IN WHICH R denotes an alkyl radical with one to 18 carbon atoms and n denotes 1 or 2. These phosphonic acid dialkyl esters are used as antioxidants for plastics, especially for polypropylene, polyethylene and polyurethane, and rubber. The combined use of the phosphonic acid dialkyl esters with flameproofing agents, may increase the flameproofing action of the flameproofing agent. The use of the compounds according to the invention in combination with other antioxidants also may show advantageous effects.

The subject of the invention is phosphonic acid dialkyl esters of the formula