Review in 2021

Hydrophobically modified polysaccharides have attracted considerable attention in the biomedical field because of their biocompatibility, biodegradability, and nontoxicity. This article reviews previous studies on micellar structures formed by hydrophobically modified polysaccharides (pullulan and amylose) in aqueous solutions by static and dynamic light scattering, small angle X-ray and neutron scattering, and fluorescence from pyrene solubilized in the polymer solution. Depending on the degree of substitution, the hydrophobically modified polysaccharides exist in aqueous solution as full or loose flower necklaces or as nanogels made up of randomly branched polymers.

TEMPO-catalyzed oxidation enables efficient and position-selective conversion of primary hydroxy groups in water-soluble and -insoluble polysaccharides to sodium carboxylate groups. TEMPO/NaBr/NaClO in water at pH 10 is an advantageous system in terms of the degrees of oxidation and reaction rates. Various new water-soluble TEMPO-oxidized polysaccharides have been prepared by TEMPO-catalyzed oxidation, and they have unique properties and functionalities. When crystalline native cellulose and chitin are oxidized by the TEMPO/NaBr/NaClO system under suitable conditions, the obtained water-insoluble oxidized products can be converted to characteristic nanomaterials by mechanical disintegration in water.

“Breath figure formation” during the casting process of polymer solutions under high atmospheric humidity provides honeycomb-patterned polymer films (honeycomb films) with regularly arranged micropores. The development of production technology for large-area honeycomb films is indispensable for their various applications. Manufacturing equipment consisting of three zones (for casting, humidification, and drying of polymer solutions) for successive formation of large-area honeycomb films was newly designed and constructed. By using this equipment, physicochemical experimental parameters, e.g., the surface temperature of polymer solutions, dew point of the humidification zone, humidification time, and interfacial tension between water and the polymer solution, were effectively changed to optimize the density and size of condensed water droplets. Large-area honeycomb films were formed by a roll-to-roll process. Herein, recent developments in biomedical applications of honeycomb films are described.

Our recent progress on the phenylazomethine dendrimers to afford advanced functionalities due to the π-conjugated azomethine structure and electronic state are reviewed. The functions include luminous dendrimers by bismuth assembly, Y-shape recognition using porphyrin core, and atomicity-controlled template of metal salts on imine parts. The precisely controlled template ability developed synthesis of multimetallic subnanoparticles and superatoms that can mimic the properties of elemental atoms.

Block copolymers are used as nano-tools for delivering hydrophobic drugs. Their formulation requires robust characterization and clarification of the critical quality attributes correlating with the safety and efficacy. Static solution scattering from block copolymers is one such technique. This paper outlines the theoretical background and current models for analyzing this scattering and then presents an overview of our recent studies on block copolymers.

Recent developments in the one-step synthesis of structurally controlled hyperbranched polymers (HBPs) in terms of molecular weight, dispersity, number of branching points, branching density, and number of chain-end groups by radical polymerization are summarized. Copolymerization of conventional vinyl monomers and a vinyl telluride, which induces the branching structure, under organotellurium-mediated radical polymerization (TERP) affords HBPs with dendrimer and dendron structures. The same synthetic strategy under atom transfer radical polymerization is also discussed.