Polyether polyols as GPC calibration standards for determination of molecular weight distribution of polyether polyols

Average molecular weights (M_n, M_w and M_p) are important characteristics of oligomers and polymers, and therefore there is a need to have a precise and reliable determination method. A gel permeation chromatography (GPC) coupled with a single refractive index detector was used to determine the molecular weight distributions of commercial polyether polyols calibrated against a series of polyether polyols with known molecular weights and low polydispersity. Results of these GPC analyses were compared to the ones calibrated against the commercially available polystyrene (PS) standards. The number‐average molecular weights (M_n) obtained with GPC using polyether polyols calibration were closer to the theoretical values than the M_n obtained using PS as calibration standards. Hence, these GPC analyses using polyether polyols as calibration standards can provide reliable determination of molecular weight distribution of polyether polyols and can be potentially applied to natural oil‐based polyols, including palm oil‐based polyols. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42698.     

Estimation of molecular weight distribution of poly(vinylpyrrolidone) from diaphragm-cell diffusion measurements

Viscometry, gel permeation chromatography (GPC) and diffusion measurements on three samples of poly(vinylpyrrolidone) (PVP) were made. The diffusion measurements were carried out by means of a Stokes cell. An equation with five parameters was derived, linking the difference in PVP amount between the two compartments of the cell to the time of the experiment: three parameters are related to the diffusional behavior of the macromolecules and the other two define the molecular weight distribution (the Tung expression has been chosen). A least-squares procedure allowed us to obtain the five parameters and the calculated weight average molecular weights agree with the ones evaluated by viscometry and GPC. The ratio M _w/M _n (heterogeneity of the polymer) calculated from the parameter z of the Tung expression is very different from the one obtained from GPC.     

Comparaison des méthodes de fractionnement par chromatographie de perméation et par gradient d'elution pour la détermination des répartitions moléculaires des polypropylénes

Molecular weight distributions for polypropylene samples have been determined by a permeation fractionation method (GPC). Porous silica beads were used as a packing material for the columns. The set of columns allows a good separation of the polypropylene macromolecular chains in a range of molecular weights from 5000 to 1.5 × 10⁶, and the thermal and mechanical stabilities of these beads are very good. The calibration has been carried out with fractions of polypropylene of narrow molecular weight distribution prepared by a large-scale column fractionation. The molecular weights M?_w and M?_n and the ratios M?_w/M?_n calculated from the GPC curves show, in general, good agreement with the ones calculated from the column fractionation curves. However, the M?_w/M?_n ratios are always highter in the case of GPC fractionation. This could be due to diffusion phenomena.     

A gel permeation chromatography calibration method for a broad molecular weight distribution polymer

A novel, precise, and simple method is described for developing a GPC calibration curve for a polymer where only broad molecular weight distribution samples are available. The method demands a GPC calibration curve for another polymer (e.g., polystyrene) and measurement of the intrinsic viscosity and an average molecular weight for each of several samples of the broad molecular weight distribution polymer in addition to GPC measurements on those samples. Results of applying the procedure to poly(n-lauryl methacrylate) are presented.     

Gel permeation chromatography of ethylene–propylene copolymerization products

A simple method to calculate average molecular weights and D (≡M _w/M _n) value from the GPC chromatogram of copolymerization products, especially for ethylene–propylene copolymerization products, was investigated by simulation technique. The method is based on the use of the calibration curve determined by the average ethylene content of the products. In addition to this method, the calibration curve prepared for polypropylene was also applied to determined the D value. Average molecular weights and D values were determined, with small errors, for narrow distribution samples with respect to molecular weight and chemical composition.     

Evaluation of GPC methods for estimation of Mark–Houwink–Sakurada constants

Constants for the Mark–Houwink–Sakurada relation can be established in principle from GPC measurements on broad distribution polymers. The method requires use of two samples with different intrinsic viscosities or a single polymer for which [η] and M ⁿ M ^w are known. The [η]–M ^w combination is not reliable because M ^v and M ^w are often very similar in magnitude. The [η]M _n method is likewise not recommended because of the influence of skewing and axial dispersion effects on the GPC measurement of M _n. The simplest and safest way to use GPC data to estimate the MHS constants involves the measurement of GPC chromatograms of two polymer samples with different intrinsic viscosities. The method is not confined to the solvent used as the GPC eluant. The MHS constants derived from GPC appear to reflect the molecular weight range of the calibration samples and may not be as widely applicable as those from the more tedious classical methods which employ a series of fractionated samples.     

The Gel Permeation Chromatography of Asphalt and the Characterization of Its Fractions in Terms of Molecular and Unit Sheet Weights

Abstract

Asphalt obtained from a refinery in Montreal was dissolved in toluene then fractionated in a preparative gel permeation chromatograph (prep.-GPC). Twenty-three fractions differing widely in molecular weights were collected and characterized by analytical GPC, viscometry, vapor pressure osmometry (VPO), element analyses, infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR). Similar studies were also carried out, for comparison purposes, on aliphatic and aromatic hydrocarbons to elucidate structure information on the different asphalt fractions.

The GPC chromatograms of the fractions generally revealed narrow distributions indicating that their separation into different component groups has been reasonably well achieved. The number-average molecular weights [mbar]n of the fractions, as computed from their GPC chromatograms making use of the calibration curve prepared with polystyrene, polyoxypropylene glycol, and polyoxyethylene glycol, did not correspond to those obtained by the VPO technique. To overcome the problem, an alternate approach was developed whereby a number of calibration curves were tested for the asphalt fractions, and the one which yielded the [mbar]n values closest to those found by VPO method was     

Molecular Weight Distribution of (Semi-) Commercial Lignin Derivatives

Absolute molecular weights of several commercially and semi-commercially available lignins were determined by gel permeation chromatography (GPC with a differential viscosity detector (DV). Solubility in THF was assured by acetylation. Polystyrene molecular weight standards were used for establishing a universal calibration curve. The lignins included those from hardwood, softwood, and sugar cane bagasse; and these were isolated by the kraft or organosolv pulping process, or by steam explosion/autohydrolysis. All lignins exhibited more or less uniform distributions with weight average molecular weights (M_w) between 3, 000 and 20, 000; with polydispersities (M_w/M_n)between 2 and 12; with Mark-Houwink-Sakurada exponential factors (α) between 0.17 and 0.35; and with intrinsic viscosities between 0.037 and 0.08 dLg^?1. A significant relationship between M_w/M_n and M_w was discovered that had a correlation factor of 0.92. This relationship has the form of M_w/M_n = 0.45 (M_w 10^?3 + 0.85.     

GPC determination of molecular weights for EPM,EPDM, and polybutadienes

Molecular weights from GPC curves are determined for EPM, EPDM, and some polybutadienes. The determinations make use of a Benoit factor, B, which is defined and tabulated for the polymers studied. The use of this factor provides a convenient method of employing the Benoit hypothesis. The M _n from the GPC curves are compared with osmotic molecular weights to provide additional confirmation of the Benoit hypothesis. The M _v from the GPC curves are used with intrinsic viscosity data to establish [η]–versus–M relations.     

Aspects of vapor pressure osmometry

Three aspects of vapor pressure osmometry were examined: drop size, solute volatility, and the constancy of the calibration factor. It was shown that there is a drop size effect which is dependent on the solute concentration. Solutes having vapor pressures as low as 0.3 mm Hg under the operating conditions were found to give unsatisfactory results. The calibration factor was determined using eight compounds in the molecular weight range of 128 to 883 in chloroform, toluene, and methyl ethyl ketone at several temperatures; a small but significant dependence of the calibration factor on molecular weight was demonstrated. The results fitted, with a high degree of accuracy, the relation log M?_n = a + b log (ΔV/C)_{C = 0}, where a and b are constants for a given solvent/temperature combination. However, measurements with standard polystyrene samples, using extrapolations of this relationship to higher molecular weights, revealed considerable discrepancies in results for the one compound under different solvent/temperature combinations.     

Characterization of poly[di(carboxylatophenoxy)-phosphazene] by an aqueous gel permeation chromatography

A water-soluble phosphazene polyelectrolyte, poly[di(carboxylatophenoxy)phosphazene] (PCPP), was characterized using aqueous gel-permeation chromatography (GPC) with concentration (UV and RI) and molecular weight sensitive (multiangle laser light-scattering) detectors. Agreement was observed between the weight-average molecular weights determined by GPC with a light-scattering detector, conventional GPC using fractionated narrow PCPP standards, and also by static light-scattering measurements. The effect of chromatography conditions, such as ionic strength of the mobile phase, column resolution, and injection volume was investigated. Mark–Houwink constants of PCPP in aqueous solution (phosphate buffer, pH 7.4, 0.42MNaCl) were determined. The validity of the universal calibration curve and the occurrence of a secondary nonexclusion mechanism of separation in aqueous GPC of phosphazene polyelectrolytes are discussed. © 1996 John Wiley & Sons, Inc.     

High-temperature coupling of high-speed GPC with continuous viscometry. I. Long-chain branching in polyethylene

The coupling of a high-temperature liquid chromatograph (Waters 150C) with a home-made continuous capillary viscometer is described. This detector is the only one suitable for high-speed GPC when the small volume of the mobile phase prohibits the coupling with a classical viscometer. The pressure drop of the GPC effluent through the capillary is continuously measured along with the refractive index change. This dual detection leads to the determination of the intrinsic viscosity as a function of the elution volume, thus allowing a precise use of Benoit's universal calibration. The accuracy of our system is demonstrated in the case of the characterization of linear and branched polyethylene samples. The results concerning the average molecular weights as well as the branching factors (structure parameter g′ and long-chain branching frequencyλ) are in close agreement with those obtained by the classical way (coupling traditional GPC and discontinuous viscometry). It is well known that an estimate of the λ coefficient is extremely dependent on several hypotheses. However, for a set of commercial low-density polyethylenes, we obtained λ values about 0.5 × 10_?4, with no marked change along the molecular weight range.     

Randomly branched styrene/divinylbenzene copolymers. I. Preparation,molecular weight characterization,and GPC analysis

A series of randomly branched copolymers of styrene and divinylbenzene were prepared using a benzoyl peroxide-initiated free-radical bulk polymerization at 78°C. DVB contents were varied from 0.01% to 2%. Two samples were polymerized with 0.4% DVB to different conversions: series 9A at 6% conversion and series 9B at 15% conversion (just short of the gelation point). Both samples were fractionated and the fractions characterized by ultracentrifugation, light scattering, osmometry, viscometry, and gel permeation chromatography. The data indicated that the fractions were not of narrow MWD and that the breadth of the MWD of the fractions from series 9B were greater than those of 9A. GPC calibration curves of M, [η], and M [η] were generated for both 9A and 9B fractions by employing curve-fitting techniques to the GPC data. For all of the fractions 9B, the molecular weight calibration provided accurate values of M?_z, M?_w, and M?_n, suggesting that no serious peak spreading had occurred in the GPC experiments. The universal calibration parameter M[η] for the 9A fractions agreed with that of linear polystyrene, while that of the high-conversion series 9B did not. It will be shown in a later paper that series 9B is highly branched, while 9A is lightly branched. Consequently, it is recommended that any GPC analysis of branching units make an allowance for the deviation of highly branched polymers from the linear M[η] calibration curve.     

Molecular Weight Distribution of Low Molecular Weight Polyols Derived from Fatty Acid Methyl Esters

A series of commercial polyether polyols with well-defined molecular weights (MW) was used along with propylene glycol and dipropylene glycol as gel permeation chromatography (GPC) calibration standards to determine the MW and oligomeric composition of the synthesized low MW fatty acid methyl ester (FAME) polyols, having an MW of lower than 600 Da. This GPC analysis was compared to the one calibrated against the commercially-available polystyrene (PS) standards and to the number-average molecular weight (M _n) obtained via vapor pressure osmometry (VPO) technique. The MW of FAME polyols obtained with GPC calibrated against polyether polyols were closer to the M _n values obtained via VPO than the MW obtained via GPC calibrated against PS standards. Using the reliable GPC calibration, the MW distribution and the hydroxyl functionality of FAME polyols were determined with greater confidence.     

Number‐average molecular weight of branched polymers from SEC with viscosity detection and universal calibration

BACKGROUND: Number‐average molecular weight, M?_n, is an important characteristic of synthetic polymers. One of the very few promising methods for its determination is size‐exclusion chromatography (SEC) using on‐line viscometric detection and assuming the validity of the universal calibration concept. RESULTS: We have examined the applicability of this approach to the characterization of statistically branched polymers using 22 copolymers of styrene and divinylbenzene as well as 3 homopolymers of divinylbenzene with various degrees of branching. SEC with three on‐line detectors, i.e. concentration, light scattering and viscosity, enables us to evaluate experimental data by various computational procedures yielding M?_n and weight‐average molecular weight, M?_w. Analysis of the results has shown that the universal calibration theorem has limited validity, apparently due to the dependence of the Flory viscosity function on the molecular shape, the molecular weight distribution and the expansion of molecules. CONCLUSION: For complex polymers, the universal calibration, i.e. the dependence of the product of intrinsic viscosity and molecular weight, [η]M, on elution volume, can differ in values of [η]M from those obtained for narrow molecular weight standards by 10–15%. The method studied is helpful for the determination of M?_n of polymers, in particular of those with very broad molecular weight distribution, such as statistically highly branched polymers. Copyright © 2008 Society of Chemical Industry     

Molecular Weight Determination of Palm Olein Polyols by Gel Permeation Chromatography Using Polyether Polyols Calibration

Natural oil polyols have been intensively developed and successfully used for the production of various polymers, notably polyurethanes. The need to access the average molecular weight (MW) and the MW distribution (MWD) has led to the efforts to have a precise and reliable determination method. A series of commercial polyether polyols, with well‐defined MW, was used as a gel permeation chromatography (GPC) calibration standard to determine the MW of palm olein polyols. This GPC analysis was compared to the one calibrated against the commercially available polystyrene (PS) standards and to the number‐average molecular weight (M_n) obtained via vapor pressure osmometry (VPO) technique. For example, the M_n obtained for palm olein polyol E‐135 calibrated against polyether polyols was 2,537 Da, which was closer to the M_n via VPO (1,618 Da), than the M_n obtained using PS as calibration standards (3,836 Da). Hence, this GPC analysis using polyether polyols as calibration standards can offer reassured determination of MWD of palm olein polyols.     

Procedure for evaluation of the Mark–Houwink constants

An iterative procedure for evaluation of the Mark–Houwink constants, using the GPC universal calibration principle and the extended [η]–M relationship, is described. The procedure is recommended for newly prepared polymers of unknown average molecular weights. An example is given for bisphenol C-2 polycarbonate.     

Bimodal polyethylene promoted by novel nickel complex

A novel nickel complex, bis[2‐methyl‐2,4‐bis(2′‐pyridyl)‐1H‐1,5‐benzodiazepine]nickel dichloride, displayed good activity for oligomerization and polymerization of ethylene with the assistance of a co‐catalyst, methylaluminoxane (MAO). The oligomers were mainly olefins from C₄ to C₁₀, while the highly branched polyethylene (PE) had molecular weights (M_w) in the range 19 000–34 000. Bimodal distributions of the PE were clearly observed by both DSC and GPC measurements, while the spherulitic structure of the PE was shown in the morphology. Copyright © 2004 Society of Chemical Industry     

Gel permeation chromatography in the study of the molecular weight distribution of the copolymer vinyl chloride–vinyl acetate. II. Influence of copolymer chemical composition

A set of statistical vinyl chloride–vinyl acetate copolymers of various vinyl acetate content was prepared. The samples were fractionated by preparative gel permeation chromatography (GPC), and the fractions were characterized by analytical GPC, light scattering, and viscometry. The original samples were characterized also by osmometry and chemical analysis. The molecular parameters calculated from GPC analysis using the universal calibration were correlated with those of light scattering measurements and viscometry. It was found that in the range of chemical compositions and molecular weights studied, the chemical composition does not significantly influence the results of GPC analysis.     

Universal calibration assessment in aqueous gel permeation chromatography

It was the objective of this paper to assess the applicability of the universal calibration method to aqueous GPC/SEC with nonionic and anionic polymers using the Viscotek differential viscosity detector. Three water-soluble polymers—polyacrylic acid, dextran, and polyethylene oxide—were chromatographed using four Ultrahydrogel^TM columns with 0.3 M NaCl and 0.1M KH₂PO₄ as the mobile phase adjusted to pH 7. Three distinct calibration curves were obtained. Upon addition of 10% methanol, a reasonably good universal calibration curve was obtained. However, quantitative analysis of the data exhibited about 5% deviation in average M_w and M_n for sodium polyacrylate as calculated from the single curve as opposed to about 40% when calculated from the composite curve. The applicability of three theoretical models for the universal calibration method was assessed, and a recommendation was made for future work. © 1993 John Wiley & Sons, Inc.