Terpene- and terpenoid-based polymeric resins for stereolithography 3D printing

Thiol–ene ‘click’ reactions utilizing terpenes and a four-arm thiol were employed to produce thermoset 3D printed structures using vat photopolymerisation. Five terpenes were characterized for reactivity using both ¹H NMR spectroscopy and photorheology, allowing for screening of both monomers and prepolymer oligomers as possible candidates for stereolithographic 3D printing. The time to crosslinking for limonene- and linalool-based resins was found to be approximately 5 s while nerol- and geraniol-based resins crosslinked over the course of 1 h, under the 3D printing conditions. The materials produced from photo-crosslinking displayed a range of thermomechanical behaviours, with varied post-printing thermal curing cycles utilized to alter thermomechanical behaviour from a brittle elastomer with strains at failure of ca. 50% (Young's modulus of ∼0.4 MPa) to more traditional engineering thermoplastic behaviours with elastic moduli above 20 MPa and strains to failure of 180%. The relationship between material properties and surface energy was elucidated through the use of thermomechanical characterizations (differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis), and select compositions are demonstrated to be suitable for printing into complex 3D shapes through additive manufacturing techniques.