Polyurethanes (PUs), in the form of coatings, adhesives, sealants, elastomers, and foams, play a vital role in the consumer goods, automotive, and construction industries. However, the inevitable disposal of nondegradable postconsumer polyurethane products constitutes a massive waste management problem that has yet to be solved. We address this challenge through the synthesis of biobased and chemically recyclable polyurethanes. Our approach employs renewable and degradable hydroxy telechelic poly(β-methyl-δvalerolactone) as a replacement for petroleum-derived polyols in the synthesis of both thermoplastic polyurethanes and flexible foams. These materials rival petroleum-derived PUs in performance and can also be easily recycled to recover βmethyl-δ-valerolactone monomer in high purity and high yield. This recycling strategy bypasses many of the technical challenges that currently preclude the practical chemical recycling of PUs.

Aliphatic polyesters are a versatile class of materials that can be sourced from bioderived feedstocks. Poly(γ-methyl-εcaprolactone) (PγMCL) in particular can be used to make degradable thermoplastic elastomers with outstanding mechanical properties. PγMCL can potentially be manufactured economically from p-cresol, a component of lignin bio-oils. A complication is that additional manufacturing processes are necessary to isolate pure cresol isomers. Using mixed feedstocks of cresol isomers to access the corresponding methyl-substituted ε-caprolactone (MCL) monomer mixtures would convey economic advantages to sourcing these materials sustainably. Moreover, the use of organocatalysts in lieu of traditional tin-based catalysts averts issues with potential environmental and human toxicity. With these motivations in mind, we explored the ring-opening transesterification polymerization (ROTEP) of MCL mixtures and characterized the molecular, thermal, and rheological properties of the resulting copolymers. The molar mass of MCL mixtures that would be obtained from meta-and para-cresol can be readily modulated. The thermal and rheological properties of these statistical copolymers and terpolymers are at parity with pure PγMCL homopolymer. The use of diphenyl phosphate (DPP) and dimethyl phosphate (DMP) as organocatalysts enabled access to these materials that have potential to improve sustainability in the synthesis of these polyesters.

Significant research effort has been directed toward the development of sustainable plastics that are high-performance, bioderived, and/or degrade into nontoxic byproducts in natural or engineered environments (i.e., industrial composting facilities). We report the low cytotoxicity of poly(γ-methyl-ε-caprolactone) (PMCL)-based materials and the hydrolysis product of PMCL, sodium 6-hydroxy-4-methylcaproate. The concentration of sodium 6-hydroxy-4-methylcaproate that leads to 50% cell death (TD 50 ) is 179 mM, a value that is similar to that of the hydrolysis product of polycaprolactone and higher than that of the hydrolysis product of polylactide. We also report the degradability of two PMCL materials with different architectures (cross-linked and linear triblock polymers) under simulated industrial composting conditions. These materials reached high degrees of carbon mineralization (>85%) over the course of 120 days as monitored by CO 2 evolution. Finally, we examined the industrial compostability of a new aromatic polyester, poly(salicylic methyl glycolide). This material reached 89% carbon mineralization after 120 days, an important finding given the recalcitrance toward degradation of ubiquitous aromatic polyesters.

Poly(4-methylcaprolactone) (P4MCL) has been successfully incorporated into mechanically competitive materials with potential for biodegradability in engineered and natural systems. The mineralization of the hydrolysis product of P4MCL, 6-hydroxy-4-methylhexanoic acid (4MHA), was herein investigated by synthesizing tailor-made molecules with 13 C labels in the carboxylic acid group (4MHA-13 COOH) or the methyl group (4MHA-13 CH 3 ) and incubating each separately in a soil. Isotope-sensitive cavity ringdown spectroscopy on the efflux gas was then used to quantitatively monitor the mineralization of each isotopomer. These experiments clearly demonstrated that 4MHA was assimilated and utilized by the soil microorganisms and provided insight into position-specific mineralization. The 13 CO 2 evolution rate profiles and overall extents of mineralization to 13 CO 2 (∼85% and ∼46% for carboxyl-and methyl-labeled carbons, respectively) are consistent with the methyl carbon being preferentially incorporated into biomass rather than respired, whereas the carboxyl carbon is preferentially used for energy production and thus mineralized more rapidly (presumably by decarboxylation). These findings agree with previous reports regarding variations in the extents of mineralization of carbon atoms in different oxidation states. Moreover, this work demonstrates the value of systematically probing biodegradation of polymer hydrolysis products by the precise design of 13 C-labeled molecules.

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