## 3 Results
### Hydrosilylation Reaction Arrests Domain Growth in Blends Containing PHMS
All \(g_{ss}(r,t)-1\) curves exhibit primary peaks at the separation \(r\approx 0.7\) corresponding to the bond length between the beads of the polymer chains set by the choice of the harmonic bond potential (see Materials and Methods section above). There are also additional smaller amplitude oscillations in \(g_{ss}(r,t)\) at relatively short distances, which can be attributed to the packing of the nearest-neighbor and next-nearest-neighbor [63] beads. At all distances beyond this small distance, \(g_{ss}(r,t)-1\) attains approximately zero values at initial times (\(t=0\), solid black line in Figure 2b), indicating that the sacrificial beads are essentially uniformly distributed at these length scales. The magnitude of \(g_{ss}(r,t)-1\) increases with time until the system reaches an equilibrium, confirming the aggregation of the sacrificial beads into distinct domains during the phase separation arrested by the hydrosilylation reaction. The characteristic length scale within this system can be defined in a straightforward manner via zero crossing [64; 65; 66] of \(g_{ss}(r,t)-1\). Specifically, herein we quantify the characteristic length scale, \(l(t)\), via first value of \(r\) at which the function \(g_{ss}(r,t)-1\) crosses zero from a positive to a negative value (Figure 2b). Alternatively, the characteristic length scale can also be calculated  
Figure 2: (**a**) Snapshots (I–IV) of the blend with \(f_{v-\text{PDMS}}=0.5\) and \(N_{v-\text{PDMS}}=100\). The time steps from the left to the right are \(1\times 10^{5}\), \(1\times 10^{6}\), \(4\times 10^{6}\), and \(1.2\times 10^{7}\). (**b**) The \(g_{ss}(r,t)-1\) at various times as listed in the legend. (**c**) The time evolution of the characteristic length scale, \(l(t)\), and the number of vinyl groups in the system normalized by the initial number of these groups, \(N_{\text{I}}(t)/N_{\text{I}}(0)\). The time instances corresponding to the snapshots in (**a**) are marked by the open circles. The inset shows evolution at early times. from the first minimum [66] of \(g_{ss}(r,t)\) at distances exceeding the short distance correlations discussed above. It had been previously shown that the characteristic length scales calculated from zero crossings of \(g_{aa}(r,t)-1\) obey expected scaling during spinodal decomposition [64; 66]. Further, it had also been shown that the ratio between the characteristic length scales corresponding to the minima of RDF and those calculated from the zero crossing of the shifted RDF remains approximately constant in various systems undergoing phase separation [64; 66]. This is also the case for the simulation in Figure 2a, as shown in Figure S2 of Supplementary Materials. The characteristic length scale \(l(t)\) (in blue, left axis) and the number of the reactive vinyl groups (beads of type 1), \(N_{l}(t)\), with respect to the initial number of these beads, \(N_{l}(0)\) (in red, right axis), are given in Figure 2c. The value of \(N_{l}(0)\) is defined by the number of \(v\)-PDMS chains in the system and can be expressed as:  
\[N_{l}(0)=2f_{v-PDMS}\rho L^{3}/N_{v-PDMS} \tag{4}\]  
where \(\rho\) and \(L\) are the dimensionless beads number density and the linear size of the simulation box as defined in Models section. The open circles on this plot mark the time instants that are chosen in the snapshots in Figure 2a, the inset shows the time evolution of both \(l(t)\) and \(N_{l}(t)/N_{l}(0)\) at early times. These results clearly show that the reactive vinyl beads are consumed significantly faster than the time required for the phase separation process to reach equilibrium and correspondingly for \(l(t)\) to reach its value at saturation, \(\bar{l}\). The observed ratio \(N_{l}(t)/N_{l}(0)\) decays exponentially; however, the apparent reaction rate calculated via exponential fitting is lower due to the contribution from the diffusion processes than that in the case of an abundant number of PHMS (Figure S3a).