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.     

Molar mass distributions of polymers from size exclusion chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry: Methods for comparison

Equations are presented for calculating molar mass averages and molar mass distributions from matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) data and from size exclusion chromatography (SEC) data. The utility of polydispersity is examined as an indicator of the expectation of MALDI‐TOF MS mass discrimination effects. Cumulative distributions are found to be rich in information for comparing the two techniques and are easily obtained from both SEC and MALDI‐TOF MS data. Analyses of a series of narrow molar mass distribution poly(methyl methacrylate) (PMMA) standards and one polydisperse sample have been performed with both methods. MALDI‐TOF MS did not detect dimer and trimer in the PMMA samples, and it often indicated lower amounts of high‐molar‐mass polymers than did SEC. The results showed that the distribution breadth, as evidenced by the standard deviation of the distribution (calculated from the polydispersity and number‐average molar mass), correlated well with the molar mass range observed in the MALDI‐TOF MS spectra, whereas the polydispersity alone did not. Ratioing the extremes in the molar mass concentrations measured with the SEC differential refractometer, which were necessary to adequately define molar mass distributions, showed that detector dynamic range values as high as approximately 370,000 were required for the polydisperse samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 627–639, 2005     

A theory of topological separation of linear and star-shaped polymers by two-dimensional chromatography

Topology influences the size of macromolecules, but polymers are usually distributed with respect to molar mass, which also results in the size distribution within a polymeric sample. Due to this fact size-exclusion chromatography (SEC) is not able to separate even moderately polydisperse polymers by topology; the same is also true for the adsorption chromatography (AC). The full separation by molar mass and topology is not possible by any single mode of chromatography. These problems can be solved by means of two-dimensional chromatography which combines SEC and AC mechanisms. A theory of interactive chromatography of linear and star-shaped ideal-chain polymers is used to analyze two-dimensional chromatographic separation of polydisperse linear and star polymers. Basing on this theory, we simulate 2D-chromatograms for model mixtures of polydisperse linear and star-shaped polymers of equal average molar mass, and demonstrate that 2D-separation of such polymers by topology is possible. A possibility to separate symmetric and very asymmetric stars by 2D-chromatography is predicted. The influence of the molar-mass heterogeneity, pore size and adsorption interaction parameter on the 2D chromatographic pattern is analysed, and the conditions for a good separation of linear and star polymers are formulated. The theoretical results are in a qualitative agreement with the experimental data, which have been reported previously by Gerber and Radke.     

Use of gradient,critical, and two‐dimensional chromatography in the analysis of styrene‐ and methyl methacrylate‐grafted epoxidized natural rubber

The growing number of heterogeneous polymeric species that are being synthesized places increasing demands on existing analytical techniques. Although size‐exclusion chromatography (SEC) has established itself as a powerful analytical tool, it has its limits when complex polymers, e.g., graft copolymers, must be analyzed. In this case, complementary techniques such as gradient HPLC and liquid chromatography at critical conditions (LCCC) are more favorable. The present study describes the synthesis and analysis of methyl methacrylate‐ and styrene‐grafted epoxidized natural rubber by different chromatographic techniques. The grafting efficiency was evaluated by gradient HPLC under normal and reversed phase conditions. Methyl methacrylate‐grafted ENR50 was further analyzed by LCCC, where separation of the rubber and grafted rubber occurred according to chemical composition but was independent of the molar mass of the methyl methacrylate homopolymers. This was followed by the combination of LCCC and SEC, where separation was achieved in two dimensions. Relevant deductions were made of both the chemical composition distribution and the molar mass distribution of the functional groups of methyl methacrylate‐grafted ENR50. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2530–2538, 2003     

Comprehensive branching analysis of polyethylene by combined fractionation and thermal analysis

Linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) differ significantly in their branching types and branching distributions. For a comprehensive analysis, preparative temperature rising elution fractionation and/or preparative molar mass fractionation are used to fractionate typical LLDPE and LDPE bulk resins into narrowly distributed fractions. The chain structures of the bulk resins and their fractions are further analysed using SEC, crystallization analysis fractionation, DSC and high‐temperature HPLC to provide detailed information on short chain branching in LLDPE and long chain branching in LDPE. For LDPE it is shown that the multiple fractionation approach is a powerful source of sample libraries that may have similar molar masses and different branching structures or alternatively similar branching but different molar masses. The analysis of these library samples by thermal analysis provides a much deeper insight into the molecular heterogeneity of the samples compared to bulk sample analysis. © 2018 Society of Chemical Industry     

Liquid chromatography of polymer mixtures applying combination of exclusion and full adsorption mechanisms. I. Analysis of polystyrene in its mixture with polymethylmethacrylate single column/single eluent approach

Components of polymer mixtures with different chemical composition can be separated by liquid chromatography by applying appropriate conditions (column packing, eluent, temperature, and pressure) in which just one type of macromolecule is eluted in the size exclusion mode while the other component is fully retained within on column packing. The feasibility of this idea has been demonstrated using the mixtures of polystyrene (PS) plus polymethylmethacrylate (PMMA) with silica gel as the column packing and toluene as an eluent. The PMMA was retained by the silica get at ambient temperature and moderate pressures of several MPa while the PS was eluted by a typical SEC mecahanism. Furthermore, the molar mass distribution of the PS could be determined in one step with the same precision as if injected alone. Surprisingly large amounts of PMMA were trapped within the column prior to its SEc characteristics being influenced. After a series of analyses the column has to be regenerated with a brief flushing with a desorbing liquid, tetrahydrofuran in the system studied. The re-equilibrization of the column with the initial eluent, toluene, was fast and a new series of analyses could be started soon after the characterization step had seen finished. © 1995 John Wiley & Sons, Inc.     

Characterization by dilute solution and rheological methods of polystyrene and poly(methyl methacrylate) produced with a tetrafunctional peroxide initiator

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) samples produced by the bulk homopolymerization of styrene and methyl methacrylate with a tetrafunctional peroxide initiator (JWEB50) are characterized in detail by various solution and rheological methods. For comparison purposes, “linear” PS and PMMA samples were produced under similar conditions with a monofunctional initiator (TBEC). The four sample types were characterized by size exclusion chromatography (SEC) setups to determine molecular weight, radius of gyration, and intrinsic viscosity distributions. Contraction factors were calculated and indicated evidence of branching for polystyrene produced with JWEB50 while no such effects were observed with PMMA. The rheological behavior of the samples was subsequently investigated by performing oscillatory shear and creep experiments. Compared to the “linear” material, samples produced with JWEB50 exhibited a reduction in zero‐shear viscosity that was attributed to long‐chain branching. Retardation spectra were calculated based on creep data and converted to dynamic compliances that were then combined with the oscillatory data. This provided master curves spanning a much wider frequency range than could be obtained experimentally. Examination of various viscoelastic functions showed evidence of long‐chain branching for both polystyrene and poly(methyl methacrylate) samples produced with JWEB50. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1340–1355, 2007     

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     

Influence of nanoparticle-polymer interactions on the apparent migration behaviour of carbon nanotubes in an immiscible polymer blend

We investigate the influence of nanoparticle-polymer interactions on the apparent migration behavior of multiwall carbon nanotubes (CNTs) in an immiscible polymer blend of ethylene-acrylate copolymer (EA) and polyamide 12 (PA). The polymer-CNTs interaction is tuned by using different surface modification strategies, comprising grafting and coating. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) are chosen as surface modifiers. The nanocomposite materials are prepared by melt-blending polymer-modified-CNTs in EA and PA. Polymer-grafted-CNTs tend to concentrate at the PA/EA interface, even if predispersed in PA, as opposed to pristine CNTs, which stay inside PA under the same circumstances. This new behavior is consistent with the morphology of PA/EA/(PMMA or PS) ternary blends and suggest a dominance of interfacial thermodynamics on CNTs localization. If we use polymer-coated-CNTs instead, the behavior depends on molar mass of the coating polymer. For low molar mass, it is similar to that of pristine CNTs and indicates desorption of the coating, owing to the weak interaction with the CNTs surface. Interestingly, we observe that long PS chains do not desorb and can drive the CNTs to the interface of the PA/EA blend. Moreover, the influence of kinetics is clearly observed through the dependence of CNTs interfacial confinement on dispersed droplet size.     

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).     

Full copolymer characterization by SEC-NMR combined with SEC-MALDI

Measurements on a series of random copolymers with units of methylmethacrylate, butylacrylate, styrene and maleic-anhydride are performed. A method is used which consists in fractionating the copolymer by size exclusion chromatography (SEC), collecting 30-40 fractions and then recording both the NMR and MALDI spectra of the fractions. In a successive step, bivariate distribution of chain sizes and composition maps are derived from knowledge of the molar mass, weight and composition of the copolymer fractions. The compositional distribution is obtained by summation of the sections of the bivariate distribution which belong to a narrow compositional range.A model for SEC fractionation of copolymers is developed. It allows to predict the composition and D(x) of the SEC fraction (D(x) is the ratio between the number-average and the weight-average molar mass, x is the fraction number).Offline SEC-MALDI measurements are performed, in order to measure experimentally D(x) for the random copolymer. The agreement between theoretical and experimental values for D(x) and for the composition of the SEC fraction (as derived from SEC-NMR measurements) is good. The predictions of the model were also compared with literature data for SEC fractionation of a copolyester with units of butileneadipate and butilenesebacate. The agreement between theoretical and experimental values is more than satisfactory.     

Separating ethylene-propylene-diene terpolymers according to the content of diene by HT-HPLC and HT 2D-LC

The separation of ethylene-propylene-diene terpolymers (EPDM) according to the three monomer units is an important task to understand the macroscopic properties of these technically important elastomers. In particular a separation with regard to the content of diene is of extreme value because the distribution of the latter along and across the molar mass axis determines the cross-linking behavior. In this study we show that high-temperature liquid chromatography (HT-HPLC) can be used for this purpose: the chromatographic retention of EPDM on porous graphite using a gradient of 1-decanol→trichlorobenzene is a function of both the content of ethylene and diene. The contribution of the diene alone to the chromatographic retention can be quantified by calculating the difference in elution volume between the EPDM and an EP copolymer having an equivalent content of ethylene. The chromatographic separation of fully hydrogenated EPDM indicates that the additional retention due to diene is the result of its geometrical nature. Coupling the HPLC separation according to the chemical composition with size exclusion chromatography (SEC) enables to reveal for the first time the complete molecular heterogeneity, i.e. the relationship between the chemical composition distribution and the molar mass distribution of EPDM.     

Purification and Characterization of Microbial Hyaluronic Acid by Solvent Precipitation and Size-Exclusion Chromatography

Abstract

Samples of hyaluronic acid (HA) produced by submerged fermentation using a synthetic culture medium were recovered, purified, fractioned, and characterized using solvent precipitation and size-exclusion chromatography (SEC). The samples showed a wide molar mass distribution in the range 10³–10⁷ Da, most of which had an average molar mass between 10⁴ and 10⁵ Da after purification by sequential precipitations. Fractions of HA with molar mass above 10⁵ Da were purified by SEC in a semi-preparative scale with nearly no protein contamination. Characterization and fractionation of the HA was carried out by SEC in a analytical and semi-preparative scale using Shodex OHPak SB806M HQ and Superose 6 columns, respectively.     

Theory of chromatography of linear and cyclic polymers with functional groups

We discuss the chromatographic behavior of linear polymers and rings having specific (functional) adsorption-active groups. Functionalized eight-shaped, daisy-like and theta-shaped macromolecules are considered as well. By using a model of an ideal chain with point-type defects in a slit-like pore we derive equations for the distribution coefficient covering all modes of chromatography of functionalized polymers of any molar mass in both narrow and wide pores. Additionally simple approximate formulae are obtained for a number of important modes of chromatography; chromatograms are simulated for model mixtures of polydisperse non-functional and functional polymers. By using the theory we analyze separation of polymers by molar mass, functionality and topology. Although there is a principal possibility to use adsorption chromatography or size-exclusion chromatography (SEC), we conclude that the liquid chromatography at the critical condition (LCCC) is especially efficient for separation of polydisperse polymers by both functionality and topology. The theory predicts that functionalized linear and cyclic polymers can be separated from each others by LCCC even better than non-functionalized ones. The LCCC behavior of some other types of polymers such as comb-like and semicyclic ones is discussed as well.     

利用体积排阻色谱法进行蛋白质折叠

以溶菌酶为模拟体系对体积排阻色谱法进行蛋白质折叠过程实验研究 .圆二色性光谱法分析结果证实了复性溶菌酶与天然溶菌酶的二级结构一致性 ;复性溶菌酶与天然溶菌酶色谱保留体积的差异揭示出折叠过程中无活性蛋白质聚集体的存在及其向复性蛋白质转化的机制 ;不同初始浓度的复性实验证实了蛋白质聚集体的存在及其与变性蛋白质初始浓度的关系 ;采用短色谱柱的折叠分离实验结果表明蛋白质折叠是一个快速过程 ;不同尿素浓度下的折叠分离实验结果表明尿素在SEC法中具有非常重要的作用 .与稀释复性法的对比实验表明 :体积排阻色谱法具有稀释倍数小、复性产品活性收率高、复性蛋白质浓度高等优点 .     

How does sequence length heterogeneity affect the dilute solution conformation of copolymers?

Sequence length heterogeneity (SLH) is defined as the change, as a function of copolymer molar mass (M), in the average number of continuous monomers of a given repeat unit. SLH can influence polymeric properties such as thermal stability, mechanical behavior, transparency, and the ability of copolymers to reduce interfacial surface tension. Here, we demonstrate the relation between SLH and the change as a function of molar mass of a dimensionless size parameter, the ratio of the viscometric radius and the radius of gyration, irrespective of chemical heterogeneity or molar mass polydispersity. Multi-detector size-exclusion chromatography (SEC) provides for a convenient method by which to experimentally establish this relation and, consequently, a method by which to determine whether SLH is present in a copolymer, whether the degree of randomness of a copolymer changes across the molar mass distribution (MMD), or whether two copolymers differ from each other in degree of randomness at a given M and/or across their MMDs. Results from our SEC and FT-IR measurements of block, random, alternating, and gradient copolymers of styrene (S) and methyl methacrylate (MMA) and their respective homopolymers agree with results from a probability theory based model of SLH in linear random copolymers. The multi-detector SEC method employs instrumentation available in most polymer separations laboratories and the relations developed should be applicable to copolymers other than the S-MMAs studied here.     

Depolarization behaviour of dilute polymer solutions: II. Angular dependence and analyzer absorption

Study of the depolarization behaviour of dilute polymer solutions leads to determination of the Cabannes factor, necessary for correcting the Rayleigh ratio used in light‐scattering calculations for deviations due to anisotropy. We present here a method to determine the Cabannes factor for polymers as a simultaneous function of both scattering angle and molar mass, accomplished by coupling size‐exclusion chromatography with depolarization multi‐angle light scattering (SEC/D‐MALS). The depolarization behaviour of brominated polystyrene (PSBr), previously studied at a right‐angle geometry, is seen to possess a non‐trivial angular dependence in addition to being a function of molar mass. We also demonstrate initial attempts at correcting SEC/D‐MALS results for absorption of light by the Polaroid filters that act as analyzers in the optical train of the system. Copyright © 2003 Society of Chemical Industry     

Fast determination of critical eluent composition for polymers by gradient chromatography

Gradient chromatography was applied in order to calculate the composition at elution for different methacrylates on normal phase columns. In addition the composition at elution was determined for polyethyleneoxide on a reverse phase column. It is shown that high molar mass polymers elute for a given homopolymer irrespective of their molar mass at the same eluent composition, which varies only slightly with gradient slope. In general the composition at elution in gradient chromatography is expected to be slightly lower than the true critical composition. For high molar mass polymers we found this composition to be close to the critical composition determined by isocratic experiments. The difference between the composition at elution and the true critical composition for a variety of polymethacrylates and for polyethyleneglycol was found to be only between 0.2 and 5%. Thus, after estimating the composition at elution, only a small number of additional isocratic experiments is needed to find the exact critical composition.     

Effect of the medium on the stereostructure of poly(methyl methacrylate) synthesized in ionic liquids

Poly(methyl methacrylate) (PMMA) was synthesized in different ionic liquids (IL) by free radical polymerization. The average molecular weight and polydispersity of the PMMA were measured by gel permeation chromatography. It is found that ILs have effect not only on the molecular weights but also on the stereostructure of PMMA. From the FTIR and NMR analysis, it was confirmed that the chemical structure of PMMA synthesized in ILs was similar to the one obtained in conventional solvents while the stereostructure was influenced by the different IL used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2199–2202, 2006     

Extension of the measuring range in size exclusion chromatography to higher molar mass by use of a light scattering detector

A new method for the extension of the measuring range of size exclusion chromatography coupled with light scattering (SEC/LALLS) to higher molar mass is presented. This method uses the fact that the light scattering signal can often be detected already at considerable smaller values of the elution volume (i. e. higher values of molar mass) than the concentration signal; furthermore, it takes into account the peak broadening effect in SEC. This procedure is tested for the case of a logarithmic normal distribution and a most probable distribution of molar mass. In the case of polypropylene with a logarithmic normal distribution (M?_w = 420 000, M?_n = 99 000), the range of molar mass covered by SEC/LALLS can be extended by a factor of about 10; with a most probable distribution (M?_n = 100 000), the attainable extension in molar mass assumes a factor of about 2.