Definitions of Resins - Unsaturated Polyester

While this family of plastics goes under the name of “polyesters,” they are quite distinct from the polyesters described above. In fact, they are thermosets, and are probably most familiar to the public for their role in fiberglass reinforced plastics. These materials were introduced to military use (i.e., naval craft) in 1942. After World War II, their characteristics proved extremely appealing to such non-military markets as automotive, marine, corrosion-resistant structures, building, electrical applications, and consumers goods such as luggage, fishing poles and cases and housings of every type and description. These thermosetting resins are made by the condensation reaction between difunctional acids and glycols. The resulting polymer is then dissolved in styrene [C6H5CHCH2] or other vinyl unsaturated monomer. The structures of the acids and glycols used and their proportions, especially the ratio of the unsaturated versus the saturated acid, and the type and amount of monomer used, are all tailored for each resin to balance economy, processing characteristics, and performance properties. One common formulation is the reaction of maleic anhydride [(COCH)2O], phthalic anhydride [C6H4(CO)2O], and propylene glycol [CH3CHOHCH2OH]. Both dicyclopentadiene [C10H12] and isophthalic acid [C6H4(COOH)2] can be substituted for phthalic anhydride. Vinyl ester resins are linear reaction products of bisphenol A [(CH3)2C(C6H4OH)2] and epichlorohydrin [CH2OCHCH2Cl] that are terminated with an unsaturated acid such as methacrylic acid [CH2C(CH3)COOH].

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