Polyesters represent one of the most important classes of polymeric materials, providing essential feedstocks for commodity products, medical devices and specialty polymers with tunable properties. Our current efforts focus on the development of polyesters derived from renewable resources, specifically targeting polymers with both microstructure and macrostructure control.We design catalysts that mediate the ring-opening polymerisation of cyclic esters for this purpose. By designing monomers, reactions and catalysts we can generate biodegradable and bioassimilable materials, many of which are new and may have unprecedented properties as functional materials. In all cases, we modify polymer stereoregularity to further tune the thermal properties, degradation rates and self-assembly of our materials. Specific research goals for this transitional grant are as follows:(1) Tacticity and an Expanding Monomer Scope. We will combine our expertise in the ROP of cyclic esters with our understanding of catalysis and ligand design to expand tacticity control to new monomer classes including (i) cyclic morpholinediones to afford poly(depsipeptide)s, cyclic phosphate esters to afford degradable flame retardants and β-butyrolactone derivatives to afford biodegradable thermoplastic elastomers.(2) Functional materials. We will synthesize new-to-the-world materials, with a particular focus on controlling under-exploited monomers, is essential to expanding the scope of green materials. We will develop novel hyperbranched polyesters, hydroxy-functionalized degradable materials and multi-functional materials prepared through immortal ring-opening (co)-polymerisation and olefin metathesis.(3) Catalyst design. We will design new catalysts capable of mediating these challenging reactions, with a particular focus on increased monomer scope. Anilido-aldimine, phosphinimine, salen and salan frameworks supporting iron and aluminium catalysts will form the foundation of these efforts.