This presentation will review our recent work in understanding the thermo-oxidative behaviour of both poly(isobutylene) and its copolymers containing up to 1.85 mol% isoprene. Transmission Fourier Transform Infrared (FTIR) spectroscopy was the method of choice to follow oxidative group development upon heat aging. Proton Nuclear Magnetic Resonance (NMR) aided to identify the stable oxidative products. Oxidation product evolution displayed linear Arrhenius behaviour in the case of the homopolymer from 40 to 100°C. In contrast, non-Arrhenius kinetics were operating in the copolymers with curvature seen in the results at 70°C. Test results were interpreted in terms of two competing thermo-oxidative zones, isobutylene and isoprene, the latter operating at low temperatures as shown by isoprene depletion and subsequent chain scission reactions. A set of thermo-oxidative reactions for the copolymers at low temperatures have been proposed comprising allylic and addition reactions at the isoprene unit.