## 2 Materials and Methods
### Introducing Hydroisylation Reaction within DPD Framework  
We model the crosslinking between PHMS and \(v\)-PDMS chains due to hydrosilylation [21; 58] as a stochastic process, similar to the approach previously used within the DPD framework to model polymerization of linear chains [36; 38] and various reactions within polymer networks [37; 39; 40]. The mapping of the group of atoms within the polymer chains into the coarse-grained DPD beads is shown in Figure 1a. In this study, all initial components are linear chains (Figure 1b) composed of \(N_{\mathrm{X}}\) beads, where X indicates the type of chemical species. Correspondingly, \(N_{\mathrm{X}}\) represents the degree of polymerization of the individual chains prior to crosslinking. For example, a PHMS chain with \(N_{\mathrm{PHMS}}=30\) consists of 28 beads of type 2 and two beads of type 6 (Figure 1a,b). The end vinyl group of \(v\)-PDMS and the repeat unit of PHMS are represented by a single DPD bead each, as shown in Figure 1a. The effective reactivity of these beads is set by selecting their states (reactive or non-reactive). The reactive moieties are classified as type 1 and type 2 beads for \(v\)-PDMS and PHMS, respectively (Figure 1a). Once a bond forms between the type 1 and type 2 beads, they become non-reactive and their type is changed to type 3 and type 4, respectively (Figure 1d). For simplicity of representation, we do not highlight the state of reactive beads in the snapshots below. The crosslinking reaction is attempted at each reaction time step \(\tau_{r}\), which is ten times larger than the DPD time step (\(\tau_{r}=10\Delta t\)), same as in previous DPD simulations of reactive systems [36; 37; 38; 39; 40].  
Figure 1: (**a**) Types of coarse-grained beads, “\(\star\)” indicates that the bead is reactive, (**b**) schematic representation of the \(v\)-PDMS and PHMS chains, (**c**) schematic of the hydrosilylation reaction, (**d**) initial morphology snapshot (generated with \(a_{ii}=78\) for all the beads; no reactions occur during the equilibration) for a sample with \(f_{\mathrm{o-PDMS}}=0.5\), \(N_{\mathrm{PHMS}}=30\), and \(N_{\mathrm{v-PDMS}}=100\). The interaction parameters between all the types of beads are provided in Table S4 of Supplementary Materials.  
During each reaction step, for each reactive bead all complementary reactive beads that are within the reaction interaction distance [36; 37; 38; 39; 40], \(r_{int}=0.7\), are identified as possible bond partners. Further, within this list of possible bond partners, the closest bead is identified as the sole bond partner for the particular bead. The reaction probability is only evaluated for the pairs in which both beads are identified as respective sole partners. A random number between 0 and 1 is generated; the bond is formed if this number is smaller than the chosen probability of reaction, \(P_{c}\). Each successful reaction results in an irreversible bond formation, with the bond energy given by \(U_{bond}\) defined above; the state of the two beads involved in the crosslinking is correspondingly changed to non-reactive. We assume that changing the bead state from reactive to non-reactive does not affect the affinity of this bead. We set \(P_{c}=10^{-3}\) as the reference value of the reaction probability. As we show below, this choice of the reference value of \(P_{c}\) results in the first order reaction kinetics of the consumption of the vinyl groups provided that there is an abundant number of PHMS with respect to the vinyl groups in the system. Notably, prior experimental studies showed the consumption of silicon-hydrogen groups to obey first-order kinetics [59; 60; 61]. In experiments, an increase in the catalyst concentration or reaction temperature speeds up the hydrosilylation reactions [61]. Finally, prior to all the production runs in this study, the systems are equilibrated as described above; an example of an equilibrated system with \(f_{v-\text{PDMS}}=0.5\), \(N_{\text{PHMS}}=30\), and \(N_{v-\text{PDMS}}=100\) is shown in Figure 1c.