Methods for stereoselective coordinative chain transfer polymerization of olefins
The present invention provides a method of producing a polyolefin composition comprising contacting a binuclear metallocene pre-catalyst and a co-catalyst, adding a excess of a metal alkyl, then adding a first olefin monomer. The method allows for the production of polyolefins with a highly stereoregular stereochemical microstructure through living coordination polymerization in which rapid reversible chain transfer between a racemic mixture of a chiral active transition metal propagating center and multiple equivalents of inert main group metal alkyl is competitive with chain-growth propagation at the active center. By virtue of the slower rate of chain-transfer relative to propagation that can be achieved with a binuclear catalyst relative to the corresponding mononuclear catalyst, the present invention provides a work-around solution to the intrinsic limitation on product volume imposed by a traditional living polymerization, as well as a work-around solution to the stereochemically random microstructure that is normally obtained as the result of rapid and reversible chain-transfer between two populations of chiral active propagating centers, of opposite absolute configuration, when a racemic mixture of the pre-catalyst is employed. In essence, the field of invention is defined as stereoselective living coordinative chain-transfer polymerization.
1. A method of producing a polyolefin composition comprising:
(a) contacting a metallocene pre-catalyst and a co-catalyst, wherein the metallocene pre-catalyst has the formula:
A-Z—B (I);
wherein A has the formula (II):
B has the formula (III):
wherein the dotted lines in A and B indicate a delocalized bond;
M 1 and M 2 are each independently Ti, Zr, or Hf;
Z is a linker covalently linking A with B;
R 1 and R 5 are each independently hydrogen, alkyl, cycloalkyl, optionally substituted phenyl, or two adjacent R 1 or R 5 form an aromatic ring;
R 2 , R 3 , R 6 , and R 7 are each independently alkyl, cycloalkyl, Si(alkyl) 3 , Si(aryl) 3 , phenyl, optionally substituted phenyl, or alkylphenyl; and
R 4 and R 8 are each independently halogen, alkyl, cycloalkyl, aryl, or arylalkyl;
(b) adding a metal alkyl;
(c) adding a first olefin monomer; and
(d) polymerizing by living coordinative chain transfer the first monomer for a time sufficient to form the polyolefin.
2. The method of claim 1 , wherein M 1 and M 2 are the same and are Hf or Zr.
3. The method of claim 1 , wherein R 1 and R 5 are the same and are selected from the group consisting of ethyl, methyl, iso-butyl, n-hexyl, n-propyl, and t-butyl.
4. The method of claim 1 , wherein R 4 and R 8 are the same and are selected from the group consisting of ethyl, methyl, iso-butyl, n-hexyl, n-propyl, and t-butyl.
5. The method of claim 1 , wherein R 2 and R 6 are the same and are selected from the group consisting of ethyl, methyl, iso-butyl, n-hexyl, n-propyl, and t-butyl.
6. The method of claim 1 , wherein Z is —(CH 2 ) w and wherein w is 2-20.
7. The method of claim 1 , wherein the metal alkyl is Zn(R 11 ) 2 and wherein R 11 is selected from the group consisting of ethyl, methyl, iso-butyl, n-hexyl, n-propyl, and t-butyl.
8. The method of claim 1 , wherein the metal alkyl is ZnEt 2 .
9. The method of claim 1 , wherein the metallocene pre-catalyst and the co-catalyst are contacted at a temperature of about −20° C. to about 25° C.
10. The method of claim 1 , wherein the metallocene pre-catalyst and the co-catalyst are contacted at a temperature of about −20° C. to about 0° C.
11. The method of claim 1 , wherein the first olefin monomer is ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, styrene, butadiene, isoprene, α-methyl styrene, acrylonitrile, methyl acrylate, methyl methacrylate, vinyl acetate, vinyl chloride, vinyl fluoride, vinylidene chloride, N-vinyl pyrrolidone, 3-methylbutene, 3-methyl-1-pentene, vinylcyclohexane, vinylcyclobutane, vinylcyclopentane, vinylcyclooctane, 1-decene, enantiomerically pure β-citronellene, 3,5,5-trimethyl-1-hexene, cyclopentene, vinylcyclohexene, or 4-methyl-1-pentene.
12. The method of claim 1 , wherein the first olefin monomer is propene.
13. The method of claim 1 , wherein the metallocene pre-catalyst is [(η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 4 —NC(Me)N(tBu)], [η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 6 —NC(Me)N(tBu)], or [(η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 8 —NC(Me)N(tBu)].
14. The method of claim 1 , wherein the co-catalyst is [PhNHMe 2 ][B(C 6 F 5 ) 4 ].
15. The method of claim 1 , wherein in the metallocene pre-catalyst and the co-catalyst are contacted in a metallocene pre-catalyst:co-catalyst molar ratio of about 1:2.
16. The method of claim 1 , wherein the metallocene pre-catalyst and the metal alkyl are contacted in a metallocene pre-catalyst:metal alkyl molar ratio of about 1:100 to about 1:1.1.
17. The method of claim 1 , wherein the metallocene pre-catalyst and the metal alkyl are contacted in a metallocene pre-catalyst:metal alkyl molar ratio of about 1:20 to about 1:1.1.
18. The method of claim 1 , wherein the polyolefin is an isotactic stereoblock polyolefin.
19. The method of claim 1 , wherein the polyolefin is isotactic stereoblock polypropene.
20. A method of producing a polyolefin composition comprising:
(a) contacting a metallocene pre-catalyst selected from the group consisting of [(η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 4 —NC(Me)N(tBu)], [(η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 6 —NC(Me)N(tBu)], and [(η 5 -C 5 Me 5 )Zr(Me) 2 ] 2 [N(tBu)C(Me)N—(CH 2 ) 8 —NC(Me)N(tBu)] with the co-catalyst [PhNMe 2 H][B(C 6 F 5 ) 3 Me] wherein the molar ratio of metallocene pre-catalyst to co-catalyst is about 1:2;
(b) adding ZnEt 2 ;
(c) adding a first olefin monomer; and
(d) polymerizing by living coordinative chain transfer said first monomer for a time sufficient to form said polyolefin.