Cross-linking and modification of saturated elastomers using functionalized azides

The main advantage of saturated elastomers, such as EPM and EPDM over their unsaturated counter-parts is the absence of carbon-carbon unsaturation in the main polymer chain, resulting in excellent ozone and heat resistance. A consequent disadvantage of the absence of unsaturation is the lack of reactivity of these saturated elastomers. Such reactivity is desired for cross-linking, providing the typical rubber properties like high tensile strength, elasticity and resistance to solvents, and/or for further chemical functionalization of the polymer chain, which yields polymers with increased polarity or reactivity and, thus, enhanced adhesion to polar substrates or compatibility with other polar polymers. The common way to overcome the lack of reactivity for saturated polymers is by pursuing free-radical reactions, usually initiated by thermal decomposition of peroxides. Peroxide cross-linking of EP(D)M-rubbers is commercially applied and also grafting of unsaturated monomers onto EP(D)M, for example maleic anhydride (MA), initiated by peroxides is performed on an industrial scale. A major disadvantage of peroxide-induced reactions is lack of selectivity which leads to a number of side reactions, the most common being disproportionation of two macro-radicals and β-scission which results in polymer degradation. Organic azides are a class of organic compounds that are known for their reactivity towards saturated hydrocarbons. Hence, it is interesting to study their performance in cross-linking/modification of saturated EP(D)M-rubbers. Upon heating nitrogen is split off from the azides and the resulting nitrene R-N species insert into a C-H bond. This reaction mechanism is expected to be completely different from the radical processes resulting from peroxides and, most importantly, no side reactions are likely to occur. The purpose of this thesis is therefore to investigate azides as viable alternatives for peroxides in cross-linking and grafting of saturated elastomers, in particular EP(D)M.