**5. Conclusions**

A series of 128-arm star-shaped PDMSs with arm lengths from 33 to 114 siloxane units were obtained using the core-first approach with a branching center based on carbosilane dendrimer G6 having a didodecylmethylsilyl layer that prevents the intermolecular aggregation of lithium atoms. It was found that the G6 dendrimer is the last generation where the packing density of the outer layer allows the existence of equally accessible and equally active terminal functional groups. When carrying out similar reactions of the terminal groups of a carbosilane dendrimer G8, the processes proceed with a noticeably lower conversion, and tougher reaction conditions, as well as an increase in their duration, lead to a number of side processes, such as the transition of the chain to neighboring arms, and unequal development of the polymerization process from the beginning. These results give us reason to say that the proposed approach for the formation of multiarm stars has limits for the formation of regular structures, and the eight generation is outside of this limit.

The rheology of the synthesized series almost completely coincides with the behavior of a linear PDMS with respect to viscous flow Eact when their viscosity characteristics differ by several orders of magnitude. In this case, specimens of 128-arm star-shaped PDMS with short arms, which are shear thinning liquids, fall out of the state of Newtonian fluids, usual for PDMS. All this characterizes even such multiarm high-density structures within the considered arm lengths as polymeric objects rather than colloidal particles. DSC data show the presence of glass transition and crystallization processes in the synthesized objects, completely identical to a linear PDMS.

**Supplementary Materials:** The following are available online. Figure S1: GPC curve of DDMSderivative of carbosilane dendrimer of 4th generation, Figure S2: GPC curve of DDMS-derivative of carbosilane dendrimer of 6th generation, Figure S3: 1H NMR spectrum of DDMS-derivative of carbosilane dendrimer of 4th generation, Figure S4: 1H NMR spectrum of DDMS-derivative of carbosilane dendrimer of 6th generation, Figure S5: 1H NMR spectra recorded during lithiation of the 6th generation DDMS dendrimers without (left) and with (right) using diffusion filtration after 20 (a) and 44 h (b), Figure S6: 1H NMR spectrum of St-128-33, Figure S7: 1H NMR spectrum of St-128-59, Figure S8: 1H NMR spectrum of St-128-87, Figure S9: 1H NMR spectrum of St-128-114, Figure S10: 1H NMR spectra of the product of lithiation with n-butyllithium of the DDMS-derivative of carbosilane dendrimer G8 using diffusion filtration after 68 (1) and 92 h (2) since the start of the reaction, Figure S11: GPC curve of DDMS-derivative of the carbosilane dendrimer G8, Figure S12: Flow curves of St-128-33 at temperatures from 20 to 120 ◦C and re-measured at 20 ◦C after cooling from 120 ◦C, Figure S13: Flow curves of St-128-59 at temperatures from 20 to 120 ◦C and re-measured at 20 ◦C after cooling from 120 ◦C, Figure S14: Flow curves of St-128-87 at temperatures from 20 to 120 ◦C and re-measured at 20 ◦C after cooling from 120 ◦C, Figure S15: Flow curves of St-128-114 at temperatures from 20 to 120 ◦C and re-measured at 20 ◦C after cooling from 120 ◦C, Table S1: Polymerization parameters of 128-arm PDMS.

**Author Contributions:** Conceptualization—A.M.M.; methodology—N.G.V., synthesis and purification—P.A.T.; validation—G.V.C. (NMR) and N.V.D. (GPC); investigation—V.G.V. (Rheology), M.O.G. (AFM), M.I.B. (DSC), and S.G.V. (PFG NMR). All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Russian Science Foundation gran<sup>t</sup> NO 19-13-00340 (Synthesis). In studies of molecular weight distribution, NMR spectra were recorded with the support of the Ministry of Science and Higher Education of the Russian Federation ( № 0086-2019-0005) using scientific equipment of the Shared Facility Center "Center for Polymer Research" ISPM RAS.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available in supplementary material.

**Acknowledgments:** Rheological measurements were provided in the laboratory of Polymer Physic INEOS RAS with financial support from the Ministry of Science and Higher Education of the Russian Federation. DSC results were obtained using the equipment of the Educational and Scientific Centre of Functional and Nanomaterials, Moscow Pedagogical State University with financial support from the Ministry of Science and Higher Education of the Russian Federation. The self-diffusion measurements were performed using the equipment of the Multi-User Analytical Center of IPCP RAS and Research Resource Center of Science Center in Chernogolovka RAS.

**Conflicts of Interest:** The authors declare no conflict of interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

**Sample Availability:** Samples of the compounds are available from the authors.
