Calorimetric study of siloxane dendrimer of the third generation with trimethylsilyl terminal groups
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The molar heat capacity of siloxane dendrimer of the third generation with trimethylsilyl terminal groups G3[OSi(CH3)3]24 was determined by precise adiabatic calorimetry and differential scanning calorimetry over the temperature range T = (6–570) K for the first time. The low-temperature structural anomaly and the glass transition were observed in the above temperature range, and the standard thermodynamic characteristics of the revealed transformations were determined and analyzed. The fundamental thermodynamic functions such as the enthalpy [H°(T) − H°(0)], the entropy [S°(T) − S°(0)], and the Gibbs energy [G°(T) − H°(0)] were calculated for the range from T → 0 to 570 K based on the experimentally determined molar heat capacity of the investigated compound. The standard entropy of formation ΔfS° of dendrimer G3[OSi(CH3)3]24 was evaluated at T = 298.15 K. The thermal stability of the studied compound was investigated by thermogravimetric analysis. The standard thermodynamic properties of siloxane dendrimer G3[OSi(CH3)3]24 were compared and discussed with the previously reported data for the studied G3 carbosilane dendrimers with different functional terminal groups on the surface layer.
KeywordsOrganosilicon dendrimers Adiabatic calorimetry DSC Heat capacity Glass transition Thermodynamic functions
This work was performed with the financial support of the Ministry of Science and Higher Education of the Russian Federation (Contract No. 4.5706.2017/8.9), the Russian Foundation for Basic Research (Project No. 19-03-00248), and the Russian Science Foundation (Project No. 18-13-00411).
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