Abstract

In the 21st century, sustainability has emerged as a guiding principle for the design of new methods and materials across a wide range of disciplines. An outstandingly versatile class of materials comprises the plastics. Contemporary plastics are synthetic polymers derived largely from hydrocarbon building blocks found in petroleum. The incredible performance range and economical production of these polymers is starkly contrasted with their disconcerting impact on the environment. Petroleum is a diminishing natural resource and there is an increasing concern with the build-up of plastic waste in oceans and natural habitats. Hence, cutting edge research across institutions is exploring biomass-based building blocks for the economical production of competitive materials that can ultimately be assimilated by natural environments. Our laboratory is interested in the synthesis of plant-derived monomers and their controlled polymerization to novel macromolecules with desirable properties. Aliphatic polyesters have emerged as important players amongst biodegradable materials, with polylactide presenting the commercially most successful contestant. We are particularly interested in the design of polymers that combine the mechanical strength of the polyhydroxyalkanoates with the hydrolytic sensitivity of polyacetals or polyketals. To obtain macromolecules of narrow molecular weight distributions the catalytic ring-opening polymerization (ROP) of cyclic esteracetal or esterketal monomers is especially promising. To this end, we have successfully synthesized and polymerized 2-methyl-1,3-dioxan-4-one (MDO) to deliver the corresponding polyesteracetal PMDO, which is effectively a perfectly alternating copolymer of 3-hydroxypropionic acid (3-HPA) and acetaldehyde. Interestingly, we found that solely by modification of catalyst loading we were able to also selectively produce poly(3-hydroxypropionic acid) (PHPA) via concurrent thermodynamically driven expulsion of acetaldehyde. Kinetic and mechanistic experiments provided insight into the mechanistically distinct avenues leading to the observed bifurcated polymerization of this single monomer. When exposing PMDO and PHPA to media varying from slightly acidic to neutral expedited degradation was observed in all cases for PMDO. Encouraged by these results we are currently investigating the one-pot synthesis of random and block-copolymers of 3-HPA and MDO as well as structurally related monomers and their synthesis from the corresponding hydroxyacids and aldehydes or ketones.