Of the variety of biodegradable polymers known, linear aliphatic polyesters have a leading position and are commonly produced by ring-opening polymerization (ROP) of cyclic esters. It is now commonly accepted that the most efficient method for the production of well-controlled polyesters in terms of molecular weight, composition and microstructure, is ROP with metal-coordination initiators. However, current aliphatic polyesters are far from being optimal and tailor-made structures are certainly needed. In particular, the control over chain microstructure (i.e. tacticity and monomer sequences) may lead to highly-optimized macromolecules with tailored properties.
Key Words: Catalysis, Ring-Opening Polymerization (ROP), Alternating, Tacticity
Synthesis of heterotactic PLA from rac-lactide using hetero-bimetallic Mg/Zn–Li systems
Biomass represents an abundant carbon-neutral renewable resource for the production of polymers. In this regard, the availability of monomer feedstocks from renewable resources has given poly(lactide) increasing prominence in the market place. Herein we report highly active and stereoselective catalytic systems for the polymerization of rac-lactide, generating highly heterotactic PLA. Given an operationally simple method, we developed magnesium and zinc hetero-bimetallic complexes in combination with diol ligands for the straightforward synthesis of PLA.
Stereocontrolled ring-opening polymerization of cyclic esters: synthesis of new polyester microstructures
Synthesis of aliphatic polyesters has been studied intensively due to their biocompatible and biodegradable properties and their potential applications in medical and agricultural fields. There has been particular emphasis over the past decade on the synthesis of discrete, well-characterized complexes that are active polymerization initiators for the ring-opening polymerization (ROP) of lactide (LA) and β-butyrolactone (BBL) to give, respectively, poly(lactide) (PLA) and poly(3-hydroxybutyrate) (PHB). These recent advances in catalyst design have led to a variety of polyester microstructures. This tutorial review focuses on the use of metal-based complexes for the stereoselective ROP of rac-LA and rac-BBL.
Polymerization of Enantiopure Monomers Using Syndiospecific Catalysts: A New Approach To Sequence Control in Polymer Synthesis
The ring-opening polymerization of a mixture of enantiomerically pure but different monomers using an yttrium complex as initiator proceeds readily at room temperature to give the corresponding highly alternating polyester.