Reinvestigation of the Mechanism of Polymerization of b – Butyrolactone from 1,5,7-Triazabicyclo[4.4.0]dec-5-ene.


The questionable mechanism initially proposed to explain how the 1,5,7-triazabicyclo[4.4.0]dec-5ene (TBD) allows to ring-open b-lactones, such as b-butyrolactone (BL), is here reinvestigated. Thanks to the use of a trisubstituted b-lactone, i.e. (R,S)-benzylcarbonyl-3,3-dimethyl-2-oxetanone,  and the association of techniques such as 1H/DOSY NMR and MALDI/ESI-MS, we demonstrated that BL is effectively polymerized by the TBD in bulk at 60°C, minorly from the reported N-acyl-a,b-unsaturated TBD species, and majorly from crotonate anions issued from the basic activation of BL. On the contrary to what has been reported, the TBD is not covalently linked to the PBL chain but mainly plays the role of counter-ion in the -C(O)O-, TBDH+ active site.

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