For the first time, ring-opening metathesis polymerization of novel 7-membered cyclic phosphate monomers and their copolymerization with cyclooctene is presented. The monomers were investigated with respect to their metathesis behavior with different Grubbs catalysts and it was found that the Grubbs third generation catalyst gives the best results resulting in polymers with a molecular weight of up to 5000 g mol-1. Also copolymers with cyclooctene (up to a molecular weight of ca. 50000 g mol-1) were synthesized and the monomer ratios were varied. The degree of polymerization could be controlled and the polydispersity index was usually below two. Acidic hydrolysis of the copolymer showed a complete shift of the molecular weight distribution to higher elution times in SEC, indicating a random incorporation into the poly(cyclooctene) backbone of the phosphate monomers and the possible degradation of the phosphate bonds along the backbone. Further, potentially degradable nanoparticles were prepared by a solvent evaporation miniemulsion technique.