Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

A series of sustainable aliphatic polyester thermoplastic elastomers (APTPEs) consisting of multi-arm star polymers with arms of poly­(l-lactide)-b-poly­(γ-methyl-ε-caprolactone) were investigated and compared to analogous linear poly­(l-lactide)-b-poly­(γ-methyl-ε-caprolactone)-b-poly­(l-lactide) triblock polymers. Linear analogues with comparable arm molar mass and comparable overall molar mass were synthesized to distinguish architectural and molar mass effects. Overall, the star block polymers significantly outperformed their linear analogues with respect to ultimate tensile strength and tensile toughness, exhibiting more pronounced strain hardening than corresponding linear APTPEs. The stars exhibited high ultimate tensile strengths (∼33 MPa) and large elongations at break (∼1400%), outperforming commercially relevant, petroleum-derived, and non-degradable styrenic TPEs. The star polymers also exhibited superior recovery characteristics during cyclic strain cycles and reduced stress relaxation compared to the linear APTPEs, highlighting the impact of architecture on improved TPE mechanical properties. Dynamic mechanical thermal analysis suggests that the star architecture increases the usage temperature range and does not negatively influence processability, an important feature for future applications. Overall, this work illustrates that simple and convenient changes in the macromolecular architecture in sustainable APTPEs result in materials with greatly enhanced mechanical properties. A comprehensive understanding of the relationship between polymer architecture and mechanical properties can be capitalized on to develop property-specific and industrially relevant sustainable materials.

Polymers are an important class of materials that are used for a broad range of applications, from drug delivery to packaging. Given their widespread use, a major challenge in this area is the development of technology for their production from renewable sources and efforts to promote their efficient recycling and biodegradation. In this regard, the synthesis of polyesters based on the natural polyhydroxy­alkanoate (PHA) pathway offers an attractive route for producing sustainable polymers. However, monomer diversity in naturally occurring polyesters can be limited with respect to the design of polymers with material properties suitable for various applications. In this work, we have engineered a pathway to produce α-methyl-branched PHA. In the course of this work, we have also identified a PHA polymerase (CapPhaEC) from activated sludge from wastewater treatment that demonstrates a higher capacity for incorporation of α-branched monomer units than those previously identified or engineered. Production in Escherichia coli allows the construction of microbial strains that produce the copolyesters with 21–36% branched monomers using glucose and propionate as carbon sources. These polymers have typical weight-average molar masses (M w) in the range (1.7–2.0) × 105 g mol–1 and display no observable melting transition, only relatively low glass transition temperatures from −13 to −20 °C. The lack of a melting transition indicates that these polymers are amorphous materials with no crystallinity, which is in contrast to the natural poly­(hydroxybutyrate) homopolymer. Our results expand the utility of PHA-based pathways and provide biosynthetic access to α-branched polyesters to enrich the properties of bio-based sustainable polymers.

Aliphatic polyesters are potential sustainable alternatives to PVC for use in medical devices, such as IV bags. Our candidate replacement of PVC-based IV bags use P4MCL, a sustainable polymer with demonstrated uses in mechanically robust materials. The goal of our project was to compare the mechanical and biocompatibility characteristics of P4MCL/PLLA star block copolymer TPEs with commercial PVC-based IV bags. P4MCL/PLLA TPEs were synthesized according to previously reported methods. Uniaxial tensile testing was conducted pre- and post-autoclave. Impact and tear resistance testing was performed on non-autoclaved specimens according to ASTM standards. Cytotoxicity was examined using NIH 3T3 Fibroblasts with an AlamarBlue assay. A student’s t-test was used to compare results with statistical significance of P < 0.05. PVC tended to be stiffer but P4MCL/PLLA was more extensible. The tensile properties for the P4MCL-based material did not change after autoclaving. When compared to PVC-based IV bags, the P4MCL/PLLA TPE demonstrated a lower peak force and average force but a greater elongation at break and total absorbed energy (P<0.05). P4MCL/PLLA, unlike PVC-based materials with DEHP plasticizer, was non-cytotoxic. In summary, P4MCL/PLLA has desirable mechanical and biocompatibility advantages compared to PVC making the material a potential sustainable alternative for medical grade plastics.