As molecular weight controls the biological activities of polysaccharides, screening the optimal molecular weight of polysaccharides is important in drug research and application. In this study, hydrogen peroxide was ...As molecular weight controls the biological activities of polysaccharides, screening the optimal molecular weight of polysaccharides is important in drug research and application. In this study, hydrogen peroxide was employed as oxidant, and temperature, reaction time, and concentration of polysaccharides and hydrogen peroxide were examined for their effects on the preparation of polysaccharides in different molecular weights from Ulva pertusa. Our experiment suggested that the optimal degradation concentrations for polysac-charides and hydrogen peroxide were 2.5% (w/v) and 8.0% (v/v), respectively. The range of degradation measured by relative viscosity was mainly controlled by temperature and time. Results revealed that 35℃ was the optimal temperature for obtaining low-degradation samples, and 50℃ was the most favorable temperature to accelerate the reaction to yield highly-degraded samples. Four samples in different molecular weights A, B, C and D were finally prepared. The controllability was evaluated by the relative standard deviation (RSD) of relative viscosity, and the peak molecular weights and the polydispersity indexes (Mw/Mn) of molecular weights were measured by high performance gel permeation chromatography (HPGPC).展开更多
The photo-controlled/living radical polymerization of methacrylic acid (MAA) was performed at room temperature by irradiation with a high-pressure mercury lamp using azo initiators and 4-methoxy-2,2,6,6-tetramethylpip...The photo-controlled/living radical polymerization of methacrylic acid (MAA) was performed at room temperature by irradiation with a high-pressure mercury lamp using azo initiators and 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate (tBuS) as the accelerator. Whereas the bulk polymerization yielded polymers with a bimodal molecular weight distribution in both the absence and presence of tBuS, the solution polymerization in methanol produced unimodal polymers with the molecular weight distribution of 2.0 - 2.3 in the presence of tBuS. The molecular weight distribution of the resulting poly (MAA) decreased with an in- crease in tBuS. The dilution of the monomer concentration also reduced the molecular weight distribution. The use of the initiator with a low 10-h half-life temperature also effectively controlled the molecular weight. The livingness of the polymerization was confirmed by obtaining linear increases in the first-order conversion versus time, the molecular weight versus the conversion, and the molecular weight versus the reciprocal of the initiator concentration.展开更多
[目的]建立甘草多糖分子量及分子量分布的测定方法,为甘草多糖质量控制提供方法。[方法]利用高效凝胶色谱法测定甘草多糖的分子量及分子量分布;色谱柱为TOSOH TSK gel G4000 PWXL凝胶色谱柱,检测器为示差折光检测器,流动相为0.7%硫酸钠...[目的]建立甘草多糖分子量及分子量分布的测定方法,为甘草多糖质量控制提供方法。[方法]利用高效凝胶色谱法测定甘草多糖的分子量及分子量分布;色谱柱为TOSOH TSK gel G4000 PWXL凝胶色谱柱,检测器为示差折光检测器,流动相为0.7%硫酸钠水溶液,柱温35℃,流速为0.8 mL/min,进样量20μL。[结果]6批样品的重均分子量在8.0×10^4-1.0×10^5之间,线性关系良好,精密度、重复性均良好。[结论]本实验方法操作简便、快速、准确,为甘草多糖规模化生产的质量控制提供了参考。展开更多
Polyether triol with molecular weight distribution index being 1\^3～1\^5 was prepared in yield around 50% by tetrahydrofuran polymerization using heteropolyacid\|H\-3PW 12 O 40 and ethylene oxide as initiator system ...Polyether triol with molecular weight distribution index being 1\^3～1\^5 was prepared in yield around 50% by tetrahydrofuran polymerization using heteropolyacid\|H\-3PW 12 O 40 and ethylene oxide as initiator system and 1,1,1\|trihydroxymethylenepropane(TMP) as molecular weight controller.The average hydroxyl functionality was estimated by end\|group analysis and VPO to be close or equal to 3. The 1H NMR spectra showed that about 1/3 hydroxyl of TMP did not react with the propagating chains in the THF polymerization.Each of the unreacted hydroxyl groups of TMP attached to the middle or to the end of a diol chain as a pendent primary hydroxyl group forming the obtained polyether triol. All the hydroxyls of polyether triol were verified to be active enough towards 4,4′ methylene bis(phenyl isocynate) in the preparation of polyurethanes.展开更多
基金This work was supported by the Scientific and Technical Bureau of Shandong Province.
文摘As molecular weight controls the biological activities of polysaccharides, screening the optimal molecular weight of polysaccharides is important in drug research and application. In this study, hydrogen peroxide was employed as oxidant, and temperature, reaction time, and concentration of polysaccharides and hydrogen peroxide were examined for their effects on the preparation of polysaccharides in different molecular weights from Ulva pertusa. Our experiment suggested that the optimal degradation concentrations for polysac-charides and hydrogen peroxide were 2.5% (w/v) and 8.0% (v/v), respectively. The range of degradation measured by relative viscosity was mainly controlled by temperature and time. Results revealed that 35℃ was the optimal temperature for obtaining low-degradation samples, and 50℃ was the most favorable temperature to accelerate the reaction to yield highly-degraded samples. Four samples in different molecular weights A, B, C and D were finally prepared. The controllability was evaluated by the relative standard deviation (RSD) of relative viscosity, and the peak molecular weights and the polydispersity indexes (Mw/Mn) of molecular weights were measured by high performance gel permeation chromatography (HPGPC).
文摘The photo-controlled/living radical polymerization of methacrylic acid (MAA) was performed at room temperature by irradiation with a high-pressure mercury lamp using azo initiators and 4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl as the mediator in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate (tBuS) as the accelerator. Whereas the bulk polymerization yielded polymers with a bimodal molecular weight distribution in both the absence and presence of tBuS, the solution polymerization in methanol produced unimodal polymers with the molecular weight distribution of 2.0 - 2.3 in the presence of tBuS. The molecular weight distribution of the resulting poly (MAA) decreased with an in- crease in tBuS. The dilution of the monomer concentration also reduced the molecular weight distribution. The use of the initiator with a low 10-h half-life temperature also effectively controlled the molecular weight. The livingness of the polymerization was confirmed by obtaining linear increases in the first-order conversion versus time, the molecular weight versus the conversion, and the molecular weight versus the reciprocal of the initiator concentration.
文摘Polyether triol with molecular weight distribution index being 1\^3～1\^5 was prepared in yield around 50% by tetrahydrofuran polymerization using heteropolyacid\|H\-3PW 12 O 40 and ethylene oxide as initiator system and 1,1,1\|trihydroxymethylenepropane(TMP) as molecular weight controller.The average hydroxyl functionality was estimated by end\|group analysis and VPO to be close or equal to 3. The 1H NMR spectra showed that about 1/3 hydroxyl of TMP did not react with the propagating chains in the THF polymerization.Each of the unreacted hydroxyl groups of TMP attached to the middle or to the end of a diol chain as a pendent primary hydroxyl group forming the obtained polyether triol. All the hydroxyls of polyether triol were verified to be active enough towards 4,4′ methylene bis(phenyl isocynate) in the preparation of polyurethanes.
