A new phosphorus-containing spiroorthoester, (1,4,6-trioxaspiro [4,4] nonan-2-yl)-methyl 3-[10-(9,10-dihydro-9-oxa-9-phosphaphenanthrene-10-oxide)]-propanoate (SOE-P), was synthesized under microwave irradiation with a short reaction time (1 h), because classical thermal heating did not lead to the desired product. The structure of the new monomer was confirmed by H-1, C-13, and P-31. SOE-P was homopolymerized and copolymerized with phenylglycidyl ether with ytterbium triflate as a cationic initiator in DSC experiments. These reactions were monitored by FTIR/ATR, and the formation of poly(ether-ester)s with a pendant bulky phosphorylated group was shown. (c) 2006 Wiley Periodicals, Inc.