A general method for the synthesis of new polyphosphonic acids is 1, are formed by the reaction of the salt of tetraisopropyl methylenediphosphonate with diisopropyl n-bromoalkanephosphonates (n = 3-4) while the hexaisopropyl alkane-2,2,n-triphosphonates (n = 5-6) are formed by the reaction of the salt of tetraisopropyl ethane-1,1-diphosphonate with diisopropyl n-bromoalkanephosphonates (n = 3-4). The esters are then hydrolyzed with HCl to give the corresponding phosphonic acids.