Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research.

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.

Neighboring Group Effects on the Rates of Cleavage of Si-O-Si-Containing Compounds.

The presence of a nearby tethered functional group (G, G = tertiary amide or amine) can significantly impact the rate of cleavage of an Si-O bond. We report here an in situ 1H NMR spectroscopic investigation of the relative rates of cleavage of model substrates containing two different Si-O substructures, namely alkoxydisiloxanes [GRO-Si(Me2)-O-SiMe3] and carbodisiloxanes [GR-Si(Me2)-O-SiMe3]. The trends in the relative rates (which slowed with increasing chain length, with a notable exception) of alkoxydisiloxane hydrolyses were probed via computation. The results correlated well with the experimental data. In contrast to the hydrolysis of the alkoxydisiloxanes, the carbodisiloxanes were not fully hydrolyzed, but rather formed an equilibrium mixture of starting asymmetric disiloxane, two silanols, and a new symmetrical disiloxane. We also uncovered a facile siloxy-metathesis reaction of an incoming silanol with the carbodisiloxane substrate [e.g., Me2NR-Si(Me2)-O-SiMe3 + HOSiEt3 ⇋ Me2NR-Si(Me2)-O-SiEt3 + HOSiMe3] facilitated by the pendant dimethylamino group, a process that was also probed by computation.

Synthesis of Isohexide Diyne Polymers and Hydrogenation to Their Saturated Polyethers.

The incorporation of renewable feedstocks into polymer backbones is of great importance in modern polymer science. We report the synthesis of 1,3-diyne polymers derived from the bispropargyl ethers of isosorbide, isomannide, and isoidide. The dialkyne monomers can be polymerized through an adaptation of the Glaser-Hay coupling using a nickel(II) cocatalyst. These well-defined diyne polymers bear an iodoalkyne end group, afforded through an unanticipated reductive elimination pathway, and display glass transition temperatures (Tg) from 55 to 64 °C. Fully saturated, analogous polyethers can be prepared from the hydrogenation of the diyne polymers, and these show Tg values between -10 and -2 °C. Both the 1,3-diyne polymers and the saturated analogues display similar trends in their Tg values vis-à-vis the stereochemical features of the isohexide unit within the backbone. This polymerization provided access to two series of isohexide-based polyethers, the thermal properties of which are influenced by the nature of the 2,4-hexadiynyl and hexamethylene linkers as well as the relative configuration of the bicyclic subunit in the backbone. The reported method represents an important step toward accessing well-defined polyethers from renewable feedstocks using readily available catalysts and convenient ambient conditions.

Rapid Synthesis of Chemically Recyclable Polycarbonates from Renewable Feedstocks.

We report the rapid, one-pot synthesis of functional polycarbonates derived from renewable alcohols (i.e., glucose tetraacetate, acetyl isosorbide, lauryl alcohol, and ethanol) and a cyclic carbonate bearing an imidazolecarboxylate. This tandem functionalization/ring-opening polymerization strategy can be performed on multigram scale and eliminates the need for rigorous purification and specialized equipment. A wide range of glass transition temperatures (Tg) was accessible from these renewable pendant groups (>75 °C Tg window). We also synthesized several statistical copolycarbonates to show the thermal properties can be tailored with this tandem method. Additionally, we demonstrate a circular polymer economy via chemical recycling to a cyclic carbonate precursor. This work may facilitate development of sustainable polycarbonates with tailored properties that work toward eliminating plastic waste streams.