A hybrid methacrylate‐norbornene‐thiol photopolymerization system with tunable physical and mechanical properties

Abstract

Photopolymerization of a hybrid methacrylate‐norbornene‐thiol system is used for the solvent‐free synthesis of polymers with tunable physical and mechanical properties. We demonstrate competitive adhesive performance of this system by examining factors such as thiol:ene ratio, thiol functionality, and the incorporation of a methacrylate as a hard monomer. Firstly, ethylene glycol dicyclopentenyl ether methacrylate (EGDEMA) and the di‐functional thiol ethylene bis(3‐mercapto propionate) (EBM) are photopolymerized to produce crosslinked networks with high conversion (up to 100%), high gel content (up to 77%), and low Tg (−2.5 to −13.5°C). Rheological studies found these formulations satisfied the Dahlquist criteria for pressure‐sensitive adhesives (PSAs) with the best adhesive/cohesive performance at thiol:ene ratios = 0.5–0.75. Secondly, a tetra‐functional thiol (PEMP) is crosslinked with EGDEMA photochemically, yielding elastomeric polymer films made to high conversion (up to 100%), with comparatively higher Tg (9–17°C), and higher gel content (up to 100%). Finally, isobornyl methacrylate (IBOMA) is incorporated as a hard monomer and crosslinked with a bifunctional thiol to produce thermoplastic polymers with negligible gel content and variable Tg (−12 to 41°C), suitable for application as temporary adhesives. These findings propose the use of the hybrid system in one‐step solventless formulations for UV curable adhesives, depending on component selection.