Study of Very Low Temperature Crystallization Process in Ethylene/alpha-Olefin Copolymers

摘要

The crystallization behavior of Ziegler-Natta (ZN) and single site (SS) based ethylene/1-butene and ethylene/1-hexene copolymers and SS copolymer fractionated by composition and molar mass (MM) has been studied by differential scanning calorimetry. it was observed that in addition to the high temperature crystallization peak (HTCP), and for ZN copolymers in addition also to low temperature crystallization peak (LTCP), a very-low temperature crystallization peak (VLTCP) is present at temperatures in between 60-75 degrees C. Peak temperature of VLTCP, T-VLTCP, decreases with increasing comonomer content (C-comon) at fixed MM. If C-comon is kept approximately constant, TVLTCP increases with increasing MM. It turns out that T-VLTCP does not depend on the type of catalyst used. The degree of crystallinity calculated from the VLTCP is independent of the chemical nature of the comonomers present, but slightly changes with C-comon. It also steeply increases with MM and levels off at MM around 50 kg/mol. it was found that the crystallinity as related to the area of the VLTCP is catalyst type dependent, and is higher for the SS catalyst used compared to the ZN catalyst.