Cross-linking of saturated elastomers using DI-azides
Agata Zielinska, Elastomer Technology & Engineering, University Twente
The main advantage of main chain saturated elastomers, such as EPM and EPDM, over their unsaturated counter-parts is their superior stability against oxygen, ozone and heat. A consequent disadvantage of the absence of unsaturation is their lack of reactivity. Saturated elastomers are reactive only under very specific conditions and towards a very limited number of reactions, what causes problems to crosslink this type of rubber. The common way to overcome the low reactivity is by performing free-radical reactions initiated by peroxides. This reaction, however, suffer from several disadvantages, the main ones being low efficiency and the occurrence of side reactions, such as the degradation of polymer chains. Azides are known as a class of organic compounds that are reactive towards alkanes. Hence, it is interesting to study the performance of di-azides in crosslinking saturated elastomers. The paper covers the synthesis of molecules with two azide-functionalities and their ability to crosslink saturated EPM-rubber. A variety of azide-types has been investigated: alkyl azides (R-N3), aromatic azides (R-C6H4-N3), azidoformates (R-O-C(O)-N3) and sulphonyl azides (R-SO2-N3). The properties of EPM vulcanized with di-sulphonyl azide or azidoformates compare favourably with these of peroxide-cured EPM. Some di-azide activity is consumed by oil plasticizers, but to a similar amount as for peroxide/co-agent combinations. Di-azide cured EPM has greatly improved mould-release properties relative to peroxide/co-agent cross-linked EPM.