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This review summarizes developments and applications of flow and thermal field-flow fractionation (FFF) in the areas of macromolecules and supramolecular assemblies. In the past 10 years, the use of these FFF techniques has extended beyond determining diffusion coefficients, hydrodynamic diameters, and molecular weights of standards. Complex samples as diverse as polysaccharides, prion particles, and block copolymers have been characterized and processes such as aggregation, stability, and infectivity have been monitored. The open channel design used in FFF makes it a gentle separation technique for high- and ultrahigh-molecular weight macromolecules, aggregates, and self-assembled complexes. Coupling FFF with other techniques such as multiangle light scattering and MS provides additional invaluable information about conformation, branching, and identity.

High temperature liquid chromatography (HT-LC) and temperature gradient interaction chromatography (TGIC) using a graphite substrate were recently invented to characterize polyolefin microstructures and composition distributions. Their separation mechanisms have been explored by using a series of random copolymers. In addition, the separation mechanism of TGIC for random copolymers was also studied with a high temperature NMR cryoprobe. The proposed separation mechanism for a random copolymer is that the separation is likely based on comonomer content, in other words, the number-averaged ethylene sequence length. Further understanding of HT-LC separation mechanism with polyethylene–octene block copolymers is beneficial in order to extend the use of HT-LC and TGIC to a wider variety of polyolefin materials, and to better characterize more challenging microstructures of new materials. With the high temperature NMR cryoprobe technology, it is possible to perform 13C NMR of polyolefins with a few milligrams of sample. This paper summarizes the NMR study of the materials obtained from preparative scale HT-LC on polyethylene–octene block copolymer with a high temperature NMR cryoprobe. The results show unambiguously that the HT-LC separation of polyethylene–octene block copolymer is mainly based on the interaction between hard block and the stationary phase, and the strength of the interaction is correlated to the total length of the hard block in the block copolymer.