β-Methyl-δ-valerolactone as a Monomer for UV-Curable and Chemically Recyclable Elastomers

Though the growth of three-dimensional printing (3D printing) by vat photopolymerization has expanded opportunities for polymer manufacturing, most commercial resins are petrochemically derived and form thermosets that are challenging to recycle. We report the solvent-free synthesis of poly(β-methyl-δ-valerolactone) (PβMVL)-based photo-cross-linkable resins from the ring-opening polymerization of the renewable monomer β-methyl-δ-valerolactone (βMVL) with a low ceiling temperature ( T c ) in the neat state. We explore the temperature dependence of the characteristic equilibrium monomer concentration and control the quantities of residual βMVL for sequestration with diamines to give diamidodiols or use as a nonreactive diluent to reduce resin viscosity. We demonstrate the advantage of diamidodiol cross-linkers in the presence of PβMVL to form a bimodal network strengthened with additional hydrogen bonding moieties, resulting in materials with tensile strengths of 8 ± 2 MPa and elongations at break of 105 ± 8%, which are comparable to commercial vat photopolymerization resins. High-resolution 3D-printed materials were produced and shown to be chemically recycled back to βMVL in high yield and purity.