Abstract
1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) polymerizes rac-lactide (rac-LA) to form highly isotactic polylactide (PLA) with a Pm = 0.88, while meso-LA yields heterotactic PLA (Pm ~ 0.8) at −75 °C. The stereocontrol of the cryogenic-based ring-opening polymerization comes from a perfect imbrication of both chiral LA and the propagating chiral end-group interacting with the achiral TBD catalyst.
Highlights
IntroductionWhile PLA can be synthesized via polycondensation of lactic acid, the ring-opening polymerization (ROP) of lactide (LA) is by far preferred, on account of the more facile access to higher molecular weight polymers with control over the molecular parameters and end groups [1]
Polylactide (PLA) is a versatile bioplastic that can be derived from annually-renewable resources.While PLA can be synthesized via polycondensation of lactic acid, the ring-opening polymerization (ROP) of lactide (LA) is by far preferred, on account of the more facile access to higher molecular weight polymers with control over the molecular parameters and end groups [1]
Because the chemical and physical properties of PLA are drastically affected by its tacticity [2], the nature of the enantiopure monomer involved in the ROP process, or the application of stereocontrolled polymerizations in which stereoregular polymers result from diastereomeric mixtures of LA, are of high importance
Summary
While PLA can be synthesized via polycondensation of lactic acid, the ring-opening polymerization (ROP) of lactide (LA) is by far preferred, on account of the more facile access to higher molecular weight polymers with control over the molecular parameters and end groups [1]. There has been significant emphasis placed on the preparation of catalysts that are able to produce isotactic PLA directly from rac-LA [3,4,5,6,7]. The isoselective ROP of rac-LA is by far dominated by metal salts and coordination complexes that operate by a coordination-insertion mechanism. The significant difference in the rates of insertion of both D- and L-LA is Catalysts 2020, 10, 620; doi:10.3390/catal10060620 www.mdpi.com/journal/catalysts
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