Free-Radical/Cationic Hybrid UV-Curable Silicone Resin for Age-Resistant Coatings

To achieve the unique advantages of silicone resin and the free-radical/cationic hybrid UV-curing mechanism, a free-radical/cationic hybrid UV-curable silicone resin (MTQ-TQ-T) is synthesized from commercially available siloxanes, hexamethyldisiloxane (MM, M segment), phenyltrimethoxysilane (PTMS, T segment), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560, T segment), (3-methacryloxy)propyltrimethoxysilane (KH570, T segment), and tetraethyl orthosilicate (TEOS, Q segment). UV-curing kinetics indicates that the polymerization efficiency of MTQ-TQ-T initiated by free-radical and cationic dual photoinitiators is better than that of a single photoinitiator. As the molar ratio of cationic to free-radical photoinitiators (C/R) increases, the double-bond conversion first increases and then decreases, but the epoxy group conversion is the opposite. The optimal C/R and dose of dual photoinitiators are 1.5 and 10 wt %, respectively. After UV-curing, the coating has excellent overall performance including a gel content of 87.8%, a Shore A hardness of 85, a tensile strength of 4.23 MPa, and an impact strength of 5.48 kJ/m2. Its thermal decomposition temperature of 5 wt % is 338 °C, and the yellowing index only increases by 0.98 after thermal aging at 85 °C for 72 h. Moreover, UVMTQ-TQ1-T0.33 (the molar ratio, T/Q of 1 and KH560/570 of 0.33) shows good hydrophobicity with a contact angle of 87°, and it is still 89° after thermal aging. In addition, the adhesion of coating increases with the increase of epoxy groups, where UVMTQ-TQ1-T1 (the molar ratio, T/Q of 1 and KH560/570 of 1) has optimal adhesion with a shear strength and 180° peel strength of 1.7 and 0.9 MPa, respectively. Therefore, this free-radical/cationic hybrid UV-curable silicone resin will be used as aging-resistant coatings.