Cationic Photopolymerization of Biobased Oxetane Monomers Obtained from Adipic, Itaconic, and Citric Acid Functionalization

Cationic photopolymerization offers a significant advantage over radical polymerization due to its resistance to oxygen inhibition and superior dimensional stability during the crosslinking process. In this study, we aim to advance the development of bio-based monomers for cationic photopolymerization by synthesizing oxetane-functionalized derivatives of adipic, itaconic, and citric acids. These three renewable acids were chosen for their multifunctionality and availability. The synthesized monomers, bis((3-methyloxetan-3-yl)methyl) adipate (BOA), bis((3-methyloxetane-3-yl)methyl) itaconate (BOI), and tris((3-methyloxetane-3-yl)methyl) citrate (TOC), were fully characterized using nuclear magnetic resonance (NMR). Fourier transform infrared (FTIR) spectroscopy and photo differential scanning calorimetry (photo-DSC) were employed to monitor the oxetane ring-opening reaction kinetics and to determine the degree of conversion, revealing high reactivity in all monomers, reaching nearly complete conversion within 90 s. The mechanical properties of the UV-cured films were assessed by dynamic mechanical thermal analysis (DMTA) and gel content measurements. Results indicated that the BOI-based films exhibited higher glass transition temperatures (Tg) and crosslinking densities compared to BOA- and TOC-based films. The findings demonstrate the potential of bio-based oxetane monomers to produce UV-curable materials with acceptable thermomechanical properties, offering a sustainable alternative to petroleum-derived precursors.