Separation of branched polystyrene by comprehensive two-dimensional liquid chromatography

Branched polystyrenes (PS) featuring a bivariate distribution in the molecular weight and in the number of branches were characterized by comprehensive two-dimensional liquid chromatography (2D-LC). The branched PS were prepared by anionic polymerization using n-butyl Li as an initiator and a subsequent linking reaction with p-(chlorodimethylsilyl)styrene (CDMSS). The n-butyl Li initiator yields polystyryl anions with broad molecular weight distribution (MWD) and the linking reaction with CDMSS yields branched PS with different number of branches. For the first dimension (1st-D) separation, reversed-phase temperature gradient interaction chromatography (RP-TGIC) was employed to separate the branched polymer according to mainly the molecular weight. In the second dimension (2nd-D) separation, the effluents from the RP-TGIC separation are subjected to liquid chromatography at chromatographic critical conditions (LCCC), in which the separation was carried out at the critical condition of linear homo-PS to separate the branched PS in terms of the number of branches. The 2D-LC resolution of RP-TGICxLCCC combination worked better than the common LCCCxsize-exclusion chromatography (SEC) configuration due to the higher resolution of RP-TGIC in molecular weight than SEC. Furthermore, by virtue of using the same eluent in RP-TGIC and LCCC (only the column temperature is different), RP-TGICxLCCC separation is free from possible 'break through' and large system peak problems. This type of 2D-LC separation could be utilized efficiently for the analysis of branched polymers with branching units distinguishable by LC separation.     

Entanglement and phase separation in hyperbranched polymer/linear polymer/solvent ternary blends

Hyperbranched polyethylene (HBPE)/linear polystyrene (PS)/chloroform (CF) solution was selected as a model system to investigate the effect of branching structure on entanglement and phase separation behavior in semi-dilute ternary polymer solutions. All the HBPE materials in this work were found to have similar chain architectures and the critical molecular weight was estimated to be 81.2 kDa. The results obtained by elastic light scattering and intrinsic fluorescence methods suggested that all ternary solutions exhibited UCST transition behavior upon cooling. Also, it was found that the increase in the molecular weight of PS led to increase in the phase separation rate, consistent with de Gennes prediction. However, the increase of molecular weight of HBPE did not monotonously reduce the compatibility of polymer components and the phase separation rate in ternary blends is as follows: medium molecular weight HBPE (HBPE-M) > high molecular weight HBPE (HBPE-H) > low molecular weight HBPE (HBPE-L). This abnormal behavior can be explained by the fact that, (i) for HBPE-L, no entanglements between HBPE chains occurred and the branching effect can be ignored, and (ii) for HBPE-M and HBPE-H, entanglement of HBPE chains can be formed, and the dilution of branches on entanglement of backbones should be taken into consideration, that is, the shorter the branches of HBPE, the higher the possibility of interpenetration of HBPE backbones between neighboring molecules and, consequently, the faster aggregation of HBPE during phase separation. Furthermore, a simple model based on decomposition reaction was proposed to quantitatively describe the phase separation kinetics and the apparent activation energies of phase separation were calculated to be −150.3 and −52.3 kJ/mol for HBPE-M/PS/CF and HBPE-H/PS/CF systems, respectively.     

Synthesis of Star-Shaped Polymers via Coordination of Bipyridyl-Terminated Polyoxyethylene with Metal Ions

Abstract

This paper describes the synthesis of various star-shaped polymers by means of complexation of bipyridyl-terminated polyoxyethylene with Ru(II) ion. Three kinds of bipyridyl-terminated polyoxyethylenes of different molecular weights were prepared from the corresponding polyoxyethylene monomethyl ethers with narrow molecular weight distributions. Bipyridyl was found to be introduced quantitatively at the end of the polymers based on the results of UV spectra. The formation of a star-shaped polymer was carried out by the reaction of RuCl₃ with three equivalents of bipyridyl-terminated polyoxyethylene. The UV spectrum of the star-shaped polymer obtained supported the formation of a typical Ru(II) tris(bipyridyl) complex. From the results of GPC, the star-shaped polymer obtained had a higher molecular weight than the pre-polymer and showed a narrow molecular weight distribution. In the case of a Ni(II) or a Co(II) complex, however, the star-shaped polymer was found to be dissociated into three linear prepolymers under the conditions of GPC measurement.     

原子转移自由基聚合制备PDMAEMA亲水作用色谱固定相及其性能评价

以甲基丙烯酸二甲氨乙酯为单体,2-溴异丁酰溴为引发剂,CuBr/五甲基二乙烯基三胺(PMDETA)为催化剂,通过原子转移自由基聚合(ATRP)反应,将甲基丙烯酸二甲氨乙酯(DMAEMA)接枝到5μm大孔硅胶表面上,得到了接枝聚合物(PDMAEMA)亲水作用色谱固定相.通过改变反应体系中单体的量,制备了三种不同接枝量的亲水作用色谱固定相,利用元素分析对所制备的固定相进行了表征.详细考察了该固定相的分离性能以及流动相中盐浓度、水含量对溶质保留行为的影响,并将该固定相用于宁心宝胶囊中核苷类化合物的分离和测定.在亲水模式下,该固定相可以基线分离7种核苷类化合物,保留时间随着接枝量的增加而增大,与氨基亲水作用色谱柱相比,该合成柱的分离效率高,溶质在该填料上的保留符合分配作用保留机理.实验结果表明,该填料具有良好的分离性能.     

Quantitative synthesis of star-shaped poly(vinyl ether)s with a narrow molecular weight distribution by living cationic polymerization

Star-shaped poly(vinyl ether)s with narrow molecular weight distributions were obtained from polymer-linking reactions of living polymers with a divinyl compound based on living cationic polymerization. For example, living polymers (DP(n) = 50-300) of isobutyl vinyl ether (IBVE), prepared with a cationogen/EtAlCl(2) at 0 degrees C in hexane in the presence of ethyl acetate, were allowed to react with a small amount of 1,4-cyclohexanedimethanol divinyl ether (DVE-1) to give a star-shaped poly(IBVE) in quantitative yield (100%). In addition, a notable feature of this star-shaped polymer was extremely narrow molecular weight distribution (M(w)/M(n) = 1.1-1.2). The structure of divinyl compounds and reaction conditions for the linking reaction are key factors for achieving quantitative yield of star-shaped polymers. To our best knowledge, this is the first example of selective preparation of star-shaped polymers with narrow molecular weight distribution via one-pot polymer-linking reactions, which has never been achieved in any other mechanisms. The M(w) and the number of arms per molecule ranged from 6 x 10(4) to 30 x 10(4) and 9 to 44, respectively. Thermosensitive star polymers were also synthesized in quantitative yield, and the products were found to undergo sensitive phase separation and physical gelation.     

Phase structure and viscoelastic properties

The phase structure and dynamic mechanical properties of three polypropylene/polystyrene (PP/PS) systems of similar composition but various dispersion of the minor PS component have been examined. Two different PP/PS systems were prepared by polymerization of styrene (ST) molecularly dispersed in PP matrices (with the same initial structure) under the conditions leading to a linear or crosslinked PS component. The third PP/PS system has been prepared blending the homopolymers in the molten state. Studies of materials containingin situ polymerized PS revealed nanoscale phase separation of PS (atomic force microscopy) and pointed to the presence of physical entanglements between PS and non-crystalline phase of PP (DSC, dynamic mechanical analysis). The PS component in material prepared by melt mixing appeared to be completely phase-separated into micron-sized domains. Dynamic mechanical analysis revealed also the dependence of viscoelastic behavior of the PP/PS systems on dispersion of the PS inclusions and on the nature of the interface.     

Improved hydrolytic stability of poly(dl-lactide) with epoxidized soybean oil

The multi-arm star polymer (ESOPLA) was obtained by ring-opening polymerization of dl-lactide using multifunctional epoxidized soybean oil (ESO) as an initiator in the presence of a stannous actuate (SnOct₂) catalyst. Gel permeation chromatography with multi-angle laser light scattering (GPC-MALLS), FTIR, ¹H NMR, thermal analysis and in vitro degradation were used to qualitatively characterize the synthesized polymers. The results revealed that ESO plays an important role in increasing the molecular weight, polymerization rate and monomer conversion rate. Degradation analysis demonstrated that the decrease in molecular weight and the weight loss ratio of the star-shaped ESOPLA were lower than that of linear poly(dl-lactide) (PDLLA). The surface topography of pre- and post-degradation materials was characterized by scanning electron microscopy (SEM). These SEM images showed that the linear PDLLA films underwent water erosion more readily than the star-shaped polymer films.     

Novel Dual-Grafted Copolymer Bearing Glassy Polystyrene and Crystalline Poly(Ethylene Oxide) as Side Chains

A novel grafted copolymer with two different types of side chains was synthesized via a combination of grafting-onto and grafting-from strategy. Graft copolymer with one side chains polybutadiene-graft-polystyrene (PB-g-PS) was first synthesized though the grafting-onto method. Following the subsequent grafting-from method, the second kind of side chain was introduced to the copolymer with anionic ring open polymerization of ethylene oxide, obtaining dual-grafted copolymer polybutadiene-graft-(polystyrene; poly(ethylene oxide)) (PB-g-(PS;PEO)). By this combined strategy, linear and star-shaped dual-grafted copolymer were synthesized. The resulting dual-grafted copolymers had controlled molecular weights and narrow molecular weight distributions (Mw/Mn < 1.20). The thermal behavior of this dual-grafted copolymer bearing glassy and crystalline side chains was determined by differential scanning calorimetry (DSC), revealing that poly(ethylene oxide) grafts underwent confined crystallization, and the star-shaped copolymer had more confinement effects than did the linear ones.     

万古霉素键合固定相的分离性能

万古霉素作为一种大环抗生素,具有复杂的分子结构。在充分考虑万古霉素分子结构特征的情况下,采用戊二醛间隔臂法制备了万古霉素键合固定相,在反相、亲水、离子交换等分离模式下研究了其色谱分离性能。结果表明,当流动相中有机调节剂含量较低时,该色谱柱表现出典型的反相色谱分离模式特征;随着有机调节剂含量的增加,逐渐转变成亲水模式,分离特性发生明显改变。由于万古霉素分子结构中含有可以解离的氨基,因此该固定相也能够用于阴离子交换模式下的分析方法的发展。分别在反相、亲水和阴离子交换模式下,将其应用于扑尔敏等多种非对映体药物和新型甜味剂甜菊糖的高效液相色谱分离;仅通过改变分离条件,即可在3种不同分离模式下完成分离。这些结果可以为新型色谱固定相的设计,以及发展采用特殊结构改性基团的色谱固定相在相应分离模式下的分析方法提供指导。     

Polymer solutions as a pseudostationary phase for capillary electrochromatographic separation of DNA diastereomers

The solutions of linear polymers traditionally used for DNA separation have been employed for the capillary electrophoresis (CE) of diastereomers of chemically modified DNA. The selectivity of diastereomeric separation of the phosphorothioate (PS) and 2'-O-methylated (2-OMe) PS oligonucleotides depends on the nature of the polymer additive in the CE background electrolyte. The selectivity of separation for different polymers increases in the line: linear polyacrylamide < polyethylene glycol < polyvinyl pyrrolidone. The separation of oligomer diastereomers was shown to be primarily based on the hydrophobic interaction with the polymer network that acts as a pseudostationary phase. While lowering the temperature resulted in improved separation, the addition of organic modifiers such as formamide, methanol or acetonitrile counteracts the solute adsorption on the polymer network, and decreases the selectivity of DNA diastereoseparation. The effect of molecular mass and concentration of the polymer on the separation selectivity was investigated.     

聚苯乙烯对酞菁铜颜料微胶囊化的研究

自１９５４年美国首先将微胶囊化应用于无碳复写纸后［１,２］,这项技术在药物、农药、食品及染料等方面已得到广泛应用［３］．微胶囊（ＭＣ）直径通常是１～５０００μｍ,构造分为囊壁和囊芯两部分［４］．囊壁材料大多使用高分子材料,少数用无机物［５］．有机颜料...     

γ-干扰素在反相高效液相色谱柱上色谱行为与分离的研究

用高效液相色谱法对基因工程下游包涵体所含目标蛋白进行分离纯化,较系统地研究了γ－干扰素在反相柱上的色谱行为及其影响因素。结果表明,复性后γ－干扰素伴有错配聚合体产生,其保留行为及洗脱谱图随构象不同而改变。分离系统的疏水性和粘度是影响γ－干扰素在固定相与流动相间传质扩散的重要因素。     

Rapid analysis using capillary supercritical fluid chromatography

Capillary supercritical fluid chromatography (SFC) is proving to be a viable and useful separation method for thermally labile and nonvolatile materials. As with other capillary chromatographic techniques, very fast separations can be accomplished by sacrificing total efficiency and optimizing the conditions for rapid analysis. This is achieved using short, small-bore capillary columns, increased mobile phase linear velocities and very fast pressure programming rates. These principles are demonstrated for the rapid separation of selected component systems.     

基于色谱方法的煤沥青指纹图谱构建

煤沥青成分极其复杂,其中含有分子量较大的多环芳烃及其氧化产物等组分。不同来源的原料煤及生产工艺得到的煤沥青在芳构化程度、组成、性质、分子结构等方面皆差别很大。该文分别采用气相色谱-质谱(GC-MS)、裂解/气相色谱-质谱(Py/GC-MS)和高效液相色谱(HPLC)手段,为煤沥青指纹图谱库的构建发展了普适、稳定、简单的分析方法。在GC-MS方法中采用常用的HP-5MS柱,在线性温度梯度条件下分析,得到33个组分的色谱图,方法对不同样品的稳定性良好。采用裂解/气相色谱-质谱方法研究探讨了较高温度下组分结构和组成的变化,对于沥青产品的加工以及老化研究具有借鉴意义。在HPLC方法建立过程中,采用最常用的C_(18)柱反相色谱分离模式,以甲醇/水为流动相,在线性梯度条件下建立方法,针对不同样品可以得到41个组分的稳定色谱峰。基于该文的方法,可为进一步建立煤沥青的指纹谱图库,以及进一步完善煤沥青的评价方法,开发煤沥青的新用途提供理论基础数据。     

Thermoplastic blend demixing by a high‐pressure,high‐temperature process

The analysis of a thermoplastic polymer blend requires a precise separation of the blend components, which is usually performed by selective solvent extraction. However, when the components are high‐molecular‐weight polymers, a complete separation is very difficult. The use of fluids in near critical and supercritical conditions becomes a promising alternative to reach a much more precise separation. In this work, a method to separate reactive and physical blends from high‐molecular‐weight commercial polymers is proposed. Polyethylene (PE)/polystyrene (PS) blends were separated into their components with n‐propane, n‐pentane, and n‐heptane at near critical and supercritical conditions. The selectivity of each solvent was experimentally studied over a wide range of temperatures for assessing the processing windows for the separation of pure components. The entire PE phase was solubilized by n‐pentane and n‐heptane at similar temperatures, whereas propane at supercritical conditions could not dissolve the fraction of high‐molecular‐weight PE. The influence of the blend morphology and composition on the efficiency of the polymer separation was studied. In reactive blends, the in situ copolymer formed was solubilized with the PE phase by chemical affinity. The method proposed for blend separation is easy, rapid, and selective and seems to be a promising tool for blend separation, particularly for reactive blends, for which the isolation of the copolymer is essential for characterization © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2361–2369, 2005     

低分子量硫酸化多糖的体积排阻色谱法分离及其组成定量分析

建立了用于分离并定量测定低分子量硫酸化多糖中不同糖链数的各个组分分布比例的体积排阻色谱方法。系统考察了流动相的组成、离子强度和pH值、流速、柱温等因素对分离的影响。最佳分离条件: 两支TSK-GEL G2000 SWxl色谱柱(300 mm×7.8 mm)串联,流动相100 mmol/L Na2HPO4-NaH2PO4 (pH 7.0),流速0.5 mL/min,柱温35 ℃,进样量5 μL,样品质量浓度10 g/L。在最佳的分离条件下,可以将低分子量硫酸化多糖样品中不同糖链数的各个组分分离并对各个组分的分布进行了定量分析。用该方法对美国药典标准品(USP)、商品和实验室制备的低分子量硫酸化多糖糖链数分布进行了定量化比较,证明该方法可用于低分子量硫酸化多糖类药物的组成成分的质量控制。     

Facile synthesis of hollow polymeric microparticles possessing various morphologies via seeded polymerization

In this paper, hollow poly(styrene-co-divinylbenzene-co-methacrylic acid) microparticles possessing various morphologies were synthesized by a combination of seeded polymerization and SPG membrane emulsification. Three families of polystyrene (PS) microspheres with various molecular weights but similar diameters were fabricated by SPG membrane emulsification. These PS microspheres were used as seeds to investigate the effect of their molecular weight on the phase separation between the PS seeds and microgel-like networks formed during seeded polymerization and on the morphologies of the resultant particles. Our study revealed that three resultant microparticles possessed diameters of ca. 10?μm and hollow cavities. The shell thickness of the particles became thinner as M _w increased from 3.5?×?10⁴ to 28.0?×?10⁴. The morphological evolution of the microparticles during seeded polymerization was monitored, and these results verified the influence of the molecular weight of the PS seeds on the phase separation behavior and hence the morphologies of the resultant particles.     

Influence of column characteristics on retention and selectivity in RP-HPLC

Summary Eight commercially available reversed-phase (RP) columns of widely different characteristics were evaluated and compared using the linear solvation energy relationships (LSER). Retention factors of 32 solutes of different types were determined under isocratic conditions using an acetonitrile-water (30∶70) mobile phase. Stationary phase properties were compared by the fitting coefficients of the LSER-based regression equations which are characteristic of the individual stationary phases and represent the extent of various molecular interactions contributing to the retention process. The good agreement between the calculated and measured logk values for different type of compounds support the adequacy and applicability of the LSER model to describe chromatographic retention. Characterization of column performance for the separation of various type of compounds was established by the determination of the different selectivity factors representing hydrophobic selectivity, polar selectivity and specific selectivity.     

Structure and performance of silica-based monolithic HPLC columns

Silica-based monolithic columns were prepared for HPLC with systematic variations of the tetramethoxysilane (TMOS) and polyethylene oxide (PEO) content as reactants in a sol-gel process accompanied by phase separation. The resulting monoliths showed differences in the macropore and silica skeleton diameter as well as in the corresponding domain sizes (the sum of macropore and skeleton diameter). All monoliths were synthesized with a diameter of 4.6 mm and cladded with a suitable polyaryletheretherketone (PEEK) polymer in a standardized and optimized manner for the subsequent chromatographic evaluation of the resulting monolithic HPLC columns. The columns were tested under normal phase conditions using n-heptane/dioxane (95:5 v/v) as a mobile phase and 2-nitroanisole as a test compound for the determination of separation efficiency and permeability. Two different sets of columns were prepared: the first one in which the amount of PEO was stepwise decreased to yield monoliths with identical macropore volumes and variations in the domain sizes. The second group of materials was synthesized adjusting both TMOS and PEO quantities to yield monolithic columns with identical macropore diameters of about 1.80 microm but different skeleton diameters and macropore volumes. The chromatographic results suggest that an increase in the column performance cannot be achieved by just arbitrarily decreasing the domain size of a given column. From a certain point of "downsizing" the monolithic structure a loss of structural homogeneity can be observed, which is apparently responsible for a lower chromatographic performance.