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Synthesis and Characterization of Supramolecular Colloids
Published on: April 22, 2016
Controlled and stereoselective polymerization of lactide: kinetics, selectivity, and microstructures.
Zhiyuan Zhong1, Pieter J Dijkstra, Jan Feijen
1Department of Polymer Chemistry and Biomaterials and Institute for Biomedical Technology, Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
Journal of the American Chemical Society
|October 14, 2005
Summary
Chiral aluminum catalysts enable stereoselective ring-opening polymerization of lactide, producing polylactides with controlled molecular weights and microstructures. These catalysts offer precise control over polymer properties for advanced material applications.
Area of Science:
- Polymer Chemistry
- Organometallic Chemistry
- Materials Science
Background:
- Ring-opening polymerization (ROP) is crucial for synthesizing biodegradable polymers like polylactide.
- Controlling polymer microstructure and stereochemistry is essential for tailoring material properties.
- Chiral catalysts offer pathways to stereoselective polymerization, but efficient systems for lactide are still being developed.
Purpose of the Study:
- To prepare and characterize chiral aluminum isopropoxides based on the cyclohexylsalen ligand.
- To investigate the stereoselective ring-opening polymerization of lactide using these catalysts.
- To determine the kinetics, selectivity, and resulting polylactide microstructures.
Main Methods:
- Synthesis of chiral aluminum isopropoxides with enantiopure or racemic cyclohexylsalen ligands.
- Ring-opening polymerization of lactide enantiomers and racemic mixtures in toluene at 70°C.
- Kinetic studies, analysis of polymer molecular weight, polydispersity, and microstructure (NMR spectroscopy).
- Determination of catalyst selectivity using rate constant ratios and selectivity factors.
Main Results:
- Polylactides with controlled molecular weight, low polydispersity, and defined end groups were consistently obtained.
- (R,R)-CyclohexylsalenAlO(i)()Pr polymerized l-lactide approximately 14 times faster than d-lactide.
- Polymerization of rac-lactide with (R,R)-1 yielded crystalline polymers with a selectivity factor of ~5.5.
- Stereoblock copolylactides with high melting points and crystallinity were synthesized from lactide mixtures and racemic catalysts.
Conclusions:
- Chiral aluminum isopropoxides are effective catalysts for stereoselective lactide polymerization.
- The catalysts provide control over polymer molecular weight, polydispersity, and stereochemistry.
- These findings enable the synthesis of tailored polylactides with specific microstructures and properties for diverse applications.
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