Time resolved in situ transmission electron microscopy shows that the reactivity of defects and unsaturated edges plays an integral role in the growth of highly defective graphene formed by the catalyst-free thermal formation of freestanding polymer films. In addition to the observed migration and merging of nanostructures at high temperatures, graphene nanoflakes are highly unstable and tend to loose atoms or groups of atoms to adjacent larger domains indicating an Ostwald-like ripening active in these 2D materials. Beam-off heating experiments were carried out to understand the effect of the electron beam on the observed processes and to separate out the inherent temperature-driven mechanisms. All of the processes observed during continuous imaging (beam on) were also observed during beam-off experiments. This confirms that the observed dynamics are inherently temperature-driven and that the electron beam is only providing additional activation energy, thereby increasing the reaction kinetics. Atomistic simulations were carried out to estimate the activation energy for the different processes and confirm that the observed dynamics are thermally accessible at the experimental temperature.