Cross epoxide groups

Epoxy resins, which are used as adhesives, are also thermoset polymers that form by cross-linking when the two components of the resin are mixed. One component is a low-molecular-mass linear polymer formed by the reaction of the conjugate base of bisphenol A with epichlorohydrin. The nucleophilic oxygens of the phenolate dianion can either displace the chlorine or open the epoxide ring of epichlorohydrin. A slight excess of epichlorohydrin is used to keep these polymer chains short and to ensure that the linear molecules have epoxide groups at their ends. 

The second component of the glue is composed of a trifunctional amine such as di-ethylenetriamine. When the two components are mixed, the three nucleophilic nitrogens of the triamine react with the epoxide groups to form a highly cross-linked polymer, as shown in the following equation ... 

This class of condensation polymers is characteristically recognized by cross-linking from the reactions of epoxide groups. The products are useful as one of the best adhesives for cementing of rigid materials, and as potting compounds for physical protection or encapsulation of electronic devices. 

In another work, improvement of polymerization reactivity of epoxides was attempted [148]. Styrene monomers were modified with epoxide functions that are inert toward radicallic species, and then polymerized in the presence of azobisiso-butyronitrile (AIBN). The polymers, ultimately, were cross-linked by sulfonium salt induced photopolymerization of the epoxide groups (Scheme 11.45) [148]. Kinetic results indicate that polymers containing silicon in their pendant group has the highest cross-linking reactivity. 

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