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We investigated a simultaneous living anionic polymerization process of isoprene (I) and styrene-d8 (S) in benzene-d6 as a solvent with sec-buthyllithium as an initiator into polyisoprene(PI)-block...

This investigation focused on the self-assembly of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) (PNIPA-block-PEG) in water. A quasi-living radical polymerization technique including a Ce(IV) ion redox system enabled us to prepare block copolymers with relatively narrow molecular weight distributions. We distinguish five regions in the phase diagram: a transparent sol, opaque sol, transparent gel, opaque gel, and syneresis. By examining the extent of changes in the spectroscopic properties of a fluorescence probe, pyrene, as a function of block polymer concentration and/or temperature, we determined the critical association concentration as well as the partition coefficient Kv for pyrene. The spectroscopic properties indicate that the hydrophobicity around the probe starts to increase far below the demixing line of the PNIPA-block-PEG, a remarkable finding which suggests that even in the temperature region below the LCST temperature of a PNIPA block (∼32 °C), this block copolymer provides more ...

To synthesize an amphiphilic block copolymer of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) (NE), an aqueous soap-free emulsion polymerization system was employed where poly(N-isopropylacrylamide) (PNIPA), polymerized from the radically activated chain ends of poly(ethylene glycol) (PEG), forms micelle cores stabilized by PEG brush chains emanating there from. When this polymerization was carried out at temperatures equal to or higher than 34 °C, narrowly-dispersed NE, which cannot be obtained by solution polymerization, was successfully obtained. To elucidate the living nature of the soap-free emulsion polymerization, time-dependent monomer conversion and molecular weight of NE was investigated by time-resolved gel permeation chromatography (GPC). The results indicate that the compartmentalization of end radicals into micelles cores leads to the quasi-living behavior of the polymerization.

Mesoscopic structures of a dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel and the re-moistened one are investigated with complementary use of the small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) methods. The SAXS profile of the dehydrated NIPA/SA gel shows a clear peak at q =0.026 A −1 but that of the re-moistened one does not. On the other hand, only the SANS profile of the re-moistened NIPA/SA gel shows a peak at q =0.022 A −1 . Taking into account that SAXS is sensitive to the fluctuation of the distribution of the SA bases and SANS is sensitive to that of the water in the NIPA/SA gel, these results indicate that inhomogeneous evaporation of water in the NIPA/SA gel occurs on the dehydration and that the SA clusters are finally generated.

Following the Fukushima Daiichi nuclear disaster in 2011, Cs radioisotopes have been dispersed over a wide area. Most of the Cs has remained on the surface of the soil because Cs+ is strongly adsorbed in the interlayer spaces of soil clays, particularly vermiculite. We have investigated the microscopic structure of an aqueous suspension of vermiculite clay over a wide length scale (1–1000 Å) by small-angle X-ray scattering. We determined the effect of the adsorption behavior of Cs+ on the structural changes in the clay. It was found that the abruption of the clay sheets was induced by the localization of Cs+ at the interlayer. This work provides important information for predicting the environmental fate of radioactive Cs in polluted areas and for developing methods to extract Cs from the soil and reduce radioactivity.

Tri-n-butyl phosphate (TBP) is an important extractant for separating hexavalent uranium and tetravalent plutonium from used nuclear fuel by solvent extraction. In such solvent extractions using TBP, the organic phase occasionally separates into two organic phases, namely, light and heavy organic phases. The latter one in particular is called the third phase. The purpose of this work is to elucidate the mechanism whereby the third phase forms in biphasic liquid-liquid solvent extraction of heavy metal ions. Toward this end, small- and wide-angle X-ray and neutron scattering (SWAXS and SWANS) experiments were conducted to examine the microscopic structures of TBP/octane mixtures. These investigations of solute associations in TBP-containing organic phases before extraction of heavy metal ions provide insights into system performance. After the extraction of heavy metal ions, for example, the microscopic structures formed in the organic phase are likely to be correlated with the initial microscopic structures, which are revealed here. SWAXS and SWANS, with accurate estimations of incoherent scattering intensities for all solution samples, revealed the following: (i) TBP self-associates in octane, and the average distance between two TBP molecules in the TBP assemblies is evaluated as 0.9-1.0 nm; (ii) the shape of the TBP assembly is ellipsoidal; and (iii) the attractive interaction among TBP assemblies in octane is miniscule, and thus, they tend to be dispersed homogeneously due to the excluded volume effect.

A poly(4-acrylamidosalicylic acid) gel (PASA gel) exhibits multiple phases as characterized by distinct degrees of swelling; the gel can take one of four different swelling values, but none of the intermediate values. The gel has remarkable memory: the phase behavior of the gel depends on whether the gel has experienced the most swollen phase or the most collapsed phase in the immediate past. The information is stored and reversibly erased in the form of a macroscopic phase transition behavior. The structure factors corresponding to these four phases were obtained by SANS, which indicated the presence of characteristic structures depending on pH and temperature, particularly in the shrunken state.

Peptide amphiphile molecules (PA) are remarkably versatile and useful as building blocks for construction of complex supramolecular structures in a bottom-up fashion. Worm-like micelles of PA have been demonstrated to have successful application to creation of synthetic extracellular matrix materials for tissue engineering and regenerative medicine. However, the pathway of the self-assembly process of the PA worm-like micelle has not been fully characterized or understood. This work analyzes the self-assembly process leading to worm-like micelle formation in our designed PA with small-angle neutron scattering and atomic force microscopy. The experimental results demonstrate the existence of transient spherical micelles in the early stage of the process and subsequent micelle chain elongation by attachment of spherical micelles to the end of growing cylindrical micelles to form worm-like micelles in a process mimicking chain-growth polymerization.

Poly(N-isopropylacrylamide)-block-poly(ethylene glycol) copolymers (NE) having nearly symmetric (s-NE) and highly asymmetric (a-NE) compositions in terms of constituent block chains were synthesized and purified: the s-NE and a-NE had a volume fraction fPNIPA of poly(N-isopropylacrylamide) (PNIPA) block chains equal to 0.46 and 0.83, respectively. Their phase behaviors in water and self-assembled structures have been studied in the parameter space of temperature (T) and weight percent of block copolymers (wP, weight/volume), by means of macroscopic observations on turbidity, fluidity and volume change, and of microscopic observations with ultra-small and small-angle neutron scattering. The results revealed that various states of the solutions exist as a consequence of interplay of short-range interactions among PNIPA, poly(ethylene glycol) (PEG) block chains, and solvent (especially temperature-dependent solvent selectivity) and with long-range interactions arising from elastic energy of PNIPA and PEG in the domain structures. At low polymer concentrations (wP wP,C), and with increasing T, the a-NE system changed from state (I), state (II), as described above, (IV) an opaque gel comprised of fractal network-like domains rich in NE in the water rich matrix, and to state (V) where syneresis of the opaque gel occurs, giving rise to coexistence of macroscopic opaque gel phase and squeezed-water phase. On the other hand, in between state (II) and state (IV), the s-NE system exhibits an extra state (VI) of transparent gel, as a consequence of ordered micelles due to microphase separation of NE in water. The ordered micelle are stabilized by long coronal PEG chains in s-NE, reflecting elastic energy contribution of coronal chains to the system state. The observed syneresis is unique in that it is involved in the system comprised of the fractal network-like domain rich in PNIPA and the medium rich in water.

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D2O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 degrees C in a temperature range of transparent sol below 30 degrees C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W(p)>3.5% (w/v), corresponding to opaque gel above 30 degrees C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 degrees C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.

Macroscopically anisotropic hydrogels were synthesized by hybridization of poly(N-isopropylacrylamide) with liquid crystalline inorganic nanosheets; their anisotropies in the structure and properties are demonstrated.