Epoxy resins homopolymerisation

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

Curing agents or hardeners are chemically active compounds which convert epoxy resins into hard, infusible thermosets. They promote the cross-linking reaction either by polyaddition or by homopolymerisation. The curing reaction occurs without the formation of any by-product. 

Epoxide groups may homopolymerise or react with active hydrogen atoms in other molecules, usually termed hardeners or co-reactants, to produce copolymers. Cure of an epoxy resin may involve either or both of these reactions, and can be very complex, since reaction of an epoxide with one functional group can produce new functional groups for additional reaction with epoxides, and so on. 

The durability of epoxy-aluminium joints that used a homopolymerised epoxy resin was studied by researchers based in Spain [15], and the effects of relative humidity, temperature, and salt concentration analysed. The homopolymerised epoxy resin absorbed little water (1.5 wt%) because of its non-polar network structure. Increasing relative humidity and temperature enhanced water uptake, but the joint strength remained constant because of epoxy plasticisation. A saline environment was damaging to the adhesive joints because of metal corrosion, but was not significantly harmful to the epoxy resin because of the lower diffusion coefficient of salt water. The decrease in glass transition temperature of the epoxy adhesive due to water absorption was dependent upon only the amount of absorbed water and was independent of hydrothermal ageing conditions. The durability of epoxy adhesive joints made underwater has been studied [16]. 

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