A perspective into ring-opening polymerization of ε-caprolactone and lactides: effect of, ligand, catalyst structure and system dynamics, on catalytic activity and polymer properties

Abstract

Polylactic acid (PLAs) and polycaprolactones (PCLs) are emerging to be polyesters of choice because they are biodegradable and biocompatible. The industrial viable method currently used for their production is catalytic ring-opening polymerization (ROP) of their respective cyclic ester monomers. The catalyst is at the core of ROP chemical transformation and as such research is dedicated towards the innovation of more efficient and selective catalysts. Catalyst structural features greatly influence catalyst performance in ROP, and this review discusses the effects of ligand and catalyst structure and system dynamics, on catalytic activity and polymer properties. The effects of associated catalyst components such as initiating groups, ligand chirality, and stereochemical in relation to catalyst activity and polymer properties were also reviewed. The effects of metal nuclearity and catalyst flexibility on catalytic activity were also reviewed. The effect of solvent and temperature was briefly considered. Graphical abstract

Heteroleptic Calcium Complexes Supported by a Phenoxy-Imine NON Ligand: Polymerization of Cyclic Esters by a Ligand-Assisted, Activated-Monomer Mechanism

“…Initial ROP of L -LA employing 6 as the catalyst in benzene- d 6 proved to be slow, achieving only 78% conversion in 25 h. This may be the result of the poorly initiating halide group, the NON ligand itself acting as the initiating group, or a combination of both; increasingly bulky aryloxide groups, which possess low nucleophilicity and can inhibit monomer coordination, have been demonstrated to result in correspondingly slower reaction kinetics . To improve the rate of polymerization, benzyl alcohol (BnOH) was added as a co-initiator; it has been proposed that, in agreement with literature, this would generate a more reactive Ca-OBn initiator in situ .…”