Synthesis and characterization of thermally cured polytriazole polymers incorporating main or side chain benzoxazine crosslinking moieties

Crosslinking is an efficient and simple approach for enhancing the thermal and mechanical properties of polymers. Numerous studies have reported such enhancements by the incorporation of benzoxazine (a cross-linker) in the polymer's structures. The great majority of these studies have focused on the effect of the benzoxazine content on the polymer matrix. As far as we know, there has been no discussion related to the effects arising from the position of benzoxazine incorporation. In order to investigate any such effects, we synthesized new benzoxazine monomers (SBz and MBz), containing bis-propargyl functional groups and new main chain and side chain benzoxazine functionalized polytriazole polymers, with the above benzoxazine moieties in the repeat unit, using click chemistry. The resulting thermal and mechanical properties of Cured-PTA-SBz-10 were better than those of Cured-PTA-MBz-10, and the Cured-PTA-SBz-4 and Cured-PTA-SBz-6 were close or even better than those of Cured-PTA-MBz-10. To better understand any thermal curing effects related to the positions of benzoxazine moieties in the polymer chain, we performed dynamic differential scanning calorimetric measurements by Kissinger and Ozawa methods. Significant enhancement of the thermal and mechanical properties comparing neat PTA with Cured-PTA-SBz-10 were noted: e.g. (i) a similar to 110 degrees C improvement of Tg; (ii) a similar to 205% improvement in storage modulus, a similar to 232% improvement of tensile strength, and a similar to 262% improvement in Young's modulus. Therefore, when designing the polymer, by giving consideration to the position of the cross-linker, the resulting thermal and mechanical properties can be enhanced to the extent that an equivalent polymer can be formed with a reduced amount of cross-linker leading to cost reduction.