Vinyl-ester resinsVinyl ester resins were first introduced commercially in the 1960s. They are produced by the reaction ('esterification') between an epoxy resin and an unsaturated monocarboxylic acid. Basically they comprise a base of polyester resin strengthened with epoxy molecules in the backbone of the molecular chain. Vinyl esters also use peroxides (e.g. MEKP) for hardening.
Vinyl ester resins combine the best properties of epoxies and unsaturated polyesters. They can be easily handled at room temperature and have mechanical properties similar to epoxy resins. They have better chemical resistance than polyester resins, especially hydrolytic stability, and at the same time offer greater control over cure rate and reaction conditions than epoxy resins.
Today, they are one of the most important thermosetting materials. Vinyl ester resins have been widely recognized as materials with excellent resistance to a wide variety of commonly encountered chemical environments. They are used to fabricate a variety of reinforced structures, including pipes, tanks, scrubbers and ducts.
Vinyl ester resins are prime candidates for use in composites for transportation and/or infrastructure. Such applications include fabrication of parts for automobiles and other surface transportation vehicles, fascia for buildings, reinforcements for bridges, etc. In addition to these applications, vinyl esters are also being used in coatings, adhesives, molding compounds, structural laminates, electrical applications and military / aerospace applications.
As mentioned before, Vinyl ester resins are addition products of various epoxies and unsaturated mono-carboxylic acids, most commonly methacrylic acid. They have terminal reactive double bonds derived from the carboxylic acid used. These reactive groups can form a cross-linked network with or without the addition of a co-monomer.
It is common to dilute the vinyl ester oligomers with a low molecular weight co-monomer, such as styrene, vinyl toluene or methyl methacrylate, to reduce the room temperature viscosity of the mixture and yield a solution with a typical viscosity in the range of 200 to 2000 cps.
In many industrial vinyl ester resins, styrene is commonly used up to 35-45 wt. %. In dental applications triethylene glycol dimethacrylate is the co-monomer.
Although vinyl ester resins have been used in industry for more than 30 years, they are generally categorized together with the unsaturated polyester family. There is much less research cited in the literature on vinyl ester resins compared to the studies on unsaturated polyesters and epoxy resins, especially the studies on the formation-structure-properties of vinyl ester resins. Most of the information concerning the cure behavior and morphology of free radical cured resins focus on unsaturated polyester resins.