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Theses

Stereoselective Ring-Opening Polymerizations of Racemic Lactide by Organocatalysis

Abstract : Have received great deal of attention considering their stereochemistries due to the fact that their mechanical, thermal and physical properties are strongly affected by their stereoregularity. Among them, polylactide (PLA) as an outstanding alternative to the conventional petroleum-based polymers, has become one of the most widely used polymers, which is formed by renewable natural resources are now being accepted as “bio-based polymer”. Due to the variety of diastereomeric structures of lactide (LA), numerous of PLA chains can be obtained in diverse stereregularities. As an example, isotactic PLA chains can be formed using enantiopure L- or D-LA, and show glass transition (Tg) at 50 oC, melting temperature (Tm) at 160-180 oC. The thermal properties of the PLA can be further enhanced by the formation of stereocomplex PLA from meso- or rac-LA in the presence of appropriate chiral or achiral initiators/catalysts under appropriate conditions, which displays a significantly increased Tm around 230–240 oC. Many metal catalysts have been reported to this end. However, there are only few organocatalysts able to prepare stereoregular PLA from rac-LA. In this thesis, we studied chiral organic (thio)urea, N-heterocyclic carben derivatives, and 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) organocatalysts for stereoselective ROP of rac-LA. Catalytic activations, stereoselectivite properties and stereocontrol mechanisms of these catalysts were investigated. In each case, high isoselectivities were promoted even sometimes at high temperatures, proved by homonuclear decoupled 1H NMR, quantitative 13C NMR, thermal analysis and kinetic studies.
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Submitted on : Wednesday, January 19, 2022 - 1:01:11 AM
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Beste Orhan. Stereoselective Ring-Opening Polymerizations of Racemic Lactide by Organocatalysis. Polymers. Université de Bordeaux; Université de Mons, 2019. English. ⟨NNT : 2019BORD0361⟩. ⟨tel-03533729⟩

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