Transition metal compound and catalyst composition comprising the same
The present disclosure relates to a novel transition metal compound represented by the following Chemical Formula 1, which exhibits excellent catalytic activity for propylene polymerization, and is useful in the preparation of a polypropylene having a narrow molecular weight distribution and a high melting point, a catalyst composition including the same, and a method for preparing a polypropylene using the same, wherein M, X 1 , X 2 , and R 1 to R 8 are described herein.
1. A transition metal compound represented by Chemical Formula 1:
in Chemical Formula 1,
M is a Group 4 transition metal,
X 1 and X 2 are the same as or different from each other, and are each independently halogen,
R 1 and R 2 are the same as or different from each other, and are each independently C 1-20 alkyl, C 2-20 alkenyl, C 2-20 alkoxyalkyl, C 6-20 aryl, C 7-40 alkylaryl, or C 7-40 arylalkyl,
R 3 to R 6 are the same as or different from each other, and are each independently C 1-20 alkyl,
R 7 is a substituted or unsubstituted C 6-20 aryl, and
R 8 is C 1-20 alkyl.
2. The transition metal compound of claim 1 , wherein M is zirconium (Zr) or hafnium (Hf).
3. The transition metal compound of claim 1 , wherein R 1 and R 2 are each independently C 1-8 linear or branched alkyl, C 2-12 linear or branched alkoxyalkyl, or C 6-12 aryl.
4. The transition metal compound of claim 1 , wherein R 3 to R 6 are each independently C 1-6 linear or branched alkyl.
5. The transition metal compound of claim 1 , wherein R 7 is phenyl, phenyl substituted with C 1-6 linear or branched alkyl, naphthyl, or naphthyl substituted with C 1-6 linear or branched alkyl.
6. The transition metal compound of claim 1 , wherein R 8 is C 1-6 linear or branched alkyl.
7. The transition metal compound of claim 1 , which is represented by Chemical Formula 1-1:
in Chemical Formulae 1-1,
M, X 1 , X 2 , R 1 , R 2 , and R 7 are as defined in Chemical Formula 1.
8. The transition metal compound of claim 1 , which is any one of compounds represented by the following structural formulae:
9. A catalyst composition comprising the transition metal compound of claim 1 .
10. The catalyst composition of claim 9 , comprising the transition metal compound and a support.
11. The catalyst composition of claim 9 , further comprising at least one cocatalyst selected from compounds represented by Chemical Formulae 2 to 4:
[Al(R 21 )—O] m — [Chemical Formula 2]
in Chemical Formula 2,
R 21 are the same as or different from each other, and are each independently halogen, C 1-20 alkyl, or C 1-20 haloalkyl; and
m is an integer of 2 or more;
J(R 31 ) 3 [Chemical Formula 3]
in Chemical Formula 3,
R 31 are the same as or different from each other, and are each independently halogen, C 1-20 alkyl, or C 1-20 haloalkyl; and J is aluminum or boron;
[E-H] + [ZQ 4 ] − [Chemical Formula 4]
in Chemical Formula 4,
E is a neutral or cationic Lewis base;
His a hydrogen atom;
Z is a group 13 element; and
Q are the same as or different from each other, and are each independently C 6-20 aryl or C 1-20 alkyl unsubstituted or substituted with at least one substituent selected from the group consisting of halogen, C 1-20 alkyl, C 1-20 alkoxy, and C 6-20 aryloxy.
12. A method for preparing a polypropylene, comprising a step of polymerizing propylene monomers in the presence of the catalyst composition of claim 9 .
13. The method for preparing a polypropylene of claim 12 , wherein the polymerization step is performed while introducing 750 ppm or less of hydrogen gas based on the propylene monomers.
14. The method for preparing a polypropylene of claim 12 , wherein the polypropylene is a homopolymer.
15. The method for preparing a polypropylene of claim 14 , wherein the polypropylene has a molecular weight distribution (Mw/Mn) of 2.45 or less, a melt index MI 2.16 , measured at 230° C. under a load of 2.16 kg, of 7.5 g/10 min to 45 g/10 min, and a melting point (Tm) of 152.5° C. or more.
16. The method for preparing a polypropylene of claim 14 , wherein the polypropylene has a weight average molecular weight (Mw) of 150000 g/mol or more.