A series of novel benzoxazine polymers containing diacetylene groups in the main chain have been synthesized. Various propargyl and ethynyl functional benzoxazine monomers have been prepared and polymerized utilizing the oxidative coupling approach. The structure of the polymers is confirmed by H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is used to study the thermal cross-linking of the polymers. The polymers show two exothermic peaks with the first exotherm exhibiting considerably lower cross-linking temperatures than conventional benzoxazines with onset at around 125 degrees C and its maximum at 185 degrees C. FTIR study shows that the lower temperature exothermic process relates to the partial benzoxazine polymerization. The number-average molecular weight is estimated from size exclusion chromatography (SEC) to be in the range from 1.5 000 to 25 000 Da. Outstandingly high thermal stability of cross-linked polymers is shown by thermogravimetric analysis (TGA).