Unsaturated polyester resins based on rosin maleic anhydride adduct as corrosion protections of steel

Unsaturated polyester resin (UP), based on 1 mol maleopimaric adduct (MPA), 1 mol maleic anhydride, 1 mol isophthalic acid, 1 mol adipic acid, 1 mol propylene glycol, and 1 mol diethylene glycol, were obtained at various times during polyesterification. They were characterized by 1H NMR and chemical titration. Increasing the reaction time to 8 h led to an increase in (a) the number-average molar mass (Mn), (b) the glass transition temperature (Tg) and (c) the compatibility with styrene. Several of these fractions were cured with styrene, in amount of UP/ST = 2.5 (weight of styrene, ST, and unsaturated polyester, UP), using initiator and activator. The curing behaviors of cured UP resins with styrene were evaluated by DSC measurements. The prepared UP curable resins were evaluated in the field of steel coating by measuring their mechanical properties and chemical resistance. The corrosion resistance of cured films was evaluated using salt fog resistance test.