The effects of flow rate and column combination on the separation efficiency in multicolumn gel permeation chromatography

Abstract

SynopsisIJsing general-purpose multicolumn sets, it was found that separations could be increased by increasing analysis time, either by decreasing flow rate or increasing column length. Several examples are shown illustrating the influence of these system variables. The generation of linear calibration curves over extended molecular weight ranges is discussed. In particular, the desirability of using high molecular weight standards to extend the Calibration curve and eliminate extrapolation of the curve is shown. Not using all available gel porosities, i.e., gapped column sets, is shown to be detrimental to the resolution of molecular species. It was found that with the use of sufficiently long column lengths and low flow rates, accurate molecular weights of both narrow and broad molecular weight distribution samples are directly calculable from the chromatogram without the need for peak spreading corrections.

Star-Branched Polymers. 2. The Reaction of Dienyllithium Chains with the Isomers of Divinylbenzene

“…As soon as two or more divinylbenzene residues become attached to a polybutadiene chain, reaction between the vinylbenzyl ion and an in-chain neutral residue becomes possible (reaction 5). This reaction is, accordingly, in more ViCHCHpCHU effective competition with the formation of the vinylbenzyl ion in run 27 than in 28, with the consequent reduced net rate of formation of vinylbenzyl ion. The occurrence of such an "incestuous" process within a dimeric associate is, of course, equally probable when the original parent is poly(isoprenyl)lithium.…”

Molecular weight characterization of polybutadiene rubber with high molecular weight and broad molecular weight distribution

“…Following characterization by membrane osmometry, light scattering, and GPC, these two samples were found to have the following molecular weights: (1) PBd-N-2, Mu, = 381,000 f 31,000; M, = 85,100 f 3,300; (2) PBd-D-1, Mw = 327,000 f 4,000; M , = 134,000 f 3,000. Precision for PBd-N-2 was an average M% relative standard deviation (RSD) in Mw and f 4 % RSD in M,, found from three GPCs on different solvents.…”

“…As a preliminary study, PBd-N-1 was characterized and a comparison was made of the results from light scattering, membrane osmometry, and GPC. (1) The data from the light scattering photometer resulted in a rectilinear Zimm plot and, when coupled with dnldc determined with the differential refractometer, provided an unambiguous value of No interferences such as depolarization of the scattered light were o b~e r v e d .~ A 4% error in dnldc, coupled with the error in the scattering data, resulted in an error of about f10% for aw. (2) mn was determined by membrane osmometry using a Mechrolab 502 membrane osmometer and an S&S-08 membrane.4 The square root plot gave a straight-line relationship to the data.…”

Calibration

“…A popular empirical guideline for linear calibration recommends the use of columns of each pore size that have finite fractionation capacity in the molar mass range of interest [31,32]. The calibration in Figure 8.13 illustrates this empirical approach of connecting columns with different pore sizes to obtain fractionation over a wide molar mass range.…”