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Controlled and Stereoselective Polymerization of Lactide: Kinetics, Selectivity, and Microstructures

Zhong, Zhiyuan, Dijkstra, Pieter J., Feijen, Jan·2003·Journal of the American Chemical Society

Abstract

Chiral aluminum isopropoxides based on enantiopure or racemic cyclohexylsalen ligand (Jacobsen ligand) have been prepared and employed for stereoelective/stereoselective ring-opening polymerization of lactide in toluene at 70 degrees C. The kinetics, selectivity of the catalysts, and microstructure of the obtained polylactides, using different combinations of lactide enantiomers and catalysts, were determined. In all cases, polylactides of controlled molecular weight, low polydispersity, and defined end groups were obtained. The polymerizations are first-order in both monomer(s) and catalyst. (R,R)-CyclohexylsalenAlO(i)()Pr [(R,R)-1] polymerizes l-lactide significantly faster than d-lactide with a rate constant ratio k(l)/k(d) of approximately 14. The polymerization of rac-lactide using (R,R)-1 yields crystalline polymers, for which a selectivity factor of approximately 5.5 could be calculated up to 50% conversion based on the optical purity of the isolated polymers. The polymerization of a l-lactide/d-lactide (molar ratio: 80/20) mixture by (R,R)-1 furnishes an isotactic-atactic block copolylactide, which is highly crystalline with a T(m) = approximately 155 degrees C. Polymerization of rac-lactide applying rac-cyclohexylsalenAlO(i)()Pr [rac-1] yields isotactic stereoblock polylactides with a high T(m) = approximately 185 degrees C and a high degree of crystallinity.

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Metadata

Authors
Zhong, Z., Dijkstra, P. J., & Feijen, J.
Venue
Journal of the American Chemical Society
Published
2003-08-19
Volume
125
Issue
37
Pages
11291-11298
ISSN
  • 0002-7863 (ISSN-L)
  • 1520-5126
OpenAlex
W2092999693
Cited by
501
References
6
FWCI
7.14
Type
journal article
Language
en
Open access
closed

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