This review surveys the main methods of preparing chitosan and its hydrophobic derivatives and their influence on the microstructure of polymers. The experimental data on the aggregation of these poly mers in dilute aqueous solutions are summarized. Basic factors affecting aggregation are analyzed, and its general regularities are revealed. It is shown that, in the case of both chitosan and its hydrophobic derivatives, the formation of aggregates is governed by the competition of attraction of associating groups promoting aggregation and their repulsion arising from the presence of charged units and counterions hindering aggre gation. Various aggregate models that were proposed for chitosan derivatives with different main chain lengths and different contents of associating groups are discussed.

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. It was shown that for both unmodified and hydrophobically modified (HM) chitosan, the size of aggregates is independent of the length of single chains, which may result from the electrostatic nature of the stabilization of aggregates. At the same time, the number of macromolecules in one aggregate increases significantly with decreasing length of single chains to provide a sufficient number of associating groups to stabilize the aggregate. The analysis of the light scattering data together with TEM results suggests that the aggregates of chitosan and HM chitosan represent spherical hydrogel particles with denser core and looser shell covered with dangling chains.

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Amphiphilic diblock copolymers composed of a thermo-responsive poly(2-isopropyl-2-oxazoline) (PIPOZ) block (M n = 7000 g/mol) linked to a poly(3acrylamidopropyl)trimethylammonium chloride) (PAMPT-MA) block (M n = 3500 or 8200 g/mol) were prepared by cationic ring-opening polymerization (PIPOZ block) and subsequent atom transfer radical polymerization (PAMPTMA block). Salt-free dilute aqueous solutions of the diblock copolymers underwent a reversible phase transition upon heating past 40 °C that led to the formation of vesicles, as established by light scattering (LS) and transmission electron microscopy (TEM) studies of solutions heated to 60 °C. The pathway toward vesicles varied depending on the heating rate. A slow heating rate (0.2 °C/min) led to the formation of small spheres as the temperature reached 40 °C; the spheres grew in size as the temperature increased and eventually converted into vesicles by diffusion of some hydrophilic charged blocks toward the center. Upon application of a fast heating rate (0.7 °C/min or faster), the copolymers formed rod-like and/or worm-like micelles at 40 °C and, at higher temperature, oblate membranes that closed up into vesicles. The kinetic control of the pathway toward vesicles may be attributed to the existence of several metastable states in the system, by analogy with studies of the isothermal self-assembly of diblock copolymers in selective solvents.

Aqueous solutions of a series of monodisperse poly(N‐isopropylacrylamide)s end‐labeled with n‐butyl‐1‐pyrene at one or both chain ends (Pyn‐PNIPAMs with n = 1 or 2) were studied by turbidimetry, light scattering, and fluorescence. For a given polymer concentration and heating rate, the cloud point (Tc) of an aqueous Pyn‐PNIPAM solution, determined by turbidimetry, was found to increase with the number‐average molecular weight (Mn) of the polymer. The steady‐state fluorescence spectra and time‐resolved fluorescence decays of Pyn‐PNIPAM aqueous solutions were analyzed and all parameters retrieved from these analyses were found to be affected as the solution temperature passed through Tc, the solution cloud point, and Tm, the temperature where dehydration of PNIPAM occurred. The trends obtained by fluorescence to characterize the aqueous Pyn‐PNIPAM solutions as a function of temperature were found to be consistent with the model proposed for telechelic PNIPAM by Koga et al. in 2006. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 308–318