A vinyl-terminated benzoxazine (VB-a), which could be polymerized through ring-opening polymerization, was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylamine. This VB-a monomer Was then subjected to blending with poly(ethylene oxide) (PEO), followed by thermal curing, to form poly(VB-a)/PEO blends. The specific interactions, miscibility, morphology, and thermal properties of these blends were investigated with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Before curing, we found that PEO was miscible with VB-a, as evidenced by the existence of a single composition-dependent glass transition temperature (T-g) for each composition. The FTIR spectra revealed the presence of hydrogen-bonding interactions between the hydroxyl groups of poly(VB-a) and the ether groups of PEO. Indeed, the ring-opening reaction and subsequent polymerization of the benzoxazine were facilitated significantly by the presence of PEO. After curing, DMA results indicated that the 50/50 poly(VB-a)/PEO blend exhibited two values of T-g: one broad peak appeared in the lower temperature region, whereas the other (at ca. 327 degrees C, in the higher temperature region) was higher than that of pristine poly (VB-a) (301 degrees C). The presence of two glass transitions in the blend suggested that this blend system was only partially miscible. Moreover, SEM micrographs indicated that the poly(VB-a)/PEO blends were heterogeneous. The volume fraction of PEO in the blends had a strong effect on the morphology. (c) 2007 Wiley Periodicals, lnc.