Computer simulations. Stoichiometric solutions of two different tetra-arm star polymers were equilibrated using a GPU-Version of the Bond-Fluctuation model. The number of Kuhn segments per star arm in the simulations was chosen to be roughly comparable with the experiments based upon literature data for the properties of Kuhn segments of PEG and PCL (see SI Table ). After equilibration of the sample, reactivity of the end groups was turned on and reactions were possible only upon collision of two different reactive groups mimicking the heterocomplementary coupling of the stars in the experiments, see Ref. for more details. Reaction kinetics was followed for 10 independent samples at five different concentrations between approximately 1 and 4 times the overlap concentration of the star polymers (for more details see SI Chapter 12). Gelation was detected by analyzing molecular weight distributions as described recently. In a subsequent simulation, a series of gels prepared at a broader range of concentrations were swollen to equilibrium, and the equilibrium degree of swelling was determined from the average polymer volume fraction inside the swollen gel. More details on the simulations with a particular focus on equilibrium swelling properties and the residual bond orientations are available in Ref.