Synthesis of linear polymers containing benzoxazine moieties in the main chain with high molecular design versatility via click reaction

Linear polymers with benzoxazine rings in the main chain have been synthesized applying click chemistry approach. These polymers possess molecular weights significantly higher than the benzoxazine polymers which have been chain extended via Mannich reaction. The number average molecular weight is estimated from size exclusion chromatography (SEC) to be between 20,000 and 40,000 Da. The structure of the polymers is confirmed by 1H and 13C nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). Differential scanning calorimetry (DSC) is used to study crosslinking behavior of the polymers. The nature of the low temperature exotherm DSC peak observed in this work and the previous work of other authors is studied by model reactions. It is due to thermal coupling of the residual propargyl and azide end groups in the absence of active catalyst. In addition, a novel diazide-functional benzoxazine monomer has been prepared, showing a tremendous flexibility for applying click reaction to obtain various polymer architectures. Three types of polymers have been prepared from dipropargyl- and diazide-functional benzoxazine monomers. These polymers have been characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).