Analysis of High Molar Mass Branched Polybutadienes by SEC-MALLS and AF4-MALLS

Abstract

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.

Field Flow Fractionation for the Size, Molar Mass, and Gel Content Analysis of Emulsion Polymers for Water‐Based Coatings

“…It has to be noted that the MALLS signal intensity is low in the region after 29 min which could also result in inaccurate molar mass readings. In previous work, multiple fractionations of the late eluting SEC fractions of branched polyolefins and polybutadienes have been performed and were characterized by AF4 . The authors proved that high molar mass species are present after fractionation by SEC followed by reinjection into AF4.…”

“…A similar study has been conducted using AF4‐MALLS‐UV‐RI coupled off‐line to NMR. Polyisoprene homopolymer was separated from the polystyrene–polyisoprene block copolymer, respectively …”

“…In a previous study, gel containing polybutadienes were analyzed by AF4 and it was reported that the diffusion coefficients of gel containing species do not differ comprehensively from the ultrahigh molar mass species . For the current kinetic samples this phenomenon will imply that the coil density of the gel species will increase as the reaction proceeds without a significant change in the diffusion coefficient.…”

“…In previous work, multiple fractionations of the late eluting SEC fractions of branched polyolefi ns and polybutadienes have been performed and were characterized by AF4. [ 10,28 ] The authors proved that high molar mass species are present after fractionation by SEC followed by reinjection into AF4. Furthermore, the polybutadiene samples showed that two different shapes of branched species were present in the late eluting fractions by observing two different slopes in the conformation plot R g versus molar mass.…”

Using light scattering to evaluate the separation of polydisperse nanoparticles

“…While polystyrene beads are inherently less polydisperse than a complex natural sample, these mixtures mimic complex samples in that baseline resolution was not possible by adjusting the V x and V x gradient alone within the designated elution window. Polystyrene beads (particles) are often used as model systems for AF 4 size calibration and system optimization prior to analysis with real, complex samples [2, 3, 21, 22] and polystyrene standards separated with AF 4 have been shown to have very good sample recoveries [21]. The application of this metric to more complex samples, like environmental samples, would require additional characterization and recovery analysis to account for non-ideal behavior, such as the potential risk of particle-membrane and particle-particle interactions, to identify any sample changes that may occur with separation parameter modification.…”