On-line viscometry combined with gel permeation chromatography. II. Application to branched polymers

Gel permeation chromatography (GPC) combined with on-line flow time measurements have been applied to the analysis of branching in polymers. Three sets of branched polymers were examined: polybutadienes lightly crosslinked by high energy radiation, a styrene-divinyl benzene copolymer and several of its fractions, and polyvinyl acetates branched by polymer transfer reactions during polymerization. The reduction in intrinsic viscosity due to branching was determined for each GPC fraction of the polybutadiene samples. The branching frequency in these fractions was known from other information, so the results were used to establish a relationship between viscosity ratio G and the theoretical size ratio g. This relationship was then used to calculate the distribution of branching and M _w in the styrene copolymers and the polyvinyl acetates. The results were compared with independent information on these polymers. The agreement was generally good.     

Calibration of gel permeation chromatography system for polycarbonate

A combination of the universal calibration method, with direct calibration with several oligomers of known molecular weight, gave excellent results in the determination of the average molecular weights and molecular weight distribution for bisphenol A type polycarbonate.     

Branching in bisphenol a polycarbonate: Gel permeation chromatography,viscometry and light scattering

Branching in bisphenol A polycarbonate has been investigated by fractionation, gel permeation chromatography, viscometry and light scattering. The samples studied (Makrolon 3000 and 3000L) are branched, Makrolon 3000 more so than Makrolon 3000L. The variation of the branching parameters with molecular weight is suggestive of random branching. Comparison of the molecular weight distribution with that expected for random trifunctional branching suggests an average of about half a branch point per weight-average molecule in Makrolon 3000.     

Simulation of gel permeation chromatography measurement for long chain branched metallocene polyethylene

The research about the polymerization reaction mechanism of long chain branched polymer provides a method to simulate the generation of LCB mPE (long chain branched metallocene polyethylene).^[1-3] In this work, after simulating the generation of one million LCB mPE molecules, we calculate the sizes (i.e. radii of gyration) of molecules in good solvents to obtain the molecular size distributions. Then we simulate the fractionation in GPC (gel permeation chromatography) measurement and the different GPC detector responses to obtain simulated GPC MWDs (molecular weight distributions). The simulated MWDs are compared to the real GPC results provided by the Dow Chemical Company.     

Gel permeation chromatography of branched polyethylene

The effect of long-chain branching must be considered in gel permeation chromatography to evaluate the molecular weight polydispersity of branched polyethylenes. Osmotic molecular weights of fractions of branched polyethylene were correlated with elution volumes; weight-average and number-average molecular weights of a branched polyethylene were determined. Molecular weight changes on crosslinking polyethylene by ionizing radiation are accompanied by branching and cannot be simply interpreted by gel permeation chromatography.     

Determination of theoretical plates in gel permeation chromatography by using polydisperse materials (polymers)

The need for an improved method of expressing performance of GPC columns and operating conditions is discussed. It is shown that theoretical plates can be calculated from chromatograms of high molecular weight materials (polymers) if the curve widths are normalized for polydispersity. The resulting value N, where N = 16d²(v/W)², is a useful measure of the real plate count afforded by the columns to polymers and is useful for comparison purposes. Since N does not provide absolute data on separation, it is better to use formulas for resolution and fractionation when such data are needed.     

Calibration procedure for gel permeation chromatography

A novel procedure is presented for calibrating a gel permeation chromatograph by using broad polymer fractions. The limit in accuracy is set by the accuracy of number-average and weight-average molecular weight measurements and the reproducibility of the chromatograph. In the particular calibration for linear polyethylene described here, low molecular weight fractions were prepared by nitric acid oxidation of annealed single crystals. The calibration is then of particular value in morphological studies of polyethylene. The influence in the calibration of polar endgroups on the polymer, as produced in these oxidized samples is discussed.     

On-line viscometry combined with gel permeation chromatography. I. Instrumental calibration and testing with linear polymers

Gel permeation chromatography (GPC) was combined with flow time measurements on the eluent to provide both the distribution of hydrodynamic volumes and the distribution of intrinsic viscosities in linear polymers. Standard polystyrene samples were used to establish a universal hydrodynamic volume calibration as well as the zone spreading and viscometer transfer line tailing parameters. Viscometry data are particularly helpful in establishing the zone spreading parameters and the calibration curve at very high molecular weights. The results were applied to measurements on samples of linear polybutadiene and polyvinyl acetate. Agreement between values of M _w from GPC with those obtained by light scattering confirmed the universal calibration principle.     

System development for aqueous gel permeation chromatography

To devise an improved gel permeation chromatography system for the analysis of macromolecules, with a strongly alkaline solution as eluent, three Fractogel TSK gels were investigated. Because primary standards are usually unavailable, calibration was achieved by using Benoit's universal procedure and polystyrene sulfonates, polyethylene glycols, and dextrans as secondary calibrants. Continuous monitoring of intrinsic viscosity resulted from coupling a viscodetector with a classical differential refractometer. It was found that column efficiency and fractionation range could be extended well beyond those of previously studied systems on a reasonably short period of analysis.     

Development of gel permeation chromatography for polymer characterization. I. Operational variables

The effects of operational variables on calibration of GPC are reported. Variables examined include (1) temperature and solvent changes, (2) sample concentration, (3) injection time, and (4) flow rate. Each of these variables significantly affected molecular weight averages calculated from GPC data. The causes and methods of minimizing the effects produced by the individual variables are discussed.     

Development of gel permeation chromatography for polymer characterization. II. Universal calibration

GPC appearance volumes have been determined for a series of linear polyethylene, polystyrene, and polybutadiene fractions (M_w/M_n < 1.1) in trichlorobenzene at 130°C. and for the latter two series in tetrahydrofuran at 23°C. A polymer-type independent relationship between appearance volumes and the equivalent hydrodynamic radii of the polymer molecules has been demonstrated. The equivalent hydrodynamic radius is calculated from intrinsic viscosity data. It is proposed that this relationship can be used to construct a universal GPC calibration curve for polymers that assume a spherical conformation in solution. Methods for applying the universal curve to the determination of molecular weight averages and molecular weight distribution are described. In addition, a method is outlined by which the universal calibration curve can be empolyed for determining number-average Mark-Houwink constants from polydisperse samples.     

Flow-rate dependence of gel permeation chromatography

Analysis of polystyrene standards by gel permeation chromatography over a wide range of flow rates revealed two sources of error in volume measurement. These errors arise from solvent evaporation in the siphon chamber and from solvent continuing to flow into the siphon during discharge. Appropriate corrections are discussed, and a vapor feedback loop to eliminate the solvent evaporation error is described. The flow rate dependence of the GPC calibration curve, expressed in the corrected elution volumes, appears different from that reported in the literature. The corrected flow rate dependence of peak elution volumes is in agreement with the expectation of diffusion and exclusion theories.     

Polymer studies by gel permeation chromatography

Samples of polystyrene and poly(methyl methacrylate) have been prepared by bulk polymerization under conditions previously investigated in the literature. The molecular weight distributions were determined for early-conversion samples by gel permeation chromatography, and the experimental distribution curves were compared with calculated curves based on kinetic data. The agreement between the experimental and calculated curves was such as to indicate the utility of gel permeation chromatography in the investigation of polymer reaction kinetics and mechanisms.     

Instrumental broadening in gel permeation chromatography

Summary Instrumental broadening corrections to gel permeation chromatograms have been demonstrated to be of minimal concern when using the newly available high efficiency packing materials. This was demonstrated using -Styragel as packing material on polymer standards with both narrow and broad molecular weight distributions.     

凝胶渗透色谱在高聚物分子量测定中的应用

本文综述了近年来凝胶渗透色谱在油溶性和水溶性高聚物分子量测定中的应用,着重分析测试条件对水溶性样品分子量的影响并归纳了解决的办法。同时,介绍了配备紫外可见和示差折光检测器、示差和光散射检测器后凝胶色谱的应用。此外,还概述了几种常见高聚物分子量的标定和校准方法,以便多种方法相互验证,得到较准确的分子量值。     

Role of diffusion in gel permeation chromatography

A theory is developed that describes the diffusion of solute into the gel particles during a gel permeation chromatographic experiment. The particles are treated as homogeneous spheres of radius a, into which diffusion takes place with diffusion coefficient D_s. The concentration in the mobile phase at any level at any time is supposed to be uniform throughout the cross-section of the column. It is shown that in the usual columns the effect of diffusion in the mobile phase is unimportant. A determinative quantity in the process is the parameter a²/D_st, where t is the time. For large values of a²/D_st an explicit expression for concentration versus time in the mobile phase at the end of the column is derived [eq. (26) and Fig. 1]. It shows a relatively long tail at large efflux volumes V, where the concentration varies at V^?3/2. For arbitrary values of a²/D_st the first three moments of the concentration versus time curve are calculated [eqs. (33)–(37)]. Pronounced skewness of the curve is found unless a²/D_st is small.