Thermodynamic properties of carbosilane dendrimers of the seventh and ninth generations with terminal butyl groups in the temperature range from T → 0 to 600 K

Abstract

Temperature dependences of the heat capacity of carbosilane dendrimers with butyl termi nal groups of the seventh and ninth generations were determined in the temperature range from 6 to 600 K by precision adiabatic vacuum calorimetry and differential scanning (dynamic) calorimetry. The physical transitions were revealed and their thermodynamic characteristics were analyzed. The experimental data obtained were used to calculate the standard thermo dynamic functions C p (T ), H°(T ) -H°(0), S°(T ), and G°(T ) -H°(0) for the temperature range from T → 0 to 600 K. The thermodynamic function-molar weight isotherms for the dendrimers of the third-ninth generations with terminal butyl groups in the glassy and highly elastic state are linear.Investigation of the synthesis and physicochemical properties of dendrimers, being monodispersed, nano sized, regularly branched macromolecular particles, is a promising direction of the modern chemistry of high molecular weight compounds. 1-11 Since the first reports on the synthesis of carbosilane dendrimers have been pub lished, 6,7 they were used, along with other compounds with dendrite organization of the molecular structure, as objects for the determination of the thermodynamic char acteristics. 12-19 In particular, methods of precision calo rimetry were used to study the low temperature depen dence of the heat capacity in a wide temperature range, and the experimental values were used in calculating the thermodynamic functions in the temperature range from T → 0 to 340-600 K.We have earlier 19 obtained the standard thermody namic functions of the carbosilane dendrimers of the third-sixth generations with the terminal butyl groups in the range from T → 0 to 340-600 K and determined and analyzed changes in these functions depending on the composition and structure of compounds. The systematic studies of the temperature dependence of the heat capac ity of the dendrimers revealed the second relaxation tran sition, which is an important principal result. The appear ance of the transition is consistent with a change in the physical state of the dendrimers. It was of interest to elu cidate whether this transition is characteristic of dendrimer samples of higher generations from the same homological series. The presence of the transition would mean that we deal with a general phenomenon for dendrimers of high generations.The purpose of this work is the calorimetric study of the temperature dependence of the heat capacity C p° = f(T ) of the carbosilane dendrimers of the seventh and ninth generations in the temperature range from 6 to 550-600 K and elucidation and physicochemical inter pretation of possible physical transitions on heating and cooling. We also intended to calculate the standard ther modynamic functions C p (T ), H°(T ) -H°(0), S°(T ), and G°(T ) -H°(0) from the experimental data for the range from T → 0 to 550-600 K and to approximate the calcu lated thermodynamic functions to the corresponding iso therms thermodynamic function-molar weight, which have been determined...

Insight into the Structure of Polybutylcarbosilane Dendrimer Melts via Extensive Molecular Dynamics Simulations

“…Our choice is determined, first of all, by numerous experimental data collected over the past 10 years on these systems and an unusual behavior reported for high generation dendrimers. In particular, extensive experimental studies of poly­(butyl­carbosilane) dendrimers by various experimental techniques (viscometry, precision adiabatic vacuum and differential scanning calorimetry, small-angle dynamic light scattering, and atomic force microscopy) have shown that increasing dendrimer generation causes a qualitative change of the melt properties. ,− Namely, while low generation dendrimers demonstrate liquid-like behavior, the high generation dendrimers acquire properties typical for solids. This transition occurs when switching from the sixth to the seventh generation in 3–3 dendrimers (the first number 3 stands for the core functionality while the second number 3 denotes the functionality of the branching points).…”

Hybrid Polycarbosilane-Siloxane Dendrimers: Synthesis and Properties

“…The rheology of the synthesized compounds in bulk is of particular interest. It has been mentioned above that a transition from a liquid-like to a solid-like behavior was found for non-functional carbosilane dendrimers with butyl-terminated groups upon increasing dendrimer generation [ 29 , 30 , 31 , 32 , 33 , 34 ]. This transition was accompanied by a very strong jump-like rise in melt viscosity [ 34 ].…”

“…The first intriguing result was obtained several years ago when extensively studying three homologues series of polybutylcarbosilate dendrimers differing in the functionalities of the core and branching Si atoms (3-3, 4-3 and 4-4 dendrimers). Namely, a transition from a liquid-like to a solid-like behavior of carbosilane dendrimer melts was detected, which was expressed as a second transition on the temperature dependence of the heat capacity [ 29 , 30 , 31 , 32 , 33 ]. This qualitative change of the melt properties was demonstrated for all homologues series and it required some explanation.…”

From the discovery of sodiumoxyorganoalkoxysilanes to the organosilicon dendrimers and back

“…Smirnova in the Institute of Chemistry of University of N. Novgorod). 33,34 It is important that the appearance of the second transition coincides with the change of the physical state of a dendrimer samples. If till the fifth generation they are viscous transparent liquids, starting from the sixth one they behave as wax-like substances.…”