Polyester Resins can be further defined by their chemistry. These categories are described as Orthophthalic (Ortho), Isophthalic (Iso), Dicyclopentadiene (DCPD). Vinylesters have a unique chemistry and that shares many working properties with the polyesters.
Orthophthalic (Ortho) resins are based upon orthophthalic acid and are a good basic, general-purpose, inexpensive resin.
They have styrene content between 35% and 45%, and are used in applications that do not require elevated service temperatures, high corrosion resistance, or high mechanical properties.
Isophthalic (Iso) resins are a step above Ortho resins, and are better suited for corrosion environments, elevated service temperatures, and have greater mechanical properties. Iso resins have between 42% and 50% styrene because the higher molecular weight more solvent is required to create a workable viscosity. Iso’s better properties do bring higher cost as compared to Ortho Resins.
Dicyclopentadiene (DCPD) resins are used for applications requiring high surface finish. This is due to their low volumetric shrink rate. Physical properties are similar to the Ortho resins, but toughness is sacrificed along with the ability to create strong secondary bonds. DCPD resins are on the low end of styrene content, ranging from 35% to 38%. DCPD resins are commonly blended with other resins to minimize the negative aspects and increase positive aspects of these resins.
Vinylesters are used in applications requiring superior corrosion resistance or toughness properties. Vinyesters are a formulation of epoxy resin and methacrylic acid, resulting in a polymer that has characteristics of polyester and epoxy.