Journal
JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL
Volume 316, Issue 1-2, Pages 139-145Publisher
ELSEVIER
DOI: 10.1016/j.molcata.2009.10.012
Keywords
Biodegradable biopolymers; Zinc; Lactide; Ring-opening polymerisation; Density functional calculations
Categories
Funding
- Fonds der Chemischen Inclustrie
- Universitat Paderborn
- Stiftung der Deutschen Wirtschaft sdw
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Two imidazolin-2-imine zinc complexes [Zn(8MeBL)Cl-2] (1) and [Zn(8MeBL)(OAc)(2)] (2) were synthesised, completely characterised and investigated for their activity in the solvent-free ring-opening polymerisation of D,L-lactide. It could be shown that these compounds are able to act as efficient initiators for lactide polymerisation,and polylactides with molecular weights (M-w) of around 23,000-55,000 g/mol could be obtained with relatively narrow polydispersities. 1 and 2 exhibit an advantageous combination of robustness towards humidity and high activity in the polymer melt. A comparative DFT study on 1 and 2 and their guanidine counterparts revealed that the two complex series possess a strikingly similar electronic structure. Although the imidazolin-2-imine is more basic, its zinc complexes have only a slightly greater positive charge on the zinc atom in comparison to the corresponding guanidine complexes. Accordingly, their activity in the initiation of the ring-opening polymerisation is increased which is directly related to the Lewis acidity of the zinc atom. These findings allow more insights into the mechanism of the lactide polymerisation with neutral N-donor stabilised zinc complexes. (C) 2009 Elsevier B.V. All rights reserved.
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