Selective experimental parameters for preparative TREF of propylene-ethylene random copolymers: Limiting undercooling of PP

Temperature rising elution fractionation (TREF) is a highly valuable and widely used tool for chemical composition separation of semicrystalline polyolefins. However, TREF operational conditions should be carefully selected due to their high impact on separation quality. This is especially true for polypropylene (PP)-based polymers due to their slow crystallizing nature and defect distribution, which can further complicate the fractionation. In order to more fully understand this behavior, a systematic investigation was designed to determine the influence of support and cooling rate on preparative TREF of PP random copolymers. Possible measures to limit undercooling of PP and thus preventing so called co-elution of different microstructures in TREF were demonstrated using glass beads as support during fractionation and cooling rate of 0.02°C/min. Support presence during fractionation acted as a nucleating agent to limit the elution of long isotactic chains in the low temperature fractions. Slow cooling rate along with support presence further improved the separation quality by giving the polymer chains enough time to overcome the undercooling.