Analysis of polyolefins and olefin copolymers using crystaf technique: Resolution of crystaf curves

An experimental technique, crystallization analysis fractionation (Crystaf), is used to analyze compositional uniformity of ethylene/alpha-olefin copolymers and isotactic polypropylene. A computerized method for quantifying Crystaf data is developed based on resolution of Crystaf curves into their elemental components, with each component representing a fraction of the polymer with the same degree of chain imperfection. This analysis of Crystaf curves gives three parameters characterizing crystallizable polymer material: (a) the number of compositionally uniform components, (b) properties of each compositionally uniform component (in the case of ethylene/alpha-olefin copolymers, the comonomer content), and (c) the quantity of each component. Crystaf analysis of several ethylene/1-hexene copolymers produced with supported Ti-based Ziegler-Natta catalysts shows the existence of two groups of copolymer components. The first group includes components with low comonomer content, in the Crystaf analysis they precipitate at high temperatures as several relatively sharp peaks. The second group includes components with high comonomer contents; they precipitate at much lower temperatures, as a broad overlapping group of peaks. The peak resolution technique was applied to analysis of ethylene/a-olefin copolymers prepared with a supported catalyst at different temperatures, a copolymer produced with a pseudo-homogenous Ziegler-Natta catalyst, and to isotactic polypropylene.