We utilized differential scanning calorimeter (DSC), Fourier-transformed infrared spectroscopy (FT-IR), and solid-state nuclear magnetic resonance spectroscopy (NMR) techniques to understand the dehydrogenation mechanism of ammonia borane (AB) and its polymer composites. The results indicated that the polymeric composites with higher polyethylene oxide (PEO) mass ratio involve the possible breakdown of dative bond and the formation of new interaction (H-bonding) between the AB and the polymer. The activation energies were calculated in the temperature range of 25 °C and 300 °C which were found to be lower than the pristine AB. 15N and 11B NMR studies at room temperature showed evidence for a possible interaction, H-bonding, between AB and PEO. The NMR experiments at 85 °C were conducted to investigate the isothermal decomposition during several hours. Results indicated that the pristine AB takes longer incubation time, however the polymeric composite readily decomposes at 85 °C. Both showed proof for the formation of byproducts. Moreover, IR study showed evidence to support the interaction between AB and PEO.