Detecting local polydispersity with multidetector SEC from reconstructed DRI chromatograms

Local polydispersity refers to variety in the types of molecules present at the same retention volume in an analysis by size exclusion chromatography (SEC). Such variety is undesired because it can be a major source of inaccuracy in SEC interpretation. A rapid, practical, method for detecting the presence of local polydispersity is presented. In this method, data from a differential viscometer (DV) and light scattering (LS) detector are used together with a universal calibration curve to generate a differential refractive index (DRI) chromatogram for the sample, while assuming that it does not exhibit local polydispersity. This “reconstructed” DRI chromatogram is compared to the actual DRI chromatogram. It is shown that any significant difference between the two indicates the presence of local polydispersity. Plots of residuals (the difference between the heights of the two DRI chromatograms vs. retention volume) allow the significance of the local polydispersity to be assessed and the retention volume range encompassing the local polydispersity to be defined. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 831–835, 1998     

A new method for correcting axial dispersion in GPC

In this paper, a new method for correcting GPC results in order to take into account the axial dispersion of a given set of columns is proposed. The idea is to evaluate the different average molecular weights and the polydispersity for a given elution volume. In order to do so, one needs only to know the efficiency of the set of columns and the different derivatives at a given point of the chromatogram. Some possible applications of this method are reviewed mainly for the characterization of polydispersity and for the determination of the viscosity law if one uses the universal calibration.     

Polymer reactors and molecular weight distribution. VIII. A method of interpreting skewed GPC chromatograms

A new-method of interpreting GPC chromatograms which accounts for skewing and symmetrical axial dispersion has been developed. General relationships for a symmetrical axial dispersion correction and for a skewing correction are derived. The method has been verified experimentally for unimodal chromatograms and linear calibration curves over a wide range of GPC operating conditions, polymer molecular weights and polydispersities. Measurements of h and skewing factors were obtained by a once-through technique. The need for performing reverse flow experiments has been eliminated. Artificial oscillations in the corrected chromatogram due to step size (Method of Pierce-Armonas), and to number of terms in a polynomial expansion (Method of Tung and Method of Smith) are eliminated. The method has yet to be evaluated for nonlinear calibration curves and multi-modal distributions. However, suggestions for its application in these circumstances are presented.     

Quantitative size exclusion chromatography of polypropylene I: Method development

Polypropylene was analyzed by size exclusion chromatography (SEC) at 145°C using a single-differential refractometer detector. The objective was to provide data for characterization of polypropylene degradation during a reactive extrusion process. Two antioxidants [tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)) methane (I) and octadecyl 3,5-di-tert-butyl-4-hydroxyhydro cinnamate (II)] were tested for their ability to prevent thermal degradation of the polypropylene during sample preparation. The use of 0.20 wt% of (I) was effective during the 36–48 h required to completely dissolve the samples in trichlorobenzene for SEC analysis. “Reshaping” of the chromatograms by resolution correction demonstrated that, while the molecular weight averages were changed by 8% because of axial dispersion, most of the individual heights of the distributions were changed by less then 2%. Tail heights of the distributions were more affected but were also shown to be highly imprecise. Selecting individual heights of the distributions rather than molecular weight averages therefore minimized axial dispersion error and also circumvented errors in molecular weight averages originating from dilution of distribution tails below detector sensitivity limits. Various forms of distributions were examined and the equations linking the chain length distribution predicted by polymerization kinetic models to the SEC chromatogram are presented. The analytical method developed provided precise data for kinetic modeling. However, absolute accuracy requires further assessment.     

Number-average molecular weight and functionality of poly(tetramethylene glycol) by multidetector SEC

Multidetector size exclusion chromatography (SEC) is used to simultaneously determine molecular weight and number of reactive end groups per chain (functionality) of poly(tetramethylene glycol)s. Hydroxyl groups are first quantitatively derivatized with phenyl isocyanate, providing an end-group-selective UV-absorbing tag. The number of end groups per chain is then determined from the SEC chromatogram using a UV detector. Molecular weight at each retention volume and the number-average molecular weight of the whole polymer are calculated by four methods involving (1) a concentration detector and a narrow standard log M calibration curve, (2) the UV detector and a narrow standard log M calibration, (3) a viscometry detector and a universal calibration curve, and (4) combined differential viscometry and concentration detectors using a universal calibration curve. The multidetector experiment provides a unique opportunity to assess the accuracy and limitations of each approach on low-molecular-weight polymers. In particular, the effect of end groups on the concentration detector response and the application of universal calibration principles at small molecular sizes are important factors. It is shown that the concentration response can be corrected by a simple relationship between detector response and reciprocal molecular weight. Also, the quality of calibration curves is critical to the calculation of accurate molecular weight. In general, log M calibration curves provide superior results to universal calibration methods. © 1995 John Wiley & Sons, Inc.     

高效液相色谱凝胶色谱法测试高分子化合物的研究

采用了高效液相色谱仪与高效凝胶色谱柱,建立了高效液相凝胶色谱分析平台。利用其不同分子量分子在凝胶色谱中表现有不同的保留时间,使用了5种高分子单分散性标准品,根据其保留时间与分子尺寸关系,建立3次拟合校正曲线,快速、高效地获得高分子化合物数均分子量、重均分子量等多种平均分子量,指导了高分子合成方向,为高分子特性研究提供了重要手段。使用了Shodex GPC K-804L8.0 mm×300 mm(A008096)刚性凝胶柱,流动相:氯仿;示差折光检测器,异丙醇稳定性测试,RSD=0.02%,3次拟合曲线,相关系数R=0.99998%,方法稳定可靠。     

Low-angle laser light scattering–aqueous size exclusion chromatography of polysaccharides: Molecular weight distribution and polymer branching determination

A low-angle laser light scattering detector (LALLS) used with size exclusion chromatography (SEC/LALLS) has been applied for the determination of molecular weight, molecular weight distribution (MWD), and degree of branching of polysaccharides in 0.5N NaOH aqueous solution. Data from both detectors [differential refractive index (DRI) and LALLS] are used to calculate the absolute molecular weight at each point in a sample chromatogram. The correct average molecular weight and MWD can be obtained without calibration methods used in conventional SEC. As a consequence of this technique, Mark—Houwink coefficients can be predicted from a single broad-distribution, homopolymer without recourse to time-consuming fractionation methods. Moreover, the hydrodynamic volume separation mechanism of SEC can be exploited with the SEC/LALLS method to gain information about polymer branching. In the studies described in this paper, SEC/LALLS has been employed to obtain data about the branching parameters g_v and g_M for samples of amylose, amylopectin, starch, and glycogen. For three homopolymers (amylose, amylopectin, and glycogen), branching frequency (as measured by chemical means), and the branching parameters (g_v and g_M) are inversely related. This trend is consistent with theoretical predictions. For starch, a nonhomogeneous branching distribution is observed as a function of molecular weight.     

High molecular weight tail and long‐chain branching in low‐density polyethylenes

The composition of the high molecular weight tail in branched low‐density polyethylenes made by both tubular and autoclave reactors was studied in detail using size‐exclusion chromatography (SEC) coupled with a viscosity detector (VD) and a two‐angle light‐scattering detector (LSD). The detection of a second peak at very small elution volumes in the light‐scattering chromatogram but not in the refractive index chromatogram and viscosity chromatogram is due to high molecular weight species. It is also indicative of a change in the long‐chain branching distribution. It was found that the intrinsic viscosity contraction factor g′ scales with the radius of the gyration contraction factor, g, with the exponent, ε, having a value in the range 0.4–1.4. Furthermore, ε shows significant molar mass dependence. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2815–2822, 2001     

Truths and myths about the determination of molar mass distribution of synthetic and natural polymers by size exclusion chromatography

This article discusses various aspects of the determination of molar mass distribution by means of size exclusion chromatography (SEC) in various application modes. The effects of erroneous specific refractive index increment (dn/dc), branching, column performance, and enthalpic interactions on the results obtained by different SEC techniques are discussed. Combination of SEC and a light scattering detector represents the most direct way to the molar mass distribution of all natural and synthetic polymers as it completely eliminates the need for column calibration and to a certain extent eliminates the dependence of the obtained results on some operational variables such as flow rate, temperature, or injected mass. A multiangle light scattering (MALS) photometer has become the most frequently used light scattering detector capable of determination of molecular size as another important polymer characteristic. This article contrasts SEC‐MALS method with other application modes of SEC from the viewpoint of some frequent confusions and misunderstandings. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40111.     

Polysaccharide Characterization by Aqueous Size Exclusion Chromatography and Low-Angle Laser Light Scattering

Abstract

Aqueous size exclusion chromatography coupled with on-line low-angle laser light scattering (SEC/LALLS) is a valuable analytical tool for characterization of polysaccharides and other important biopolymers. This work reviews the fundamental size separation mechanism of polymers chromatographed via SEC, the development of SEC/LALLS methods for characterization of eluted polymers, and applications of this technique to determine polysaccharide physical and chemical properties. Important nonsize exclusion effects encountered in aqueous SEC of polysaccharides are discussed and attributed to intramolecular and polymer-support interactions, as well as flow-related anomalies. The necessity of absolute molecular weight detection as a direct means of calibration is presented. Low-angle laser light scattering coupled to SEC provides a simple method of direct calibration and allows determination of polymer molecular weight and molecular weight distribution. Recent applications of SEC/LALLS to determine polysaccharide branching characteristics are detailed. The combined knowledge of molecular weight distributions and branching distributions provides insight into the molecular kinetic events of polysaccharide processing operations.     

Construction and testing of a specific viscosity detector for size exclusion chromatography

This article describes our experiences incorporating a viscosity detector directly within a conventional differential refractive index (DRI) detector. This results in a system in which the collection of the necessary data for universal calibration in size exclusion chromatography (SEC) can be readily attained. The system described is constructed from available materials, and yields output which can be used directly in the calculation of the intrinsic viscosity of the eluant from a chromatographic column. Values for various polymer molecular weight distribution parameters, as well as reasonable estimates of the Mark—Houwink constants, can be obtained. Additionally, a measurement related to long-chain branching in the polymer is available using this method.     

The determination of particle size distribution by hydrodynamic chromatography. An analysis of dispersion and methods for improved signal resolution

Various methods are described and compared for the determination of particle size distributions (PSD) in the submicron range by a technique known as hydrodynamic chromatography (HDC). Data are presented for a series of monodisperse latexes to establish the validity of the Mie theory of light scattering in describing the detector optical density signal. Analyses for the PSD involve corrections to the experimental HDC chromatograms for the effects of dispersion and are broadly classified as integral and numerical methods. Comparisons of calculations are made to chromatograms for polydisperse latexes as well as synthetic, discontinuous distributions and show the critical role of the optical density–particle size relationship in determining resolution and calculation stability. An integral method involving a non-Gaussian form for the dispersion function and a polynomial expansion for the chromatogram and an iterative numerical method involving modifications of a previously published technique are shown to give the best results for the PSD. The discussion includes an analysis of the possibility of improved signal resolution using turbidity in the absorption wavelength region and refractive index measurements. The conclusion is reached that increased resolution with turbidity is preferable to refractive index measurement since lower particle concentrations can be used.     

Kinetic Correlation for the Hindered Diffusion of Proteins in a Porous Packing Column*

Abstract Hindered diffusion of proteins in a porous packing plays an important role in proteinchromatographic purification.The HETP method was adopted to analyze the influence of axialdispersion, film mass transfer and hindered diffosion in the porous packing employing a size-exclusionchromatography(SEC)process.The retention behavior with eight proteins of different relativemolecular mass was experimentally detected with a commercial SEC column.A correlation basedon the relative molecular mass of the proteins and the packing porosity was developed and used topredict the effective diffusion coefficient of a protein in the Porous packing.The predicted valuesof effective diffusion coefficient were very consistent with the experimental results with the averageerror of 8.6%.     

丙烯酸树脂分子量及其分布的测定

建立了液相凝胶渗透色谱法（ GPC）测定丙烯酸树脂分子量及其分布的方法。利用不同分子量分子在凝胶色谱中有不同的保留时间,使用了5种高分子单分散性标准品,根据其保留时间与分子尺寸关系,建立线性拟合校正曲线,快速、高效地获得高分子化合物数均分子量、重均分子量等多种平均分子量。以四氢呋喃作为流动相,使用RID检测器。数均分子量RSD=0.413％,重均分子量RSD=0.367％,线性拟合曲线,相关系数r=0.994。结果表明,该方法简便、准确,适用于丙烯酸树脂分子量及其分布的测定。     

SEC–viscometer detector systems. II. Resolution correction and determination of interdetector volume

The closely related topics of resolution correction and the determination of interdetector volume were examined. In determining the interdetector volume (δ) by searching to superimpose two types of intrinsic viscosity calibration curve (one from narrow standards and one from a broad standard), the underlying equation based upon symmetrical axial dispersion theory was derived. This equation combined with experimental results showed that the local intrinsic viscosity value is very similarly affected by interdetector volume and by band spreading. The result supported the idea of using an effective δ to effect an axial dispersion correction to local intrinsic viscosity data. However, it also increased the difficulty of finding both δ and standard deviation (δ) simultaneously by numerical search. Furthermore, attempts to apply the method to the chromatograms of narrow standards showed inadequate superposition. Following calculation of skewing factors, the superposition problems were attributed to skewing of the chromatograms of the monodisperse polymer standards used. © 1993 John Wiley & Sons, Inc.     

Interactions and mechanical properties of rod-coil ionomer blend

Polymer-polymer blends of rigid-rod and random-coil macromolecules are obtained by ionomer blend formation. The molecular dispersion of the rod molecules in the matrix polymer is achieved by acid-base interactions. The reinforcement effect in terms of the Young's modulus is discussed as a function of the degree of polymerization of the rods. By treating the reinforcer molecule as a fuzzy cylinder the reinforcement effect can be correlated to the reinforcers' size and shape.     

高温凝胶渗透色谱法在聚苯硫醚树脂测试中的应用

通过高温凝胶渗透色谱(GPC)，采用普适校准法对线性聚苯硫醚树脂(PPS)的摩尔质量、多分散系数以及摩尔质量分布进行测定。结果表明，此法不仅数据准确、可靠、重现性好；而且根据绘出的图谱可以直观地观察到各个摩尔质量段的含量和摩尔质量的情况，这对研究树脂的机械性能、流动性和成型加工性等有着极其重要的意义。     

Solution properties of poly(diallyldimethylammonium chloride) (PDDA)

Size exclusion chromatography (SEC) with dual detection, i.e. employing a refractive index (RI), concentration sensitive, detector together with a multiangle light scattering (MALS) detector which is sensitive to molecular size, has been applied to study the solution properties of poly(diallyldimethylammonium chloride) (PDDA) in water containing different electrolytes, namely: NaCl, NaBr and LiCl, at 25 °C. The analysis of a single highly polydisperse sample is enough for obtaining calibration curves for molecular weight and radius of gyration and the scaling law coefficients. The effect of the ionic strength on the conformational properties of the polymer can also be analyzed and unperturbed dimensions can be obtained by extrapolation of the values measured in a good solvent. The values of the characteristic ratio of the unperturbed dimensions thus obtained were: 17, 11 and 17, respectively, for NaCl, NaBr and LiCl solutions. Viscosity and conductivity measurements support the results obtained by SEC. Moreover, the experimental results are in good agreement with the theoretical calculations performed by combining molecular dynamics and Monte Carlo sampling procedures.     

Characterization of star-block copolymers having PS-b-PI arms via SEC/RI/RALLS/DV

Summary Poly (styrene-b-isoprene) (PS-b-PI) star-block copolymers were studied by triple detector size exclusion chromatography (SEC³), utilizing a combination of refractive index (RI), right angle light scattering (RALLS), and differential viscosity (DV) detectors. The relationships between the number of arms, the composition, and molecular size of the star polymers were investigated. The effect of the number of arms of the star polymer on elution behavior was established and compared to a linear polystyrene calibration curve. It was found that universal calibration was valid for star polymers having up to 32 arms. The branching parameters (g and g') were calculated from intrinsic viscosity and radius of gyration data. The results indicate that, in addition to molecular weight determinations, much useful conformational information on star-block copolymers can be obtained from SEC³. The technique is an especially useful tool for characterizing branched copolymers, which are difficult to characterize by conventional SEC. Received: 31 January 2000/Revised version: 24 February 2000/Accepted: 25 February 2000     

Characterization of polyester/polycarbonate blends by size exclusion chromatography and melt rheometry

A major obstacle to the study of polymer blends has been the lack of a convenient technique for measurement of molecular weight. Melt rheometry, while giving useful information related to processing and end-use performance, is incapable of providing detailed information on the individual components. This work describes the use of size exclusion chromatography (SEC) to study the molecular-weight distributions of polycarbonates and aromatic polyesters in blends of the two. SEC of the polycarbonate is achieved in a solvent which dissolves the polycarbonate, but not the polyester, while SEC is performed in a solvent which dissolves both components, but using selective detection. Thus, SEC is used to examine the individual components of the blend, while rheometry can be used to study the blend as a whole. This combination of techniques has been successfully used to analyze the effect of moisture, processing conditions, and recycling on blend properties.