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J. Am. Chem. Soc. 1996, 118, 11664-11665
Living Polymerization of r-Olefins Using NiII-r-Diimine Catalysts. Synthesis of New Block Polymers Based on r-Olefins Christopher M. Killian, Daniel J. Tempel, Lynda K. Johnson, and Maurice Brookhart* Department of Chemistry UniVersity of North Carolina at Chapel Hill Chapel Hill, North Carolina 27599-3290 ReceiVed July 22, 1996 Living polymerization techniques1 allow the synthesis of polymers with predictable molecular weights and narrow molecular weight distributions, end-functionalized polymers and well-defined block copolymers. While intense efforts have recently focused on development of homogeneous single-site, early metal d0 and d0fn catalysts for polymerization of ethylene and R-olefins (particularly propylene),2 rapid chain transfer processes in these systems have limited their use as living polymerization catalysts. The living polymerization of R-olefins has been achieved only in rare instances and at very low temperatures.3,4 We describe here the development of a procedure for living polymerization of R-olefins based on recently reported NiII-R-diimine catalysts5 and application of this procedure to the synthesis of diblock and triblock poly(R-olefins).6 As previously reported, catalysts derived from [ArNdC(R)sC(R)dNAr]NiBr2 (1) plus methylaluminoxane (MAO) are quite active for the polymerization of R-olefins in toluene (eq 1).5 Additional examples of polymerization at 23 °C using
(1)
catalyst precursors 1a and 1b are shown in Table 1, entries 1, 3, 7-9, 11, 13, and 15. Polymerization of propylene (1 atm) yields polypropylene with molecular weight distribution (MWD) of 1.44 (entry 1) for 1a/MMAO7 and 1.59 (entry 11) for 1b/ MAO. Polymerization of 1-hexene (>2 M in toluene) gives poly(1-hexene) with Mw/Mn values in the range of 1.4-1.8 (entries 6-8). While reasonably narrow, these molecular weight (1) (a) Odian, G. G. Principles of Polymerization, 3rd ed.; John Wiley & Sons, Inc.: New York, 1991. (b) Webster, O. W. Science 1991, 251, 887. (2) For leading references, see: (a) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (b) Giardello, M. A.; Eisen, M. S.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 12114-12129. (c) Mitchell, J. P.; Hajela, S.; Brookhart, S. K.; Hardcastle, K. I.; Henling, L. M.; Bercaw, J. E. J. Am. Chem. Soc. 1996, 118, 1045-1053. (d) Ewen, J. A.; Jones, R. L. J. Am. Chem. Soc. 1988, 110, 6255-6256. (e) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H. H.; Wild, F. R. W. P. Angew. Chem., Int. Ed. Engl. 1985, 24, 507-508. (f) Waymouth, R. M.; Coates, G. W. Science 1995, 267, 217. (g) Wu, Z.; Jordan, R. F.; Petersen, J. L. J. Am. Chem. Soc. 1995, 117, 5867-5868. (3) (a) Doi, Y.; Ueki, S.; Keii, T. Macromolecules 1979, 12, 814-819. (b) Doi, Y.; Hizal, G.; Soga, K. Makromol. Chem. 1987, 188, 1273-1279 and references therein. (4) For examples of living polymerization of ethylene, see: (a) Brookhart, M.; DeSimone, J. M.; Grant, B. E.; Tanner, M. J. Macromolecules 1995, 28, 5378-5380 and references therein. (b) Mashima, K.; Fujikawa, S.; Urata, H.; Tanaka, Y.; Urata, H.; Oshiki, T.; Tanaka, E.; Nakamura, A. Organometallics 1995, 14, 2633-2640. (5) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, 6414-6415. (6) This work was reported in part at 211th National ACS Meeting New Orleans, LA; Inorganic Division, Abstr. 261. (7) MMAO is a modified methylaluminoxane activator containing 25% isobutyl aluminoxane.
S0002-7863(96)02516-4 CCC: $12.00
Figure 1. GPC trace of poly(1-hexene) prepared by complex 1a + MAO at -10 °C.
Figure 2. Plot of Mn and Mw/Mn as a function of reaction time for propylene polymerization at -10 °C.
distributions suggest chain transfer is significant under these conditions. However, when polymerizations are carried out at somewhat lower temperature (-10 °C) and low monomer concentrations (
