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971.
Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature Ts was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from Ts, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to Ts deviations were observed for G' at low frequencies (the so-called terminal zone). Above Ts G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near Ts can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″2) as a function of temperature were shown to be sensitive to this anomalous behavior.  相似文献   
972.
973.
Summary: Raspberry‐like aggregates containing secondary nanospheres were studied. The formation of raspberry‐like aggregates was due to complexation between core‐shell microspheres and core‐corona micelles. The core‐shell microspheres were synthesized with soap‐free polymerization of styrene and methyl acrylic acid, which included carboxyl groups in the periphery. The micelles were self‐assembled by polystyrene‐block‐poly(4‐vinylpyridine), which contained pyridine groups in the corona. The driven force to form raspberry‐like aggregates was due to the affinity between the carboxyl and pyridine groups. The morphology of the raspberry‐like aggregates could be tuned by changing the ratio of the microspheres to micelles. IR measurements suggested that the raspberry‐like aggregates were like zwitterions.

TEM image of the raspberry‐like aggregates formed at a molar ratio of MAA to 4VP at 1:4.  相似文献   

974.
Syndiotactic Polystyrene (sPS) was sulfonated to different levels in a mixture of 1,1,2–trichloroethane and chloroform. Sulfonation levels were determined by nonaqueous titrations using phenolphthalein indicator. Thermal properties of sulfonated sPS (SsPS) ionomers depend on the sulfonation level. Incorporation of sulfonic acid groups in to the syndiotactic polystyrene backbone was found to affect the crystallization behavior of sPS. DSC data indicated that the melting temperature (Tm), heat of fusion, crystallization temperature (Tc), crystallization rate and degree of crystallization were lowered by the incorporation of sulfonic acid group on the syndiotactic polystyrene backbone. Thermal and FTIR data indicated that the sulfonic groups did not enter into the crystal lattice but remained in the amorphous phase.  相似文献   
975.
The empty δ (δe) form of uniaxially-oriented syndiotactic polystyrene (sPS) samples were obtained by extracting the solvent molecules from the δ form of sPS and solvent complex in acetone and methanol. Temperature dependence of the X-ray fiber diagrams starting from the uniaxially-oriented δe and δ form has been measured successfully at various temperatures for the first time. The transition behavior was traced clearly by separating the equatorial and layer line reflections. The δe form transformed to the γ form via an intermediate form. The intermediate form is speculated to take disordered structure due to the empty cavities present in the δe form. Calorimetric studies showed an endotherm followed by an exotherm during this phase transition, which is consistant with such a speculation. On the other hand the δ form transformed to the γ form directly without passing through the intermediate form or δe form. During the δ to γ phase transition the solvent molecules evaporate through the columnar structure in a broad range of temperature, allowing the transition to occur smoothly.  相似文献   
976.
掺三异丁氧基钬聚苯乙烯的性能   总被引:1,自引:0,他引:1  
王文  章文贡  林美娟 《应用化学》2002,19(12):1146-0
添加三异丁氧基钬的苯乙烯经本体聚合制备了掺钬聚苯乙烯新材料。用FT-IR、XPS、SEM、DTA-TG和DMTA等分析技术研究了钬对PS性能的影响,并测定了掺杂物的冲击强度。结果表明,掺钬聚苯乙烯中存在着Ho与苯环π电子之间的配位作用,掺钬聚苯乙烯的热稳定性随着钬含量的增加而提高,其冲击强度有明显提高,并在钬的质量分数为5.0%时达最高值,SEM和DMTA分析从微观上解释了稀土钬对聚苯乙烯的增韧机理。  相似文献   
977.
Summary: The solvent‐free syndiospecific styrene polymerization as an example of a coordination polymerization has been investigated with a catalyst system consisting of η5‐octahydrofluorenyl titanium trimethoxide as a transition metal catalyst, MAO as a cocatalyst, and TIBA, in the presence of reaction products of sterically hindered phenolic compounds, usually applied as heat stabilizers of polymers. Unexpectedly, such reaction products led to a significant increase in polymerization activity of the catalyst system. Second, after deactivation of the catalyst system, such activators result in a significantly enhanced thermal stability of the syndiotactic polymers received.

Effect of the P8‐activator on polymerization activity in dependence on polymerization time (molar ratio–styrene:MAO:TIBA:P:Ti = 700 000:50:25:25:1; molar ratio–phenolic compound:TIBA = 1:3.2; polymerization temperature: 50 °C).  相似文献   

978.
Wu S  Xu Z  Yuan Q  Tang Y  Zuo X  Lai J 《Journal of chromatography. A》2011,1218(10):1340-1346
The homogeneous molecularly imprinted microspheres (MIMs) based on a biologically inspired hydrogen-bond array were prepared using allobarbital as the novel functional monomer and divinylbenzene as the cross-linker. The host-guest binding characteristics were examined by molecular simulation and infrared spectroscopy. The resultant MIMs were evaluated using high performance liquid chromatography and solid-phase extraction. The results obtained demonstrate that the good imprinting effect and the excellent selectivity of MIMs are mainly due to the interaction involving the formation of three-point hydrogen bond between host and guest. The complete baseline separation was obtained for five triazine analogues and a metabolite on the MIM HPLC column. The MIMs were further successfully used as a specific sorbent for selective extraction of simetryne from corn and soil samples by molecularly imprinted solid phase extraction. Detection limits and recoveries were 5.8 μg/kg and 0.14 μg/kg and 87.4-105% and 94.6-101% for simetryne in corn and soil sample, respectively.  相似文献   
979.
不同溶剂制备的聚乳酸多孔微球的形成机理   总被引:1,自引:0,他引:1  
利用改进的双乳液溶剂挥发法制备了多孔聚乳酸( PLA)微球.通过采用具有不同沸点和水溶性的有机溶剂制备得到不同多孔结构的PLA微球.结果发现以二氯甲烷、氯仿和甲苯为溶剂制备的微球具有相似的均匀多孔结构,而以乙酸乙酯制备的微球却具有中空结构和多孔的壳层.通过进一步的实验研究了溶剂种类对于微球多孔结构的影响.结果表明溶剂的...  相似文献   
980.
Polystyrene supported TiCl4 (Ps‐TiCl4) and polystyrene supported FeCl3 (Ps‐FeCl3) were prepared by coordinating Lewis acids with polystyrene. The catalysts were characterized by TGA, BET, SEM, IR and pyridine‐adsorbed IR. The loading of Ps‐TiCl4 and Ps‐FeCl3 were 0.35 and 0.3 mmol·g?1 respectively. Both catalysts were found to be efficient for the tetrahydropyranylation and detetrahydropyranylation of various alcohols and phenols in different solvents. Two catalysts can be recovered and reused for five times with good activity.  相似文献   
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