The invention relates to a method for producing novel reactive organic compounds containing poly-DOPO and having a higher phosphorus content than known comparable DOPO (9,10-dihydro-9-oxa-10-phospha-phenenthrene-10-oxide) adducts, and to the use thereof for flameproofing thermoplastic polymers, such as polyesters and polyamides. The same flameproofing effect is achieved with smaller additive quantities than previously, thus reducing the influence of the physical, especially textile-physical properties of the polymers. The adducts containing poly-DOPO are formed by reacting DOPO with acetylenes carrying reactive groups, in the presence of a catalyst.