Industrial polybutadienes synthesized by Ziegler–Natta
catalysts
may exhibit very high molar masses, significant degrees of branching,
and gel species. Such samples were analyzed by size exclusion chromatography
(SEC) and asymmetric flow field-flow fractionation (AF4). Both fractionation
techniques were coupled to a multiangle laser light scattering (MALLS)
detector as well as a refractive index (RI) detector. The initial
results obtained from SEC measurements completely contradicted the
processing behavior of the materials. SEC seemed not to be suitable
for accurate characterization of these materials. SEC separation was
strongly influenced by coelution of linear (low molar mass) and branched
(high molar mass) macromolecules, shear degradation of the larger
macromolecules, and filtration of the gel fraction. For this reason
the polybutadienes were subsequently analyzed by AF4 in order to compare
the results and identify the limitations of SEC. The results showed
that, as a specialized tool, AF4 can be used for the extended and
more accurate analysis of synthetic rubber materials, especially in
the case of very high molar masses. SEC is not suitable for such samples
because it does not properly address the high molar mass fraction
and the branched macromolecules.
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