It is likely that a half-century ago even enthusiastic and optimistic proponents of the synthetic polymer industry (Mr. McGuire included) could not have predicted the massive scale on which synthetic polymers would be manufactured and used today. Ultimately, the future success of this industry will rely on the development of sustainable polymersmaterials derived from renewable feedstocks that are safe in both production and use and that can be recycled or disposed of in ways that are environmentally innocuous. Meeting these criteria in an economical manner cannot be achieved without transformative basic research that is the hallmark of this journal. In this Perspective we highlight five research topicsthe synthesis of renewable monomers and of degradable polymers, the development of chemical recycling strategies, new classes of reprocessable thermosets, and the design of advanced catalyststhat we believe will play a vital role in the development of sustainable polymers. We also offer our outlook on several outstanding challenges facing the polymer community in the broad area of sustainable polymers.

Aliphatic polyester block polymers constitute a highly useful and amazingly versatile class of self-assembled materials. Analogous to styrenic block polymers in both design and function, the property profiles of these degradable materials can be precisely tailored by altering the chemical structure of the components. Driven by this ideal, we have examined the impact of n-alkyl substituents on the polymerization thermodynamics and kinetics of substituted δ-valerolactone monomers and developed guiding design principles based on critical structure–property relationships in the resulting aliphatic polyesters. Under bulk room temperature conditions the polymerization rate depends strongly on substituent position and exhibits a more modest dependence on alkyl length (from −CH3 to −(CH2)8CH3). The enthalpy and entropy of polymerization are significantly influenced by substituent position, but both are largely insensitive to n-alkyl length. However, the physical properties of the resulting aliphatic polyesters depend much more on substituent length than on substituent position. Notably, we demonstrate that polymer entanglement molar mass and solubility parameter can be systematically tuned by changing the substituent length. We discuss how these key structure property relationships can be used to inform the design of advanced sustainable materials for future technologies important in the arena of environmentally friendly materials.

Significance In recent years there has been extensive research toward the development of sustainable polymeric materials. However, environmentally benign, bioderived polymers still represent a woefully small fraction of plastics and elastomers on the market today. To displace the widely useful oil-based polymers that currently dominate the industry, a bioderived synthetic polymer must be both cost and performance competitive. In this paper we address this challenge by combining the efficient bioproduction of β-methyl-δ-valerolactone with controlled polymerization techniques to produce economically viable block polymer materials with mechanical properties akin to commercially available thermoplastics and elastomers.

A one-pot, one-catalyst, sequential ring-opening transesterification polymerization (ROTEP) was used to prepare fully renewable amorphous poly(D,L-lactide)−poly(ε-decalactone)−poly(D,L-lactide) (LDL) triblock polymers. These α,ω hydroxy-telechelic polymers were subsequently coupled to prepare linear alternating (LDL) n multiblock polymers. Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) indicated microphase separation into two domains in both the triblock and multiblock architectures. The temperature dependent Flory−Huggins interaction parameter for this system, χ(T) = 69.1/T − 0.072, was estimated from the experimentally determined order−disorder transition temperature (T ODT ) values of four symmetric LDL triblock polymers. Uniaxial extension tests revealed a dramatic dependence of the room-temperature mechanical properties on overall molar mass. Additionally, coupling low molar mass LDL triblocks to prepare (LDL) n multiblocks led to substantial increases in the ultimate elongation and tensile stress at break. Compared to high molar mass triblocks with inaccessible T ODT values, (LDL) n multiblocks of similar composition and molar mass were found to disorder at much lower temperatures (T ODT < 150°C). Because of this, it was possible to process (LDL) n using injection molding. The simple synthetic procedure and melt processability of the (LDL) n multiblock polymers make these multiblocks attractive as renewable thermoplastic elastomers (TPEs).

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.