Tuning the short chain branch distribution of ethylene and 1-hexene copolymers by SiO2-supported silyl chromate catalyst with different Al-alkyl co-catalysts

SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge. In this work, ethylene and 1-hexene copolymers were synthesized using SiO2-supported silyl chromate catalyst combined with triisobutylaluminium (TIBA), triethylaluminium (TEA) and mixed TIBA/TEA at molar ratio 1:1 (TIBA/TEA/1:1) as three different Al-alkyl co-catalysts.The temperature rising elution fractionation (TREF) and successive self-nucleation and annealing (SSA, by DSC) methods were combined to analyze the short chain branch distribution (SCBD) of these ethylene/1-hexene copolymers. The results showed that different types of co-catalyst had a great influence on SCBD of ethylene/1-hexene copolymers. The copolymer produced with TIBA showed better SCBD than the copolymer produced with TEA, and the copolymer produced with TIBA/ TEA/1:1 showed a SCBD in between those with TIBA and TEA.