Photo-crosslinked Diels–Alder and thiol–ene polymer networks

Abstract

Compositions of ethylene glycol dicyclopentenyl ether methacrylate (EGDEMA), a vegetable oil based alkyl methacrylate (C13MA), and furfuryl methacrylate (FMA) were terpolymerized for dual-crosslinked networks with tailored mechanical and thermal properties. Specifically, initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP) afforded materials with tailored glass transition temperature (T_g) and incorporation of furan and norbornene functionalities within a single chain. The terpolymer with high furan and norbornene functionality (Ter2: F_FMA = 0.42, F_EGDEMA = 0.46, F_C13MA = 0.12) is crosslinked to form single-crosslinked reversible networks with 1,1′-(methylenedi-4,1-phenylene)bismaleimide (BM) via Diels–Alder (DA) chemistry and dual-crosslinked networks incorporating additional non-reversible thiol–ene crosslinks. The reactions were photo-initiated using 254 nm UV light with BM : FMA molar ratios of 0.1 and 0.2 for both systems. FTIR analyses for crosslinked Ter2 samples confirmed the successful formation of DA and thiol–ene adducts, while DSC confirmed the reversibility of the DA reaction. A terpolymer with higher C13MA composition (Ter3: F_C13MA = 0.75, F_FMA = 0.17, F_EGDEMA = 0.08) was similarly crosslinked in single and dual crosslinked networks with BM : FMA of 0.1 and 0.2. Crosslinking efficiency was evaluated for both single and dual crosslinked networks with a BM : FMA = 0.1 by comparing thermal and UV curing methods, with UV curing proving more effective for dual-crosslinked systems, leading to increased gel content (71% with UV compared to 61% thermally) and improved material properties. FTIR and DSC results confirmed the formation of the DA adducts and the reversibility of the DA reaction. The terpolymers were further analyzed for adhesive applications through rheological testing. These studies demonstrated that the incorporation of thiol–ene crosslinking alongside Diels–Alder crosslinking offers a balanced combination of reversible and permanent bonds, resulting in materials with enhanced mechanical strength, thermal stability, and functional versatility that are suitable for applications such as recyclable adhesives.