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

摘要

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 degrees C in melting temperature (T-m) 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 (L-c) was established. Two linear functionalities were found for T-m versus ET and crystallization temperature (T-c) 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 (T-max) and the SCB content was acquired, which showed less sensitivity to the SCB content than T-m. Also, it was found that the degradation initiation temperature (T-5%) and activation energy (E-a) are increased by the decreasing SCB content. Moreover, it was demonstrated that Hosoda equation is not applicable for different ethylene/alpha-olefin copolymers based on different catalyst types with dissimilar fractionations and experimental conditions.