title: Mechanism of the living lactide polymerization mediated by robust zinc guanidine complexes.
abstract: Zinc bis(chelate) guanidine complexes promote living lactide polymerization at elevated temperatures. By means of kinetic and spectroscopic analyses the mechanism has been elucidated for these special initiators that make use of neutral N-donor ligands. The neutral guanidine function initiates the polymerization by a nucleophilic ring-opening attack on the lactide molecule. DFT calculations on the first ring-opening step show that the guanidine is able to act as a nucleophile. Three transition states were located for ligand rearrangement, nucleophilic attack, and ring-opening. The second ring-opening step was modeled as a representation for the chain growth because here, the lactate alcoholate opens the second lactide molecule via two transition states (nucleophilic attack and ring-opening). Additionally, the resulting reaction profile proceeds overall exothermically, which is the driving force for the reaction. The experimental and calculated data are in good agreement and the presented mechanism explains why the polymerization proceeds without co-initiators.
authors: Department Chemie, Anorganische Chemie, Universität Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany.
authors: Janna
authors: J
authors: Börner
authors: Ines dos Santos
authors: Idos S
authors: Vieira
authors: Alexander
authors: A
authors: Pawlis
authors: Artjom
authors: A
authors: Döring
authors: Dirk
authors: D
authors: Kuckling
authors: Sonja
authors: S
authors: Herres-Pawlis