Novel zirconocene catalysts for the production of high molecular weight LLDPE in high-temperature polymerization

Abstract

SUMMARY: Ethylene polymerization and ethylene/a-olefin copolymerization were conducted using diphenylmethylidene(cyclopentadienyl)(fluorenyl)zirconium dichloride (Ph 2 C(Cp)(Flu)ZrCl 2 ) as a catalyst activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me 2 PhNH N B(C 6 F 5 ) 4 )/triisobutylaluminium (i-Bu 3 Al) at high temperature and different ethylene pressure. This catalyst produces high molecular weight polyethylene with high activity. The molecular weight of the copolymers hardly decreases with increasing amount of comonomer in the feed. This is attributed to the control of b-H transfer from the propagating chain containing primary inserted comonomer. The occurrence of inner trisubstituted double bonds was confirmed. These bonds are probably formed by dehydrogenation reactions after b-H transfer from the propagating chain followed by ethylene insertion. Therefore, this reaction might play an important role in the production of high molecular weight ethylene/1-hexene copolymers at high temperature. At high ethylene pressure, isomerization reactions from inserted ethylene or primary inserted a-olefin as terminal units, which were observed under low ethylene pressure, can be controlled at low level.

High-temperature ethylene/?-olefin copolymerization with a zirconocene catalyst: Effects of the zirconocene ligand and polymerization conditions on copolymerization behavior

“…We already reported that the change of the substituents in the bridge structure from phenyl to methyl groups resulted in a drastic decrease in the activity and molecular weight of the obtained polyethylene. 6 Actually, Razavi and Atwood 10(b) indicated that the enhancement of the molecular weight in propylene polymerization was caused by the change of the substituents in the bridge structure from methyl to phenyl groups and concluded that the bridge structure of the fluorenyl-based metallocene compounds was important for the production of high molecular weight polyolefins. Table III indicates the results of the ethylene/ 1-hexene copolymerizations with the Ph 2 C(Cp)-(Flu)ZrCl 2 -based catalyst.…”

“…5 However, it was reported that diphenylmethylene(cyclopentadienyl)(fluorenyl)zirconium dichloride [Ph 2 C(Cp)(Flu)ZrCl 2 ] in conjunction with Me 2 PhNH ⅐ B(C 6 F 5 ) 4 /i-Bu 3 Al produced high molecular weight ethylene/␣-olefin copolymers with good activity even at a high polymerization temperature, 6 and the MAO-activated catalyst also indicated high catalyst performance. 7 Furthermore, hafnocenes activated with Me 2 PhNH ⅐ B(C 6 F 5 ) 4 /iBu 3 Al showed high activity and good copolymerization reactivity in ethylene/␣-olefin copolymerizations and produced high molecular weight copolymers.…”

Study on chain end structures of polypropylenes prepared with different symmetrical metallocene catalysts

“…13 C NMR spectra were recorded on a JEOL JNM GSX-400 series spectrometer operated at 100 MHz in pulse Fourier transform mode. Instrument conditions were as follows: pulse angle, 458; pulse repetition, 5.0 s; spectral width, 18,050 Hz; temperature, 118 8C; data points, 32,768.…”