Analysis of high molar mass branched polybutadienes by SEC-MALLS and AF4-MALLS
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. © 2012 American Chemical Society.