The invention relates to the use of a specific generically defined copolymer for stabilising a peroxide compound against decomposition. The invention also relates to a particular embodiment of the copolymer specifically a copolymer containing repeating units derived from N vinylpyrrolidone (or from N vinyl 2 caprolactam) and at least one comonomer selected from the group consisting of vinyl phosphonic acid 2 acrylamido 2 methylpropane sulphonic acid and combinations of these monomers.
