We describe a new strategy for preparation of benzoxazine monomers based on in situ preparation of a thiol-functionalized benzoxazine and successive chemical modification of the thiol moiety. The thiol-functionalized benzoxazine can be prepared from its precursor bearing two benzoxazine moieties linked by disulfide bond. Reductive cleavage of the disulfide bond of the precursor with using triphenylphosphine as a reducing agent allows successful preparation of the thiol-functionalized benzoxazine. By performing this reduction process in the presence of epoxides and acrylates, the formation of the thiol moiety and its successive reaction with those electrophiles proceed efficiently to give the corresponding benzoxazines with sulfide moieties. The benzoxazine monomers thus prepared exhibit much higher polymerization ability than those without sulfide moiety. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1448-1457