Morphology development of isotactic poly(4-methylpentene-1) during melt crystallization

The morphology of melt-crystallized isotactic poly(4-methylpentene-1) samples, prepared by varying crystallization temperature and time, as well as annealing temperature, has been probed by small and wide angle x-ray scattering, and electron microscopy. This was then correlated with the thermal properties investigated by differential scanning calorimetry. Relationships among melting behavior, morphological evidences and X-ray results have been found. Different populations of lamellae, grown with a time-dependent sequence, can be obtained: their relative amount and thermal stability is determined by crystallization and annealing conditions.     

The influence of stereoregularity defects on crystals of isotactic poly(propylene)

The local conformation and the defect Gibbs energy of stereoregularity defects in isotactic poly(propylene), i-PP, is calculated by means of the thermodynamic-integration approach. For i-PP with high isotacticity, where the atactic inclusions do not interfere with each other, we found changes in the torsion angles next to the defect, which bring the methyl unit to the position it would have in the conformation of the purely isotactic chain. The Gibbs energy of this inclusion is low and enables cocrystallization corresponding to the uniform inclusion model. For sequences of adjacent defects in the polymer chain, the local chain deformation was found to be much more complex, and a considerable defect Gibbs energy remains that makes the inclusion of atactic sequences less likely.     

Synthesis and characterization of conducting poly (1-aminonaphthalene), poly (2-aminonaphthalene) and poly (aniline-co-1-aminonaphthalene)

Poly (1&2)-aminonaphthalene and poly (aniline-co-1-aminonaphthalene) have been synthesized in high yields by chemical oxidative polymerization method. The polymers are soluble in polar solvents such as DMSO, NMP etc. In PNA-2 as head-to-tail coupling cannot occur, the electrical conductivity is lower than PNA-1. The copolymer exhibits distinct morphology, higher viscosity, characteristic exciton peak, appreciable thermal stability and electrical conductivity compared to PNA-1.     

From heterogeneous to homogeneous nucleation of isotactic poly(propylene) confined to nanoporous alumina

The crystallization of highly isotactic polypropylene confined in self-ordered nanoporous alumina is studied by differential scanning calorimetry. A transformation from a predominantly heterogeneous to predominantly homogeneous nucleation takes place if the pore diameter is smaller than 65 nm. Crystallization is suppressed with decreasing pore size, and the absence of nucleation below 20 nm pores indicates the critical nucleus size. The results reported here might enhance the understanding of nanocomposites containing semicrystalline polymers and reveal design criteria for polymeric nanofibers with tailored mechanical and optical properties.     

Fracture behaviors of isotactic polypropylene/poly(ethylene oxide) blends: Effect of annealing

As a part of serial work about the toughening of isotactic polypropylene (iPP) during annealing treatment, this work reports the effect of annealing on fracture behaviors of iPP blend with a little of poly(ethylene oxide) (PEO). Injection-molded bars of an iPP/PEO blend were annealed at different temperatures (50-160 °C) for 12 h and at 100 °C for different durations (12-96 h). The fracture behaviors of the annealed samples, including notched Izod impact fracture, universal tensile fracture, and single-edge notched tensile (SENT) fracture, were comparatively investigated to establish the role of annealing in improving the fracture resistance of the sample. The results showed that the annealing treatment greatly influences the fracture resistance of the blend. The impact-fractured surface morphologies were characterized by scanning electron microscope (SEM) to clarify the possible mechanisms for the improvement of the fracture resistance. It was proposed that, the excellent fracture resistance of iPP with a minor phase of which exhibits relatively low melting temperature can be easily achieved through the simple annealing treatment, even if the minor phase is immiscible with iPP.     

聚偏氟乙烯的多晶型及结晶行为的研究进展

详述聚偏氟乙烯(PVDF)五种晶型的结构特点,分析了各晶型之间的相互转化关系、引起转化的各种因素及分子内缺陷对结晶行为的影响.评述了近年来PVDF在应力场下熔融纺丝过程中的结晶行为、结晶形成机理以及纺丝条件对结晶结构的影响.     

聚碳酸酯/聚(1, 4-环己烷二甲酸- 1, 4-环己烷二甲醇酯)共混物的光学特性及机理分析

采用熔融共混法制备一系列聚碳酸酯(PC)与聚(1, 4-环己烷二甲酸-1, 4-环己烷二甲醇酯)(PCCD)形成的共混物。光学性能测试表明,PC/PCCD共混物具有高透光率、低雾度的光学特征。采用SEM、TEM、DSC、红外光谱及核磁共振等多种手段对PC/PCCD进行研究,以揭示共混物呈现光学透明性的内在机理。结果表明：PC/PCCD在几十纳米尺度下具有均相结构,均相结构是其在宏观上表现高透明性的直接原因; 不同PCCD含量的PC/PCCD共混物均表现出单一玻璃化温度,表明PC和PCCD完全相容。这种均相结构的完全相容,是PC/PCCD共混物呈现高透明性的内在原因。通过进一步分析PCCD和PC相容的机理,发现PC与PCCD熔融共混过程中未发生酯交换反应,PC和PCCD的相容源于结构相似,与是否发生酯交换反应无关。     

In Situ Fourier transform infrared spectroscopic study of the thermal degradation of isotactic poly(propylene)

The conformational change of isotactic poly(propylene) (iPP) during the thermal degradation process has been carefully studied by in situ Fourier transform infrared (FT-IR) spectroscopy. This new method of studying thermal degradation of iPP not only shows the conventional kinetic parameter information of thermal degradation such as the degradation activation energy DeltaE and the degradation factor n, which are in accord with the results of traditional thermogravimetry experiments, but also indicates that many significant molecular structure changes occur during the thermal degradation process that come from some characteristic absorption band changes of in situ FT-IR. A multivariate approach, principal components analysis (PCA), is applied to the analysis of infrared (IR) data, and the results further confirm the multi-step processes of the thermal degradation of iPP. Above all, this is a new application to polymer thermal degradation by in situ FT-IR that connects the intermediate conformational change with final results during thermal degradation.     

Consecutively spin-assembled layered nanoarchitectures of poly(sodium 4-styrene sulfonate) and poly(allylamine hydrochloride)

The recently established spin-coating electrostatic self-assembly (SCESA) technique has been shown to facilitate not only the rapid fabrication of polyelectrolyte multilayer assemblies, but also allow each layer to be easily controlled on a monomolecular scale by minimizing the film thickness across a substrate surface. In this paper, the influence of polyelectrolyte concentration on the amount and thickness of spin-deposited polymer films has been examined for a multilayer system of poly(allyamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS), when the washing steps employed for removing weakly bound polyelectrolytes on a resultant film on a substrate are excluded from the standard fabrication procedure of the SCESA method. The thickness of the spin-deposited PAH/PSS bilayer increased linearly for the PSS concentrations in the range from 1 to 10 mM with PAH constant at 1 mM, which demonstrates the uniform deposition of each layer material onto the thin film. The thickness of PAH/PSS bilayers increased from 1.43 ± 0.06 to 3.37 ± 0.08 nm as the PSS concentration increased from 1 to 10 mM, while the PAH concentration was kept constant at 1 mM. The multilayer films were found to be stable in a good solvent (H₂O) for at least 30 h, without any noticeable loss of the adsorbed layer component of the polyelectrolyte. This improvement to the SCESA method (exclusion of washing steps) provides a convenient way to create multilayer heterostructures with the thickness of each layer being easily adjusted.     

Crystallization of 4He in Aerogels

Static behaviors of crystallization of ⁴He in porous materials, such as the increase of melting pressure, have been studied extensively, but nonequilibrium dynamics of the phase transition is hardly known. Our interest was in how ⁴He crystals grow in a 90.4% porosity aerogel. Aerogels are transparent and the dynamics in them can be studied visually. A Pomeranchuk-type variable-volume cell was used to study crystallization at a fixed temperature with a blocked capillary condition. By continuously compressing a chamber, the pressure rose above the bulk melting pressure and at a pressure 1.7 bar above the bulk melting pressure these crystals began to invade the aerogel. A clear crystal-superfluid interface was moved smoothly by the steady compression. No macroscopic facets were observed in the aerogel well below the bulk roughening transition temperature.      

Co1-xZnxFe2O4铁氧体气凝胶的制备及其性能研究

采用醇-水溶液加热法结合超临界流体干燥(SFCD)制备了Co10xZnxFe2O4铁氧体气凝胶,对样品进行了XRD、BET、VSM、ICP及TEM等表征.结果表明.所得铁氧体气凝胶为单一尖晶石结构,具有较高的比饱和磁化强度、较大的矫顽力以及较高的比表面积;在一定范围内,改变Zn含量可以改善CoZn铁氧体气凝胶的性能.     

Adsorption of poly(4-vinylpyridine) onto bentonites

The preparation of new adsorbents based on the coating of a poly(4-vinylpyridine) (P₄VP) polymer onto industrial bentonites was investigated. Two ways of synthesis were investigated, using dibromohexane (DBH) or its absence as a difunctional quaternizing agent in order to fasten the polymer by cross-linking. Several parameters (reagents ratio, type of bentonite, chemical stability in liquid media) were studied. Qualitative (IR and RMN spectroscopies) and quantitative (thermogravimetric) analyses of the samples were carried out.     

Evaluation of molecular orientation and alignment of poly(3-hexylthiophene) on Au (111) and on poly(4-vinylphenol) surfaces

The orientation and alignment of regioregular poly(3-hexylthiophene) (P3HT) molecules on Au (111) surface and on poly(4-vinylphenol) (PVP) thin film were investigated. The P3HT molecules on the smooth Au (111) are oriented with both the backbones and the side chains parallel to the substrate (plane-on orientation) as revealed by the scanning tunneling microscope (STM) images. However, the P3HT molecules on the PVP thin films are preferably oriented with side chains perpendicular to the surface (edge-on orientation). Surface modification of the PVP by hexamethyldisilazane (HMDS) can increase the crystalline size in the P3HT semicrystalline films. The performance of an all-polymer organic field-effect transistor (OFET) with the drop-cast P3HT semiconductor layer and the crosslinked PVP gate insulator on poly(ethylene naphthalate) (PEN) substrate was evaluated.     

The influence of solvent quality on the mechanical properties of thin cast isotactic poly(methyl methacrylate) coatings

Thin coatings of isotactic poly(methyl methacrylate) were cast on glass from solvents of different quality, which was expected to result in different molecular morphologies. The elastic moduli and hardness of the coatings were measured using a nanoindenter. The aim was to examine the viability of this technique for assessing the influence of the morphology on the mechanical properties. The interpretation of the data was complicated by both the influence of the hard substrate and possibly by the plasticising effect of retained solvent in the bulk. Nevertheless, it was reasonable to conclude that a coating cast from a good solvent was stiffer and harder than that from a poor solvent. This is consistent with previous frictional and spectroscopic studies.     

聚1-萘胺纳米颗粒的合成及表征

采用界面聚合法合成了聚(1-萘胺)纳米颗粒.利用红外光谱(FT-IR),紫外可见吸收光谱(UV-vis),电子扫描显微镜(SEM),投射电镜(TEM),X射线衍射(XRD),循环伏安(cyclic voltammogram)等测试方法,对聚合物进行了表征并对聚合物形貌、结构及性能进行了初步探讨.结果表明,界面聚合法合成的聚(1-萘胺)呈现直径在100nm内的颗粒状分布;XRD结果显示,聚(1-萘胺)为半结晶态聚合物;界面聚合法合成的聚(1-萘胺)具有一定的电化学活性.     

Electro-optical properties of poly(1-(difluorophenyl)-2-(4-alkylcyclohexyl phenyl)acetylene) organic light-emitting diodes

For organic light-emitting diodes (OLEDs) applications, we have investigated novel polymers, using substituted polyacetylenes (PA), poly(1-(fluorophenyl)-2-(alkylcyclohexylphenyl)acetylene) (PDPA-nF) (n = 1 or n = 2) which exhibit air stability, better solubility in common organic solvent and higher luminescence than polyacetylene. In this study, we have used poly[(1-(3,4-difluorophenyl)-2-(4-pentylcyclohexylphenyl)acetylene)] (PDPA-2F) as an emitter in OLEDs and their performance was determined by measuring the current-voltage-luminance characteristic. The devices have a maximum brightness of 827 candela (cd)/m² at 12 V and a maximum current efficiency of 0.78 cd/A at 9 V with a maximum luminescence at 536 nm. Influence of the metal electrode on the charge injection was studied using several cathode configurations (Ca, Al and Au) for the devices. Furthermore, the charge injection and transport processes were correlated to the presence of traps inside the polymer, determined by deep level transient spectroscopy (DLTS).     

Fusion of porous isotactic poly(methyl methacrylate) thin films fabricated on silica nanoparticles with stepwise stereocomplex assembly

Structures of silica nanoparticles coated with stereocomplex thin films composed of isotactic (it) poly(methyl methacrylate) (PMMA) and syndiotactic (st) poly(methacrylic acid) (PMAA) and with porous it-PMMA thin films under gentle stirring or static conditions were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), respectively. The porous it-PMMA films were fabricated by stepwise stereocomplex assembling of it-PMMA and st-PMAA, and subsequent extraction of the st-PMAA from the films. From DLS results, an evident difference was not observed between the it-PMMA films and the stereocomplex films, whereas the it-PMMA films after 10 h of stirring in acetonitrile/water (4/6, v/v) and drying on a SEM stage fused to form nanostructured networks. The fusion of the it-PMMA films on the silica nanoparticles occurred not by the dissolution of it-PMMA in the mixed solvent, but rather by an interaction of the it-PMMA chains driven by the slight solvation of acetonitrile without dissolution. Thus, leaving the solution at rest would be important for film fusion on the particles, and multiple spherical substrates could promote the crosslinking of the it-PMMA chains on the particles.     

Synthesis of polystyrene,poly(styrene/4-vinylpyridine), poly(p-nitrostyrene) and poly(p-aminostyrene)-coated silica and their extraction capabilities for amphetamine

Several novel organic–inorganic hybrid materials, including polystyrene-coated silica (SG-PS), poly(styrene/4-vinylpyridine)-coated silica (SG-PVP), poly(p-nitrostyrene)-coated silica (SG-PS-NO₂) and poly(p-aminostyrene)-coated silica (SG-PS-NH₂), were synthesized in order to improve the extraction methods of harmful stimulants via solid phase extraction. The materials were characterized using infrared spectra (IR), scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) surface area measurement and thermogravimetric analysis (TG). The application of the new materials in solid phase extraction columns to extract methamphetamine revealed that the extraction capability of poly(styrene/4-vinylpyridine)-coated silica is the best among the four materials, which provides novel supporter materials for extracting amphetamine-derived drugs.