A propargyl ether-containing benzoxazine (4) was prepared from a potassium carbonate-catalyzed nucleophilic substitution of propargyl bromide and a phenolic OH-containing benzoxazine (3), which was prepared from 1-(4-hydroxyphenyl)-1-(4-aminophenyl)-1-(6-oxido-6H -dibenz <1,2> oxaphosphorin-6-yl)ethane (1) by a three-step procedure. The curing reactions of (4) were monitored by IR and DSC. A reaction mechanism was proposed based on the observation. Benzoxazines (3) and (4) were applied as epoxy curing agents. The microstructure and the structure-property relationship of the resulting thermosets are discussed. The double-strand structure in (4)-cured epoxy thermosets afforded higher crosslinking density, and led to higher thermal properties. In addition, the (4)-cured epoxy thermosets possess half the amount of highly polar hydroxyl groups than those of the (3)-cured epoxy thermosets, resulting in a lower dielectric constant, dissipation factor, and water absorption. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1359-1367