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SUMMARY:In an adiabatic vacuum calorimeter the temperature dependence of the heat capacity C p 0 of tetramethylene urethane (TMU) (2-oxo-hexahydro-1,3-oxazepine) and poly(tetramethylene urethane) (PTMU) was studied between 4.3 and 300 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield the energies of combustion D U comb of the monomer and the polymer were measured. From the experimental data the thermodynamic functions

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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...

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