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.     

Molecular weight distribution of cellulose as its tricarbanilate by high performance size exclusion chromatography

Cellulose tricarbanilates (CTCs) were prepared from a range of cellulose samples (cotton linters, wood pulps, Avicel, amorphous cellulose, and cellulose II) for molecular weight distribution (MWD) studies by high performance size exclusion chromatography (HPSEC). The HPSEC columns were calibrated using CTC standards with the aid of a microcomputer. CTCs were prepared by reaction of cellulose samples with phenylisocyanate in pyridine at 80°C. For some samples, e.g., cellulose II, activation with liquid ammonia and pyridine was necessary prior to reaction in pyridine. All samples tested were also derivatised in dimethylsulfoxide at 70°C, although for high molecular weight (MW) cellulose samples some MW reduction occurred in this solvent. Conditions were determined for optimum precipitation of CTCs in aqueous methanol without coprecipitation of low MW impurities.     

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.     

一种用高效凝胶渗透色谱测试褐藻胶分子量及分子量分布的方法

提出了一种用凝胶色谱与常规检测器检测褐藻胶分子量及其分布的方法。用高效凝胶渗透色谱(GPC)与示差检测器(RID)结合,建立了以普鲁兰标准品为对照的相对重均分子量、相对数均分子量与GPC–MALLS(多角度激光散射)测试的褐藻胶绝对重均分子量、绝对数均分子量间的转换关系,得到了用GPC–RID检测相对分子量计算褐藻胶绝对分子量和多分散系数的方法。结果表明,GPC–RID法经转换公式得到的重均分子量、数均分子量和多分散系数与GPC–MALLS法的相对误差在?12%以内。基于GPC–RID法可较准确地获得褐藻胶的绝对分子量及多分散系数,使用通用检测器可节约仪器投资,降低检测成本。     

Molecular weight determination of 83% degree of decetylation chitosan with non‐Gaussian and wide range distribution by high‐performance size exclusion chromatography and capillary viscometry

Molecular weight determination of 83% degree of deacetylation (DD) chitosan with non‐Gaussian and broad molecular weight distribution by high‐performance size exclusion chromatography (HPSEC) and by capillary viscometry were proposed. The relationships between weight average retention volumes (RVw) of HPSEC and intrinsic viscosities ([η]) measured by capillary viscometer and the weight average molecular weight (Mw) measured by static light scattering were established for routine molecular weight determination of chitosans either by HPSEC or by the capillary viscometry method, respectively. These results showed: relationships of RVw and Mw for different Mw of 83.0% DD chitosans can be expressed by the equation Log Mw = −0.433 RVw + 11.66. The RVw of other DD chitosans do not correlate well with this equation. It indicated that DD of chitosan affected the relationship of RVw and Mw of chitosans studied. The Mark–Houwink constant a decreased from 0.715 to 0.521, as the solution ionic strength increased from 0.01M to 0.30M, whereas constant k increased from 5.48 × 10⁻⁴ to 2.04 × 10⁻³ over the same range of ionic strength solutions. The established RVw and Mw equation and [η] and Mw equation (Mark–Houwink equation) can be routinely used to determine the molecular weight from RVw or [η] of chitosan by HPSEC or by capillary viscometer, respectively, without the need of expensive instrumentation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1905–1913, 1999     

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.     

Porous structure and swelling properties of styrene–divinylbenzene copolymers for size exclusion chromatography

Small spherical particles of styrene–divinylbenzene copolymers have been synthesized by modified suspension polymerization. The effects of divinylbenzene (DVB) contents, dilution degree of the monomers and diluent composition on the porous structure and swelling properties of the copolymers were investigated. Toluene uptakes of macroporous copolymers were considered as a result of three contributions: filling of the fixed pores, expansion of the fixed or collapsed pores, and nuclei swelling and heptane uptakes as a result of the two first contributions. The increase of DVB content in the copolymers synthesized in presence of a solvating diluent (toluene) provoked a decrease on the nuclei swelling. The increase of dilution degree with solvating diluents changed the toluene and heptane uptakes, and when the diluent–copolymer affinity was reduced, the fixed pore volume increased. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1257–1262, 1997     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

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.     

Determination of molecular weight for poly(vinyl butyral) using size exclusion chromatography/low-angle laser light scattering (SEC/LALLS) in hexafluoroisopropanol

Size exclusion chromatography/low-angle laser light-scattering (SEC/LALLS) determinations of molecular weight for poly(vinyl butyral) (PVB) using hexafluoroisopropanol (HFIP) as the polymer solvent and chromatographic mobile phase are described. The use of HFIP provided aggregate-free SEC/LALLS chromatograms from which molecular weight distribution averages were calculated. Comparison of SEC/LALLS molecular weights determined in HFIP with similar data obtained using tetrahydrofuran as the polymer solvent and chromatographic mobile phase indicated that the former is more generally applicable for PVB of different vinyl alcohol content.     

Simultaneous measurement of the molecular weight distribution and 5‐ethylidene‐2‐norbornene content across the molecular weight distribution of ethylene–propylene–diene terpolymer via a new size exclusion chromatography–ultraviolet–refractive index method

A size exclusion chromatography (SEC)–UV–refractive index (RI) method was developed to measure the 5‐ethylidene‐2‐norbornene (ENB) content across the molecular weight distribution (MWD) in ethylene–propylene–diene terpolymer (EPDM) at room temperature. The ratio of the UV and RI signals at the same effective elution volume was converted to ENB content. The feasibility of using this method to measure the ENB content across the MWD in EPDM at high temperature was also demonstrated. Prior understanding was that ENB had insufficient UV absorbance relative to high‐temperature SEC solvents to allow for useful measurements. We demonstrated this by using high‐boiling‐point solvents, such as decalin, with a low UV absorbance in the UV wavelength range of interest for ENB. These solvents also gave rise to a high enough specific RI increment (dn/dc) for EPDM that a suitable RI detector response was obtained. Additionally, this methodology could be readily applied to other polymers soluble at high temperature as long as the polymers contained a UV chromophore. These include polymers containing vinyl, conjugated vinyl, aromatic ring, carbonyl, or halocarbon groups. This UV‐absorption‐based detection concept might also be extended to high‐temperature thermal‐gradient interactive chromatography‐UV, high‐temperature solvent‐gradient interactive chromatography‐UV (high‐temperature liquid chromatography‐UV), temperature‐rising elution fractionation‐UV, crystallization analysis fractionation‐UV, and crystallization elution fractionation‐UV. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43911.     

Molecular weight distribution of a segmented copolymer of PET–PCL

A recently developed method of combining both the results of static and dynamic laser light scattering (LLS) was applied to characterize the segmented copolymer of poly(ethylene terephthalate-co-caprolactone) (PET–PCL) with 48% PET content. Unlike the traditional three-solvent method proposed by Bushuk and Benoit for copolymers, this method requires only two solvents. For each solvent, the apparent weight average molecular weight (M_w,app) was measured by static LLS. Then M_w,app was used as a constraint to convert the line-width distribution from dynamic LLS into the apparent molecular weight distribution. Finally, the two apparent molecular weight distributions were combined to give both the true molecular weight distribution and the estimated chain composition distribution of the copolymer. We found that the PET–PCL sample with 48% PET is nearly uniform in the chain composition. © 1995 John Wiley & Sons, Inc.     

Low-angle laser light scattering from polystyrene solutions: intensity measurements and photon correlation spectroscopy

Light scattering measurements have been made on polystyrenes with a range of molecular weights in toluene and for one polystyrene with a range of molecular weights in toluene and for one polystyrene in a range of solvents including a theta solvent. Intensity data were used to calculate second virial coefficients and molecular weights, whilst photon correlation spectroscopy was used to calculate diffusion coefficients. All measurements were made at 30°C and at a scattering angle of ca.4°. The data were used to examine current theories of polymer diffusion and the relation between hydrodynamic radius (R_H) and radius of gyrations ($\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$). The results support accepted theories of polymer diffusion, but suggest that the relation between R_H and $\text{〈s}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ requires further analysis.     

Influence of structural parameters on the degradation of ultrahigh‐molecular‐weight vinyl‐type network‐polymer precursors during elution through size exclusion chromatography columns

Network‐polymer precursors obtained in various crosslinking monovinyl/divinyl copolymerization systems, including benzyl methacrylate/1,6‐hexanediol dimethacrylate, benzyl acrylate (BzA)/1,6‐hexanediol diacrylate (HDDA), and vinyl benzoate/divinyl adipate, were subjected to degradation during elution through size exclusion chromatography (SEC) columns, although the copolymerizations were conducted under specified conditions where the factors for the greatly delayed gelation from the Flory–Stockmayer gelation theory were reduced. The most remarkable degradation was observed for the BzA/HDDA copolymerization, which provided prepolymers with the most flexible backbone chains. Thus, the BzA/HDDA precopolymers were chosen, and their degradation behavior during elution through SEC columns was explored in detail as one of the representatives of vinyl‐type network‐polymer precursors. The results were correlated with the structural parameters of network‐polymer precursors, including primary polymer chain length, branched structure, and multiple crosslink or network structure. The degradation became more remarkable with decreased primary polymer chain length, that is, the increment of branching, whereas reduced degradation was observed with the incorporation of loop and network structures into the prepolymer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 577–582, 2003     

肺炎链球菌荚膜多糖分子大小及分子量分析方法的比较

目的 3种方法分析10个血清型肺炎链球菌荚膜多糖(pneumococcal capsular polysaccharides,Pn Ps)样品的分子大小及分子量,并对这3种方法进行比较。方法采用Sepharose CL-4B凝胶排阻层析(SEC)技术检测1型、2型、4型、8型、9N型、12F型、14型、18C型、19A型和23F型Pn Ps各2~3批次样品在色谱柱中的分配系数(KD)和样品组分特征;采用高效凝胶排阻色谱-示差折光检测器(high performance size-exclusion chromatography with refractive index,HPSEC-RI)法建立Pullulan标准品分子量标准曲线,计算各Pn Ps样品的重均分子量(weight-average molecular weight,Mw);采用高效凝胶排阻色谱-多角度激光光散射仪/示差折光检测器联用技术(high performance size-exclu-sion chromatography with multi-angle laser light scattering and refractive index,HPSEC-MALLS/RI)检测各Pn Ps样品的Mw、数均分子量(number-average molecular weight,Mn)、多分散水平(Mw/Mn)及均方根旋转半径(root mean square ratio of gyration,Rg);对HPSEC-RI法和HPSEC-MALLS/RI法检测Pullulan分子量标准品的结果进行比较。结果 SEC技术不同化学方法检测的同批次Pn Ps样品的KD值十分接近,且主峰形态也比较近似,个别批次Pn Ps不同化学方法获得的峰形有差别。经HPSEC-RI检测Pullulan分子量标准品获得的回归方程为y=-0.278 x+10.13,r2=0.998,各Pn Ps样品的分子量为1.812×105~1.246×106。HPSEC-MALLS/RI联用技术检测的各批Pn Ps样品的Mw分布于9.898×105~1.471×105,Rg为84.9~25.4 nm,同一血清型不同批次样品Rg间的大小关系与其Mw间的大小关系具有较好一致性。结论结合多种方法检测多糖样品的分子大小和分子量,可更客观、全面地了解Pn Ps分子的各种性质。     

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.     

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.     

凝胶色谱法在聚丙烯分子量及分子量分布测定中的应用

根据聚丙烯在凝胶色谱柱上的淋洗特点,确定了测定其分子量及分子量分布试验条件;采用示差和黏度双检测凝胶色谱系统,利用普适校正方法,不需要Mark常数K、α值,可直接测定聚丙烯分子量分布并给出分子量分布曲线;采用统计方法计算数均分子量、重均分子量、黏均分子量,可以为课题研究提供一定的依据和指导。