Chemically recyclable elastomers from β-caryophyllene polymerization

Background

The field of polymer science is increasingly focused on transitioning away from petroleum-based precursors toward sustainable, renewable feedstocks. There is a significant industrial need for low-cost, non-toxic, and bio-based materials to manufacture high-performance elastomers, adhesives, and composite binders. For example, solid propellants and explosives heavily rely on polymeric binders, such as hydroxy-terminated polybutadiene, to provide structural integrity. As environmental concerns mount, identifying abundant, naturally derived alternatives is a critical priority. Plant-derived sesquiterpenes, particularly those generated as byproducts from essential oil production, represent highly attractive, renewable feedstocks to meet this growing demand.

Despite the promise of these renewable feedstocks, current approaches to utilizing them in advanced polymer synthesis face significant limitations. Traditional polymers derived from sesquiterpenes exhibit exceptionally poor functionalization options, severely restricting their utility. Without the ability to introduce controlled end-group functionalities, these conventional bio-polymers cannot effectively serve as cross-linkers or reactive precursors for polyurethanes. Furthermore, existing polymeric binders and thermoset materials are notoriously difficult to recycle once cured. The inability to chemically depolymerize these conventional cross-linked networks leads to substantial material waste and prevents the establishment of circular lifecycles for structural composites.

Technology

This technology synthesizes functionalized polycaryophyllenes from β-caryophyllene using ring-opening metathesis polymerization (ROMP) with transition-metal catalysts and chain-transfer agents. Key features include tunable molecular weights ranging from 2 to 24 kg/mol, low glass transition temperatures, and customizable end groups such as hydroxy, acetoxy, carboxyl, or amino functionalities. These tailored polymers easily react with diisocyanates to create robust thermoplastic or thermoset polyurethanes. The resulting materials exhibit excellent thermal and mechanical properties, making them highly effective as structural elastomers, high-strength adhesives, and energetic binders for solid propellants and explosives due to their high enthalpy of combustion.

This solution is highly differentiated by its use of a low-cost, non-toxic, renewable clove oil byproduct, providing a sustainable alternative to petrochemical-based polymers like hydroxy-terminated polybutadiene. It overcomes historical functionalization barriers of polycaryophyllenes through precise end-group control during polymerization. Furthermore, the technology enables true material circularity. Because the polymer backbone retains residual unsaturation and pendant vinylidene groups, even fully cured thermosets can undergo chemical recycling. This metathesis-driven depolymerization allows the materials to be broken down and reprocessed, offering an environmentally friendly lifecycle rarely achieved in advanced elastomers.

Benefits

• Utilizes a low-cost, non-toxic, and renewable feedstock derived from clove oil production for sustainable polymer manufacturing- Provides highly tunable molecular weights and tailored functional end groups to suit diverse material requirements- Enables the creation of versatile thermoplastic and thermoset polyurethanes for use as adhesives, elastomers, and polyesters- Offers excellent thermal stability, low glass transition temperatures, and strong mechanical properties including high strain at break- Serves as a high-performance binder replacement for solid propellants and explosives due to its high enthalpy of combustion- Facilitates chemical recycling and reprocessing of cured materials through metathesis-driven depolymerization to support circular lifecycles

Applications

• Solid rocket propellant binders- Chemically recyclable polyurethane adhesives- Renewable structural polyurethane elastomers- Reprocessable thermoset polyurethane components- Explosive composite material binders

Additional info

Functionalized polycaryophyllenes are synthesized from bio-renewable β-caryophyllene via ring-opening metathesis polymerization using ruthenium catalysts and functional chain-transfer agents. Exhibiting tunable molecular weights (2–24 kg/mol) and low glass transition temperatures, these polymers feature customizable end-groups such as hydroxyls. When cured with diisocyanates, they yield thermoplastic or thermoset polyurethanes suitable for adhesives, elastomers, and propellant binders, which can undergo chemical recycling via metathesis-driven depolymerization at backbone unsaturations.