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

Abstract

Nickel diimine late transition metal (LTM) and Cp 2 TiCl 2 metallocene catalysts were supported on the TIBA-modified MgCl 2 ÁnEtOH 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°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 b transition could be correlated with the branching level and catalyst composition accordingly.

Effect of different additives and their mixtures on thermal stability of polyethylene synthesized using iron and titanocene hybrid catalysts

“…AS in the polymerization reactor stopped the degradation by neutralizing the metal in the catalyst, because of its acid scavenging nature which resulted in a higher activity of the AS compared to AO‐1 and AO‐2. However, in the hybrid of catalysts due to the complex interaction between the catalysts, the MgCl 2 support and antioxidant showed different behaviors …”

“…The results suggested that the different antioxidants did not have a notable effect on the thermal properties of polymers when the single catalyst was used in the polymerization reactor, however, when the hybrid of two catalysts (Cat 3) was used in the polymerization reactor, the X c % changed from 43 to 60. This is probably due to difference in the structures of the catalysts used …”

“…According to the catalyst activities listed in Table , it can be deduced that although the antioxidant mixture has synergetic effect on the activity of metallocene catalyst, it has an adverse effect on the iron and hybrid catalysts activities and decreases the catalyst activities to lower than the activity of samples without antioxidants. This could be attributed to the difference between the behaviors of both the catalysts regarding their activities and thermal properties which were studied before …”

“…Therefore, synthesis of linear/branched PE mixture using a hybrid of two catalysts can be attractive . Recently, hybrids of metallocene and LTM catalysts have been taken into considerations …”

Single and binary catalyst systems based on nickel and palladium in polymerization of ethylene

“…One of the main strategies used for the improvement of polyolefin catalysts, which is still being investigated at the laboratory scale, is the use of a combination of different types of catalysts during polymerization. Catalyst alloys, hybrid catalysts and multi‐catalyst systems are commonly used in this respect . In these systems, each of the catalysts produces polymers with different properties, and therefore the final polymer is a blend of two or more kinds of polymers.…”