The moving equation for the physical pendulum with clearance in the joint

Aluminum salts of alkylhydroxymethylphosphinic acids are prepared by reacting phosphonous acids with aluminum hydroxide or paraformaldehyde or trioxane or mixtures thereof in water at 110 to 250° C. under pressure. The resulting aluminumphosphinates are incorporated into polymers, in particular into polyesters, and have a flame retardant action therein.