α—甲基苯乙烯离子聚合体分子量分布

聚α-甲基苯乙烯-丁二烯-α-甲基苯乙烯嵌段共聚物是一种性能优异的热塑性弹性体。常温下,α-甲基苯乙烯的聚合是在极性添加剂存在下进行的,添加剂的种类,用量及聚合温度不仅影响聚合动力学,尚且影响聚合物分子量及其分布,控制α-甲基苯乙烯聚合速率、     

聚合物连续分级

本文较系统地介绍了聚合物连续分级的理论基础、实验室装置及其实际应用。     

聚2,6-二甲基苯醚树脂分子量分布及其与冲击强度关系的研究

本工作建立了室温下用凝胶色谱法(GPC)测定聚2,6-二甲基苯醚(PPO)树脂分子量、分子量分布的方法。淋洗剂不采用文献申报道的毒性较大者,也不在较高柱温下进行,而采用甲苯(或氯仿)在室温下测定。对样品在甲苯中溶解温度、浓度和稳定性等都进行了系统研究,找到了最优化条件。GPC数据结合改性PPO(MPPO)产品性能测定结果,经仔细分析找到了影响MPPO产品质量的一个重要因素是PPO树脂中低分子量部分含量。它与产品冲击强度有明显的依赖关系。提出了一个从CPC谱图确定低分子量部分含量的方法。     

New PVC materials for medical applications—the release profile of PVC/polycaprolactone–polycarbonate aged in aqueous environments

Medical grade PVC plasticised with polycaprolactone–polycarbonate (PCL–PC) was subjected to aqueous environments at different temperatures. The release profile during ageing was determined by solid phase microextraction (SPME) and GC–MS. At the same time changes in the surface composition due to, for example, migration of PCL–PC from the blend were followed by FTIR. Almost no changes in the material or its surface composition were observed during 98 days at 37 °C in water or phosphate buffer. Only trace amount of 6-hydroxyhexanoic acid the final hydrolysis product of PCL–PC was detected in the GC–MS chromatograms and the weight loss was negligible. Even when the ageing temperature was raised to 70 °C only minor increase in the amount of 6-hydroxyhexanoic acid was observed and the weight loss after 98 days was under 1%. Changes in the FTIR spectra indicating migration of PCL–PC towards the surface of the PVC/PCL–PC tubing were observed first after 70 days at 70 °C. Large increase in the hydrolysis rate of PCL–PC and almost complete depletion of PCL–PC from the blend was observed when the ageing temperature was raised to 100 °C.     

Averaged molecular weight of complex mixtures as determined by rapid measurements of diffusion

Summary The concept of a diffusion-averaged molecular weight, M_d is presented, and M_d is defined for polydisperse samples. It is shown via oligostyrene mixtures that M_d can be determined in 20 minutes with common chromatographic equipment. If M_d is measured and M_n or M_w is known, the polydispersity can be obtained.     

Molecular weight effect on the photoinduced birefringence and surface relief gratings formation of a methacrylate azopolymer

Samples of a methacrylic side-chain azopolymer were synthesized by a radical copolymerization of methyl-methacrylate with the methacrylic derivative of the commercial dye Disperse Red-13 (DR13). Copolymers with different molecular weight were obtained by varying the reaction time and the concentration of initiator. Samples with molecular weight averages (M_w) from 3 to 8 × 10⁴ g/mol and 1.4-1.7 polydispersity were obtained. The glass transition temperature of the samples increased linearly from the lower to the highest molecular weight. Optical quality cast films were prepared for all samples and photoinduced birefringence was successfully carried out in all samples as well as surface relief gratings could be inscribed in the cast films.     

极性介质中醋酸乙烯酯的辐照引发分散聚合

用钴 60γ射线引发醋酸乙烯酯的分散聚合 ,通过选择各种极性溶剂体系 ,确立了醋酸乙烯酯在极性介质中稳定的分散聚合体系 .对异丙醇 水体系 ,聚合物分子量随剂量率的降低、稳定剂含量的增加、单体浓度的增大、反应温度的升高以及醇水比的降低而增加 .运用XPS、元素分析等表征聚合物粒子 ,及通过辐射接枝理论的分析 ,可以判断稳定剂所起的稳定作用主要是以物理吸附为主     

MOLECULAR WEIGHT DISTRIBUTION OF AB, A, TYPE CONDENSATION POLYMERS OBTAINED BY ADDING AB MONOMERS IN BATCHES

The molecular weight distribution (MWD) and arm length distribution of AB, Ar type condensation polymers obtained by adding AB monomers in batches have been derived by statistical and kinetic methods. Calculations show the MWD of condensation polymers obtained by this process is much narrower than that of one batch reaction and agrees with the Monte Carlo results very well.     

INFLUENCE OF MOLECULAR WEIGHT AND PERIODATE-MODIFICATION OF β-D-GLUCANS FROM PORIA COCOS SCLEROTIUM ON ANTITUMOR ACTIVITIES*

In this work, influence of molecular weight and periodate modification ofβ-D-glucans isolated from Poria cocos sclerotium on the antitumor activities against Sar-coma 180 and Ehrlich ascites carcinoma (EAC) tumor was studied. The results show thattwo glucans PC3 (linear β-(1→3)-D-glucan) and PC4 [β-(1→3)-D-glucan with a fewof branches and glucuronic acid] are devoid of antitumor activity. However, when theglucans were modified by periodate oxidation, borohydride reduction and mild hydrolysisor partially hydrolysis, the derivatives have obvious antitumor activities. The decreasein molecular weight of glucans after periodate modification hardly affects their antitumoractions, but on the other hand, the decrease of molecular weight without periodate modi-fication could lead to an enhancement of the antitumor activities. Moreover, the glucansand these derivatives have much higher enhancement ratios of body weight of mice thanthat of 5-Fluorouracil (5-Fu), suggesting that they are less toxic than 5-Fu.     

Effect of method of solution on observed molecular weight distribution of barley starch and starch derivatives in size exclusion chromatography

Summary Samples of native barley starch and six starch derivatives were suspended (0.1% sample concentration) in four different solvents: the eluent (pH 11 buffer), dimethylsulfoxide, 0.1 M NaOH or 0.5 M NaOH and kept in a boilling water bath for 5 to 60 minutes or shaken for 60 minutes. The average molecular weight values , and the polydispersity value were determined with a TSK PW-type column using narrow standard calibration. Only a small part of the samples dissolved in the eluent. The dissolution of sample in dimethylsulfoxide was dependent on sample type. Of the NaOH solutions, 0.5 M NaOH was the only one that dissolved all the samples. Therefore, 0.5 M NaOH appears to be the solvent of choice for starch molecules.