Dynamic mechanical analysis is performed on polybenzoxazines from acetylene-terminated benzoxazine monomers, and glass transition temperatures of these polybenzoxazines are found in the range of 329-368 degrees C. It has been identified that the high glass transition temperature and high thermal stability are due to polymerization of the acetylene terminal group, in addition to oxazine ring polymerization through a comparison study with analogous polybenzoxazines that are obtained from monomers without an acetylene functional group.