A linear structure (see linear polymer) polyester resin containing -CH匉CH-double bond in the main chain can be mixed with ethylenic monomers such as styrene, acrylate, vinyl acetate, etc. Under the action of initiator and accelerator, it polymerizes into insoluble and infusible products at room temperature. The English abbreviation for unsaturated polyester is UP.
Polymerization Premium industrial products were produced during the Second World War. The typical product is obtained by polycondensation of 1,2-propanediol, maleic anhydride and phthalic anhydride to obtain unsaturated polyester, and then add styrene monomer (the monomer content is 18% to 40%). Under the action of the agent, styrene and the double bond in the unsaturated polyester undergo copolymerization and cross-linking reaction, changing from the original flowable viscous liquid to an insoluble and infusible thermosetting resin. Since the resin becomes brittle when the degree of crosslinking is too high, saturated dibasic acid is often added to control the degree of crosslinking. 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. Glycol is commonly used in 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.
The specific process is to mix 1,2-propanediol, maleic anhydride, and phthalic anhydride in a molar ratio of 1.1:0.67:0.33, in an atmosphere of nitrogen or carbon dioxide, at 150～200℃
Condensation polymerization is carried out for more than ten hours until a polyester with a low acid value (molecular weight 1000-2500) is produced. Cool to about 90℃, dilute with styrene containing hydroquinone polymerization inhibitor (accounting for 0.01% of the total resin), the amount of which is 1.5 to 2.0 times the unsaturated acid on a molar basis. It can be stored for several months to more than one year at room temperature.
There are two kinds of curing: room temperature curing and thermal curing: ① room temperature curing, add an initiator (such as benzoyl peroxide, cyclohexanone peroxide, etc.) and an accelerator (such as N,N-dimethylaniline, cobalt salt), make the polyester liquid form a gel at room temperature, and then solidify. ②Thermal curing can be done by adding benzoyl peroxide initiator and heating to about 100℃. Whether it is room temperature curing or thermal curing, the reaction is that the primary free radicals generated by the decomposition of the initiator first initiate the polymerization of styrene to form an active free radical of the oligomer, and then connect 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.
Application is mainly used to make glass fiber reinforced plastic products for shipbuilding, building materials, transportation equipment, chemical equipment, etc. Unreinforced unsaturated polyester resins are mainly used in coatings, decorative castings, electrical castings, polyester putty and glue, etc.