Optimal combination of UV‐induced cationic ring opening polymerization monomers for light‐weight automotive plastic coating

Abstract

AbstractCROP 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′ from 104 to 107 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.