Bibliographic Details
| Title: |
Robust chiral zirconium alkoxide initiators for the room-temperature stereoselective ring-opening polymerisation of rac-lactideThe HTML version of this article has been enhanced with colour images.CCDC reference numbers 665065–665068. For crystallographic data in CIF or other electronic format see DOI: 10.1039/b716304eElectronic supplementary information (ESI) available: Representative MALDI-TOF mass spectra of PLA prepared in solution. See DOI: 10.1039/b716304e |
| Authors: |
Amanda J. Chmura1, David M. Cousins1, Matthew G. Davidson1, Matthew D. Jones1, Matthew D. Lunn2, Mary F. Mahon3 |
| Source: |
Dalton Transactions: An International Journal of Inorganic Chemistry. Mar2008, Vol. 2008 Issue 11, p1437-1443. 7p. |
| Subject Terms: |
*POLYMERIZATION, *CRYOSCOPY, *MOLECULAR weights, *SPECTRUM analysis |
| Abstract: |
Chiral Schiff bases (1H to 4H) and a series of their Group 4 metal alkoxide complexes [(R-1)2Ti(OiPr)2, (R-2)2Ti(OiPr)2, (R-1)2Zr(OiPr)2, (R-2)2Zr(OiPr)2, (R-3)2Zr(OiPr)2, (R-4)2Zr(OiPr)2, (S-1)2Zr(OiPr)2 and (rac-1)2Zr(OiPr)2] have been prepared and characterised by 1H, and 13C NMR spectroscopy. In solution, both Λ and Δ isomers were observed, suggesting a low degree of chiral induction from the ligand. One ligand (R-4H) and three complexes [Δ-(R,R-2)2Ti(OiPr)2, Λ-(R,R-1)2Zr(OiPr)2 and Δ-(R,R-3)2Zr(OiPr)2] have also been characterised by single crystal X-ray diffraction. All complexes were found to have a pseudo-octahedral α-cis geometry. The complexes were tested as initiators for the ring-opening polymerisation of rac-lactide in solution and in the melt. The titanium complexes are inactive in solution and afford atactic polylactide in the melt. Zr(iv) complexes afford heterotactically enriched polylactide both in toluene solution (at 20 °C and 80 °C) and in the melt. Polymerisations were generally found to be well-controlled, giving predictable molecular weights and low molecular weight distributions. Ligand variation (substituents and/or chirality) has little effect on either the activity or selectivity of initiators. Zirconium initiators were found to be unusually robust as they were able to maintain well-controlled polymerisation following addition of water to reactions in solution and when using unpurified monomer for reactions in the melt. [ABSTRACT FROM AUTHOR] |
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