Effect of Substituent on Titanocene/MMAO Catalyst for Ethylene/1-Hexene Copolymerization
Copolymerization of ethylene with 1-hexene was carried out using two ansa-fluorenyl titanium derivative complexes. The substituent effect on the catalytic activity, monomer reactivity ratio and polymer property was investigated. It was found that the presence of t-Bu groups on fluorenyl ring exhibited remarkable catalytic activity and produced polymer with high molecular weight. However, these catalysts produce polymer with narrow molecular weight distribution, indicating the characteristic of single-site metallocene catalyst. Based on C NMR, we can observe that monomer reactivity ratio was affected by catalyst structure. The rH values of complex 2 were lower than that of complex 1 which might be result from the higher steric hindrance leading to a reduction of 1hexene insertion step. Keywords—Constrained geometry catalyst, linear low density polyethylene, copolymerization, reactivity ratio
SUBSTITUENT EFFECTS OF tert-BUTYL GROUPS ON FLUORENYL LIGAND OF [t-BuNSiMe2FLu] ZrMe2
[t-BuNSiMe2(2,7-t-Bu2Flu)]ZrMe2 and [t-BuNSiMe2(3,6-t-Bu2Flu)]ZrMe2 were synthesized, and the solid structure of complex [t-BuNSiMe2(2,7-t-2Flu)]ZrMe2 was elucidated by single crystal X-ray analysis. These complexes were applied for propylene polymerization using dried modified methylaluminoxane as a cocatalyst at 0°C and 20°C in toluene. Both systems did not show activity at 0°C, but they conducted the polymerization at 20°C. The introduction of t-butyl substituents to the fluorenyl ligand improved the activity more than six times regardless of the position of the substituents, and both systems gave low molecular weight polypropylenes (PP) with narrow molecular weight distribution. The introduction of t-butyl substituents also improved the syndiospecificity and [t-BuNSiMe2(3,6-t-Bu2Flu)]ZrMe2 gave highly syndiotactic PP with the syndiotactic pentad of 0.91 and the melting point of 145°C.
Properties of ethylene/1-octene, 1-tetradecene and 1-octadecene copolymers obtained with Cp2ZrCl2/MAO catalyst: effect of composition and comonomer chain length
SummaryCopolymers of ethylene and 1-octene, 1-tetradecene and 1-octadecene were synthetized in order to study the effect of the comonomer chain length and amount on density, melting temperature and heat of fusion. They were also compared with the properties of the copolymers obtained with the heterogeneous titanium catalyst.It could be seen that the density/melting-area of the copolymers obtained with the zirconocene catalyst was much broader than with the titanium catalyst. It could also be seen that with the same comonomer content 1-tetradecene gave lower density of the copolymers than 1-octene. However, no difference were seen between the densities of the copolymers obtained with 1-tetradecene and 1-octadecene.The melting temperature of the copolymers was seen to be the lower the longer the comonomer was. In the area of the high branching amount the linear correlation was not in work. It was also shown that the differences in the heat of fusions could only be seen at high amount of branches (>15 branches/1000C): the longer the comonomer the lower amount of heat was needed to melt the copolymer.