Bio-Based Thiazolium-Eugenol Copolymers with Tunable Thermal, Antioxidant and Antimicrobial Properties

The increasing demand for biobased antimicrobial materials has driven the development of bio-based polymer systems that integrate renewable feedstocks with advanced functional performance. In this work, a series of multifunctional copolymers derived from vitamin B-based thiazolium and a hydrophobic eugenol-based methacrylate monomer were synthesized via free radical copolymerization followed by quaternization reaction. The eugenol-derivative comonomer was specifically designed to exhibit a low glass transition temperature, acting as a flexible, biobased segment that moderates the rigidity and high charge density typically associated with cationic thiazolium polymers was planned to modulate the antimicrobial activity and their selectivity against bacteria and not against mammalian cells. The resulting copolymers are amorphous materials with tunable glass transition temperatures and stable positive zeta potentials in aqueous media after quaternization. Antioxidant properties, evaluated by DPPH radical scavenging assays and expressed as Trolox equivalent antioxidant capacity, depend strongly on copolymer composition and increase with the content of thiazolium units in quaternized systems, while non-quaternized polymers show enhanced antioxidant activity with increasing eugenol content. The antimicrobial performance of the quaternized copolymers was assessed against both Gram-positive and Gram-negative bacteria, revealing strong activity against Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA), and moderate activity toward Gram-negative bacteria. Importantly, incorporation of the hydrophobic eugenol-based units improves cytocompatibility and bacterial selectivity compared to the corresponding homopolymers. These results demonstrate that the incorporation of renewable eugenol-based segments into thiazolium-based cationic polymers provides an effective strategy to modulate thermal, biological, and physicochemical properties, yielding biobased antimicrobial materials with balanced performance and improved biocompatibility.