The main raw materials for producing polyester resins include phthalic anhydride, maleic anhydride, fumaric acid, propylene glycol, ethylene glycol, diethylene glycol, and styrene, among others.
Polyester resin is the abbreviated term for unsaturated polyester adhesive. Unsaturated polyester adhesives are primarily composed of unsaturated polyester resin, an initiator, a promoter, fillers, thixotropic agents, and other additives. It is a linear‑structured polyester resin containing –CH=CH– double bonds in its main chain; when blended with vinyl monomers such as styrene, acrylates, and vinyl acetate, it undergoes polymerization at room temperature under the action of initiators and promoters, yielding an insoluble, infusible product. The English abbreviation for unsaturated polyester is UP. It is mainly used in the production of coil coatings.
Polyester resins are a class of high-molecular-weight compounds formed by the polycondensation of diols with dicarboxylic acids, or of polyols with polycarboxylic acids.
Polyester resins are classified into saturated polyester resins and unsaturated polyester resins. Unsaturated polyester adhesives are primarily composed of unsaturated polyester resin, pigments and fillers, initiators, and other additives. These adhesives exhibit low viscosity, excellent wettability, and good processability; the cured adhesive layer is highly rigid, transparent, and highly glossy, can cure rapidly at room temperature under pressure, and demonstrates good heat resistance and superior electrical properties. However, they suffer from significant shrinkage, relatively low adhesive toughness, and poor resistance to chemical media and water, making them suitable for non‑structural applications. They are mainly used for bonding fiberglass-reinforced plastics, rigid plastics, concrete, and for sealing electrical enclosures.
The raw materials for synthesizing saturated polyester resins primarily include diols, dicarboxylic acids, and triols; in some cases, monofunctional alcohols or monocarboxylic acids are also used. A commonly employed diol is neopentyl glycol, whose esters exhibit significantly superior water resistance compared to those of ethylene glycol and propylene glycol. Triols typically comprise trimethylolpropane and tris(2‑hydroxyethyl)ethane. Among the aromatic dicarboxylic acids, isophthalic acid is widely used; owing to its markedly better salt‑spray resistance, chemical resistance, and water resistance than phthalic acid, it finds more extensive application in polyester resins. Aliphatic dicarboxylic acids—such as adipic acid, azelaic acid, and sebacic acid—are also incorporated into polyester resin synthesis, with adipic acid being the most prevalent. Most polyester resins contain both aromatic and aliphatic dicarboxylic acids, and the molar ratio of aromatic to aliphatic dicarboxylic acids is a key factor in controlling the resin’s glass transition temperature (Tg).
