Myrcene-itaconate Diels-Alder cycloadducts in the synthesis of photocurable polyesters for the 3D printing of fully biobased resins

Photopolymerization-based 3D printing techniques, such as vat photopolymerization (VP), unfortunately still strongly rely on the use of fossil-based (meth)acrylate monomers for the formulation of photo hardening resins. Because of that many researchers have recently directed their efforts towards the replacement of methacrylic and acrylic acid derivatives with biobased counterparts. Indeed, in this work, we introduce a novel approach for producing sixteen fully biobased resins for VP, based on photocurable polyesters synthesized starting from bio- sourced reagents. Itaconic acid, widely recognized as an effective biobased photocurable monomer, and myrcene, a terpene consisting of two isoprene units, are employed in a Diels-Alder cycloaddition to achieve a co-monomer (My-DMI) for the new photocurable polyesters. By exploring various molecular weights, diols and ratios between itaconate and My-DMI, we synthesized eight different polyesters. By combining these with appropriately designed reactive diluents, we successfully tuned the mechanical properties of the 3D printed materials, ranging from very flexible to extremely rigid, depending on the diol chain length and itaconate contents. Additionally, we provide a detailed evaluation of the biobased content of each formulation according to the OK BIOBASED labelling for plastics, finding biobased content as high as 97 % in most cases.