Sustainable Polyester Elastomers from Lactones: Synthesis, Properties, and Enzymatic Hydrolyzability.

Chemically cross-linked elastomers are an important class of polymeric materials with excellent temperature and solvent resistance. However, nearly all elastomers are petroleum-derived and persist in the environment or in landfills long after they are discarded; this work strives to address these issues by demonstrating the synthesis of renewable, enzymatically hydrolyzable, and mechanically competitive polyester elastomers. The elastomers described were synthesized using a novel bis(ß-lactone) cross-linker and star-shaped, hydroxyl-terminated poly(γ-methyl-ε-caprolactone). Using model compounds, we determined that the bis(ß-lactone) cross-linker undergoes acyl bond cleavage to afford ß-hydroxyesters at the junctions. The mechanical properties of the cross-linked materials were tunable and competitive with a commodity rubber band. Furthermore, the elastomers demonstrated high thermal stability and a low glass transition (-50 °C), indicating a wide range of use temperatures. The polyester networks were also subjected to enzymatic hydrolysis experiments to investigate the potential for these materials to biodegrade in natural environments. We found that they readily hydrolyzed at neutral pH and environmentally relevant temperatures (2-40 °C); complete hydrolysis was achieved in all cases at temperature-dependent rates. The results presented in this work exemplify the development of high performance yet sustainable alternatives to conventional elastomers.

Total synthesis of tetrahydrolipstatin and stereoisomers via a highly regio- and diastereoselective carbonylation of epoxyhomoallylic alcohols.

A concise enantioselective synthesis of tetrahydrolipstatin (THL) and seven stereoisomers has been achieved. The synthesis of THL was accomplished in 10 steps and 31% overall yield from an achiral ynone. Key to the success of the approach is the use of a bimetallic [Lewis acid](+)[Co(CO)4](-) catalyst for a late-stage regioselective carbonylation of an enantiomerically pure cis-epoxide to a trans-ß-lactone. The success of this route to THL and its stereoisomers also demonstrated the practicality of the carbonylation catalyst for complex molecule synthesis as well as its functional group compatibility.

High Morphological Order in a Nearly Precise Acid-Containing Polymer and Ionomer.

Linear polyethylenes with functional groups at precise intervals along the backbone possess a number of remarkable properties, but the current synthetic methods that produce these precise polymers are difficult to scale up beyond the laboratory setting. When evaluating alternative synthetic routes, a critical question is how precise must the polymer microstructure be to achieve the properties of interest? As a first step in answering this question, we present morphological characterization of a nearly precise polymer-that is, an acid-containing polymer wherein the acid groups are separated by either n or n + 1 methylene groups. We find that the size scale and uniformity of the amorphous morphologies of the nearly precise acid-containing polymer and its sodium-neutralized ionomer are essentially indistinguishable from the precise polymers based on X-ray scattering. Meanwhile, the nearly precise polymer is strikingly distinct from a pseudorandom copolymer with similar average composition. This result suggests that the properties of nearly precise polymers could likewise be quite similar to truly precise polymers and beckons future work to explore their properties.

Rapid Determination of Polymer Stereoregularity Using Band-Selective 2D HSQC.

We report the use of band-selective 2D HSQC NMR spectroscopy to rapidly determine the stereoregularity of polymers usually analyzed by 1D 13C NMR spectroscopy. This approach reduced the time required to characterize the triad stereosequences of polyacrylonitrile from about an hour to a few minutes, and can be performed with sufficient 13C resolution to resolve higher-order stereosequences, such as the pentads of polypropylene.