NQR spectra of complexes of low-molecular acceptors with polymers

Thermo- and pH-sensitivity of aqueous poly(N-vinylpyrrolidone) solutions in the presence of organic acids

“…2a (curve a) T c of 0.8% PVP solutions is plotted against the TCA concentrations (C). It is seen that in the TCA concentration range 0.17-0.30 mol/l, T c drops from 80 to 10 C. Whether the TCA concentration is increased by gradual addition of it or it is decreased back by addition of the polymer solution, in both cases experimental points lie on the same curve which evidences the reversible coordination between TCA and VP units similarly to PVP complexes with many other organic compounds mentioned above [2,23,24]. It is obvious that only a small part of TCA added takes part in this interaction.…”

“…Even stronger effect on the behavior of PVP aqueous solutions is observed if TCA is used as an additive, which, according to nuclear quadrupole resonance data [24], forms complexes with PVP via hydrogen bonding. In Fig.…”

“…The fact that stability constants of PVP complexes with phenols and organic acids are much greater than those in the case of unsubstituted aromatic compounds [2,23,24] and increase with increasing acidity of OH groups in phenol derivatives indicates the contribution of hydrogen bonds between these groups and C]O groups of the polymer. Apparently, these two types of interactions take place also between carboxylic acids studied and PVP, violating the polymer-hydrate complex and resulting in phase separation on heating.…”

“…As it has been mentioned above, PVP forms complexes with many organic compounds, including a number of organic acids such as benzoic, salycylic, aminobenzoic ones, and aromatic compounds, for example, naphtalene, biphenyl, and phenols [23,24] where hydrophobic interactions are also supposed to take place. The fact that stability constants of PVP complexes with phenols and organic acids are much greater than those in the case of unsubstituted aromatic compounds [2,23,24] and increase with increasing acidity of OH groups in phenol derivatives indicates the contribution of hydrogen bonds between these groups and C]O groups of the polymer.…”

“…Ionic surfactants [22], phenols and other aromatic compounds [2,23,24], and also some organic acids [2,14,24] form complexes with PVP, apparently, changing the hydrophobicity of the polymer. pH-responsive intermacromolecular complexes between PVP and PAA, PMAA or polyvinyl alcohol are also known [25].…”