Thermal degradation of poly( l-lactide): Accelerating effect of residual DBU-based organic catalysts

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) organic catalyst has generated a tremendous impact in the metal-free ring-opening polymerization of (di)lactones. Interestingly, its extraction after use has never been studied so far and a simple deactivation by addition of benzoic acid to generate the corre...

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Bibliographic Details
Published in:Polymer degradation and stability 2011-05, Vol.96 (5), p.739-744
Main Authors: Coulembier, Olivier, Moins, Sébastien, Raquez, Jean-Marie, Meyer, Franck, Mespouille, Laetitia, Duquesne, Emmanuel, Dubois, Philippe
Format: Article
Language:English
Subjects:
1,8-Diazabicyclo[5.4.0]undec-7-ene
Applied sciences
Benzoic acid
Catalysis
Catalysts
Chemical reactions and properties
Degradation
Exact sciences and technology
Extraction
Liquids
Melts
Organic polymers
Organocatalysis
Physicochemistry of polymers
Poly( l-lactide)
Precipitation
Racemisation
ROP
Transesterification
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Summary:1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) organic catalyst has generated a tremendous impact in the metal-free ring-opening polymerization of (di)lactones. Interestingly, its extraction after use has never been studied so far and a simple deactivation by addition of benzoic acid to generate the corresponding salt has always been supposed to kill its activity. This study reveals and highlights the importance of the work-up to remove or at least drastically limit the presence of the benzoic acid/DBU salt from poly( l-lactide). Three different extraction methods allowed us to conclude that a two-step work-up gathering liquid/liquid extractions and a drop by drop precipitation is highly required to keep the enantiomerically pure lactic acid polymer safe. If not perfectly extracted the benzoic acid/DBU salt has been proved to degrade the materials during a melt process even during a differential scanning calorimetry experiment. The importance of the extraction of DBU/benzoic acid salt after the ROP of l-lactide is discussed. DSC, 1H-NMR, GPC, polarimetry and TGA measurements show the accelerating degradation effect on the poly( l-lactide) during a melt process (even a simple DSC) if the quenched catalyst is not properly removed. [Display omitted]
ISSN:0141-3910
1873-2321
DOI:10.1016/j.polymdegradstab.2011.02.014