RESUMEN
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.
Asunto(s)
Polímeros , Polímeros/químicaRESUMEN
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 (Mw) 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.
Asunto(s)
Aciltransferasas/genética , Aciltransferasas/metabolismo , Poliésteres/química , Ingeniería de Proteínas , Aciltransferasas/química , Modelos Moleculares , Conformación ProteicaRESUMEN
Star block (ABC)4 terpolymers consisting of a rubbery poly(γ-methyl-ε-caprolactone) (PγMCL) (C) core and hard poly(l-lactide) (PLLA) (B) and poly(d-lactide) (PDLA) (A) end-blocks with varying PDLA to PLLA block ratios were explored as high-performance, sustainable, aliphatic polyester thermoplastic elastomers (APTPEs). The stereocomplexation of the PDLA/PLLA blocks within the hard domains provided the APTPEs with enhanced thermal stability and an increased resistance to permanent deformation compared to nonstereocomplex analogs. Variations in the PDLA:PLLA block ratio yielded tunable mechanical properties likely due to differences in the extent and location of stereocomplex crystallite formation as a result of architectural constraints. This work highlights the improvements in mechanical performance due to stereocomplexation within the hard domains of these APTPEs and the tunable nature of the hard domains to significantly impact material properties, furthering the development of sustainable materials that are competitive with current industry standard materials.