Comparative Thermodynamic Studies of the Micellization of Amphiphilic Block Copolymers before and after Cyclization.

The enthalpy and entropy of micellization in water, Δ and Δ, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) ( ∼ 1200 and 700 Da) or poly(ethyl acrylate) ( ∼ 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, ∼ 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The Δ and Δ of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The Δ value of the cyclic copolymers was smaller than that of their linear precursors.

Effect of solvent quality and chain density on normal and frictional forces between electrostatically anchored thermoresponsive diblock copolymer layers.

Equilibration in adsorbing polymer systems can be very slow, leading to different physical properties at a given condition depending on the pathway that was used to reach this state. Here we explore this phenomenon using a diblock copolymer consisting of a cationic anchor block and a thermoresponsive block of poly(2-isopropyl-2-oxazoline), PIPOZ. We find that at a given temperature different polymer chain densities at the silica surface are achieved depending on the previous temperature history.

Temperature-responsive telechelic dipalmitoylglyceryl poly(N-isopropylacrylamide) vesicles: real-time morphology observation in aqueous suspension and in the presence of giant liposomes.

Telechelic α,ω-di(twin-tailed poly(N-isopropylacrylamides)) form polymersomes in water that increase in size by fusion when the water temperature exceeds the polymers cloud point temperature. Hybrid vesicles form in mixed suspensions of giant phospholipid liposomes and polymersomes by adsorption/fusion, and undergo further transformations, such as fission.

Effects of hydrophobic substituents and salt on core-shell aggregates of hydrophobically modified chitosan: light scattering study.

In this study we examine two methods of enhancement of aggregation of hydrophobically modified chitosan in dilute aqueous solutions: by increasing the content of n-dodecyl substituents, favoring hydrophobic association, and by increasing the amount of added low molecular weight salt, screening the electrostatic repulsion between similarly charged aggregating chains. By static and dynamic light scattering it was demonstrated that at the growth of the content of hydrophobic groups in the polymer (2-4 mol %) and of the amount of salt in solution (0.025-0.

Aggregation of some water-soluble derivatives of chitin in aqueous solutions: Role of the degree of acetylation and effect of hydrogen bond breaker.

By dynamic light scattering in combination with fluorescence spectroscopy and TEM it was shown that aggregation in aqueous solutions is inherent not only to chitosan, but also to two other water-soluble derivatives of chitin: O-carboxymethylchitin and di-N,N-carboxymethylchitosan. Aggregation is observed even for the samples without N-acetyl-d-glucosamine units, which remain upon incomplete chemical modification of chitin, indicating that specific interactions between residual chitin repeat units cannot be the main reason for the aggregation. At the same time, 7M urea weakens the aggregation, thus testifying that hydrogen bonding and/or hydrophobic interactions are partially responsible for this phenomenon.

Multichain aggregates in dilute solutions of associating polyelectrolyte keeping a constant size at the increase in the chain length of individual macromolecules.

Multichain aggregates together with individual macromolecules were detected by light scattering in dilute aqueous solutions of chitosan and of its hydrophobic derivatives bearing 4 mol % of n-dodecyl side groups. It was demonstrated that the size of aggregates and their aggregation numbers increase at the introduction of hydrophobic side groups into polymer chains. The key result concerns the effect of the chain length of individual macromolecules on the aggregation behavior.