Lanthanide dodecyl sulfates, LnDSx, are remarkably effective to catalyze the reaction of diepoxides with diamines in the liquid and solid states, a key reaction in the formation of epoxy thermosets. Among all lanthanides, the lanthanum complex LaNa(DS)4(H2O)2 is the most active, allowing a decrease of 60 kJ mol-1 of the activation energy between polyethylene imine and limonene dioxide, a biobased epoxy monomer.