Summary: New crystallization procedures have been developed for the analysis of the chemical composition distribution in polyolefins by pumping a small flow of solvent during the crystallization cycle. One of the new techniques, crystallization elution fractionation (CEF) combines the separation power of TREF and CRYSTAF and has been shown to provide very fast analysis of the composition distribution.

Summary Since the introduction of high temperature interaction chromatography for the analysis of polyolefins the technique has demanded a particular interest in the analysis of elastomers where crystallization techniques will meet a limitation given the low crystallinity of these polymers. In this paper the introduction of non carbon adsorption supports such as molybdenum sulfide, boron nitride and tungsten sulfide with equivalent separation to graphitized carbon packing in TGIC analysis of polyolefins is presented. A mechanism for the separation of polyolefins by adsorption chromatography on layered substrates is proposed. The influence of solvent polarity in interaction chromatography is discussed.

Crystallization Elution Fractionation has been optimized to improve resolution power and reduce co-crystallization. Most important step to be optimized is the first separation cycle of Dynamic Crystallization which can be investigated with the help of Crystallization Analysis Fractionation experiments. A new approach to reduce co-crystallization and improve resolution is presented by applying successive cooling and heating cycles in a long column. The new process known as Multiple Crystallization Elution Fractionation adds extended separation at each cooling and heating cycles.

The fractionation of industrial polypropylene resins by crystallization or adsorption is a challenging task due to the existence of stereoregularity and the fact that homopolymer and propylene‐rich copolymers are semicrystalline, as is the case with polyethylene homopolymer, which is usually present in complex polypropylene resins. The separation mechanisms involved in crystallization and adsorption techniques are investigated. Crystallization techniques and adsorption chromatography on graphitized carbon using a temperature gradient separate the full range of propylene ethylene copolymers following a U‐shaped curve and cannot provide unequivocal compositional results. The addition of an infrared detector to measure the level of branches at each elution temperature provides a new dimension that better defines the separated components. A step further in separation is using cross‐fractionation chromatography (composition followed by molar‐mass separation), which makes use of all the mechanisms investigated to provide the most‐extended separation of complex high‐impact polypropylene resins.

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