With the aid of model compounds it has been possible to determine the crosslinking structures of polychloroprene vulcanizates as a function of the crosslinking agent. When the crosslinking temperature rises, there is also greater formation of diene structures. The findings confirm the results of the model reaction, i.e. that MgO promotes the formation of reactive structures in the vulcanizate. These are susceptible lo atmospheric oxygen and cause undesirable ageing effects. A lower MgO content means improved ageing behaviour.