Photocurable Itaconic Acid-Functionalized Star Polycaprolactone in Biobased Formulations for Vat Photopolymerization

Photopolymerization-based three-dimensional (3D) printing techniques, such as stereolithography (SLA), are becoming more popular due to their ability to create complex geometries and material properties that are difficult to achieve with other methods. However, a major issue with photopolymerization-based techniques is that they rely on the use of harmful (meth)acrylic acid esters derived from fossil fuels. To address this, researchers have been exploring the use of biobased alternatives such as itaconic acid, which is a building block obtained through fermentation and has a photocurable double bond. Additionally, aliphatic polyesters, such as polycaprolactone (PCL) and its hyperbranched star-like polymers, have been discovered to be biodegradable and low cost and have intricate 3D structures. However, their solid thermoplastic features make them unsuitable for vat photopolymerization-based techniques. This study proposes the one-pot synthesis of a liquid itaconic acid-functionalized branched polycaprolactone macromer, named sorbitol hexa(pentacaprolactone methyl itaconate), SH(PCI). The synthesized (meth)acrylic-free low-molecular-weight polymer was then used to create photocurable resins that could be 3D-printed into biobased thermosets with high resolution and printability. The polymer and the printed object were tested and characterized for structural, mechanical, and thermal properties, and 10 different resins were proposed with biobased contents of up to 97%, which are among the highest reported in the literature so far. These resins lead to printed materials that cover a broad range of mechanical properties, including elastic moduli ranging from 22.1 to 218 MPa, elongations at breaks from 3.9 to 20%, and tensile strengths from 3.6 to 11.6 MPa.