Characteristics of linear/branched polyethylene reactor blends synthesized by metallocene/late transitional metal hybrid catalysts

摘要

Nickel diimine late transition metal (LTM) and Cp2TiCl2 metallocene catalysts were supported on the TIBA-modified MgCl2 center dot nEtOH adduct, separately and concurrently, at different ratios, to yield hybrid catalysts, where the catalytic precursors were activated in the ethylene polymerization with TEA as the cocatalyst. Polymerization activities revealed that supported LTM catalysts show very high levels of activity, in an adverse trend with polymerization temperature ranging from 30 to 70 A degrees C, in opposition to the activity of metallocene component. Consequently, the proportion of corresponding polymer fractions were tuned by changing reaction temperature as well as catalyst composition. Study of thermal properties confirmed that LTM component is responsible for production of less crystallizable branched chains, while metallocene fraction makes highly crystallizable linear chains. All samples showed noticeable thermorheological complexity due to coexistence of linear and branched microstructures. Interestingly, it was found that increase in metallocene fraction of the hybrid catalyst stalls the terminal relaxation of the produced polymers and increases the entanglement density by decreasing the extent of branching. Study of dynamic mechanical properties revealed that the intensity of beta transition could be correlated with the branching level and catalyst composition accordingly.