Triblock copolymer poly(ethylene glycol)-poly(alkylene phosphate)-poly(ethylene glycol) was prepared by first reacting hexamethylene glycol with dimethyl-H-phosphonate at conditions of transesterification and then replacing the CH3OP(O)(H)O-... endgroups by monomethyl ether of poly(ethylene glycol). The course of reaction was studied by P-31 NMR indicating complete conversion. After oxidation the poly(alkylene H-phosphonate was converted into the final triblock polyphosphate. This triblock copolymer was used as a modifier of CaCO3 crystallization. Unusual semi open empty spheres resulted, composed of small crystallites of the size (diameter) equal to 40-90 nm. (C) 2004 Wiley Periodicals, Inc.