What Is Unsaturated Polyester Resin?

Generally, it is a linear polymer compound with ester bonds and unsaturated double bonds formed by the condensation of unsaturated diacid diols or saturated diacid unsaturated diols. Usually, the polyester polymerization reaction is carried out at 190-220 ℃ until the expected acid value (or viscosity) is reached. After the polyester polymerization reaction is completed, a certain amount of vinyl monomer is added while hot to form a viscous liquid. This polymer solution is called unsaturated polyester resin. Unsaturated polyester has many varieties due to the different raw materials used. Unsaturated dicarboxylic acids or anhydrides commonly used in industrial production include maleic anhydride, fumaric acid, and tetrahydrophthalic anhydride. The commonly used saturated dicarboxylic acids or anhydrides are phthalic anhydride, isophthalic acid, and adipic acid. The most commonly used diols are propylene glycol, diethylene glycol, and dipropylene glycol. Ethylene monomers used as crosslinking agents include styrene, methyl methacrylate, and diallyl phthalate. In addition to the above-mentioned main raw materials, there are also various additives and inhibitors, catalysts or initiators, promoters, fillers, dyes, and lubricants. The most commonly used unsaturated polyester is synthesized from maleic anhydride, phthalic anhydride, and propylene glycol. The condensation methods include: ① melt condensation method. Directly melt and condense acid and alcohol without adding any other components. Utilize the difference in boiling range between alcohol and water to separate the water generated by the reaction through a separation column. This method has simple equipment, short production cycle, and is widely used Solvent azeotropic dehydration method. Add toluene or xylene (solvent) during the condensation process, utilizing the lower boiling point of toluene and water compared to water, to quickly remove the water generated by the reaction and promote the condensation reac