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.
Isosorbide is a renewable chemical of considerable interest as a monomer and monomer precursor due to its potential use in replacements for fossil-fuel derived polymers. In the present study, a facile microwave-assisted condensation of isosorbide with succinic anhydride was developed that dramatically reduced the reaction time. The resulting isosorbide disuccinic acid derivative (I-S-2) was polymerized under solvent-free conditions with glycerol to produce a renewable, cross-linked polyester with high modulus and appreciable thermal stability. Inclusion of 13 wt % or more of low molar mass hydroxy-telechelic poly(ethylene oxide) (PEO) (M n = 300 g/mol) produced materials with a notable decrease in modulus and glass transition temperature. Degradation studies at 50 °C in acidic and basic solutions demonstrated the ability of the I-S-2 thermosets to be readily hydrolyzable. Furthermore, the resulting aqueous degradation solutions can be concentrated and reheated to produce new materials, albeit with a reduction in tensile properties. These I-S-2/glycerol thermosets represent economic, sustainable materials with tunable mechanical properties.
Recycling crosslinked polyurethanes (PUs) is accomplished through mechanical or chemical processes that are energy-intensive or produce plastics of lesser value. Polymer recycling processes are notably intolerant of polymer mixtures, yet the ability to reprocess and compatibilize two or more crosslinked PUs together will make this process more amenable to mixed waste streams while offering an opportunity to tune the properties of the recycled polymer products. Here, we blend a rigid polyester PU and a soft polyether PU using twin-screw extrusion to yield materials with tunable mechanical properties based on the feed composition. Their material properties were compared to those of compression-molded reprocessed blends and blends where the monomers were mixed prior to synthesis. The extruded materials showed similar mechanical and thermal properties to newly prepared blends and had higher-value mechanical properties compared to the samples reprocessed via compression molding. The morphologies of the blends were observed using phase imaging via atomic force microscopy to show that there is less phase separation in the extruded materials compared to compression-molded blends. The mechanical properties of these materials were tunable from soft to elastomeric to rigid based on the feed composition, and this tunability was demonstrated through four consecutive reprocessing cycles, through which the mechanical properties were steadily varied from rigid to soft by incorporating increasing amounts of soft polyether PU material. This blending method for reprocessing mixed waste compatibilizes different PUs and provides a means to tune the mechanical properties of a PU product, even if starting from waste streams of varying compositions. As such, this process represents an intriguing new approach for polymer reprocessing.
Macrocycles that assemble into nanotubes exhibit emergent properties stemming from their low dimensionality, structural regularity, and distinct interior environments. Here, we report a versatile strategy to synthesize diverse nanotube structures in a single, efficient reaction by using a conserved building block bearing a pyridine ring. Imine condensation of a 2,4,6-triphenylpyridine-based diamine with various aromatic
Despite recent progress for efficient and precise synthesis of functional polymers, few reports describe postpolymerization functionalization strategies for the controlled incorporation of multiple pendent groups per repeat unit. Cyanuric chloride, or 2,4,6-trichloro-1,3,5-triazine (TCT), offers a facile method to introduce distinct pendent functionalities. An acrylamide monomer containing a triazine ring with two electrophilic sites was prepared from TCT and polymerized via reversible addition−fragmentation chain transfer (RAFT) polymerization. Subsequent nucleophilic aromatic substitution reactions using a combination of amine and thiol nucleophiles introduced two functionalities into each repeat unit of the RAFTderived polymers. The success of each postpolymerization modification reaction was confirmed by 1 H NMR spectroscopy and size-exclusion chromatography, and small molecule model studies corroborated the high chemoselectivity of the nucleophilic aromatic substitution reactions. This postpolymerization modification strategy based on TCT enables a facile and efficient synthesis of multifunctional homopolymers.
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