Number‐average molecular weight by size exclusion chromatography

Abstract

SYNOPSISIt is now theoretically possible to obtain absolute accurate values of number-average molecular weight of complex polymers (e.g., branched polymers or copolymers) using size exclusion chromatography (SEC) with only a detector that measures the difference between the eluting polymer solution viscosity and the viscosity of the pure mobile phase ( a differential viscometer [ DV] detector). However, both precision and accuracy of these "DV Mn" values are of concern. In this work, the precision of NBS 706 polystyrene was found to be two to three times worse for the DV Mn than for the conventionally calculated Mn. Also, regarding accuracy, the DV Mn values were affected by the location of the universal calibration curve along the retention volume axis ( a problem intimately associated with the problem of specifying the correct interdetector volume), the sensitivity of the DV detector to low molecular weights present in the sample, and axial dispersion. Each of these sources of error are examined in turn and two methods of calculating M n values are proposed.

Separation of polystyrenes by means of open tubular capillary chromatography

“…For polymers with MM higher than 180 kDa, experimentally measured peak dispersion was lower than theoretically calculated values. Similar observations were reported also by other researchers [] and a possible reason for that is indication by manufacturer an upper limit of sample polydispersity.…”

Band broadening in size-exclusion chromatography of polydisperse samples

“…Stegeman et al [28] claimed that h PDI is overestimated, probably due to an overestimation of the PDI reported by the manufacturer of the standards. Also other authors [29,32] claim that the real PDI is considerably smaller than the nominal values reported, because SEC, which is used for their estimation, is significantly affected by band-broadening effects.…”

“…PDI < 1.05). Some researchers have suggested that the real PDI values are much smaller than those specified by the suppliers [28,29,32]. Stegeman et al [28] claimed that h PDI is overestimated, probably due to an overestimation of the PDI reported by the manufacturer of the standards.…”

“…In SEC of synthetic polymers band broadening results in distortion of the calculated MMD, as well as in errors in the average molar-mass values obtained [28,29]. To achieve ideal-SEC conditions (Eq.…”

Molar mass distribution by size exclusion chromatography: Comparison of multi‐angle light scattering and universal calibration

“…In contrast to the MALS detection, where the molar mass in a polydisperse elution volume slice is the weight‐average, it has been shown that the VIS detector combined with universal calibration yields the number‐average molar mass . This fact gives a theoretical possibility to estimate the polydispersity in the elution volume slices as already suggested in Ref.…”