A new method of preparation of poly(alkylene H-phosphonate)s by ring-opening bulk polymerization of the five- and six-membered cyclic phosphonates monomers using the nontoxic Maghnite-H(+) as the initiator is described. Cyclic phosphonate monomers have been first synthesized. In particular, a new one-step synthesis of 2-hydro-2-oxo-1,3,2-dioxaphospholane is reported with a yield of 70%. The efficiency of the montmorillonite sheet silicate clay which exchanged with protons, called Maghnite-H(+), as cationic initiator has been proved and the resulting biomimetic poly(alkylene H-phosphonate) s have been characterized. The Maghnite-H(+) regenerated after one turn-over has showed to be still efficient as initiator for the ring-opening polymerization. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 891-897, 2011