The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of fractionated ethylene/1-butene copolymer

Abstract

The interrelationships between microstructure and melting, crystallization and thermal degradation behaviors of a commercial Ziegler–Natta (Z–N)-based ethylene/1-butene copolymer were investigated. The copolymer was fractionated based on short chain branch (SCB) content by preparative temperature-rising elution fractionation (P-TREF) method. A broad multipeak chemical composition distribution was obtained for both molecular weight distribution and short chain branch distribution. A difference of about 48 °C in melting temperature (Tm) has been observed for fractions with 50 branches of different SCB contents. A logarithmic relationship was obtained between the methylene sequence length calculated based on proton-1 nuclear magnetic resonance results and the P-TREF elution temperature (ET). A relationship between the SCB content and the inverse of lamellae thickness (Lc) was established. Two linear functionalities were found for Tm versus ET and crystallization temperature (Tc) versus the SCB content. To the best of our knowledge, as a first effort, surprisingly a linear relationship between the temperature at the maximum rate of degradation (Tmax) and the SCB content was acquired, which showed less sensitivity to the SCB content than Tm. Also, it was found that the degradation initiation temperature (T5%) and activation energy (Ea) are increased by the decreasing SCB content. Moreover, it was demonstrated that Hosoda equation is not applicable for different ethylene/α-olefin copolymers based on different catalyst types with dissimilar fractionations and experimental conditions.