Rheology and structure of molten, olefin multiblock copolymers

Several samples of a recently developed olefin multiblock copolymer were studied by means of rheology, differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The synthesis involves a chain shuttling agent (CSA) that switches the growing chain between two catalysts, one that favors the incorporation of an α-olefin comonomer and one that suppresses incorporation. The data were used to determine the effect of octene comonomer content and CSA level on rheological behavior and the occurrence of mesophase separation transition (MST) in the melt. To distinguish between crystallization and MST, we made calorimetry scans and measured the density and rheological properties over a range of temperatures. Small angle X-ray scattering analysis of a sample that had undergone planar extensional flow revealed strong alignment of lamellar mesodomains, which maintained their alignment after annealing. This result confirmed the hypothesis based on rheological evidence that a lamellar mesophase is present in the melt at temperatures well above the melting point.