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 poly (N‐vinyl formamide) by size exclusion chromatography–multiangle light scattering and asymmetric‐flow field‐flow fractionation–multiangle light scattering

The molar mass and the radius of gyration of three poly N‐vinyl formamide (polyNVF) synthesized in aqueous solution polymerization were characterized using two different fractionation techniques: size exclusion chromatography (SEC) and asymmetric‐flow field‐flow fractionation (AF4) coupled with a multiangle light scattering (MALS) and a refractive index (RI) detector. For the sake of comparison, the polymers were also characterized by MALS using the Zimm plot approach (no fractionation). The dn dc^?1 of the poly (N‐vinyl formamide) was measured (0.1564 mL g^?1) and it was found to be insensitive to the molar mass (in the range 150–450 kDa) and also to the eluents used (DDI water or mixed eluent DDI water/acetonitrile (80 : 20) at pH = 5.5). Interestingly, the concentrations of the samples injected in the SEC and AF4 should be different because concentrations in the range of 20–40 mg mL^?1 used for the AF4 caused overloading and anomalous elution in the SEC and hence misleading molar masses. At adequate concentrations in each fractionation equipment, the molar masses were in reasonable good agreement although AF4/MALS provided larger values than the other two techniques likely because samples were not filtered before injection. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42434.     

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     

Characterization of molecular structure of acrylic copolymers prepared via emulsion polymerization using A4F‐MALS technique

The study is primarily focused on the possibility to utilize organic asymmetric flow field‐flow fractionation (A4F) coupled to a multi‐angle light scattering (MALS) detector for the characterization of copolymers of methyl methacrylate with various acrylates prepared by emulsion polymerization. The effects of acrylate monomer type and content on the molar mass distribution and degree of branching of acrylic copolymers have been studied by A4F‐MALS using tetrahydrofuran as a carrier solvent. It has been found that the growing amount of acrylate results in the increase of molar mass, polydispersity, and branching degree as a result of chain transfer to polymer. Highly branched compact macromolecules with ultra‐high molar mass were identified in all copolymers containing a high level of acrylate. In contrast to size traditionally used exclusion chromatography, organic A4F‐MALS has been proved as a very efficient technique for the characterization of high molar mass acrylic emulsion copolymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40995.     

Characterization of polyamideamine‐epichlorohydrin (PAE) resin: Roles of azetidinium groups and molecular mass of PAE in wet strength development of paper prepared with PAE

Polyamideamine‐epichlorohydrin (PAE) resin is a crosslinked heteropolymer having cationic charges, and has been widely used as a wet strength agent of paper in the papermaking process. In this study, more accurate molecular mass values of PAE were determined by size exclusion chromatography attached with a multi angle laser light scattering detector (SEC‐MALS). The obtained weight average molecular mass (M_w) values of commercial and laboratory‐made PAE samples were 1,140,000 and 494,000, respectively, and these values were much higher than those reported so far. SEC‐MALS analysis also revealed that PAE molecules had highly crosslinked structures and extremely wide molecular mass distributions. Molecular mass values and content of 3‐hydroxy‐azetidinium (AZR) groups in PAE and PAE intermediates during the course of PAE synthesis were also determined by the SEC‐MALS and ¹H NMR methods, and the relationships between these values and the wet strength development of handsheets prepared with these PAE samples were studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2249–2255, 2005     

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.     

Better characterization of raw natural rubber by decreasing the rotor speed of Mooney viscometer: Role of macromolecular structure

The objective of our work was to characterize natural rubber (NR) samples with different macromolecular structures by measuring Mooney viscosities (V_R) at variable rotor speeds ≤2 rpm, called variable speed Mooney viscosity (M_VS). Model samples of technically specified rubbers of constant Mooney viscosity (TSR5CV) were prepared with chosen specific clones. The structures of the samples were characterized by size‐exclusion chromatography coupled with an online multi‐angle light‐scattering detector (SEC‐MALS). Rheological properties of the samples were also characterized by a dynamic moving die rheometer. Measuring monoclonal model samples by M_VS showed three types of V_R flow curves. The V_R at high rotor speed (2 rpm) was correlated with number‐average molar mass (M_n), whereas V_R at low rotor speed (0.05 rpm) was correlated with weight‐average molar mass (M_w). Measuring M_VS revealed the rheological behaviors of samples and enabled discrimination between samples with different macromolecular structures and should thus help in predicting processability. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

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     

Characterization of enzymatically synthesized amylopectin analogs via asymmetrical flow field flow fractionation

Asymmetrical flow field flow fractionation (AF4), when coupled with multi-angle laser light scattering (MALLS), is a very powerful technique for determination of the macromolecular structure of high molar mass (branched) polysaccharides. AF4 is a size fractionation technique just as size exclusion chromatography (SEC), nevertheless can overcome some crucial problems found in SEC analysis especially in starch like structures. This paper describes a detailed investigation of the macromolecular structure of two groups of well-defined synthetic amylopectin analogs – synthesized via an in vitro enzyme-catalyzed reaction using the enzymes phosphorylase b from rabbit muscle and Deinococcus geothermalis glycogen branching enzyme (Dg GBE). Size, molar mass distributions and structural data were studied by AF4 coupled with online quasi-elastic light scattering (QELS) and multi-angle light scattering (MALLS).     

Mid‐chain grafting in PVB‐graft‐PVB

The polymer commonly referred to as poly(vinyl butyral) is actually the statistical terpolymer poly(vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate), the main component of the polymeric interlayer in automotive and architectural safety glass, amongst other uses. Here, the effects of ‘self‐grafting’ or ‘auto‐grafting’ in this polymer are examined using size‐exclusion chromatography (SEC) with triple detection. These and supporting experiments (eg, batch‐mode multi‐angle light scattering) allow study of the effects of induced branching in the resultant PVB‐graft‐PVB molecule, and comparison with the ungrafted (though not linear) base polymer. This was done by application and extension of the classic Zimm–Stockmayer long‐chain branching (LCB) theory, by determination of the fractal dimension (d_f) of the polymers and of the change in d_f as a function of molar mass, as well as by the multiplicity of size parameters that are measured in a multi‐detector SEC experiment. Copyright © 2004 Society of Chemical Industry     

Molecular characterization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide derivatives as potential self-assembling copolymers forming polymeric micelles

A family of graft copolymers derivatives obtained from α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) have been studied as potential self-assembling macromolecules forming stable polymeric micelles at low critical micellar concentration. These polymers are obtained grafting on PHEA poly(ethylene glycol) (PEG) (M_w 5000 g/mol) (PHEA-PEG), hexadecylamine (PHEA-C₁₆) or both moieties (PHEA-PEG-C₁₆). The PHEA derivatives were characterised by a multi-angle light scattering (MALS) photometer on line to a size exclusion chromatography system in obtaining the molar mass distribution of the polymers. In addition, to investigate the capacity to form micellar aggregates in aqueous medium the MALS photometer was used in off-line batch mode in obtaining molar mass and dimension of the polymeric aggregates.     

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.     

Monitoring the grafting of epoxidized natural rubber by size‐exclusion chromatography coupled to FTIR spectroscopy

The evaluation of heterogeneous polymeric species by a selective, dual detector size‐exclusion chromatography setup can provide accurate results on the incorporation of specific functional groups in copolymers as a function of the molar mass distribution. However, when non‐UV‐absorbing species are used in copolymerization reactions, the dual detector method becomes less reliable. By interfacing a Fourier transform infrared (FTIR) spectrometer with size‐exclusion chromatography (SEC), the problem can be overcome, making it possible to map non‐UV‐absorbing species as a function of the molar mass distribution. Coupling takes place via a solvent‐evaporation stage, which delivers the mobile phase as a dry, solvent‐free polymeric film onto a germanium disk. In this article, styrene and methyl methacrylate were grafted onto epoxidized natural rubber (ENR50) and analyzed by SEC. The accuracy of FTIR as a suitable detector was evaluated by comparing results from a dual detector SEC setup and FTIR coupled to SEC. FTIR proved to be a successful detector for the analysis of non‐UV‐absorbing species. This was consequently followed by the characterization of methyl methacrylate‐grafted ENR50. From the relevant data, Gram–Schmidt and contour plots could be made to indicate the incorporation of methyl methacrylate into the grafted epoxidized natural rubber as a function of the molar mass distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2539–2549, 2003     

High-temperature dynamic laser light-scattering characterization of polyethylene in trichlorobenzene

Polyethylene samples were characterized in trichlorobenzene at 135°C by high-temperature dynamic laser light scattering (LLS). Precise measurements of the intensity-intensity time correlation function permit us to make a Laplace inversion to obtain an estimate of the normalized translational diffusion coefficient distribution [G(D)]. After establishing a calibration between the translational diffusion coefficient (D) and molar mass, by using six moderately dispersed polyethylene samples, we were able to transform G(D) to molecular weight distribution (MWD), and to calculate the weight average molecular weight (M_w), which weights were comparable with the ones obtained by using static LLS and size exclusion chromatograph (SEC). The advantages and limitations of using dynamic LLS as a routine method to characterize of polyethylene are discussed. © 1993 John Wiley & Sons, Inc.     

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     

Methacryloylpropyl–βcyclodextrin and vinylpyrrolidone copolymers: Synthesis and characterization as potential chiral selector

The free radical copolymerization of vinylpyrrolidone (VP) with 2‐hydroxy‐3‐methacryloyloxypropyl β‐cyclodextrin (βW7 MAHP), a derivative of hydroxypropyl β‐cyclodextrin (CD) substituted by polymerizable methacryloyl groups, is carried out in water by varying the molar ratio of the comonomers. It is found that the higher the molar ratio of βW7 MAHP to VP, the larger the molar mass of the water‐soluble copolymer. A size exclusion chromatography analysis coupled with multiangle laser light scattering detection (SEC–MALLS) suggests that VP‐rich copolymers with a mass‐average molar mass (MM) of about 2.5 × 10⁴ g mol^?1 may consist of βW7 MAHP dimers, trimers, and oligomers containing few CD units whereas βW7 MAHP rich copolymers with an MM of about 5.5 × 10⁶ g mol^?1 are likely to be dominated by crosslinked polymer materials. βW7 MAHP‐co‐VP copolymers coated on porous silica are used as high‐performance liquid chromatography chiral selectors. The effects of the structural features of the guest molecule and the characteristics of the chiral stationary phases on the retention and resolution are evaluated. SEC–MALLS detection shows that, by varying the comonomer feed, copolymers with different molar masses and macromolecular structures are formed. The chiral separation ability of Copo VP is evaluated toward enantiomers having one or more aromatic rings as a function of the amount of copolymer adsorbed onto the silica surface, the βW7 MAHP content, and the concentration of solute. It is clear that the column combining the greater amounts of adsorbed copolymer and βW7 MAHP exhibits better resolving power. Moreover, the size, geometry, and functionality of the guest molecule are important factors that strongly affect the enantioselectivity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2364–2374, 2005     

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.     

Improved methods for evaluating the molar mass distributions of cellulose in kraft pulp

Multi‐angle laser light scattering (MALLS) was used to characterize birch kraft pulps with respect to their absolute molecular mass distributions (MMDs). The pulps were dissolved in lithium chloride/N,N‐dimethylacetamide and separated by size exclusion chromatography (SEC). The weight‐average and number‐average molecular masses of the cellulose fractions of the pulps obtained from the absolute MALLS measurements were compared with the molar masses obtained by direct‐standard‐calibration relative pullulan standards. Discrepancies between the two detection methods were found, and two ways of correlating the relative pullulan molar masses to the absolute molar masses were examined. In the first method, the correlation was made over a large range of molecular masses. The second method correlated the molecular masses of the standards to the molecular masses of samples by the calculation of fictitious, cellulose‐equivalent molar masses of the standards. With the preferred second method, a more correct MMD of kraft pulp samples could, therefore, be obtained from an SEC system calibrated with narrow standards. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1170–1179, 2003     

Synthesis and structural characterization of N,N,N-trimethyl chitosan

N,N,N-trimethyl chitosan (TMC) with molar mass 29 ~ 136 kg/mol and degree of quaternization 70% ~ 82% was synthesized from chitosan via N,N-dimethyl chitosan (DMC) by a two-step method. Size exclusion chromatography (SEC) coupled with multiangle laser light scattering was employed to characterize the molar mass and chain conformation of DMC and TMC. Nearly no degradation was found for DMC, but degradation by ~50% was observed from TMC. Apart from degradation, the shift of SEC peak toward higher elution volume for N-methylated chitosan was attributed to the increase in chain flexibility. It was shown that chitosan, DMC, and TMC took a random coil conformation in 200 mM acetate buffer, with persistence length decreased from 10 nm for chitosan, to 5.7 nm for DMC and 3.2 nm for TMC. The significant increase in chain flexibility upon N-methylation is most probably due to the breakage of intramolecular hydrogen bonds between chitosan repeating units.     

Size Exclusion Chromatography as a Method for Routine Check‐Up and Quality Control of Industrial Thermoplastic Polyurethane Systems – Correlation between Molecular Weight and Mechanical and Thermal Properties

A method has been developed which allows an accurate molecular characterization of linear prepolymers end‐capped with diisocyanates which is correlated with the properties of the finally formed thermoplastic polyurethane elastomer (TPU). Therefore, this method is suitable for a fast routine check‐up in quality control in the polyurethane (PU) processing industry. A homologous series of three toluene‐2,4‐diisocyanate (TDI) end‐capped PU prepolymers with poly(oxytetramethylene) glycol (POTM) as soft segment (number‐average degree of polymerization: 3, 4, and 7) have been characterized according to their molar mass and its distribution by means of size exclusion chromatography (SEC) calibrated with commercially available POTM standards. The validation of this method was carried out by SEC with double detection, using a combination of a concentration (differential refractive index detector, DRI) and an end group specific detector (ultraviolet detector, UV), which allows the determination of the absolute number‐average molar mass of the PU prepolymers as well as their content of soft and hard segment. The values for the number‐average molar mass were confirmed by osmometry. The PU prepolymers were reacted each with the same aromatic diamine to give the corresponding TPU elastomers which have been examined according to their thermal and dynamic behavior (transition temperature of soft and hard segment, temperature range of application) by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Also the hardness, tear strength and elongation at break could be related to the molecular structure, leading to a judgement for the efficiency of the final product for special fields of application.