Nanosized water soluble poly(organophosphazenes) were synthesized by grafting hydrophilic methoxy poly(ethylene glycols) and hydrophobic dipeptide ethyl esters as side groups to the phosphazene backbone. Their hydrodynamic volume could be controlled in the range of 10-30 nm in diameter depending on the length of the side groups and the molecular weight of the polymers. These polymers exhibited a lower critical solution temperature in the range of 60-105 degreesC and hydrolytic degradability, which can afford applications to a variety of drug delivery systems. The hydrolytic properties of the present poly(organophosphazenes) have been studied at 37 degreesC in different pH buffer solutions by means of gel permeation chromatography. The polymers substituted with the more hydrophobic and more bulky dipeptide groups caused slower hydrolysis and the polymer hydrolysis occurred more rapidly in the acidic buffer solution than in the neutral and basic solutions. (C) 2004 Elsevier Ltd. All rights reserved.