A combination of ring-opening metathesis polymerization (ROMP), ring-opening polymerization (ROP), and acyclic diene metathesis (ADMET) polymerization approach was first time utilized in the preparation of novel ABC miktoarm star terpolyphosphoesters (PPEs). Acrylate-terminated monotelechelic PPE was first prepared through ROMP of 7-membered cyclic phosphate monomer in the presence of a terminating agent, and then terminal acrylate group was readily converted, by thiol-Michael addition click reaction and esterification, to a heterodifunctional PPE with hydroxyl and acrylate groups, which was a key precursor for the preparation of ABC miktoarm terpolymers. ROP of the cyclic phosphoester monomer initiated by this PPE was successively carried out to generate the acrylate-functionalized block PPE, which utilized as a selective macromolecular chain stopper in subsequent ADMET polymerization of ,-diene phosphate monomer, finally producing miktoarm terpolyphosphoester. These prepared miktoarm star terpolyphosphoesters demonstrated superior thermal and flame retardant properties via TGA, limiting oxygen index, and microscale combustion calorimetry tests. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 692-701