Solvent size effect on the static and dynamic properties of polymer chains in athermal solvents

The static and dynamic properties of polymer chains in athermal solvents with different sizes are studied by molecular dynamics method. With increasing solvent size, the radius of gyration and the diffusion coefficient of the polymer decay fast until a critical solvent size is reached. For the polymer diffusion coefficients, this decay only depends on the solvent size; while for the radius of gyration of polymers, this decay depends on both solvent size and the length of the polymers. The increase of solvent size also makes the polymer tend to be thicker ellipsoid until a critical solvent size is reached. The static scaling exponent of the polymer also shows the solvent size dependence. Moreover, four regions are identified where the polymers show different dynamic behaviors according to the dynamic structure factors of the polymer.

Influence of molecular topology on the static and dynamic properties of single polymer chain in solution

The influence of molecular topology on the structural and dynamic properties of polymer chain in solution with ring structure, three-arm branched structure, and linear structure are studied by molecular dynamics simulation. At the same degree of polymerization (N), the ring-shaped chain possesses the smallest size and largest diffusion coefficient. With increasing N, the difference of the radii of gyration between the three types of polymer chains increases, whereas the difference of the diffusion coefficients among them decreases. However, the influence of the molecular topology on the static and the dynamic scaling exponents is small. The static scaling exponents decrease slightly, and the dynamic scaling exponents increase slightly, when the topology of the polymer chain is changed from linear to ring-shaped or three-arm branched architecture. The dynamics of these three types of polymer chain in solution is Zimm-like according to the dynamic scaling exponents and the dynamic structure factors.

Study of beta-alpha recrystallization of the polypropylene

The crystalline modifications alpha and beta of polypropylene (PP) were studied by using polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC). Typically beta crystals surrounded by alpha spherulites were observed at low temperature. With increasing temperature the beta crystals melted and a new crystal appeared. More interestingly, the melting temperature of the new crystal was about 5degrees higher than that of alpha spherulites originally present in the sample formed isothermally. It was assumed that this new crystal was the recrystalline alpha crystal. This assumption was supported by the DSC results. Furthermore, the crystallization kinetics of the PP used was studied on the basis of the traditional Avrami analysis. As a result, the Avrami exponents of crystallization temperature from 120 to 130degreesC ranged between 4.21 and 3.60, indicating that the crystallization mechanism of PP order melt was spherulitic growth and random nucleation.

Hydrodynamic radius characterization of a vinyl-type polynorbornene by size-exclusion chromatography with a static and dynamic laser light scattering detector

Both absolute molecular weight and molecular sizes (radius of gyration and hydrodynamic radius) of a vinyl-type polynorbornene eluting from size-exclusion chromatography columns were determined by combined with a static and dynamic laser light scattering detector. The hydrodynamic radius of polymer fraction eluting from size-exclusion chromatography columns was obtained from dynamic laser light scattering measurements at only a single angle of 900 by introducing a correction factor. According to the scaling relationship between molecular sizes and molecular weight and the ratio between radius of gyration and hydrodynamic radius, the vinyl-type polynorbornene took a random coil conformation in 1,2,4-trichlorobenzene at 150 degreesC.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Epitaxial recrystallization of HDPE-quenched ultrathin films on oriented iPP substrates

The recrystallization behavior of high-density polyethylene (HDPE) on the highly oriented isotactic polypropylene (iPP) substrates at temperatures below the melting temperature of HDPE has been investigated by means of transmission electron microscopy. The results obtained by the bright-field observation and the electron diffraction show that upon annealing the HDPE-quenched films on the oriented iPP substrates at temperatures below 125 degrees C, only a small amount of HDPE recrystallizes on the iPP substrate with [001](HDPE)//[001](iPP), while annealing the HDPE-quenched films at temperatures above 125 degrees C, all of the HDPE crystallites recrystallize epitaxially on the iPP substrate with [001](HDPE)//[101](iPP). (C) 1997 John Wiley & Sons, Inc.

Recrystallization of HDPE in HDPE/iPP quenched films

Epitaxial crystallization behavior of HDPE/iPP double layers under quenching and annealing conditions has been studied by means of transmission electron microscopy (TEM). The results obtained from bright field TEM observations indicate that in the as-quenched state the HDPE that is in direct contact with the surface of the oriented iPP substrate recrystallizes in the form of oriented crystallites dispersed on the iPP substrate. The electron diffraction results show that besides the two normally observed epitaxial orientations between HDPE and iPP, there is also a special orientation with [001](HDPE)parallel to[001](iPP). The HDPE which is in contact with the clean surface of a glass slide crystallizes in small lamellae with random orientation. In the boundary region, the epitaxially crystallized HDPE small lamellae stop right on the boundary of the oriented iPP film. If the quenched samples are annealed at 128 degrees C (below T-m of HDPE) for 2 h, the small HDPE crystals grow to thick lamellae in both areas. But only the epitaxial orientation of HDPE with [001](HDPE)parallel to[101](iPP) has been observed.

两株海藻内生真菌次生代谢产物及其生物活性研究

海洋微生物拥有丰富多样的次生代谢途径，其中海洋生物内生真菌次生代谢产物研究日益受到天然产物化学界的重视。本论文以菌丝体生物量、发酵产物重量、抗菌与细胞毒活性、薄层色谱分析结果以及高效液相色谱分析结果等为评价依据对采自青岛沿海的13株海藻内生真菌在四种液体培养基上的静置发酵产物进行了综合评价，并从中选择了黑曲霉Aspergillus niger EN-13（分离自褐藻囊藻Colpomenia sinuosa）和杂色曲霉A. versicolor EN-7（分离自褐藻鼠尾藻Sargassum thunbergii）两株真菌进行了30升规模发酵（分别采用GPYM培养基和PDB培养）和化学成分的研究，对分离得到的大部分化合物进行了初步的生物活性筛选。 发酵提取物采用常规的硅胶柱层析、反相硅胶柱层析，凝胶Sephadex LH-20柱层析、制备薄层层析、半制备高效液相色谱以及重结晶等分离手段，得到单体化合物。利用各种现代波谱技术(IR、UV、EI-MS、FAB-MS、HR-ESI-MS、1H-NMR、13C-NMR、DEPT、1H-1H COSY、HSQC、HMBC等)并结合化学方法从两种菌株发酵提取物中鉴定了55个化合物的结构。其中从菌株A. niger EN-13分离鉴定了31个化合物，发现9个新化合物，包括2个鞘酯类化合物（AN-1~2）、3个萘并-γ-吡喃酮类化合物（AN-3~5）、3个苯乙基取代的α-吡喃酮类化合物（AN-17, AN-19~20）和1个甾体Diels-Alder加成产物（AN-21），另有1个新的天然环二肽（AN-27）被分离鉴定；从菌株A. versicolor EN-7分离鉴定了24个化合物，发现2个新化合物，为蒽醌AV-12与AV-17，另外，从前一菌株（A. niger EN-13）中鉴定的2个新鞘酯类化合物（AN-1~2）在A. versicolor EN-7中也被再次分离到。 对大部分单体化合物进行了抗菌活性、DPPH自由基清除活性和细胞毒活性测试。结果显示新化合物AN-1、AN-5和AN-20具有弱或中等强度的抑制白色念珠菌生长的活性，AN-4、AN-5、AN-21显示了弱或中等强度的抑制黑曲霉生长的活性，AV-12、AV-17显示了弱的抑制大肠杆菌生长的活性。在DPPH自由基清除活性筛选中，AN-5显示了中等强度的活性，其EC50为109.3 mM，与阳性对照BHT相近（EC50为81.8 mM）。其它部分已知化合物在抗菌和DPPH自由基清除活性的筛选中也显示了弱或中等强度的活性。在针对人肝癌细胞株SMMC-7721和人肺腺癌细胞株A549的体外细胞毒活性筛选中，所测样品均未显示显著活性。