligned according to a Mold symmetry.

Crystallization of weakly segregated poly(styrene-b-epsilon-caprolactone) diblock copolymer in thin films

The surface morphology and crystallization behavior of a weakly segregated symmetric diblock copolymer, poly(styrene-b-6-caprolactone) (PS-b-PCL), in thin films were investigated by optical microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). When the samples were annealed in the molten state, surface-induced ordering, that is, relief structures with uniform thickness or droplets in the adsorbed monolayer, were observed depending on the annealing temperature. The polar PCL block preferred to wet the surface of a silicon wafer, while the PS block wet the air interface. This asymmetric wetting behavior led to the adsorbed monolayer with a PCL block layer having a thickness of around 4.0 nm. The crystallization of PCL blocks could overwhelm the microphase-separated structure because of the weak segregation. In situ observation of crystal growth indicated that the nucleation process preferred to occur at the edge of the thick parts of the film, that is, the relief structures or droplets. The crystal growth rate was presented by the time dependence of the distance between the tip of crystal clusters and the edge. At 22 and 17 degreesC, the average crystal growth rates were 55 +/- 10 and 18 +/- 4 nm/min, respectively.

Synthesis and characterization of maleated poly(3-hydroxybutyrate)

Graft copolymerization of maleic anhydride (MA) onto poly(3-hydroxybutyrate) (PHB) was carried out by use of benzoyl peroxide as initiator. The effects of various polymerization conditions on graft degree were investigated, including solvents, monomer and initiator concentrations, reaction temperature, and time. The monomer and initiator concentrations played an important role in graft copolymerization, and graft degree could be controlled in the range from 0.2 to 0.85% by changing the reaction conditions. The crystallization behavior and the thermal stability of PHB and maleated PHB were studied by DSC, WAXD, optical microscopy, and TGA. The results showed that, after grafting MA, the crystallization behavior of PHB was obviously changed. The cold crystallization temperature from the glass state increased, the crystallization temperature from the melted state decreased, and the growth rate of spherulite decreased. With the increase in graft degree, the banding texture of spherulites became more distinct and orderly. Moreover, the thermal stability of maleated PHB was obviously improved, compared with that of pure PHB.

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n = 3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U-* = 1500 cal mol(-1), T-infinity = 30 K and T-g = 278 K, the nucleation parameter K-g was determined, which was found to be 3.14+/-0.07 x 10(5) (K-2), lower than that for pure PHB. The surface-free energy sigma = 2.55 x 10(-2) J m(-2) and sigma(e) = 2.70+/-0.06 x 10-2 J m(-2) were estimated and the work of chain-folding (q = 12.5+/-0.2 kJ mol(-1)) was derived from sigma(e), and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate)

In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Chang's method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.

Miscibility and crystallization behavior of poly(3-hydroxyvalerate-co-3-hydroxyvalerate)/poly(propylene carbonate) blends

Blends of synthetic poly(propylene carbonate) (PPC) with a natural bacterial copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 8 mol % 3-hydroxyvalerate units were prepared with a simple casting procedure. PPC was thermally stabilized by end-capping before use. The miscibility, morphology, and crystallization behavior of the blends were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction (WAXD), and small-angle Xray scattering (SAXS). PHBV/PPC blends showed weak miscibility in the melt, but the miscibility was very low. The effect of PPC on the crystallization of PHBV was evident. The addition of PPC decreased the rate of spherulite growth of PHBV, and with increasing PPC content in the PHBV/PPC blends, the PHBV spherulites became more and more open. However, the crystalline structure of PHBV did not change with increasing PPC in the PHBV/PPC blends, as shown from WAXD analysis. The long period obtained from SAXS showed a small increase with the addition of PPC.

Electrochemical study of PW12O403- in poly(ethylene glycol) electrolyte

The electrochemical properties Of PW12O403- (abbreviated as PW12) anion in poly(ethylene glycol) (PEG) have been studied by cyclic voltammetry, complex impedance and FT-IR spectroscopy. The PW12 anion in PEG-LiClO4 electrolyte shows reasonable facile electrochemistry, and the diffusion coefficients Of PW12 were measured with microelectrode. It is shown that ionic conductivity of polymer electrolytes based on low molecular weight PEG can be improved by the addition of PW12. The increase of conductivity is coupled with decrease of transient cross-links density of polymer chains which is evidenced by the downshift of C-O-C stretching mode. The phenomena are explained in view of ion-ion and ion-polymer interactions.

Liquid-liquid phase behavior of toluene/polyethylene oxide/poly(ethyleneoxide-b-dimethylsiloxane) polymer-containing ternary mixtures

The experimental data of phase diagrams for both polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) binary and toluene/polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) ternary polymer-containing systems was obtained at atmosphere pressure by light scattering method. The critical points for some pre-selected compositions and the pressure effect on the phase transition behavior of ternary system were investigated by turbidity measurements. The chosen system is a mixture of ternary which is one of the very few abnormal polymer-containing systems exhibiting pressure-induced both miscibility and immiscibility. This unusual behavior is related to the toluene concentration in the mixtures. The effect of toluene on the phase transition behavior of the ternary polymer-containing mixture was traced. Such behavior can make it possible to process composite materials from incompatible polymers.

Pressure-dependent glass-transition temperatures of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends

The pressure-dependent glass-transition temperatures (T-g's) of poly(methyl methacrylate) (PMMA)/poly(styrene-co-acrylonitrile) (SAN) blends were determined by pressure-volume-temperature (PVT) dilatometry via an isobaric cooling procedure. The Gordon-Taylor and Fox equations were used to evaluate the relationships between the T-g's and compositions of the PMMA/SAN system at different pressures. The relationships were well fitted by the Gordon-Taylor equation, and the experimental data for T-g positively deviated from the values calculated with the Fox equation. Also, the influence of the cooling rate (during the PVT measurements) on T-g was examined.

Synthesis of the complex fluoride LiBaF3 and optical spectroscopy properties of LiBaF3 : M(M = Eu,Ce) through a solvothermal process

The complex fluoride LiBaF3 and LiBaF3:M(M = Eu, Ce) is solvothermally synthesized at 180 degreesC and characterized by means of X-ray powder diffraction, scanning electron microscopy, thermogravimetric analysis and infrared spectroscopy. In the solvothermal process, the solvents, molar ratios of initial mixtures and reaction temperature play important roles in the formation of products. The excitation and emission spectra of the LiBaF3:M(M= Eu,Ce) have been measured by fluorescence spectrophotometer. In the LiBaF3: Eu emission spectra, there is one sharp line emission located at 360 nm arising from f --> f transition of Eu2+ in the host lattice, and typical doublet 5d-4f emission of Ce3+ in LiBaF3 powder is shown.

Synthesis of barium fluoride nanoparticles from microemulsion

The cetyltrimethylammonium bromide (CTAB)/2-octanol/water microemulsion system was used to synthesize barium fluoride nanoparticles. X-ray powder diffraction (XRD) analysis showed that the products were single phase. The results of scanning electron microscopy and calculations using the Scherrer equation from the line widths of the XRD have been used to estimate the average particle sizes of the powder products. The results showed that the nanoparticle size was affected by water content and surfactant (CTAB) concentration. As water content decreases from 14.2 to 9.47% (w/w), the particle size decreases from 75 to 40 rim. In addition, increasing the reaction times from 5 to 120 min increases the particle size from 75 to 150 rim, and increasing the amount of surfactant decreases the size of the particle. Luminescence spectra of the BaF2:Ce nanoparticles are also discussed.

Hydrothermal and solvothermal synthesis of the complex fluoride alpha '-SrAlF5

The complex fluoride alpha'-SrAlF5 has been synthesized through hydrothermal and solvothermal methods under mild conditions. The effects of the molar ratio of starting materials, temperature, reaction time and solvents on the synthesis of alpha'-SrAlF5 were discussed. The final products were characterized by XRD and SEM. The rod-like shape of alpha'-SrAlF5 is shown in SEM images.

Thermal degradation kinetics of poly(propylene carbonate) obtained from the copolymerization of carbon dioxide and propylene oxide

The kinetics of the thermal degradation of poly(propylene carbonate) (PPC) were investigated with different kinetic methods with data from thermogravimetric analysis under dynamic conditions. The apparent activation energies obtained with different integral methods (Ozawa-Flynn-Wall and Coats-Redfern) were consistent with the values obtained with the Kinssinger method (99.93 kJ/mol). The solid-state decomposition process was a sigmoidal A(3) type in terms of the Coats-Redfern and Phadnis-Deshpande results. The influence of the heating rate on the thermal decomposition temperature was also studied. The derivative thermogravimetry curves of PPC confirmed only one weight-loss step.