Novel flame retarding compounds that comprise at least one sterically hindered nitroxyl, hydroxylamine or hydrocarbyloxyamine moiety and at least one conventional organohalogen or organophosphorus flame retardant moiety, represented by ##STR1##

• where
• HA is independently of each other a sterically hindered nitroxyl, sterically hindered hydroxylamine or sterically hindered hydrocarbyloxyamine moiety,
• L is independently of each other a direct bond or chemical linking group,
• FRM is independently of each other an organohalogen or an organophosphorus flame reatardant moiety, and
• x, y and z are each independently greater than or equal to 1,

  are especially effective towards providing flame retardancy to organic polymer substrates.