Water resistance study on fast UV-curable polybutadiene coatings crosslinked by multifunctional mercaptan in different aqueous conditions

Fast UV-curable coatings were prepared through thiol-ene reaction in 10 s, and their waterproof performance was evaluated in different aqueous conditions. The FTIR spectra showed that UV polybutadiene (PB) coatings could be successfully prepared by using mercaptan pentaerythritol tetra (3-mercapto propionate) (PETMP) as the crosslinking agent reacting with maleic anhydride-grafted polybutadiene under photo initiator. Their gel content increased from about 78–92% with the addition of PETMP from 10% to 20%, and then, this increment was less than 2% with the addition of PETMP from 20% to 30%. Their water absorption rate decreased from about 7%–4% with the addition of PETMP up to 20%−25% after 240 h immersion in DI water. The coating containing 25% PETMP demonstrated a significant cleanliness relative to that of plywood and the other coatings as observed from the stain flushing test. The EIS impedance after 96 h immersion revealed a great enhancement in corrosion resistance with the addition of PETMP at about 20%–25%, while the decline in impedance for the coating with 30% PETMP implied the probable aggregation of excessive PETMP; these were confirmed by the semi-immersion test in which the sample containing 20% PETMP exhibited much better salt water resistance than that of the other samples after 168 h immersion in 3.5% NaCl solution. An appropriate addition of PETMP at around 20%–25% resulted in a high crosslinking degree that enhanced waterproof performances of UV-cured PB coatings in DI water, stain water, and salt water. This study provides valuable reference in designing fast UV-curable coatings with good water resistance used as electronic packaging sealants, flexible protective coatings, and so on.