Field-Flow Fractionation

Abstract

Size exclusion chromatography separates polyolefins according to hydrodynamic size in solution and it is assumed that one hydrodynamic size corresponds strictly to one molar mass. This, however, is not always the case as has been shown, e.g. for high molar mass branched polymers. For such materials, co-elution of linear and branched molecules having different molar masses has been observed. On the other hand, samples with very high molar masses cause problems in SEC because the largest molecules are frequently shear degraded by the pores and frits of the columns, resulting in molar masses that are lower compared to those of the injected sample. Most of the above problems can be avoided when channel-based fractionation methods are used. This chapter presents some latest results on polyolefin analysis by field-flow fractionation. The fundamentals of the technique are discussed and a number of experimental approaches are given.