CROP reactivity of organic coatings composed of three structurally different monomers with epoxy or oxetane derivatives was investigated, focusing on rheological and surface mechanical properties. Real-time crosslinking behavior of CROP monomers was monitored using a rotational rheometer. Results of differential scanning calorimetry with in situ UV irradiation revealed that the ring opening reactivity of CROP monomers protonated by a photoacid generator (PAG) was correlated with the heat released during the exothermic polymerization reaction. In addition, reaction conversions of monomers with epoxy and oxetane groups were compared using Fourier transform infrared spectroscopy (FT-IR) under dark curing conditions. Surface and internal mechanical properties of coating films, including adhesion with polycarbonate substrate, were comprehensively evaluated by nano-indentation, nano-scratch, and surface and interfacial cutting analysis system (SAICAS) tests. By understanding the unique crosslinking characteristics of each CROP monomer, the ternary CROP monomer system, optimally containing with ECC of 53.6 wt%, DOX of 22.9 wt%, and DEO of 15.3 wt%, exhibited improved crosslinking density (G 0 from 10 4 to 10 7 Pa) and exceptional mechanical (with scratch resistance increasing from 7.11 to 16.17 mN for Lc1), adhesion (with crosscut resistance increasing from 0 to 5B), and transparency properties, surpassing the performance of unitary ECC coating system.cationic ring opening polymerization (CROP), crosslinking, epoxy and oxetane, photocuring, surface coatings
| INTRODUCTIONUltraviolet (UV) photopolymerization offers many benefits over thermal curing, including a shorter processing time that allows formulation of solvent-free coatings and processing under ambient temperature with maximized energy efficiency. [1][2][3] Thus, it has been used in many coating industries for printing inks, adhesives, varnishes, and protective coatings. 4,5 Photopolymerization is performed through a chain reaction mechanism including propagation of the active center (e.g., radical, cation, or rarely anion) by interaction with monomers. Most research efforts in this field have been focused on free radical polymerization (FRP) through the development of novel photoinitiators Junyoung Park and Do Wan Lee contributed equally to this study.