Handbook of Size Exclusion Chromatography and Related ...

Table 2 Measurement of Branching by SEC-Viscometry: Selected Applications
Macromolecule References
Polystyrene 34
Polyvinyl acetate 34,45,71
Polyethylene 72–75
Acrylic polymers 69,70,76
Polybutadiene 77,78
4.1.5 Biopolymer Characterization
In our laboratory,SEC-viscometry has been used to estimate the aspect ratio of
proteins (79). This ratio, whichdescribes the shape of proteins, is calculated from
the Scheraga–Mandelkern b function (80). To determine this function, the
intrinsic viscosity of the protein must be known accurately.Through the use of
SEC-viscometry, proteins can be separated from interfering conformers and
associated species, and intrinsic viscosities can be determined accurately.
4.2 Light Scattering
4.2.1 Molecular Weight Distribution
SEC-LS is used to measure molecular weight distribution directly as apolymer
elutes from the SEC without universal calibration. For each polymer–solvent
system, the specific refractive index increment dn=dc is required, and for most
instrumentsthesolventrefractiveindexisalsoneeded.Table3listsselectedpapers
describing SEC-LS measurements of synthetic polymers, copolymers, polysaccharides,
cellulosics, and related polymers.
SEC-LShasbeenusedattemperaturesof1458C,forexample,forpolyolefln
analysis. It has also been used with aqueous mobile phases. In the latter case
particulatecontaminationofthemobilephaseisaseriousproblem,andthesolvent
requires careful filtration before use.
Aggregation has been studied by SEC-LS (see later) as well as the
polyelectrolyteeffect. Schornetal.(93) usedSEC-LS toillustrate howelectrolyte
was required to suppress the polyelectrolyte effect for nylon 6in hexafluoroisopropanol.
Without the electrolyte, bimodal peaks were observed by
conventional SEC.
4.2.2 Copolymer Molecular Weight Distribution
The analysis of copolymers by SEC-LS is complicated by the compositional
heterogeneity of the sample in two ways: first is in the determination of the
© 2004 by Marcel Dekker, Inc.