Modified novolac resins with benzoxazine rings were prepared and copolymerized with a glycidyl phosphinate. Their curing behavior and the thermal properties of the curing resins were studied. Copolymerization was studied with model compounds considering the functionality of the benzoxazine-based phenolic resins and the easy isomerization of the glycidyl phosphinate. Phenolic novolac resin acts as an initiator but p-toluensulfonic acid had to be used to decrease the curing temperature and to prevent glycidyl phosphinate from isomerizing. The materials obtained exhibited high glass-transition temperatures and retardation on thermal degradation rates. V-0 materials were obtained when the materials were tested for ignition resistance with the UL-94 test. (C) 2003 Wiley Periodicals, Inc. J Polym. Sci Part A: Polym Chem 42: 279-289, 2004