Thermodynamic investigation of G2 and G4 siloxane dendrimers with trimethylsilyl terminal groups Semen S. Sologubov a , Alexey V. Markin a,⇑ , Yuliya A. Sarmini a , Natalia N. Smirnova a , Konstantin L. Boldyrev b,c , Elena A. Tatarinova b , Ivan B. Meshkov b , Aziz M. Muzafarov b,c a National Research Lobachevsky State University of Nizhny Novgorod, 23/5 Gagarin Av., 603950 Nizhny Novgorod, Russia b Enikolopov Institute of Synthetic Polymeric Materials of Russian Academy of Sciences, 70 Profsoyuznaya St., 117393 Moscow, Russia c Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences, 28 Vavilov St., 119334 Moscow, Russia article info Article history: Received 15 July 2020 Received in revised form 22 September 2020 Accepted 10 October 2020 Available online 15 October 2020 Keywords: Siloxane dendrimers Adiabatic calorimetry Differential scanning calorimetry (DSC) Heat capacity Glass transition Thermodynamic functions abstract In this work, we report results of the calorimetric study of the second (G2[OSi(CH 3 ) 3 ] 12 ) and fourth (G4 [OSi(CH 3 ) 3 ] 48 ) generation siloxane dendrimers with trimethylsilyl terminal groups. The heat capacities of dendrimers were precisely measured in the temperature range T = (5–520) K using a fully automated adi- abatic calorimeter and a heat-flux differential scanning calorimeter. In the above temperature interval, the physical transformations of the studied compounds were detected, and its thermodynamic character- istics were determined. The fundamental thermodynamic functions (the enthalpy [H°(T)  H°(0)], the entropy [S°(T)  S°(0)], the Gibbs energy [G°(T)  H°(0)]) of dendrimers were calculated over the range from T ? 0 to 520 K using the experimentally determined heat capacities of the investigated compounds. The standard entropies of formation of dendrimers G2[OSi(CH 3 ) 3 ] 12 and G4[OSi(CH 3 ) 3 ] 48 were evaluated at T = 298.15 K. The obtained thermodynamic data of the investigated dendrimers were compared with those of the studied earlier siloxane dendrimers G1[OSi(CH 3 ) 3 ] 6 and G3[OSi(CH 3 ) 3 ] 24 , which represent the structurally related homologous series of organosilicon dendrimers. As a result, the dependences between thermodynamic properties of the studied siloxane dendrimers and their molecular mass were established. Ó 2020 Elsevier Ltd. 1. Introduction Dendrimers are nanoscaled well-defined globular macro- molecules with a low polydispersity (in comparison with tradi- tional polymers) and a highly branched three-dimensional architecture constituted of three main structural elements: a core (a multifunctional atomic group, considered as the zeroth genera- tion, i.e. G0), an inner sphere (tree-like branches emanating from the core, consisted of the repeating units, whose repetition is orga- nized in a geometrical progression that results in a series of radi- ally concentric layers called generations, i.e. G1, G2, G3, etc.), and an outer layer (many terminal functional groups, increased expo- nentially as a function of generation and located on the macro- molecule surface, which play a key role in the properties of dendrimers) [1–3]. After the publication of the pioneering papers [4–7], which dealt with the development and the realization of this principally new molecular architecture, there has been a rapid and impressive progress in dendrimer science. As a result, the step-by- step controlled synthetic methods have been modified to produce representative series of dendrimers differing by their chemical nat- ure and structure [8–10]. At present, the design of functional den- drimers is an area with unlimited possibilities for fundamental discoveries and practical applications. In light of their unique molecular architecture, dendrimers have attracted increasing attention in the past few years. Due to the ver- satile physical and chemical properties of dendrimers, arising from the structural features, they are potential candidates for biomedi- cal fields, nanoengineering, electronics, and catalysis [11–16]. Among the numerous dendritic macromolecules, carbosilane (Si–C) and siloxane (Si–O) dendrimers have emerged as one of the most important and promising classes of silicon-containing dendrimers [17,18]. The first oxygen-containing organosilicon den- drimers were synthesized by Rebrov et al. up to the fourth gener- ation [19]. After that, series of siloxane dendrimers with longer branches was developed in the early 1990s [20–24]. These fully amorphous compounds, built from very flexible siloxane chains, have a lower glass transition temperature, a smaller hydrodynamic volume, and a lower viscosity than their linear analogues having the same chemical composition and molecular mass. Furthermore, https://doi.org/10.1016/j.jct.2020.106318 0021-9614/Ó 2020 Elsevier Ltd. ⇑ Corresponding author. E-mail address: markin@calorimetry-center.ru (A.V. Markin). J. Chem. Thermodynamics 153 (2021) 106318 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct