On the temperature and pressure dependence of the dynamic viscosity of n-alkanes

Isotherms of the coefficient of dynamic viscosity and isobars of n-alkanes are considered. One-parameter correlations for the isobars are constructed based on the literature data. A linear correlation is revealed between the boiling and melting temperatures and the found parameter of the baric dependence of viscosity for a homological series of alkanes.     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.     

Physico-chemical study of ionic equilibria for poly-2 and poly-4-vinylpyridines in alcohol-water solutions

The ionic equilibria for poly-4-vinyl pyridine (P4VP) and poly-2-vinyl pyridine (P2VP) were studied by physico-chemical techniques such as potentiometry, viscosity and NMR-¹H. The mixture of ethanol (45 per cent w.p.) and water was used as solvent to obtain the total range of ionization (0–1). It was found that the dissociation constants of pyridine residue of polymers in the absence of electrostatic interaction (pK₀ = 3·3–3·9) are lower than for the monomer analogues 4-ethylpyridine and 2-ethylpyridine (5·02) and depend on ionic strength (NaCl).A sharp decrease of pK_app at the beginning of titration and increase of specific viscosity for P4VP and P2VP are both explained by electrostatic interactions between positive charges forming during titration of the macromolecules. Most probably, these interactions act through the organic part of the macromolecule. On the other hand, it is shown by NMR-¹H that sharp changes in pK_app and specific viscosity at the beginning of the titration are not associated with changes in the average conformation of the monomer unit in the polymer. This conformation can be destroyed only when the energy of electrostatic interactions is large enough and this occurs when the mean distance between positive charges is relatively short.     

Comparison of properties of an oxime-bound partially quaternized poly-4-vinylpyridine and a monomer analogous oxime

Six copolymers of 4-vinylpyridine and 4-vinyl-N-phenacyloximepyridinium bromide (PPyOx-12, 23, 40, 50, 60 and 72 per cent) were prepared from poly-4-vinylpyridine partially quaternized by phenacylbromide (PPyKt) and hydroxylamine. The potentiometric data of the polymer acid groups (oxime, keto-enol tautomerism) in PPyOx and PPyKt were compared with those of 4-ethyl-N-phenacyloximepyridinium bromide (PyOx) and 4-ethyl-N-phenacylpyridinium bromide (PyKt) respectively. In addition, the second-order constants of the nucleophilic reaction for all the copolymers (PPyOx) and the analogue towards p-nitrophenylacetate (NPA) were determined at various pH values in water at 25°. In contrast to the known potentiometric behaviour of polyacrylic and polymethacrylic acids, the dissociation constants (pK_a) of acid groups in PPyKt and PPyOx were found to be independent of the degree of ionization. Moreover, the values of pK_a of these groups for all PPyKt and PPyOx samples were appreciably less than the pK_a of the corresponding analogues. As a consequence, the oxime of PPyOx-12 in the range of pH between 7·5 and 9·0 reacts about two order of magnitude faster than the monomer with the ester. These results indicate that, in contrast to the known correlation between reactivity (nucleophilicity) and basicity for monomer compounds, the activity of the polymer oxime does not diminish with a decrease of the basicity. On the contrary, the reactivity of polymer anion towards the ester is markedly higher than that of the monomer anion of PyOx. An explanation may be found in the effects of microenvironment on the property of the functional groups attached to the side pyridine residues of PVP.     

13C NMR study of the enol forms of β-diketones

Carbon-13 NMR spectra of a series of β-diketones in the enol form with various β-substituents have been studied. An additive influence of the β-substituents on the chemical shifts of the carbon atoms in the hydrogen bonded chelate ring has been found. It is shown that the α- and β-carbon chemical shifts can be calculated by means of a set of increments for arbitrary combinations of the X and Y substituents. Analysis of the experimental data enables the conclusions to be drawn that enol–enolic tautomerism with different populations of the forms (A) and (B) is absent in β-diketones and that the carbon chemical shift changes are caused by electron density redistribution in the hydrogen bonded chelate ring (C).