Main raw material
Ethylene glycol is the simplest structure of diol. Due to its structural symmetry, the resulting polyester resin has obvious crystallinity, which limits its compatibility with styrene, so it is generally not used alone. In combination with other glycols, such as 60% ethylene glycol and 40% propylene glycol, the compatibility of the polyester resin with styrene can be improved; if used alone, the resin-forming end should be used. Acetylation or propionylation to improve its compatibility.
1,2 propylene glycol, due to structural asymmetry, can obtain a non-crystalline polyester resin, can be completely soluble in styrene, and its price is relatively low, so it is currently the most widely used diol. Other useful glycols are:
Diethylene glycol - can improve the flexibility of polyester resin; dipropylene glycol - can improve resin flexibility and corrosion resistance;
Neopentyl glycol - improves the corrosion resistance of resins, especially alkali and hydrolytic stability.
The above diols may lose strength due to too much flexibility of the resin, or should improve the compatibility of the resin with styrene. They are generally not used alone and should be mixed with other glycols. A polyester resin with highly durable chemical corrosion, often using bisphenol A or hydrogenated bisphenol A as a raw material. To form a glycol suitable for reaction with a dibasic acid, bisphenol A should be previously propylene oxide or epoxy. The ethane reacts to form a glycol having an alcoholic hydroxyl group at both ends, such as a D-33 glycol.
The use of chlorinated or brominated glycols not only exhibits flame retardancy but also improves corrosion resistance.
The addition of a small amount of a polyol such as glycerol and pentaerythritol improves the heat resistance of the resin to a large extent.
The chemical resistance of unsaturated polyester resins depends on the chemical structure of the resin. The ester bond is the weakest link in the polyester resin and is susceptible to hydrolysis by the action of acids and bases. The different chemical structures surrounding the ester bond have different steric hindrance protection for the ester bond, leaving the article exhibiting different corrosion resistance.