Thermodynamics of hard poly(phenylene-pyridyl) dendrimers

The temperature dependences of heat capacity C ^○ _p = f(T) of hard poly(phenylene-pyridyl) dendrimers of the first and the second generations based on 1,3,5-triethynylbenzene were studied over the temperature range from 7–180 to 455–470 K for the first time. Over the range 290–350 K, the relaxation transition supposedly caused by sample devitrification was detected and characterized for the dendrimer of the first generation. The experimental results were used to calculate the standard thermodynamic functions, namely, heat capacity, enthalpy, entropy, and change in the Gibbs energy on heating. The standard entropy of formation of the compounds under study was determined at T = 298.15 K. The qualitative and quantitative dependences of the thermodynamic properties of the poly(phenylene-pyridyl) dendrimers on their composition and structure were revealed by comparison of the determined parameters with similar data for the earlier studied dendrimers of this series.     

Radiothermoluminescence of linear polyethylene with extended-chain crystals

It has been shown that a radiothermoluminescence curve of polyethylene with extended-chain crystals can be separated into components corresponding to intracrystalline and disordered regions of the polymer by introducing an electron scavenger.     

Thermodynamic properties of second generation poly(phenylene-pyridyl) dendrimer

The temperature dependence of heat capacity C _p ^o = f (T) of second generation hard poly(phenylene-pyridyl) dendrimer (G2-24Py) was measured by a adiabatic vacuum calorimeter over the temperature range 6–320 K for the first time. The experimental results were used to calculate the standard thermodynamic functions: heat capacity C _p ^o (T), enthalpy H ^o(T)–H ^o(0), entropy S ^o(T)–S ^o(0) and Gibbs function G ^o(T)–H ^o(0) over the range from T → 0 K to 320 K. The standard entropy of formation at T = 298.15 K of G2-24Py was calculated. The low-temperature heat capacity was analyzed based on Debye’s heat capacity theory of solids. Fractal treatment of the heat capacity was performed and the values of the temperature characteristics and fractal dimension D were determined. Some conclusions regarding structure topology are given.     

A water-soluble aromatic dendrimer as a model basis for dual-action drugs

The affinities of two anionic pyrenyl probes for pyridinium high-molecular-mass cations of different topologies—poly(N-ethyl-4-vinylpyridinium bromide) and a water-soluble poly(pyridylphenylene) dendrimer—are studied by the method of fluorescence quenching. The hydrophilic probe carrying three sulfonate groups in a molecule more efficiently interacts with a flexible highly charged linear polycation throughout the studied pH range. The binding of the dendrimer with a relatively hydrophobic probe containing a single carboxyl group is improved by acidification of solutions, and it becomes dominant in weakly acidic solutions. The interaction of DNA with the dendrimer containing the hydrophobic probe has no effect on the formation of the dendriplex and leads to displacement of only a small fraction of the bound probe into solution. Our model studies demonstrate that dual-action dendrimer carriers capable of simultaneous delivery of genetic material and hydrophobic drugs to target cells can be created.     

Interaction of water-soluble polypyridylphenylene dendrimers with a polymethacrylate anion

Cationic water-soluble dendrimers have been prepared by the alkylation of pyridyl groups in polypyridylphenylene dendrimers of the first four generations, and their interaction with a polymethacrylate anion has been studied. The stability of polyelectrolyte complexes in aqueoussaline solutions has been studied by fluorimetric titration with the use of the pyrenyl-tagged polyanion, and it has been shown that the stability of these complexes significantly increases with the dendrimer generation number and the content of hydrophobic phenylene groups. Based on sedimentation analysis and turbidimetric titration, it is inferred that a significant part of charged groups of dendrimers are inaccessible to interaction with the polyanion and that water-soluble nonstoichiometric polyelectrolyte complexes develop in mixtures of higher generation dendrimers. Modeling results of this study may be useful for designing efficient cationic dendrimer carriers of genetic material and hydrophobic physiologically active compounds.     

Thermodynamic Properties of Polyphenylquinoxaline in the Temperature Range of <Emphasis Type="Italic">T</Emphasis> → 0 to 570 K

The thermodynamic properties of amorphous polyphenylquinoxaline in the temperature range of 6 to 570 K are studied via precision adiabatic vacuum calorimetry and differential scanning calorimetry. The thermodynamic characteristics of glass transition are determined. Standard thermodynamic functions C^°_p, H°(T) ? H°(0), S°(Т) ? S°(0), and G°(T) ? H°(0) in the range of T → 0 to 570 K and the standard entropy of formation at T = 298.15 K are calculated. The low-temperature (T ≤ 50 K) heat capacity is analyzed using a multifractal model for the processing of heat capacity, fractal dimension D values are determined, and conclusions on the topological structure of the compound are drawn.     

Radiothermoluminescence of surface layers of n-tetracosane crystals

A radiothermoluminescence (RTL) curve of surface layers of n-tetracosane crystals has been obtained, which appear to be similar but not identical to the RTL of the evacuated sample or the sample with CCl₄. Since CCl₄ does not penetrate the crystal, the difference between the RTL curves of the evacuated sample and the one with CCl₄ represents the RTL of crystal surface layers. The RTL curve of tetracosane with the scavenger is that of RTL of intracrystalline areas of the alkane. The difference in shape between the surface and bulk RTL curves is manifested well in the ratio of the RTL curves for the surface and the evacuated sample.     

Thermodynamic properties of pyridine-containing polyphenylene dendrimers of the first-fourth generations

The temperature dependence of the heat capacity C _p° = f(T) of hard pyridine-containing polyphenylene dendrimers of the first, third, and fourth generations was studied for the first time in an adiabatic calorimeter at 6–300 K. Using the experimental data obtained, the standard thermodynamic functions, viz., heat capacity, enthalpy, entropy, and Gibbs energy in the range from T → 0 to 300 K, were calculated for these dendrimers and the value of standard entropy of formation of the studied compounds at T = 298.15 K was estimated. The low-temperature heat capacity of the dendrimers was analyzed on the basis of the Tarasov and Debye theories of heat capacity of solids and by the multifractal method. The characteristic temperatures and fractal dimensionality D were determined, and some conclusions about the type of structure topology were drawn. The isotherms of the dependence of thermodynamic functions of the dendrimers on the molecular weight were obtained.     

Thermodynamics of a third-generation poly(phenylene-pyridyl) dendron decorated with dodecyl groups in the range of <Emphasis Type="Italic">T</Emphasis> → 0 to 480 K

The heat capacity of a glassy third-generation poly(phenylene-pyridyl) dendron decorated with dodecyl groups is studied for the first time via high-precision adiabatic vacuum and differential scanning calorimetry in the temperature range of 6 to 520 K. The standard thermodynamic functions (molar heat capacity C_p^°, enthalpy H°(T), entropy S°(T), and Gibbs energy G°(T)-H°(0)) in the range of T → 0 to 480 K, and the entropy of formation at 298.15 K, are calculated on the basis of the obtained data. The thermodynamic properties of the dendron and the corresponding third-generation poly(phenylene-pyridyl) dendrimer studied earlier are compared.