The scission kinetics of bottle‐brush molecules in solution and on an adhesive substrate is modeled by means of Molecular Dynamics simulation with Langevin thermostat. Our macromolecules comprise a long flexible polymer backbone with L segments, consisting of breakable bonds, along with two side chains of length N, tethered to segments of the backbone with grafting density σg. In agreement with recent experiments and theoretical predictions, we find that bond cleavage is significantly enhanced on a strongly attractive substrate even though the chemical nature of the bonds remains thereby unchanged. Our simulation results indicate that the mean life time of covalent bonds decreases by more than an order of magnitude upon adsorption even for brush molecules with comparatively short side chains $N = 1 \div 4$. The distribution of scission probability along the bonds of the backbone is found to change significantly when the length and/or the grafting density of the side chains are varied. The tension, experienced by the covalent bonds is found to grow steadily with increasing σg. The mean life time declines with growing contour length L as $\langle \tau \rangle {\propto} L^{- 0.17} $, and also with growing side chain length N. The probability distribution of fragment lengths at different times is compatible with experimental observations and reveals a two‐stage (initially fast, then slow) process with different rates. The variation of the mean length L(t) of the fragments with elapsed time characterizes the thermal degradation process as a first order reaction.