Azide-Functionalized PET Fibers via Graft Copolymerization of 4-Vinylpyridine: Synthesis, Characterization, and Energetic Properties

Poly(ethylene terephthalate) (PET) fibers were successfully functionalized through a multi-step modification strategy involving graft copolymerization of 4-vinylpyridine (4VP), followed by chlorination and subsequent azidation. The grafting process introduced pyridine functionalities onto the PET surface, providing reactive sites for further chemical transformation. Chlorination enabled the formation of reactive chloro groups, which were subsequently substituted by azide groups via nucleophilic substitution using sodium azide (NaN₃). The optimum azidation conditions were determined as 0.2 M NaN₃ concentration, 60 °C reaction temperature, and 12 h reaction time, which provided the highest degree of functionalization without compromising the structural integrity of the fibers (15%). The successful incorporation of azide functionalities was confirmed by Fourier Transform Infrared (FTIR) spectroscopy through the appearance of a characteristic absorption band at 2100–2150 cm⁻¹. Scanning electron microscopy (SEM) analysis revealed significant changes in surface morphology, indicating successful surface modification while preserving the fibrous structure of PET. Thermal analysis demonstrated that the azide-functionalized fibers exhibited a distinct exothermic decomposition peak at approximately 280 °C in differential scanning calorimetry (DSC), confirming their energetic nature. Thermogravimetric analysis (TGA) showed an earlier onset of degradation compared to grafted PET fibers, attributed to the presence of thermally labile azide groups. The results indicate that PET-g-4VP-N₃ fibers possess enhanced chemical reactivity and energetic characteristics, making them promising candidates for advanced applications such as click chemistry-based functionalization, adsorption systems, and energetic polymer materials.