## 2 Results and Discussion  
### Synthesis of PSt-\(l\)-PDMS and PSt-\(l\)-PDMS/DVB Polymer Conetworks  
The polystyrene-\(l\)-poly(dimethylsiloxane) (PSt-\(l\)-PDMS) conetworks were prepared by the so-called macromonomer method via free radical copolymerization of styrene (St) with methacryloxymethyl-telechelic poly(dimethylsiloxane) (MA-PDMS-MA) (\(M_{\text{n}}\) = 4700 g/mol) serving as macromolecular crosslinker as displayed in Scheme 1 (\"\(l\)\" stands for \"_linked by_\"). In order to investigate the effect of divinylbenzene (DVB), which is a conventional crosslinker in polystyrene networks, polystyrene-\(l\)-poly(dimethylsiloxane)/divinylbenzene (PSt-\(l\)-PDMS/DVB) conetworks with additional DVB crosslinkers were also synthesized (Scheme 2). Two series of conetworks were prepared in the presence of DVB with 36:1 and 5:1 St/DVB ratios (\(m/m\)). In the case of the higher DVB content, i.e., with the 5:1 St/DVB ratio, hypercrosslinked conetworks were expected. For both the PSt-\(l\)-PDMS and PSt-\(l\)-PDMS/DVB series, the PDMS content in the feed was varied in the range of 30-70 wt%, resulting in a library of conetworks with a broad composition range. All polymerizations were carried out in THF, a common solvent for the starting materials, the initiator and the polystyrene homopolymer, ensuring a homogeneous starting solution and fully swollen gels during the copolymerization reaction (see Tables S1-S3 for feed compositions in the Supplementary Materials). Taking into account that the copolymerization reactivity ratios of styrene and methyl methacrylate are close to each other in the range of 0.5 (see e.g., Refs. [107; 108] and references therein), random crosslinking between styrene and the methacrylate-telechelic MA-PDMS-MA is expected in the course of the conetwork formation under the applied conditions. **Scheme 1. ** The synthesis of polystyrene-\(l\)-poly(dimethylsiloxane) (PSt-\(l\)-PDMS) polymer conetworks and the structure of the crosslinking sites by the MA-PDMS-MA macrocrosslinker. **Scheme 2. ** The synthesis of polystyrene-\(l\)-poly(dimethylsiloxane)/divinylbenzene (PSt-\(l\)-PDMS/DVB) polymer conetworks and the structure of the crosslinking points by DVB and the methacryloxyppropyl-telechelic PDMS (MA-PDMS-MA) macrocrosslinker. The conetwork forming reaction by the copolymerization of styrene with the MA-PDMS-MA macrocrosslinker successfully resulted in conetworks with reasonably high gel fractions in the range of 53-63% as presented in Table 1. The use of the highly reactive DVB as additional crosslinker leads to higher gel fractions in the range of 84-92% (Table 1). As displayed in Figure 1, all the conetworks are fully transparent materials regardless of their composition, demonstrating their uniformity and optical clarity. The composition of the synthesized conetworks was determined by elemental analysis and by evaluating the PDMS content of the extraction residues (determined by \({}^{1}\)H NMR spectroscopy) and that of the feed ratio. As presented in Table 1, the composition values of the conetworks, determined by these two methods show good agreement. This finding indicates that the composition of two- or multi-component polymer networks, gels or blends can be reliably determined by measuring the composition of the extractables by spectroscopic or chromatographic methods. Applying such a process might be especially important for multicomponent crosslinked polymers where elemental analysis is not sufficient for composition determination, or even in cases when the elemental analysis is unavailable due to its complexity or cost, particularly because the properties of multicomponent polymer networks strongly depend on the composition of such materials. The data in Table 1 also indicate that the PSt-\(l\)-PDMS conetworks contain a higher proportion of PDMS than that initially present in the feed. However, when DVB was added, conetworks with compositions close to the feed ratios were obtained.