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The unsaturated polyester is a linear polymer compound having a multifunctional group having a polyester chain bond and an unsaturated double bond in its main chain, and a carboxyl group and a hydroxyl group at both ends of the macromolecular chain.
The double bond on the main chain can be copolymerized and crosslinked with the vinyl monomer to convert the unsaturated polyester resin from a soluble, fusible state to an insoluble, infusible state.
The ester bond on the main chain can undergo a hydrolysis reaction, and an acid or a base can accelerate the reaction. When copolymerized with styrene, the hydrolysis reaction can be greatly reduced.
In acidic media, hydrolysis is reversible and incomplete, so polyester can withstand the attack of acidic medium; in alkaline medium, due to the formation of a resonance-stable carboxylate anion, hydrolysis becomes irreversible, so polyester is resistant to alkali Poor sex.
The carboxyl group at the end of the polyester chain can react with an alkaline earth metal oxide or hydroxide [e.g., MgO, CaO, Ca(OH)2, etc.) to expand the molecular chain of the unsaturated polyester, eventually forming a complex. The molecular chain extension can be such that the initial viscosity is 0.1 to 1.0 Pa·s of a viscous liquid resin, and the viscosity is sharply increased to 103 Pa·s or more in a short period of time until it becomes a non-flowable, non-sticky gel-like substance. When the resin is in this state, it is not crosslinked, it is still soluble in a suitable solvent, and has good fluidity upon heating.
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