Thermoresponsive hydrogel nanoparticles were prepared by self-assembly of two different hydrophobically modified polymers, namely a cholesterol-bearing pullulan (CHP) and a copolymer of N-isopropylacrylamide butyl]-N-n-octadecylacrylamide] (PNIPAM-C 18Py). The interactions between CHP and PNIPAM-C18Py were investigated by fluorescence spectroscopy, dynamic light scattering, and size exclusion chromatography. After ultrasonication of a mixture of CHP and PNIPAM-C18Py (5:1 by weight) at 25°C, monodisperse nanoparticles (Dh ) 45 nm) were obtained, consisting of self-assembly of the two polymers associated via their hydrophobic moieties. Evidence from fluorescence and dynamic light scattering demonstrated that, above 32°C, the lower critical solution temperature (LCST) of PNIPAM-C18Py, the colloidal mixed nanoparticles increase in diameter (from 47 to 160 nm), but no macroscopic aggregation could be detected. This phenomenon was thermoreversible: upon cooling the particles recovered their original diameter.

Coating the outermost surface of a liposomal membrane with several different hydrophobized polysaccharides was investigated by fluorescence depolarization, gel chromatography, and dynamic light scattering methods. The binding of cholesterol-bearing pullulan to the liposomal surface was biphasic. The first process was finished within minutes while the subsequent slow stages took over several hours. The binding isotherms followed Langmuir-type adsorption. The binding constant (K) increased with increases in the substitution degree of the cholesteryl moiety and the molecular weight of the pullulan derivatives used, while the maximum amount of the polysaccharide coating (qs) was almost the same. The apparent liposome size increased by 20-30 nm upon coating. Chemical structure of the parent polysaccharide had only a slight effect on the binding constant, while the structures of the hydrophobic moiety had a significant effect on the coating behavior of the liposomes. In the case of dodecyl diglyceryl group-bearing pullulan, both K and qs were smaller than those of other cholesterol-bearing polysaccharides. The addition of hexadecyl-bearing pullulan to the liposome induced aggregation of the liposomes. The cholesteryl moiety is an excellent hydrophobic anchor for polysaccharide coating liposomal surfaces compared with simple monoalkyl or dialkyl chains.

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In aqueous two-phase systems, such as PEO/pullulan and PEO/dextran systems, partitioning of linear and cyclic oligosaccharides was investigated. The α 1-4 linked linear oligosaccharides, such as glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose were partitioned more to the bottom polysaccharide-rich phase than to the top PEO-rich phase. The partition coefficient, K (the ratio of the concentration of oligosaccharide in the polysaccharide-rich phase to that in the PEO-rich phase), increased with an increase in the glucose units in the oligosaccharide. The extent of the partition of the oligosaccharides was affected by the structure of polysaccharide employed in the two-phase system. Compared with the PEO/pullulan system, the PEO/dextran system showed a higher partition selectivity for the linear oligosaccharides. The structural characteristics of dextran with branched skeleton should be more suitable for multipoint interactions with the linear oligosaccharides, however, more cyclodextrin (CD) was always found in the PEO phase than in the polysaccharide phase. The partition coefficient sequence of the cyclodextrins to the PEO-rich top phase was β-CD > α-CD > γ-CD. The partitioning of more β-CD to the PEO phase may be due to better incorporation of the PEO chain into the β-CD cavity.

Poly(aramid silicone) (PAS) multiblock copolymers were synthesized by the low‐temperature solution polycondensation of isophthaloyl dichloride (IPC) and two diamines, diamino poly(dimethyl siloxane) (PDMS; number‐average molecular weight = 1680) and 3,4′‐diaminodiphenylether (3,4′‐DAPE), in tetrahydrofuran/dimethylacetamide (2/1 v/v). Two synthetic methods for the control of the PAS sequence were used: a one‐step synthesis that presumably gave PAS with a random sequence and the polymerization of 3,4′‐DAPE with a presynthesized dimer, IPC–PDMS–IPC (two‐step synthesis), that presumably gave PAS with an alternating sequence of 3,4′‐DAPE and PDMS segments. In a 1H NMR study of the amide protons of the 3,4′‐DAPE component in PAS, the relative length of the 3,4′‐DAPE segment of randomly sequenced PAS to that of ideally sequenced PAS could be estimated. The glass‐transition temperatures of the 3,4′‐DAPE and PDMS segments of random PAS were 152–234 and −104 to −117 °C, respectively, whereas the alternating PAS sequences showed no glass transition for the 3,4′‐DAPE segments. A tensile test indicated that randomly sequenced PAS behaved like a rubber‐toughened material at lower PDMS contents and like a thermoplastic elastomer at higher PDMS contents, whereas the alternately sequenced PAS behaved like a very soft rubber, showing a high value of elongation at the breaking point. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 841–852, 2003