Diol, fumaric acid crosslinked with

A different type of crosslinking is possible for esters with the diacids (or diols) containing double bonds in the molecule. This is more common for ester copolymers. For example, an isophthalic acid/fumaric acid/ethylene glycol polyester has the structure shown below ... 

Polyethylene can be crosslinked with peroxides to make it more suitable for coatings for electrical power cables [18]. Peroxides are also used to crosslink (also called cure) thermoset polyesters. Thermoset polyesters have a reactive alkene and are used to make fiberglass compositions such as used for boat hulls. Variations are possible, but commonly they are copolymers of fumaric acid or maleic anhydride with phthalic acid or isophthalic acid and a diol. The oligomer is typically dissolved in styrene. When a peroxide is mixed with the solution, crosslinking occurs and the polyester cures. The styrene solvent takes part in the reaction and the solution hardens. 

Unsaturated polyesters 44 containing multiple electron-deficient maleate and/or fumarate double bonds along the polymer chain are readily prepared by the reaction of maleic anhydride or fumaric acid with a diol. In many cases, other diacids or dianhydrides are also included as comonomers to improve the final mechanical properties. The polyester is combined with styrene monomer and photopolymerization is carried out using a radical photoinitiator. Due to the reactivity ratios of the two vinyl components, there is a tendency toward alternation. However, the length of crosslinks between the polymer chains can be controlled by the amount of excess styrene present. This allows appreciable control over the structure of the network polymer formed, and this has a considerable impact on its mechanical and chemical properties. Photocurable unsaturated polyester-styrene systems have found numerous uses, but the major applications are in wood... 

Fumaric and itaconic acids are also used as the diacid component. Most reaction formulations involve a mixture of a saturated diacid (iso- and terephthalic, adipic) with the unsaturated diacid or anhydride in appropriate proportions to control the density of crosslinking (which depends on the carbon-carbon double-bond content of the prepolymer) for specific applications [Parker and Peffer, 1977 Selley, 1988], Propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, and bisphenol A are also used in place of ethylene glycol as the diol component. Aromatic reactants are used in the formulation to improve the hardness, rigidity, and heat resistance of the crosslinked product. Halogenated reactants are used to impart flame resistance. 

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