On-line measurement of the RMS radius of gyration and molecular weight of polyimide precursor fractions eluting from a size-exclusion chromatograph

The recent introduction of multiangle light-scattering detectors for size-exclusion chromatography has made possible the measurement of the root mean square radius of gyration (R_g) and molecular weight (M) of polymer fractions eluting from a size-exclusion chromatography column. The characterization of the dimensions of a polymer may be accomplished with only a few milligrams. The dimensions of a polyimide precursor prepared by the condensation of the meta-diethyl ester of pyromellitic dianhydride with para-phenylene diamine have been measured with this technique. The dependence of R_g on M across the distribution is compared with that predicted for a freely rotating chain, and with other similar polymers measured with hydrodynamic techniques.     

Equilibration of mixtures of polyamic acids studied using size-exclusion chromatography and light scattering

The transamidation reaction in a polyamic acid solution has been investigated using size-exclusion chromatography and low-angle light scattering. Mixtures of a high-molecular weight (DP = 150) and a low-molecular weight (DP = 10) polymer and of the high-molecular weight polymer with monomer were studied. Mixtures were made at high and low concentrations. The polyamic acid studied is the product of the polycondensation of 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) with oxydianiline (ODA). In all cases the molecular weight distribution equilibrated with time to a most-probable distribution with a DP consistent with the stoichiometry of the mixture. Equilibration required about 2 weeks for mixtures of 10% by weight at ambient temperatures. The effect of addition of a small amount (5%) of low-molecular weight material to sample of high-molecular weight is dramatic; for DP = 150 the molecular weight is decreased by more than one-half. In an entangled solution or melt, this would reduce the viscosity by an order of magnitude.     

Molecular weight characterization of soluble high performance polyimides. 2. Validity of universal SEC calibration and absolute molecular weight calculation

Six different soluble high-performance aromatic polyimides, each prepared by solution imidization to three controlled average molecular weights, were analyzed by size exclusion chromatography (SEC) using on-line parallel coupled refractometric and viscometric detectors. N-methylpyrrolidone (NMP) with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phase for four of the polyimides; NMP with 0.06 M LiBr and NMP stirred over P₂O₅ were used as mobile phases for four of the polyimides; NMP with 0.06 M LiBr tetrahydrofuran (THF) and chloroform served as mobile phases for the other two polyimides. For all the samples the stationary phase in the SEC columns was cross-linked polystyrene beads. Molecular weight averages of the polyimides were calculated using universal SEC calibration with polystyrene standards in each solvent. The agreement of the calculated molecular weight averages in the different solvents confirms that the universal SEC calibrations are valid for these semiflexible polymers. There was good agreement with weightaverage molecular weights obtained by low-angle laser light scattering (LALLS) performed in pure NMP. Intrinsic viscosity and molecular weight data for a series of nine samples of one polyimide covering a M_w = 20,000–70,000 g mol^–1 interval were treated to obtain Mark-Houwink-Sakurada constants. Unperturbed chain dimensions of this polyimide were obtained by application of the Stockmayer-Fixman extrapolation procedure to these data. ©1995 John Wiley & Sons, Inc.     

Chromatographic methods for the analysis of crude tall-oil

Chromatographic methods currently used for isolation, separation, and identification of the components of crude tall-oil have been reviewed, and their resolution and analytical methodology compared. Sample introduction by cold on-column, rather than vaporizing, injection provides good reproducibility and operational convenience for capillary GC analysis. Size exclusion chromatography for isolation followed by capillary GC-MS for identification, gave the best performance for analysis of acidic and dimeric compounds.     

化学中考试题与课程标准一致性研究*——以聊城市化学中考试题为例

通过利用SEC“一致性”分析工具对聊城市2016-2018年化学中考试题与《义务教育化学课程标准(2011年版)》的一致性进行分析,得出2016-2018年的聊城市化学中考试题与课程标准不具有统计学意义上的一致性。在内容主题及认知层次分布上,3个年份的试题与课程标准均存在着明显的差异。     

Radiation effects on a linear model compound for polyethers

Radiation effects on a model polyether - poly(tetramethylene) glycol (PTMG) induced by high energy radiation were investigated. To understand the degradation mechanism, electron paramagnetic resonance (EPR), Fourier transform infra-red spectroscopy (FTIR), electrospray and gas mass spectrometry (ESI-MS and gas-MS), were carried out to identify radicals and chemical modifications. Size exclusion chromatography (SEC) was used to follow the evolution of the distribution of molecular weight. On the basis of the results, a mechanism of degradation for PTMG is proposed.     

Some theoretical and practical aspects in the separation of humic substances by combined liquid chromatography methods

Permanent need to understand nature, structure and properties of humic substances influences also separation methods that are in a wide scope used for fractionation, characterization and analysis of humic substances (HS). At the first glance techniques based on size-exclusion phenomena are the most useful and utilized for relating elution data to the molecular mass distribution of HS, however, with some limitations and exceptions, respectively, in the structural investigation of HS. The second most abundant separation mechanism is reversed-phase based on weak hydrophobic interactions beneficially combined with the step gradients inducing distinct features in rather featureless analytical signal of HS. Relatively great effort is invested to the developments of immobilized-metal affinity chromatography mimicking chelate-forming properties of HS as ligands in the environment. Surprisingly, relatively less attention is given to the ion-ion interactions based ion-exchange chromatography of HS. Chromatographic separation methods play also an important role in the examination of interactions of HS with pesticides. They allow us to determine binding constants and the other data necessary to predict the mobility of chemical pollutants in the environment. HS is frequently adversely acting in analytical procedures as interfering substance, so more detailed information is desired on manifestation of its numerous properties in analytical procedures. The article topic is covered by the review emphasizing advances in the field done in the period of last 10 years from 2000 till 2010.     

分离技术在新型冠状病毒研究和防疫检测中的应用

新型冠状病毒肺炎(COVID-19)疫情的爆发给世界公共卫生安全带来前所未有的挑战.随着新型冠状病毒(SARS-CoV-2)相关研究的不断深入,众多分析检测技术相继被应用,推动了病毒检测、疫苗和创新疗法的研发,从而使疫情早日得到控制.分离技术作为生命科学、医学、药学领域的关键技术,操作简单,分离效率高,选择性强,在新型...     

体积排阻色谱法定量检测9种型别人乳头瘤病毒原液中病毒样颗粒

据统计,5％以上的人类癌症由人乳头瘤病毒(HPV)导致.HPV疫苗的使用,尤其是多价HPV疫苗的使用,可有效预防HPV感染和肿瘤的发生.例如,9价HPV疫苗可有效预防90％以上HPV相关癌前病变.人乳头瘤病毒样颗粒(VLP)是HPV疫苗的唯一抗原.VLP由360份衣壳蛋白L1组成.VLP的含量测定对HPV原液和HPV疫...     

Advances in the Synthesis and Characterization of Polypeptide-Based Hybrid Block Copolymers

Linear polystyrene-block-poly(Z-L-lysine) copolymers with a very narrow molecular weight distribution (polydispersity index < 1.03) could be obtained via the ring-opening polymerization of Z-L-lysine-N-carboxyanhydride using ω-(primary amino hydrochloride)-polystyrenes as macroinitiators in N,N-dimethylformamide as the solvent at 40-80 °C. The block copolymer samples were analyzed by means of NMR, size exclusion chromatography, and analytical ultracentrifugation.