Determination and correction of peak broadening in size exclusion chromatography of controlled rheology polypropylene

The peak broadening in size exclusion chromatography of seven commercial polystyrene (PS) standards with narrow molar mass distribution (MMD) and of 6–9 polypropylene (PP) fractions (M?_w/M?_n = 1.34–2.10) obtained by direct extraction was determined in four different column sets. The dependence of the Gaussian peak broadening parameter, σ², on the peak elution volume was different for PS and PP. For a commercial grade of controlled rheology PP (CR-PP) (Daplen PT55) with M?_w/M?_n < 3 it was shown that disregard of the peak broadening effect leads to considerable errors in the MMD at low and higher molar mass and in the polydispersity parameter M?_w/M?_n. The same lot was studied in an Austrian National Research program for its physical propeties in processing and application and in a round-robin test of IUPAC working party IV.2.2. on molecular characterization of commercial polymers. © 1994 John Wiley & Sons, Inc.     

Linear copolymer analysis with dual-detection size exclusion chromatography: Correction for instrumental broadening

This article deals with data treatment problems associated with the estimation of the combined distribution of molecular weights and chemical composition in linear copolymers by size exclusion chromatography, when correction for instrumental broadening is considered. Standard dual detection is assumed, i.e., the chromatograph is fitted with a “universal” detector (a differential refractometer) and a specific sensor to one comonomer only (a UV spectrophotometer). A real and a “synthetic” example (involving the analysis of a diblock styrene–butadiene rubber) are presented. Also, a propagation of errors study associated with the deconvolution operations is developed. It is concluded that the best calculation procedure is to first compute the combined distributions from the raw chromatograms and then correct such distributions for instrumental broadening. © 1992 John Wiley & Sons, Inc.     

Asphaltene analysis using size exclusion chromatography

A common technique used in coal liquefaction investigations is the asphaltene analysis, whereby products are separated into four major fractions (insolubles, preasphaltenes, asphaltenes and oils) by solvent extraction techniques. The fractions are defined by their solubility in organic solvents such as tetrahydrofuran, toluene and pentane. An instrumental method of analysis, using gel permeation liquid chromatography, was developed to reduce the problems with the conventional solvent separation. The technique relies upon the fact that the fractions differ in molecular size as well as solubility. The method uses one solvent (THF) and a single 100 Å microstyragel column to separate the three soluble fractions. The trends in the data obtained with the molecular size separation agree with the trends obtained by conventional solvent separations on the same samples.     

Number-average molecular weight by size exclusion chromatography

It is now theoretically possible to obtain absolute accurate values of number-average molecular weight of complex polymers (e.g., branched polymers or copolymers) using size exclusion chromatography (SEC) with only a detector that measures the difference between the eluting polymer solution viscosity and the viscosity of the pure mobile phase (a differential viscometer [DV] detector). However, both precision and accuracy of these “DV M?_n” values are of concern. In this work, the precision of NBS 706 polystyrene was found to be two to three times worse for the DV M?_n than for the conventionally calculated M?_n. Also, regarding accuracy, the DV M?_n values were affected by the location of the universal calibration curve along the retention volume axis (a problem intimately associated with the problem of specifying the correct interdetector volume), the sensitivity of the DV detector to low molecular weights present in the sample, and axial dispersion. Each of these sources of error are examined in turn and two methods of calculating M?_n values are proposed. © 1994 John Wiley & Sons, Inc.     

Elution behaviour of diolmodified epoxides in size exclusion chromatography

The reaction of bisphenol A-diglycidyl ether (BADGE) with butane-1,4-diol (BD) in the presence of Mg(ClO₄)₂ leads to linear and branched oligomers. The formation ratio of these products depends on the reaction temperature. In experiments at 100°C, an epoxide consumption of up to 70% can be observed using HPLC. In this range all products show good solubility in THF, so that it is possible to follow the increasing molar mass by using SEC. A characteristic relation of the molar mass against the conversion rate is derived and SEC data of a branched product are discussed.     

Characterization of block copolymers by size exclusion chromatography

Summary Poly(ethyl methacrylate-b-deuterated methyl methacrylate), poly(styrene-b-methyl methacrylate), and poly(styrene-b-dimethylsiloxane)diblock copolymers have been characterized by means of size exclusion chromatography (GPC) apparatus fitted with four detectors in series, viz continuous viscometer, UV spectrophotometer, low angle light scattering photometer, and differential refractometer. The continuous measurements of the scattered light intensity, the limiting viscosity number, the concentration, and the chemical composition permits complete determination of the molecular characteristics of block copolymers.     

System development for size exclusion chromatography of starch hydrolysates

A system for the aqueous size exclusion chromatography (SEC) of starch hydrolysates has been developed. Sepharose CL is the chromatographic support material, and aqueous sodium hydroxide solution is the eluent. Various factors affecting the resolution of the proposed system are discussed. Support materials having small particle size and narrow particle size distribution are necessary for maximizing separation efficiency. The ionic strength of the eluent, however, has a negligible effect on separation efficiency. The fractionation range of the system has been broadened by connecting in series columns containing two different Sepharose-CL gel types according to the bimodal pore size distribution concept. Well-characterized sodium polystyrene sulfonate and dextran standards are used to calibrate this SEC system. The Coll–Prusinowski calibration procedure leads to a linear calibration curve over a wide molecular weight domain.     

Local polydispersity detection in size exclusion chromatography: Method assessment

Local polydispersity is the term describing the variety of molecules present at the same retention volume in size exclusion chromatography (SEC) analysis. In the analysis of a linear homopolymer, local polydispersity is generally attributed to the effect of axial dispersion: it can cause molecular size variety (i.e., imperfect resolution) at each retention volume and thus local polydispersity in the molecular weight. In the analysis of polymer blends (copolymers and branched polymers), it is possible to have local polydispersity, even when the resolution is perfect, because molecules of different compositions (or degrees of branching) can have the same molecular size in solution. Conventional SEC interpretation assumes no local polydispersity if the axial dispersion effects are negligible. Three methods are currently available for detecting local polydispersity by using a combination of differential refractive index, light scattering, and viscometer detectors: the chromatogram comparison method, the conventional calibration curve comparison method, and the universal calibration comparison method. Here we experimentally assess these three methods using polymer blends and emphasize the chromatogram comparison method. All three are shown to be useful for assessing triple detector systems, but they are capable of detecting local polydispersity due to molecular heterogeneity only for very large differences in specific refractive index increments in the blend components. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 370–383, 2001     

体积排阻色谱法在药物蛋白检测中的应用

探讨了单克隆抗体A、抗体融合蛋白B两种蛋白在不同的体积排阻色谱柱上的分离效果及流动相条件对体积排阻色谱柱分离抗体融合蛋白B的影响。结果表明,分析抗体融合蛋白B纯度和相对分子质量需要正确选择体积排阻色谱柱和合适的流动相条件。     

Studies on hyperbranched polyurethane by multidetector size exclusion chromatography

Hyperbranched polyurethane (HP) and its linear analog (LPU) were studied by size exclusion chromatography (SEC), utilizing a combination of refractive index (RI), right angle light scattering (RALLS), and differential viscosity (DV) detectors. The relationships between retention volume (V_e), intrinsic viscosity (η), radius of gyration (R_g), and the molecular structure were investigated. It was shown that the hyperbranched polyurethane had lower V_e, η, and R_g than its linear analog when they had the same molecular weight. The branching parameter g and g′ were calculated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2445–2450, 2002     

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.     

Correction for interdetector volume in size exclusion chromatography (SEC)

In a multidetector SEC system it is necessary to match the outputs of the detectors that sense eluant concentration with that are molecular weight dependent. There are several methods to accomplish this. The most common is to determine the interdetector volume or time difference between detectors. The difficulty with this technique is that with detector systems where the column eluent is split, the interdetector time difference varies with solution viscosity. Two new techniques were implemented on a high temperature SEC/DRI/LALLS/VISC system which take into account changes in solution viscosity due to high molecular weight polymers. Both techniques use calibration curves of hydrodynamic volume versus elution volume for the different detectors to determine the “instantaneous” time difference between the detectors as it varies with solution viscosity. Either method provides the correct interdetector time lag information. We note also that in multidetector systems the configuration of the detectors should be such as to maximize solvent flow rates through each detector and hence to minimize band broadening effects. © 1995 John Wiley & Sons, Inc.     

Separation of acylglycerols,FAME and FFA in biodiesel by size exclusion chromatography

Size‐exclusion chromatography separates solutes according to their molecular sizes. Free fatty acids (FFA), fatty acid methyl esters (FAME) and monoacylglycerols (MG) of vegetable oils or animal fats have very close molecular sizes and they cannot be baseline‐separated on a single Phenogel column (100 Å, 300 mm × 7.8 mm ID, 5 µm) by using tetrahydrofuran (THF) as the mobile phase. When toluene is used as the mobile phase, triacylglycerols (TG), diacylglycerols (DG), MG and FAME are well separated but there is no baseline resolution between DG and FAME. In addition, the elution order of MG and FAME is reversed. However, baseline separation of all the above lipid classes can be achieved by using toluene containing THF, acetone, dichloromethane, ethyl acetate or acetic acid as the solvent modifier. Acetic acid (0.25%) as the solvent modifier gives the best resolution and all the reference peaks are symmetrical. The detection limit of each class of lipids is 0.1 µg. The correlation coefficient values (between 1 and 100 µg) of all the lipid classes are better than 0.99. Thus, the determination of biodiesel products in the biodiesel reactor is very much simplified.     

Characterization of poly(diethoxyphosphazene) by size exclusion chromatography and viscometry

Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10^-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving C_n = r²_o/n² 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), C_n13 and poly (dichlorophosphazene), C_n13.5.     

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.     

Fractional complexation in a miscible polymer blend. Calorimetry and size exclusion chromatography

Poly(N‐methyldodecano‐12‐lactam) (PMDL) is miscible with poly(4‐vinylphenol) (PVPh). In the system PMDL + PVPh + tetrahydrofuran containing low‐molar‐mass polymer pair, this miscible blend is soluble in the solvent. In this work, it has been found that the system containing high‐molar‐mass polymer pair undergoes associative phase separation into a gel‐like interpolymer complex and a soluble residual phase (RP). The complex and RP samples were characterized using differential scanning calorimetry, size exclusion chromatography and thermogravimetric analysis. The average molar ratio of PMDL to PVPh in the complex is 1:2, considered an optimum composition of the interpolymer complex. The complex shows higher glass transition temperature and higher thermal stability than the RP. Formation of the interpolymer complex in the studied system and differences in its properties from the RP are caused by higher molar mass/length of associated polymer chains as a result of fractionation during which the high‐molar‐mass fraction forms the gel‐like interpolymer complex and the low‐molar‐mass fraction forms the soluble RP. © 2014 Society of Chemical Industry     

High performance size exclusion chromatography of poly(organo)phosphazenes

The determination of the molecular weights of polyorganophosphazenes can only be achieved with great care. The nature of the substituents, the proportion of residual chlorine atoms after substitution, and also any traces of hydrolysis can considerably modify the behavior of these polymers in solution and thus lead to erroneous results. In our current research we have been developing a characterization method based on steric exclusion chromatography, coupled with a light scattering detector. We have used columns with styrene–divinylbenzene organic micropacking as the stationary phase and THF with added LiBr (0.1 mol/L) as the eluent. This method has enabled us to establish accurate correlations between molecular weight, hydrodynamic volume, and viscosimetric measurements for polyaryloxyphosphazenes of varying structures and origins. The method also provides results which agree very well with the variables for the preparation of polyphosphazenes, which is based on polycondensation of P-trichloro-N-dichlorophosphoryl monophosphazene Cl₃P = N? P(O)Cl₂. Finally this method allows us to show that, despite their mineral backbone, these polymers obey Benoit's universal calibration concept.