| POLYMERS Vol.68 No.9 |
| >> Japanese | >> English |
COVER STORY
Soft Nano/Microspheres |
| COVER STORY: Highlight Reviews |
| Preparation of Gel-Particles Based on Association of Polymer Chains | Shin-ichi YUSA |
| <Abstract> Generally, nanogels and microgels are 3D cross-linked inside. These gels can be called gel-particles. Gel-particles are a quite unique material possessing both gel and particle properties. Various kinds of preparation methods of gel-particles have been reported and one of the typical ones is cross-linking within the polymer aggregate. The cross-linking points of the gel-particles are physical and chemical cross-linking, which are the same as those in conventional bulk gel. Gel-particles have been prepared by various cross-linking methods. Furthermore, external stimuli-responsive and biodegradable properties can be easily added to the gel-particles. It is expected that preparation methods and applications of gel-particles will be further developed in the future. In this article I mainly focused on the cross-linking method to prepare “soft particles”. Keywords: Gel-Particles / Self-Association / Physical Cross-Linking / Chemical Cross-Linking / Random Copolymer / Block Copolymer / Hydrogel / Control Release |
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| Rheology of Microgel Pastes | Kenji URAYAMA, Saori MINAMI |
| <Abstract> Microgel suspensions can be unusually concentrated because the microgels undergo deformation, interpenetration and volume change. The concentrated microgel suspensions called pastes behave as a yield fluid which acts as elastic solid in the quiescent state but flows when external stress exceeds the threshold value. We explain what governs the modulus, yield value, and flow behavior of the pastes, and the interesting rheological response to temperature change. Keywords: Microgel / Suspension / Rheology / Viscoelasticity / PNIPAM / Yield Fluid / Paste |
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| Theory of Electrokinetic Phenomena of Soft Particles | Hiroyuki OHSHIMA |
| <Abstract> Electrokinetic phenomena in a suspension of soft particles (i.e., particles covered with an ion-penetrable surface layer of polyelectrolytes) are theoretically discussed with special emphasis on the electrophoretic mobility of soft particles in an electrolyte solution. Comparison is made with the electrophoresis of hard particles without surface structures and of spherical polyelectrolytes without particle core. Recent progress in electrophoresis of soft particles is also reviewed. Keywords: Soft Particle / Electrokinetic Phenomena / Electrophoretic Mobility |
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| COVER STORY: Topics and Products |
| Self-Assembly of Amphiphilic Random Copolymers | Takaya TERASHIMA |
| <Abstract> We have recently developed controlled self-assembly systems of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic alkyl or functional pendants to produce various nanostructure polymer materials in aqueous/organic media and solid/film state: size-controlled, core-crystalline, reverse, and multicompartment micelles, vesicles, hydrogels, and sub-10 nm microphase separation materials. Typically, random copolymers carrying PEG and dodecyl pendants induced chain folding via the self-assembly of the hydrophobic pendants in water to form uniform and thermoresponsive micelles. The size, aggregation number, and cloud point temperature were controlled by the composition and chain length of the polymers. Uniquely, the random copolymers further afforded self-sorting in water: self-recognition of identical copolymers via dynamic chain exchange in the presence of different copolymers. Owing to such unique self-sorting properties, ABA-triblock copolymers consisting of the amphiphilic random copolymer A segments gave self-healing and selectively adhesive hydrogels. Keywords: Amphiphilic Random Copolymer / Self-Assembly / Self-Sorting / Micelle / Vesicle / Hydrogel |
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| Molecularly Imprinted Nanogels Functionalized by Interacting with Endogeneous Biomacromolecules In Situ | Yukiya KITAYAMA, Toshifumi TAKEUCHI |
| <Abstract> Stealthiness is a criteria of nanocarriers for drug delivery systems (DDS). In this issue, we report molecularly imprinted polymer nanogels (MIP-NGs) acquiring stealth capability in situ via protein corona regulation as a novel nanocarrier for DDS. Molecular imprinting is a powerful approach to implement molecular recognition properties into polymer-based materials. Thus, MIP-NGs capable of dysopsonic protein recognition were prepared by molecular imprinting in a precipitation polymerization system. The fluorescent resonance energy transfer between fluorescein-labeled MIP-NGs and rhodamine-labeled albumin was observed in vivo, indicating that the protein corona was regulated in situ using intrinsic dysopsonic proteins. Thus MIP-NGs show prolonged blood circulation compared to the reference nanogels prepared without a molecular imprinting process. Due to the passive targeting property toward the tumor tissue of the MIP-NGs, we are currently developing MIP-NGs containing gold nanoparticles as a novel stealth radiation sensitizer. Keywords: Molecularly Imprinted Polymers / Nanogels / Stealth / Protein Corona / Drug Delivery / Molecular Recognition / Radiation Therapy |
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| Gel Particles Seen by Light | Takuma KUREHA, Mitsuhiro SHIBAYAMA |
| <Abstract> In this issue, we describe investigations of the dynamics for soft microgel suspensions by dynamic light scattering (DLS). In the diluted concentration region, the microgels were regarded as conventional colloidal particles. With increasing their concentration up to the intermediate concentration region, the dynamics was decomposed to the concentration fluctuations of the microgel inside as fast mode and the dynamics of large clusters formed by neighboring microgels as slow mode. At high concentration region, the slow mode became a long-time relaxation and the nonergodicity appeared, resulting in the formation of glass. The concentration fluctuations of the gel remained in the microgel paste. This result shows that DLS is a powerful tool to investigate the dynamics ranging from a dilute colloidal suspension to a microgel paste. Keywords: Dynamics Light Scattering / Microgels / Ergodicity / Speckle / Glass |
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| Polymer Science and I: A Personal Account |
| Be Ambidextrous | Shunsuke YAMAMOTO |
| <Abstract> This is an essay by a researcher who just arrived at the UK as a visiting scholar reviewing his research career from undergraduate onwards. “Boundary”, “interface”, and a prefix “ambi- / amphi-” are important keywords throughout the story. |
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| Front-Line Polymer Science |
| Mechanochromic Polymers | Yoshimitsu SAGARA |
| <Abstract> Polymers that change absorption and emission properties in response to mechanical stimuli are useful materials because such “mechanochromic polymers” can visualize mechanical stress applied to materials. Several mechanisms to induce changes in photophysical properties have been established so far. In this contribution, firstly, dye-doped polymers are briefly introduced as well as explanation on their working mechanism. Aggregation behavior of dyes in host-polymers plays a pivotal role to induce emission color changes upon tensile deformation. Secondly, polymers in which so-called “mechanophores” are covalently introduced are described. When mechanical stimuli are applied, weak bonds in mechanophores cleave to result in significant changes in absorption and emission properties. Finally, new mechanophore types that never require covalent bond scission for activation are also described. Keywords: Mechanochromic Polymers / Dye-Doped Polymers / Mechanophores / Supramolecular Mechanophores / Stimuli Responsive Materials / Luminescence |
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