Ryosuke Sakai

Synthesis, thermomorphic characteristics, and fluorescent properties of poly[2,7-(9,9-dihexylfluorene)]-block-poly(N-isopropylacrylamide)-block-poly(N-hydroxyethylacrylamide) rod-coil-coil triblock copolymers

New thermoresponsive conjugated rod-coil-coil triblock copolymers were successfully synthesized from terminal azido functionalized poly(N-isopropylacrylamide)-b-poly(N-hydroxyethylacrylamide) (PNIPAAm-b-PHEAA) and alkynyl functionalized polyfluorene (PF) via a click reaction. The azido functionalized PNIPAAm-b-PHEAA copolymers with different block ratio was prepared by atom transfer radical polymerization from an initiator bearing the azide group, whereas alkynyl functionalized PF was synthesized by Suzuki coupling reaction. The lower critical solution temperature (LCST) of the block copolymers increased with an enhanced hydrophilic PHEAA block ratio, since the longer PHEAA segment facilitated the copolymer chains to stretch at an elevated temperature. The micelles of PNIPAAm-b-PHEAA with different block ratio changed into spheres, aggregate spheres, vesicles, and wormlike micelles as the temperature was increased, due to the variation on the hydrophilic/hydrophobic characteristic of PNIPAAm. However, the micellar morphologies became worms, bundles of wormlike micelles, and hollow tubes in the triblock PF-b-PNIPAAm-b-PHEAA, which were probably induced by the π–π interaction among the fluorene segments. The variation of the micelle morphology with temperature was consistent from the results of transmission electron microscopy, atomic force microscopy, and dynamic light scattering. Also, the micelle morphologies of PF-b-PNIPAAm-b-PHEAA showed a thermoreversible property based on its LCST. The photoluminescence characteristics behaved as an on/off fluorescence indicator of temperature, showing an “on-off-on” profile at an elevated temperature in water at a higher block ratio of PNIPAAm and switching to “on-off” as the block ratio of PNIPAAm decreased. The present study suggests that the PF-b-PNIPAAm-b-PHEAA copolymers have tunable morphologies and could be potentially used as thermoresponsive sensory materials.

Size-specific, colorimetric detection of counteranions by using helical poly(phenylacetylene) conjugated to L-leucine groups through urea acceptors.

A colorimetric detection susceptible to the dimensions of guest counteranions has been demonstrated by using poly(phenylacetylene) with L-leucine and urea functionalities (poly-PA-Leu). Poly-PA-Leu was prepared from N-(4-ethynylphenylcarbamoyl)-L-leucine ethyl ester (PA-Leu) by using [Rh(+){eta(6)-C(6)H(5))B(-)(C(6)H(5))(3)}(2,5-norbornadiene)] as a catalyst. The biased helical conformation of poly-PA-Leu was demonstrated through Cotton effects in the circular dichroism (CD) spectra. The addition of ammonium salts, including tetra-n-butylammonium acetate, tetra-n-butylammonium chloride, and tetra-n-butylammonium bromide anions (CH(3)COO(-), Cl(-), and Br(-)), into the poly-PA-Leu solution intensified the CD responses of poly-PA-Leu, which is indicative of the chiral adjustability of anion recognition by using urea groups. In addition, the combination of poly-PA-Leu with the CH(3)COO(-), Cl(-), and Br(-) anions promoted large redshifts in the absorption spectra, thus providing dramatic color changes from pale yellow to red. Guest dependency in the CD and UV/Vis spectra was clearly correlated with the size of the counteranions. Fundamentally, the addition of tetra-n-butylammonium nitrate, tetra-n-butylammonium hydrogen sulfate, tetra-n-butylammonium perchlorate, tetra-n-butylammonium azide, tetra-n-butylammonium fluoride, and tetra-n-butylammonium iodide anions (NO(3) (-), HSO(4) (-), ClO(4) (-), N(3) (-), F(-), and I(-)) has no effect on either the CD or UV/Vis profiles of poly-PA-Leu. The guest specificity observed in the CD and UV/Vis spectra clearly demonstrated the guest-dimension selectivity of poly-PA-Leu in counteranion recognition.

Control of thermoresponsive property of urea end‐functionalized poly(N‐isopropylacrylamide) based on the hydrogen bond‐assisted self‐assembly in water

The hydrogen bond has been recognized as one of the representative non-covalent interactions for realizing a three-dimensionally organized molecular architecture. In fact, biological macromolecular systems ingeniously construct specific higherorder structures that are stable in an aqueous medium, in which multiple hydrogen bonds are indispensable for stabilizing the structures. Although there are a number of artificial molecular architectures fabricated through hydrogen bonding in organic solvents, the realization of a supramolecular assembly based on hydrogen bonding in water has still remained an interesting issue because the intermolecular hydrogen bonds are easily disrupted in protic and polar solvents, such as water. For the supramolecular assembly based on hydrogen bonding in water, the hydrophobic microenvironment approach that is inspired by a biological system have been developed for protecting the hydrogen bonding capability from disruptive solvation by water molecules, thus making it possible to construct a wellordered self-assembly from synthetic molecules in water [1–3]. For example, Meijer et al. revealed that bifunctional ureidotriazines can self-assemble to form a helical supramolecular polymer in water through cooperative hydrogen bonds that are shielded by the hydrophobic microenvironment [4]. Kimizuka et al. achieved fabrication of a hierarchically self-assembled bilayer membrane in water through complementary hydrogen-bond pairs [5]. Sijbesma et al. further succeeded in the formation of the self-assembly from an amphiphilic triblock copolymer in water, in which urea groups that are placed at the center of a nonpolar segment contribute to the strong intermolecular hydrogen bonding [6]. Despite the definite validity of these approaches, the construction of stable intermolecular hydrogen bonding in water has still been a challenging task because an accurate and strict molecular design is required for the functional groups involved in the intermolecular hydrogen bonding, hydrophilic chains for water-solubility, and a hydrophobic microenvironment for realization of the hydrogen bonding properties. Additionally, only the construction of the self-assembly with a specific structure and morphology Chapter 2 Control of Thermoresponsive Properties of Urea End-Functionalized Poly(N-isopropylacrylamide) Based on the Hydrogen Bond Assisted Self-Assembly in Water

Hyperbranched 5,6-glucan as reducing sugar ball

The ring-opening polymerization of 5,6-anhydro-1,2-O-isopropylidene-α-D-glucofuranose (1) as a latent cyclic AB2-type monomer was carried out using potassium tert-butoxide (t-BuOK) or boron trifluoride diethyletherate (BF3·OEt2) as an initiator in order to synthesize a novel hyperbranched glycopolymer. The anionic and cationic polymerizations proceeded via the proton-transfer reaction mechanism to produce the hyperbranched poly(5,6-anhydro-1,2-O-isopropylidene-α-D-glucofuranose) (2). In particular, the cationic polymerization with the slow-monomer-addition strategy is a facile method leading to the hyperbranched glycopolymers with high molecular weights and highly branched structures. The weight-average molecular weight (Mw,SEC-MALLS) values of 2 measured by multi-angle laser light scattering (MALLS) varied in the range from 7400 to 122 400, which were significantly higher than the weight-average molecular weight (Mw,SEC) values determined by size exclusion chromatography (SEC). The intrinsic viscosities ([η]) of these polymers were very low in the range of 3.3–4.6 mL g−1 and the Mark–Houwink–Sakurada exponents, α, were calculated to be 0.08–0.27. These results of the MALLS, SEC, and viscosity measurements suggested that these polymers exist in a compact spherical conformation in solution because of their highly branched structure. The synthesis of the hyperbranched 5,6-glucan (3) by hydrolysis of polymer 2 was also demonstrated. Polymer 3 is a novel water-soluble hyperbranched glycopolymer arranged with numerous reducing D-glucose units on the peripheries of the polymer, and has a higher reducing ability than D-glucose because of the glyco-cluster effect or the multivalent effect of the reducing D-glucose units. Therefore, polymer 3 should be called a “reducing sugar ball”.

Influence of Helical Structure on Chiral Recognition of Poly(phenylacetylene)s Bearing Phenylcarbamate Residues of L-Phenylglycinol and Amide Linage as Pendants.

Four poly(phenylacetylene)s (PPA-1~4) bearing phenylcarbamate residues of L-phenylglycinol and amide linkage as pendants were prepared to be used as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC), and the influences of coating solvents, dimethylformamide (DMF) and tetrahydrofuran (THF), which were used for coating the polymers on silica gel, on the helical structure of the polymers and their chiral recognition abilities were investigated. The structure analysis of PPA-1~4 by (1) H nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), optical rotation, and circular dichroism (CD) spectra indicated that the polymers possess the cis-transoidal structure with dynamic helical conformation. The polymers in THF seem to have shorter conjugated helical main chains along with a tighter twist conformation than those in DMF. The chiral recognition abilities of PPA-1~4 with the different helical structures induced by the coating solvents were evaluated as the CSPs in HPLC. The helical structures of PPA-1~4 induced with THF are preferable for chiral recognition for some racemates compared to those induced with DMF, and higher chiral recognition abilities of PPA-1~ were achieved using THF.

Polyacetylenes as Colorimetric and Fluorescent Chemosensor for Anions

ABSTRACT This review describes the recent progress in the design and fabrication of polyacetylene-based chemosensors applicable to colorimetric and fluorescence anion sensing that has been increasingly demanded in diverse fields. The validity of polyacetylene derivatives as an anion sensor material has been demonstrated based on the evaluation of the anion-induced optical responses for various types of polyacetylenes with different binding sites and pendant structures. Suitable molecular designs of the polyacetylene have been found to exert a beneficial influence on the anion detection abilities, which are specifically highlighted in this review article.