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A theory for the equilibrium and dynamic properties of a solution of telechelic polymers in the limit of high aggregation number is presented. It is shown that (1) the micelles formed by telechelic chains (flowers) in a dilute solution strongly attract each other, (2) at some concentration * the flowers form a reversible gel where they Eire connected by multiple bridges, (3) the dynamics of individual micelles in the gel is governed by the bridge/loop exchange rate and by the effective barrier associated with the hopping of a micelle to a new position; this barrier is determined by the energy Eissociated to a deformation/ compression of a micelle, (4) the viscosity is changing exponentially in the region > * (it is increasing in the vicinity of *); however, it can decrease (with ) in a limited concentration range above *.

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The compactization of a single DNA molecule in polyethylene glycol (PEG) solution was investigated both theoretically and experimentally. A theory is proposed taking into account the polyelectrolyte effect and redistribution of PEG within DNA coils. This approach makes it possible to describe the dependence of critical value, c, of PEG concentration at the point of DNA collapse on the degree of PEG polymerization, P, and on the concentration of low-molecular salt, ns. Observation of single DNA molecule in solution of PEG has been carried out by means of fluorescence microscopy which allows one to observe the conformation of individual DNA directly. Direct evidence that the coil–globule transition of DNA occurs as first order phase transition was obtained. It was confirmed that the critical concentration of PEG decreases with an increase of the degree of PEG polymerization and salt concentration. The width of the coexistence region of coil and globule was found to be dependent on salt concentration and degree of polymerization of PEG. It was found that DNA undergoes re-entrant globule–coil transition in concentrated solution of high-molecular weight PEG. These experimental results correspond well to the theoretical predictions.

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pH-responsive gels of hydrophobically modified (HM) weak polyacid were prepared from acrylic acid and n-alkyl acrylates (n = 8, 12, 18). The HM gels obtained bear up to 20 mol % of n-alkyl acrylate units randomly distributed along the network chains. The pH-driven swelling of these gels upon ionization in an aqueous medium was studied. The effect of the fraction and of the side chain length of n-alkyl acrylate groups on the equilibrium degree of swelling was examined. It was shown that the swelling transition shifts to alkaline pH with increasing hydrophobicity of the gel. This was explained by the stabilization of the collapsed state of the gel by hydrophobic aggregation of n-alkyl side chains. The formation of such aggregates, which break down in the course of gel ionization, was confirmed by the fluorescent probe method with pyrene as a probe and by NMR spectroscopy. Potentiometric titration data of HM poly(acrylic acid) (PAA) gels and of the corresponding linear copolymers evidence that the introduction of hydrophobic repeat units only slightly affects the apparent dissociation constant of PAA, except for the most hydrophobic gels.

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