A linear structure (see linear polymer) polyester resin containing -CH and CH-double bonds in the main chain of unsaturated resin, which can be mixed with ethylenic monomers such as styrene, acrylate, vinyl acetate, etc. Afterwards, under the action of initiators and accelerators, it polymerizes into insoluble and infusible products at room temperature. The English abbreviation for unsaturated polyester is UP.
Adipic acid can also be used instead of phthalic anhydride to obtain products with better toughness. Unsaturated dibasic acid can also be used fumaric acid, itaconic acid and so on. The most commonly used glycol is 1,2-propanediol, and sometimes ethylene glycol, diethylene glycol, dipropylene glycol, 1,3-butanediol, etc. are also used. However, when using ethylene glycol, the miscibility of the prepared unsaturated polyester and styrene is very poor, so it should be mixed with other glycols to reduce the crystallinity of the polyester and improve its mixing with styrene Solubility. Co-monomer can also use methyl methacrylate, which can get polyester products with better weather resistance.
Condensation polymerization is carried out for more than ten hours until a low acid value polyester (molecular weight of 1000-2500) is produced. Cool to about 90℃, dilute with styrene containing hydroquinone polymerization inhibitor (0.01% of total resin), and its dosage is 1.5 to 2.0 times of unsaturated acid on a molar basis. It can be stored for several months to more than one year at room temperature. For thermal curing, only benzoyl peroxide initiator can be added and heated to about 100℃ to cure. Whether it is room temperature curing or thermal curing, the reaction is that the primary free radical generated by the decomposition of the initiator first initiates the polymerization of styrene to form an active free radical of the oligomer, and then connects to the double bond on the unsaturated polyester main chain On the copolymerization cross-linking reaction. In addition, it can also be cured by irradiation with ultraviolet rays, electron beams, gamma rays, etc.