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

Abstract

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.

A second‐generation ionic liquid matrix‐assisted laser desorption/ionization matrix for effective mass spectrometric analysis of biodegradable polymers

“…This solution was used for matrix‐sample preparation. The molecular weights of some polymers tested are not known (Table 1) and these were obtained by SEC, meaning they may not be accurate 30–32. Consequently, molar solutions could not be prepared.…”

“…However, characterization of these polymers often is difficult. Size‐exclusion chromatography (SEC) will give a mass range but it can over‐ or underestimate the molecular weight because the standards used are not structurally similar to the unknown polymer 30–32. MALDI‐MS of biodegradable polymers has been studied extensively 33–44.…”

Viscosimetric detection in size‐exclusion chromatography (SEC/GPC): The Goldwasser method and beyond

“…Previous tests of the determination of M n of branched polystyrenes by Netopilik et al have been successful [30]. The method is now tested for the determination of the number hydrodynamic volume distribution.…”

“…The Goldwasser method has however attracted little attention. It was successfully tested on model polymer blends [28], poly(tetramethylene glycol)s [29] and branched polystyrenes [30]. In the polyglycols case, the Goldwasser method however suffered from a lower precision and some bias toward high values of M n compared with SEC with conventional calibration or end-group detection.…”

Can the Branching Exponent Reliably Relate the Branching Indexes?

“…Obtaining the experimental evidence of the relations between the indexes is difficult. The attempts to find ϵ for branched polymers experimentally using size‐exclusion chromatography with multiple detection faces problems, as high scatter of values of ϵ which may be caused by local dispersity which reaches its maximum in high‐molecular weight region for this type of branching but the reported values of g and g ′ are frequently close to each other . In this paper, the relations between g and g ′ are examined on the basis of our computer generated and literature data.…”