Epoxy resins are very versatile polymers generally known not only for their adhesive and mechanical strengths but also their inherent thermo-oxidative stability. These properties have been widely exploited in many applications ranging from composites used aerospace components to electronics packaging. However neat epoxy materials suffer from relatively poor strain bearing ability and attempts to improve this brittle behaviour have been an area of many research interests. Toughening of epoxy using elastomers is not new and this is reflected in numerous publications and some have been successfully commercialised.
This paper presents a relatively new method of incorporating a rubber modifier into Diglycidyl ether of Bisphenol A (DEGBA) epoxy resin via the formation of an isocyanurate-oxazolidone-urethane structure. The synthesis involves several simultaneous reactions involving the following reactions: (a) epoxide and the isocyanate to form the oxazolidone, (b) trimerisation of the isocyanate to form isocyanurate and (c) isocyanate with polyols to form polyurethane. The synthesis and characterisation of the modified DEGBA resin will be presented. In addition, the effects of rubber content on the thermomechanical behaviour of the cured resin will also be discussed. In summary, it was found that the introduction of the isocyanurate-oxazolidone-urethane chemical groups into the epoxy molecular chain not only enhances the fracture toughness of the final resin but also improves on the thermal stability. This rubber-modified epoxy system shows excellent promise for adhesive and structural applications where thermal stability and fracture toughness are pre-requisites.