The invention pertains to a process for the addition of at least one (per)fluoropolyether peroxide comprising at least one peroxidic moiety and at least one fluoropolyoxyalkene chain (chain Rf) (i.e. a fluorocarbon segment comprising ether linkages in main chain) [peroxide (P)] onto a per(halo)fluorinated aromatic compound [compound (F)], so as to yield an addition compound of said compound (F), said addition compound [compound (A)] comprising at least one perfluorinated non-aromatic cyclic moiety having at least two substituents comprising a chain Rf and, optionally, conjugated or non conjugated double bond(s). Said addition compounds have been notably found useful as additives for (per)fluorinated fluids and lubricants or as base materials for the manufacture of gum and/or graft polymer compositions.