Unsaturated polyester is the polycondensation of unsaturated dicarboxylic acid (or acid anhydride) or their mixed acid composed of saturated dicarboxylic acid (or acid anhydride) and polyhydric alcohol, and has linear ester bond and unsaturated double bond. polymer compounds. Usually, the polyesterification polycondensation reaction is carried out at 190-220°C until the desired acid value (or viscosity) is reached. After the polyester condensation reaction is completed, a certain amount of vinyl monomer is added while hot to form a viscous liquid. Such a polymer solution is called an unsaturated polyester resin.
1. Physical and chemical properties
1. Physical properties. The relative density of unsaturated polyester resin is about 1.11 to 1.20, and the volume shrinkage rate during curing is relatively large. Some physical properties of the cured resin are as follows: (1) Heat resistance. The heat distortion temperature of most unsaturated polyester resins is 50-60℃, and some resins with good heat resistance can reach 120℃. The red thermal expansion coefficient α1 is (130～150)×10-6℃. ⑵ mechanical properties. Unsaturated polyester resins have high tensile, flexural, and compressive strengths. ⑶ chemical corrosion resistance. Unsaturated polyester resin has good resistance to water, dilute acid and dilute alkali, but poor resistance to organic solvents. At the same time, the chemical corrosion resistance of resin can vary greatly with its chemical structure and geometric switch. ⑷ Dielectric properties. The dielectric properties of unsaturated polyacid resins are good.
2. Chemical properties. Unsaturated polyester is a linear polymer compound with multifunctional groups, with polyester chain bond and unsaturated double bond on its backbone main chain, and carboxyl group and hydroxyl group at both ends of macromolecular chain. The double bond on the main chain can undergo copolymerization and cross-linking reaction with vinyl monomers, so that the unsaturated polyester resin changes from a soluble and fusible state to an insoluble and infusible state. The ester bond on the main chain can undergo a hydrolysis reaction, which can be accelerated by acid or base. If it is copolymerized and crosslinked with styrene, the occurrence of hydrolysis reaction can be greatly reduced. In acidic medium, hydrolysis is reversible and incomplete, so polyester can resist the erosion of acidic medium; in alkaline medium, due to the formation of resonance-stabilized carboxylate anions, the hydrolysis becomes irreversible, so polyester is resistant to alkali. Poor sex. The carboxyl group on the end of the polyester chain can react with alkaline earth metal oxides or hydroxides [such as MgO, CaO, Ca(OH)2, etc.] to expand the molecular chain of the unsaturated polyester, which may eventually form a complex. Molecular chain extension can make the initial viscosity of 0.1-1.0Pa·s viscous liquid resin, and the viscosity increases sharply to more than 103Pa·s in a short period of time, until it becomes a non-flowable, non-stick-like gel-like substance. In this state, the resin is not cross-linked, still soluble in suitable solvents, and has good fluidity when heated
Edited by Suzhou Eastop Chemical Co., Ltd.
