Molar mass distribution by size exclusion chromatography: Comparison of multi-angle light scattering and universal calibration

Series of polymers of various molar mass, chemical composition, and molecular architecture was analyzed by size exclusion chromatography (SEC) coupled with a multi-angle light scattering (MALS) photometer and an online viscometer. The molar mass averages were determined from the signal of MALS or calculated from the intrinsic viscosity and universal calibration. The comparison of the obtained results showed significant differences between the two methods. The MALS detection was shown to be more accurate for the determination of the weight-average molar mass and less vulnerable to the spreading of polymer peak by band broadening. The universal calibration can yield more accurate estimation of the number-average molar mass of branched polymers. It is also significantly more accurate for the characterization of fluorescent polymers than MALS with a regular laser of 660 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47561.     

Characterization of branched polymers by size exclusion chromatography coupled with multiangle light scattering detector. I. Size exclusion chromatography elution behavior of branched polymers

The elution behavior of branched macromolecules during their separation by size exclusion chromatography (SEC) was studied. The elution behavior of branched polymers was investigated using samples of randomly branched polystyrene and star branched poly(benzyl methacrylate) of different levels of branching by means of a SEC chromatograph coupled with a multiangle light scattering detector. Abnormal SEC elution behavior was found to be typical for highly branched polymers. After a normal elution at small elution volumes the molar mass and root mean square radius of the eluting molecules increased with increasing elution volume. Several SEC experiments were carried out to find explanation for this effect and SEC separation was compared with the separation by thermal field flow fractionation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1588–1594, 2001     

Determination and comparison of molar mass distributions of substituted polystyrenes and block copolymers by using thermal field-flow fractionation, size exclusion chromatography and light scattering

Anionic polymerisations of p-methoxystyrene, p-methylstyrene, p-chlorostyrene and p-cyanostyrene were carried out in tetrahydrofuran (THF) and methylcyclohexane. The block copolymers poly(styrene-b-p-methoxystyrene-b-styrene), poly(styrene-b-p-methylstyrene-b-styrene) and poly(styrene-b-p-cyanostyrene) were also polymerised by using THF as solvent. The initiators included n-butyllithium (n-BuLi) and sodium naphthalenide. The use of both n-BuLi and sodium naphthalenide usually produced higher values of _n than were calculated. In the former case this could be explained by the lower reactivity of the initiator, which has been found to aggregate in THF. The molar masses were determined by thermal field-flow fractionation (ThFFF), size exclusion chromatography (s.e.c.) and light scattering (LS). ThFFF and the s.e.c. were used for determining the molar mass distributions. The agreement between the three methods was satisfactory. © 1997 Elsevier Science Ltd.     

An investigation of the use of size exclusion chromatography for the determination of molar mass distributions and fractionation of coal tars

The use of size exclusion chromatography (SEC) for the determination of molar mass distribution and fractionation of coal tars has been investigated. The construction of a calibration graph based on typical components of the tars for use in the determination of molar mass distributions has revealed anomalously low retention volumes for phenols and amines when THF is used as the mobile phase. Consequently the molar mass distribution for a tar with a high phenolic content was not reliable when determined in THF but chloroform was shown to be a suitable solvent for this purpose. However the effect was used to fractionate the tar into two components, one of which contained a mixture of mainly phenols and long chain paraffins while the other was composed predominantly of polynuclear aromatics. A coke oven tar of low phenolic content was also fractionated into two components according to molecular weight and the fractions characterised in detail.     

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.     

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.     

Gel permeation chromatography of the xanthan gum using a light scattering detector

Summary This work gives the first gel permeation chromatogramms obtained on native xanthan using a refractometric and a light scattering detectors. Results of molecular weights distribution analysis give a polydispersity 1.2 for the native polymer and 1.7 for enzymic partially degraded polymer. The experimental conditions and chromatogramms interpretation are briefly discussed.Laboratoire Propre de C.N.R.S., associé à l'Université Scientifique et Médicale de Grenoble     

Quantitative branching of linear and branched polysaccharide mixtures by size exclusion chromatography and on-line low-angle laser light scattering detection

The quantitative branching characterization of polysaccharide via size exclusion chromatography (SEC) and on-line low-angle laser light scattering (LALLS) detection is presented from both theoretical arguments as well as direct experimental evidence. The two measurable branching parameters g_v(m) [= (M_l/(M _n)_m)_v] and g′_v(m) [ = (M_l/(M _w)m)v] of a sample mixture have been related theoretically to the mixture's composition. There exists linear relationships between g_v(m) and W_b,v (the mass fraction of branched component in mixture) as well as between g′_v(m)^?1 and w_b,v. The latter correlation has been demonstrated experimentally employing a combined SEC/LALLS technique, and displays excellent agreement with the theoretical predictions. Furthermore, this polymer branching characterization method has been applied to study enzymatic starch hydrolysates products. The molecular weight distribution and branching distribution have been obtained.     

Molar mass analysis of polyamides-11 and -12 by size exclusion chromatography in HFiP

The SEC analysis of polyamide-11 and polyamide-12 can be conducted free of association and aggregation phenomena when hexafluoroisopropanol + 0.05 mol/L potassium trifluoroacetate are used as the mobile phase. The calibration of the SEC system can be conducted in different ways. As stationary phases non-polar polystyrene and polar perfluoro silicagel were tested. The investigations showed that the polystyrene gel exhibits hydrophobic interactions with the polyamides while with the silicagel selective interactions were not found. Investigating different options for SEC calibration it was found that conventional PMMA calibration does not yield correct results. The universal calibration approach based on PMMA calibration did not work either. Correct molar masses were obtained when the PMMA calibration curve was corrected with data from polyamide blends using a simplex algorithm. Alternatively, calibration can be conducted with broadly distributed polyamides that were first fully characterized by SEC-MALLS. The resulting molar mass distributions for different sets of polyamides were compared with molar masses that were determined directly by SEC-MALLS and excellent correlation was obtained.     

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.     

Characterising high mass materials in heavy oil fractions by size exclusion chromatography and MALDI-mass spectrometry

Several petroleum vacuum residues and a Maya asphaltene have been examined using size exclusion chromatography (SEC), using 1-methyl-2-pyrrolidinone as eluent. Aliphatic components are not dissolved in this solvent. All the samples showed a bimodal distribution. Material under the early eluting peak, excluded from column porosity corresponded to apparently very large molecular masses. The later eluting peak corresponded to molecules with a smaller range of masses and was relatively intense. The material excluded from column porosity is concentrated in the heptane-insoluble fraction; the peak of this fraction corresponding to smaller molecules shifted to earlier times than was found for the whole sample. In UV-fluorescence spectrometry, the heptane-insoluble materials did not fluoresce strongly. Materials excluded from column porosity showed no fluorescence, indicating that UV-fluorescence based methods are unable to detect high mass materials. MALDI-mass spectrometry indicated a bimodal distribution for the Maya asphaltene with a mass range up to m/z 40,000. Comparison of the low mass range of the spectrum with the small-size molecules detected by SEC indicated broad agreement for masses up to about 5000 u. However, if the excluded peak of SEC corresponds to the higher mass range up to m/z 40,000, then it is likely that these molecules are adopting three-dimensional conformations. Data from the hydrocracking of heavy oils was used to confirm some of the outlined findings.     

Determination of molecular weight and size distribution and branching characteristics of PVAc by means of size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS)

SEC/MALLS has been applied for the determination of molecular weight and size distributions and to quantify branching in polyvinyl acetate (PVAc). Linear and branched samples obtained by solution and bulk polymerization were analyzed. The molecular weight distribution of the branched polymer was broader and the mean square radius was found to be smaller, 38.8 nm (with molecular weight of 770?000), than for the linear polymer, 42.3 nm (with molecular weight of 740?000). Branching characteristics could be determined by using Zimm and Stockmayer equations. It has been found that the number of branches for the branched sample increases from about 1 to 9, per molecule, with increasing molecular weight.     

Comparison of size distribution data from dynamic light scattering and size-exclusion chromatography

The intensity-defined distribution functions of hydrodynamic radii of equivalent spheres, R_h, obtained from dynamic light-scattering experiments using the CONTIN procedure via the Stokes formula were compared with distributions of gyration radii, R_g, determined by size-exclusion chromatography. The number-, weight-, and intensity- (z)-defined R_g distributions accessible from size-exclusion chromatography experiments were calculated using the Flory-Fox relation. Reliable ratios of average radii, R_g/R_h, for linear polystyrenes having narrow, broad, or bimodal molecular weight distributions were obtained in toluene. Care should be taken to utilize properly averaged experimental quantities. For instance, the CONTIN DLS data evaluation procedure yields the z-average of the inverse of the hydrodynamic radius, 〈1/R_h〉_z^?1. © 1995 John Wiley & Sons, Inc.     

New use of size exclusion chromatography in kinetics of mechanical degradation of polymers in solution

A new method to investigate the mechanical degradation of polymers in solution is described that uses size exclusion chromatograms of the initial polymer and of the degraded sample. The incipient parts of these chromatograms are analyzed to obtain kinetic data about degradation at the level of infinitesimal fractions. The procedure is based on the fact that mechanical degradation of the polymers is a first-order reaction and macromolecules are cleaved mostly in their central region. The rate constant and the variation in the rate constant with molecular weight are determined in a single experiment, avoiding additional fractionation steps. Moreover, the slope of the size exclusion chromatographic calibration curve is derived, opening new ways to determine polydispersities or even to make rapid calibration for unknown polymers. To verify the method, the rate constant and the molecular weight dependence of the rate constant were determined for the sonic degradation of polystyrene in toluene. The rate constant is found to vary with the square of the molecular weight, and its value is in good agreement with results reported using much more laborious methods. © 1993 John Wiley & Sons, Inc.     

Comments on the measurement of long chain branching by size exclusion chromatography

Summary A technique for measuring long chain branching as a function of polymer molecular weight uses SEC with a low angle laser light scattering (LALLS) detector to compare M_W of an eluting species with the molecular weight of the linear counterpart that has the same retention time. This technique is correct only if all species in the SEC detector cells have the same constitution. Evidence is presented that indicates that this condition prevails for low density, high pressure polyethylene and polyvinyl alcohol. Alternative forms of data representations are suggested. A major uncertainty in the data treatment is the value to be assigned to the ratio of radii of gyration of linear and branched polymers with the same molecular weight. A method is suggested to measure this ratio directly, as a function of molecular weight, if the eluting species at any instant are uniform in branching character.     

Molar mass determination of poly(octadecene-alt-maleic anhydride) copolymers by size exclusion chromatography and dilute solution viscometry

The number average molar mass M_n of poly(octadecene-alt-maleic anhydride) (PODMA) copolymers calculated from data obtained by size exclusion chromatography (SEC) using a polystyrene (PS) calibration was found to be inaccurate. The use of SEC combined with dilute solution viscometry enabled a method to be developed using an iterative approach, which does not require knowledge of the Mark-Houwink constants for PODMA samples. A new calibration curve was constructed as a plot of molar mass M_u for PODMA. True number-average molar masses M_n (true) calculated using the new calibration are approximately twice the apparent molar mass M_n (app) based on a PS calibration for higher molar mass samples (>10?000 g mol⁻¹).     

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.