三螺旋DNA分子Poly(dT)·Poly(dA)·Poly(dT)碱基振动模式

利用晶格动力学方法计算了三螺旋 DNA分子 poly(d T)· poly(d A)· poly(d T)碱基振动模式 ,并根据势能分布矩阵对碱基振动模式进行了指定。计算的模式频率同拉曼光谱实验相符合     

Effects of Poly(Propylene Oxide)–Poly(Ethylene Oxide)–Poly(Propylene Oxide) Triblock Copolymer on the Gelation of Poly(Ethylene Oxide)–Poly(Propylene Oxide)–Poly(Ethylene Oxide) Aqueous Solutions

Poly(ethylene oxide)-poly(propylene oxide)–poly(ethylene oxide) ((EO)_n–(PO)_m–(EO)_n) block copolymers, commercially available as Pluronics (BASF Corp.) and Poloxamers (ICI Corp.), have been widely applied in medicine, biochemistry, and other fields because of their ability to form reversible micelles and physical gels in aqueous solution. Generally, for PEO–PPO–PEO block copolymers with higher ethylene oxide concentration, the micellization and gelation in aqueous solution are easier. However, if we introduce the reverse block copolymer PPO–PEO–PPO into PEO–PPO–PEO aqueous solutions, the micellization and gelation of the system will be more complex. In this work, the reverse block copolymer PO₁₄–EO₂₄–PO₁₄ (17R4) was added to the Pluronics EO₂₀–PO₇₀–EO₂₀ (P123), EO₁₀₀–PO₆₅–EO₁₀₀ (F127), and EO₁₃₃–PO₅₀–EO₁₃₃ (F108) aqueous solutions with different molar ratios. The rheological properties of different mixtures were measured to study the additive effect on the gelation behavior. The sol–gel transition temperature of the P123, F127, and F108 solutions shifted to a higher temperature when 17R4 was added to the solutions. In addition, the existence of 17R4 greatly affected the stability of gels. These results help to better understand the gelation of Pluronic aqueous solutions.     

A Study on Properties of Poly(vinyl chloride)/Poly(α-methylstyrene-acrylonitrile) Binary Blends

Blends of poly(vinyl chloride) (PVC) and poly(α-methylstyrene-acrylonitrile) (α-MSAN) with variable composition of 0 to 100 wt% were prepared by melt mixing. Properties of binary blends were extensively studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), heat distortion temperature (HDT), mechanical properties, melt flow rate (MFR), and scanning electron microscope (SEM). A single glass transition temperature (T_g ) was observed by DSC and DMTA, indicating miscibility between PVC and α-MSAN. The results of ATR-FTIR indicated that specific strong interactions were not present in the blends and the miscibility was due to interaction between –CN and PVC. With increasing amount of α-MSAN, considerable increase occurred in HDT, flexural strength, and flexural modulus compared with reverse s-shaped decrease in impact strength and elongation at break. Synergism was observed in tensile strength and MFR. No phase separation was observed in SEM photographs, indicating miscibility between PVC and α-MSAN. In addition, morphology of the impact-fractured surfaces, including roughness and non-fused particles, correlated well with the mechanical properties and MFR.     

Poly(3,4-ethylene dioxythiophene): Poly(styrene sulfonate)的共振拉曼光谱研究

通过拉曼光谱方法分别对PEDOT:PSS掺杂和去掺杂状态进行了详细分析. 实验结果表明, 去掺杂的PEDOT:PSS由于其在激发波长附近的吸收增强而引起了共振效应, 拉曼信号得到大幅度增强, 可见, 以633 nm(He-Ne)激光为激发波长的拉曼光谱是研究PEDOT:PSS掺杂状态的有效方法. 此外, 显微拉曼光谱也是分析聚合物发光二极管器件内各层材料的有效手段.     

Designing and Characterization of Poly(L-Lactide)/Poly(ϵ-Caprolactone) Multiblock Copolymers

A series of poly(L-lactide)/poly(?-caprolactone) (PLA/PCL) biodegradable multiblock copolymers was synthesized by a two-step process and characterized. Ring-opening polymerization was used to prepare a series of HO-PLA-PCL-PLA-OH copolymers initiated by hydroxyl-terminated PCL. Then the triblock copolymers and 1,6-hexamethylene diisocyanate (HDI) were reacted with different copolymer/HDI weight ratios. Consequently, a series of PLA/PCL multiblock copolymers with designed molecular chain structure was obtained. Gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, and ¹H NMR were used to characterize these copolymers and the results showed that the designed PLA/PCL copolymers had been synthesized. Dynamic mechanical analysis (DMA) was applied to characterize their thermal properties. Stress–strain curves showed that a PLA/PCL copolymer with adjustable mechanical properties had been achieved.     

Shear Effect on Morphology of Poly(Butylene Terephthalate)/Poly(Styrene‐co‐Acrylonitrile) Blends

Abstract

The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.     

Preparation and Characterization of Gelatin–Poly(L-lactic) Acid/Poly(hydroxybutyrate-co-hydroxyvalerate) Composite Nanofibrous Scaffolds

Poly(L-lactic) acid (PLLA) scaffolds, prepared by electrospinning technology, have been suggested for use in tissue engineering. They remain a challenge for application in biological fields due to PLLA's slow degradation and hydrophobic nature. We describe PLLA, PLLA/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), and PLLA/PHBV/gelatin (Gt) composite nanofiberous scaffolds (Gt–PLLA/PHBV) electrospun by changing the electrospinning technology. The morphologies and hydrophilicity of these fibers were characterized by scanning electron microscopy (SEM) and water contact angle measurement. The results showed that the addition of PHBV and Gt resulted in a decrease in the diameters and their distribution and greatly improved the hydrophilicity. The in-vitro degradation test indicated that GT–PLLA/PHBV composite scaffolds exhibited a faster degradation rate than PLLA and PLLA/PHBV scaffolds. Dermal fibroblasts viabilities on nanofibrous scaffolds were characterized by [3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide] (MTT) assay and cell morphologies after 7 days culture. Results indicated that the GT–PLLA/PHBV composite nanofibers showed the highest bioactivity among the three scaffolds and increased with increasing time. The SEM images of cells/scaffolds composite materials showed the GT–PLLA/PHBV composite nanofibers enhanced the dermal fibroblasts's adhesion, proliferation, and spreading. It is suggested that the nanofibrous composite scaffolds of GT–PLLA/PHBV composites would be a promising candidate for tissue engineering scaffolds.     

Poly(acrylamide‐co‐acrylic acid)/Poly(vinyl pyrrolidone) Polymer Blends Prepared by Dispersion Polymerization

The structure and properties of a three‐component system, a poly(acrylamide‐co‐acrylic acid)/poly(vinyl pyrrolidone) [P(AM‐co‐AA)/PVP] polymer blend prepared by dispersion polymerization, were studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the resulting P(AM‐co‐AA) microspheres with diameters between 200–300 nm were well‐dispersed in the PVP matrix. Fourier transform infrared spectra (FTIR) showed that intermolecular hydrogen bonding interaction occurred between the dispersed phase and the continuous phase. The mechanical properties of P(AM‐co‐AA)/PVP polymer blends were also determined. With different mass ratios of acrylamide to acrylic acid, it was found that the blends had better mechanical properties with increased AA content.     

Hydrogen Bonding Interactions in Miscible Blends of Poly(hydroxyether ester)s with Poly(N‐vinyl pyrrolidone)

Studies on the miscibility and intermolecular specific interactions in the blends of two structurally similar poly(hydroxyether ester)s, poly(hydroxyether terephthalate ester) (PHETE), and poly(hydroxyether benzoate) (PHEB) with poly(4‐vinyl pyrrolidone) (PVPy) are reported. In the miscible blends there are intermolecular specific interactions between PHEEs and PVPy. It was found that intercomponent hydrogen‐bonding interactions in PHETE/PVPy blends are much stronger than those in PHEB/PVPy blends. It seems that the higher ratio of hydroxyl to carbonyl groups results in the stronger intermolecular hydrogen bonding interactions. The difference in intermolecular specific interactions between the two miscible systems is interpreted on the basis of the impact of macromolecular structures on intermolecular specific interactions. The structural characteristics of macromolecular chains, such as chain connectivity, accessibility (or screening effect), and rigidity of the macromolecular chains have a profound effect on the intermolecular interactions. These factors constitute steric hindrance and reduce the specific interactions among functional groups. These factors can become dominant in the blends of polymers.     

Miscibility Determination in Poly(ε-caprolactone)/Poly(Vinyl Formal) Blend by Equilibrium Melting Temperature and Spherulite Morphology

Miscibility of poly(ε-caprolactone), (PCL), containing 1, 5, and 10 wt.% poly(vinyl formal) (PVF) blends was investigated by polarized optical microscopy (POM), atomic force microscopy (AFM), and differential scanning calorimetry (DSC) for spherulitic morphology and equilibrium melting temperature (T°_m, via Hoffman-Weeks plot). The T°_m of PCL in the blends was similar to that of pure PCL, indicating immiscibility. Isothermally, melt crystallized virgin PCL between 30°C and 50°C showed spherulitic morphology with negative birefringence, Maltese cross, and without extinction rings. The nucleation and growth rates of PCL spherulites were found to be dramatically reduced with the addition of PVF. Extinction rings and a change in the sign of the birefringence of the PCL spherulites were observed and were found to be dependent on blend composition and crystallization temperature. The presence of a ring pattern in spherulites was an indication of miscibility between the two polymers that had failed to be detected by thermal methods. The formation of a ring pattern is discussed in terms of lamella twisting originating from a change in the crystallization mechanism.     

Preparation and Degradation Behaviors of Poly(L-lactide-co-glycolide-co-ε-caprolactone)/1,4-butanediamine Modified Poly(lactic-co-glycolic acid) Blend Film

Abstract

Polymer blending is an attractive method for producing new polymer materials with excellent properties. In this work the blended polymers were prepared from poly(L-lactide-co-glycolide-co-ε-caprolactone) and 1,4-butanediamine modified poly(lactic-co-glycolic acid) (PLLGC/BMPLGA). The hydrophilicity was studied by static water contact angle tests. The in-vitro degradation behaviors of the PLLGC/BMPLGA blended films were investigated during various degradation periods. The results showed that the introduction of the PLLGC reduced the hydrophilicity and degradation rate of the blended polymers while improved the tensile strength and elongation percentage. Therefore, we suggest the blends of the PLLGC and BMPLGA could supply a potential biomaterial for application in the medical field for use as tissue engineering scaffolds or drug delivery.     

Effect of Non‐Ideal Mixed Solvents on Dimensions of Poly(N‐Vinylpyrrolidone) and Poly(Methyl Methacrylate) Coils

An addition of a small amount of non‐solvent tetrahydrofuran (THF) to good solvent water gave rise to a strong solvent power for poly(N‐vinylpyrrolidone) (PVP). It was found that PVP coils in mixtures of water and THF first swelled as the fraction of THF was increased, and then the coils contracted after a critical composition of the solvent mixture based on the measurement of dilute solution viscosities. It was reached that the power of the mixed solvents was not the simple average of the power of individual components. The influence of the non‐ideal mixing of water and THF on the power of these mixtures for PVP and the dimensions of PVP coils was taken into account. Especially the formation of pseudo‐clathrate hydrate structure with the composition φ _THF ≈ 0.44 was found to be an important factor to change the solvation and dimensions of PVP coils. Some other solvent mixtures for PVP and poly(methyl methacrylate) (PMMA) were also found to be non‐ideal mixtures. The viscosities of these solvent mixtures could show positive or negative deviation from the values obtained from the addition rule. It was shown again that the influence of the non‐ideality of these solvent mixtures on the dimensions of polymer coils was great. The action of mixed solvents changed the dimension of polymer coils, not only because of excluded volume effects but also because of the different molecular interactions present in these mixed solvents.     

Polypropylene/Poly (Trimethylene Terephthalate)–Blend Fibers

Polypropylene (PP)/polyester (PES)–blend fibers were prepared by extruder melt spinning. The polymer blend consisted of PP and a “master batch” (MB) based on polytrimethylene terephthalate (PTT) or polyethylene terephthalate (PET), binary PTT/PET or PP/PTT blends, and also on a ternary PP/(PTT/PET) blend. The phase structure of PP/PES–blend fibers was examined. PES microfibers showed separation from the PP matrix in blend fibers. The impact of MB composition and rheological characteristics on phase structure parameters indicate a significant contribution of the PTT in the binary MB on the length of dispersed PES microfibers in the PP matrix. However, the blends of PP and ternary MB (PP/PTT/PET) have a lower diameter and length of the PES microfibers. The presence of PTT/PET (PES) enhances the structural and mechanical properties of the blend PP/PES fibers. In addition, PTT increases the tensile strength of the PP/PES–blend fibers if a binary MB is used, while the fiber nonuniformity is reduced in the presence of a ternary MB.     

Poly(organylsilylene)s — perspective materials for optoelectronics

Poly(organylsilylene)s with their uninterrupted chains of silicon atoms are a new class of materials with significant delocalization of electrons along the polymer chain. Their electronic structure, optical properties, photoconductivity, electroluminescence, and photorefractivity are discussed on the model compound poly[methyl(phenyl)silylene]. Their unusual electrical and optical properties, such as high quantum generation efficiency, high charge-carrier mobility, efficient luminescence, and optical non-linearity, can be utilized in some optoelectronic devices. Presented at the 1st Czech-Chinese Workshop “Advanced Materials for Optoelectronics”, Prague, Czech Republic, June 13–17, 1998. This work was suported by the Grant Agency of the Academy of Sciences of the Czech Republic (grant No. A1050901) and by the Grant Agency of the Czech Republic (grant No. 106/98/0700).     

Apatite formation on Poly (vinyl alcohol)-coated Poly (?-caprolactone) films by incubation in simulated body fluids

In this study, biodegradable poly (?-caprolactone) (PCL) films were coated with poly (vinyl alcohol) (PVA) and then incubated in a simulated body fluid 1.5SBF to prepare an apatite (HA)/PCL composite. It was found that the bone-like apatite formability of PCL was enhanced by PVA coating. The changes of surface properties induced by PVA coating were effective for apatite formation. The apatite formability increased with increasing coating amount. After 24 h incubation, apatite was formed on PVA-coated PCL film but hardly any apatite was found on uncoated PCL plate. The surface chemistry of the specimens was examined using XPS, FT-IR-ATR. The apatite formed was characterized by using SEM, TF-XRD, FT-IR, EDS. The apatite formed was similar in morphology and composition to that of natural bone. This indicated that simple PVA coating on PCL substrate could serve as a novel way to accelerated apatite formation via biomimetic method.     

Luminescence Properties of Poly(3-Methoxythiophene)—Bithiophene Composite Oligomers

The electronic absorption and fluorescence spectra of electrosynthesized poly(3-methoxythiophene)— bithiophene (PMOT-BT) composite oligomers were studied in organic solution (DMSO) and/or in the solid state on ITO plates. Different spectral properties (absorption and fluorescence maximum wavelengths, fluorescence quantum yields, etc.) were found to depend on the bithiophene initial concentration used during electrosynthesis and, subsequently, on the film composition and oligomer chain length.     

Rheological Behaviors of Poly(Vinylidene Fluoride)/“Bud-Branched” Nanotubes Nanocomposites

Bud-branched nanotubes, fabricated by growing metal particles on the surfaces of multiwall carbon nanotubes (MWCNTs), were used to prepare poly(vinylidene fluoride) (PVDF)-based nanocomposites. The melt viscoelastic behaviors of PVDF and its nanocomposites were characterized. The results showed that the introduction of both the MWCNTs and bud-branched nanotubes (MWCNTs-B) increased the storage modulus, loss modulus, and complex viscosity of the nanocomposites. However, the bud-branched nanotubes were more efficient to increase the elasticity than the MWCNTs that have relatively smooth surfaces. In particular, it was observed that the bud-branched nanotubes caused an increase of normal force and crossover modulus, while for MWCNTs, no variation in the normal force and a decrease of the crossover modulus were observed.     

Rheological Characterization of Poly(3,3′-Diaminodiphenylsulfone Terephthaloylchloride) Solutions in Dimethylsulfoxide

Steadyshear and oscillatory shear rheological measurements were performed to characterize the solution rheological behavior of poly(3,3′-diaminodiphenylsulfone terephthaloylchloride) (P(3,3′-DDS-TPC)) in dimethyl sulfoxide (DMSO). The effects of temperature, concentration, and weight-average molar mass () on the rheological properties were investigated. From the temperature dependence of zero-shear viscosity, the flow activation energies, E_η, of P(3,3′-DDS-TPC)/DMSO solutions were calculated. Both the overlap concentration, C*, and the entanglement concentration, C_e, were determined from the concentration dependence of the specific viscosity η_sp. All the P(3,3′-DDS-TPC) solutions, we studied, can be separated into three regimes: the dilute, semidilute-unentangled, and entangled regime with slopes of 1, 1.3, and 3.9, of concentration versus η_sp plots, respectively, which are consistent with scaling predictions for flexible polymers in a good solvent.     

Infrared Spectra of Poly(Ethylene Terephthalate) γ-Irradiated in Organic Solvents

The infrared spectra of poly(ethylene terephthalate) γ-irradiated in presence of organic solvents were recorded over the spectral region 200–300 cm^?1. The analysis of these spectra showed that the combined effect of solvent and γ-irradiation results in appearance of two strong bands at 1550 and 1630 cm^?1, increase in the intensities of the gauche bands at 1450 and 1370 cm^?1 and decrease in the intensity of the trans-band at 1340 cm^?1. The aromatic ring C=C stretching band at 1410 cm^?1 was also affected. The profound spectral changes were observed only in samples irradiated in presence of solvents and were not observed in samples treated with solvents or only irradiated in atmosphere of air, these spectral changes were attributed to the changes in the intermolecular of intramolecular forces as a result of penetration of solvent molecules in the polymer and the ionizing effect of γ-iffadiation. It was found that the extent of the intensity variations depends on the nature of the solvent.     

Steady–shear‐induced Isothermal Crystallization of Poly(L‐lactide) (PLLA)

The isothermal crystallization of poly(L‐lactide) (PLLA) under steady‐shear flow was investigated in situ using an optical polarizing microscope with a hot shear stage. The steady–shear‐induced crystalline morphology of PLLA, to a great degree, depends on the crystallization temperature. There is a critical temperature, 120°C, below which shear‐induced row nuclei enhance nucleation ability, leading to the improvement of crystallinity, and above which cylindrite structure is generated. Their numbers increase and size reduces with temperature owing to the better movement and relaxation behavior of chains in the presence of shear flow. The results of 2D wide‐angle x‐ray diffraction (WAXD), showing the oriented structure at high T _c , and differential scanning calorimetry (DSC), detecting the rising of T _m with increasing T _c , well confirm the effect of T _c on the crystallization of PLLA under shear flow.