We have conducted computer simulation to understand the feature of the grain coarsening of polymer microdomains. For this purpose, the phase field crystal model was utilized with the conserved potential field and perpendicularly oriented cylindrical microdomains were simulated, being evoluted from the disordered state. As a result, the power-law behavior was confirmed as the grain size is proportional to tα, where t is the simulation time. The growth exponent α was further found to be dependent on the noise strength ζ in the simulation. Two different power-law behaviors were found for early and late stages for all of the results except for zero noise strength for which a single power-law behavior was observed over the entire time range. α increased from 0.16 to 0.33 (for the late stage) with increasing noise strength. Although the result (0.16 ≤ α ≤ 0.33) contradicts our previous experimental result (α = 0.45) obtained by atomic force microscopy and small-angle X-ray scattering [Polymer Journal, 2017, 49, 655.], simulated images are rigorously examined to understand the features of the grain coarsening. The following features are found. First of all, not only point defects but also line defects can exist in a grain. Both of them can trigger to create a new grain boundary or a small grain. Such formation of small grains was just transient so that they disappeared immediately. The reason why such transient grains are necessarily formed may be due to an instability in larger grains in the course of their growth. Such instability is caused by the localized energy due to a heavy distortion of the hexagonal lattice. As an example of the slow process of grain coarsening, it is suggested that slow movement of the grain boundaries can be driven by the change of the position of individual cylinders from the original grain to a neighboring grain. Furthermore, heavily curved grain boundaries are forced to be immediately straightened due to the high energy of the bent grain boundaries. Thus, we can recognize that the grain coarsening is driven by a dynamic movement and exchange of grain boundaries, as we have speculated in our previous publication. [Polymer Journal, 50, 1029–1042 (2018)].
We overview both theoretical and experimental studies on the following kinetics of block copolymer micelles formed in a selective solvent reported so far: 1) the exchange kinetics of block copolymer chains among micelles was investigated by time-resolved small-angle neutron scattering for deuterated block copolymer micelles mixed with corresponding non-labeled micelles; 2) the growth of the micelles after a temperature jump was studied by time-resolved light scattering; 3) the nucleation-growth kinetics of the block copolymer micelles in solution was investigated by light and small-angle X-ray scattering using a stopped flow apparatus; 4) the morphology transition kinetics from cylindrical micelles to spherical micelles of block copolymers was studied by transmittance electron microscopy and time-resolved small-angle X-ray scattering.
Sequential copolymerization of l-lactide (LLA) with ε-caprolactone (CL) followed by that of d-lactide (DLA) with CL was carried out to synthesize Poly(LLA-r-CL)-b-Poly(DLA-r-CL). The obtained Poly(LLA-r-CL)-b-Poly(DLA-r-CL) showed only one Tmca. 30°C higher than that of Poly(LLA-r-CL), indicating selective formation of stereocomplex crystals. The stereoblock Poly(LLA-r-CL)-b-Poly(DLA-r-CL) exhibited high elongation at break similarly to homochiral Poly(LLA-r-CL). Their biodegradation test using proteinase K showed lower degradability than that of homochiral Poly(LLA-r-CL).
In situ Raman spectroscopy was performed to evaluate microscopic deformation behavior such as the load sharing of molecular chains and the molecular orientation for high-density polyethylene and isotactic polypropylene under uniaxial stretching. Below the α1 relaxation temperature, the compression stress is applied to the crystalline chains in the yielding region due to the macroscopic shrinkage with necking. Moreover, the crystalline chains orient in the 30–50° direction, suggesting that the molecular orientation of the crystalline chains is hindered by the excluded volume effect of the lamellar cluster units. On the other hand, above the α1 relaxation temperature, the crystalline chains immediately orient in the stretching direction after the yielding point and the stretching stress is applied on the crystalline chains. The enhancement of the molecular orientation of the crystalline chains is caused by the thermal activation of the molecular motion within the crystalline phase owing to the onset of α1 relaxation.
Dinuclear complex catalysts often show different catalytic bahavior compared to the corresponding mononulcear complex catalysts. Most of the previously reported dinuclear catalysts contain two mononuclear complexes connected by a flexible tether. Herein we report double-decker type dinuclear complex catalysts having two metal centers located on cyclic ligands in close proximity. They show a higher catalytic activity than the mononuclear analogue, and gave polymers with higher molecular weight. The dinuclear catalysts also promote copolymerization of olefins with various comonomers and gave copolymers with unique structures. It was also revealed that the dinuclear catalysts are stable at elevated temperature.
The development of valuable functional materials using abundant and renewable resources has been recognized as one of the most important aspects to break out of the over-dependence on exhaustible fossil fuels. In nature, we can find a variety of organic compounds with unique molecular structures. The incorporation of interesting structural features of natural products into molecular designs is highly attractive for material development because it provides a new avenue for creating innovative functional materials that would be otherwise unimaginable. This review summarizes our latest studies on the synthesis of novel optically active polymers containing a structural element of naturally-occurring compounds, particularly (poly)saccharides, and their application to chiral functional materials.
Induction of cancer-specific cellular immunity is necessary for establishment of cancer immunotherapy. For induction of cellular immunity, antigen delivery to immunocompetent cells such as dendritic cells and activation of these cells into a suitable state for immunity-induction are required. Here, intracellular antigen delivery systems have been developed using antigen-loaded liposomes modified with pH-responsive fusogenic polymers. Furthermore, polysaccharide-based pH-responsive polymers have been synthesized by introduction of carboxylated moieties to utilize polysaccharide-derived immunity-activation functions. Polysaccharide derivative-modified liposomes were taken up by dendritic cells efficiently and achieved cytoplasmic delivery of antigenic proteins via membrane fusion with endosomal membranes responding to weakly acidic pH in endosomes. After subcutaneous administration of these liposomes to mice, antigen-specific cellular immunity was induced by cytoplasmic delivery of antigen and activation property of immune cells derived from the polysaccharide backbone. In addition, combination of polysaccharide derivative-modified liposomes and TGF-β signaling inhibitor-embedded PEG-modified liposomes induced strong antitumor effects in tumor-bearing mice through induction of cellular immunity and cancelling of immunosuppression by the tumor.
Static light scattering, dynamic light scattering, and small-angle X-ray scattering are powerful tools to analyze structures of various polymer assemblies formed in solution. In this article, we briefly explain those experimental techniques along with their historical background, and review their applications to the following polymer solution systems: (1) associating homopolymer solutions, (2) aqueous solutions of the polyanion–polycation mixture forming polyion complex colloids, (3) block copolymer solutions forming polymer micelles of various morphologies, (4) aqueous solutions of amphiphilic random and alternating copolymers forming the flower micelle or flower necklace, and (5) aqueous solutions of the globular protein–surfactant mixture. Different scattering techniques are combined with other experimental and theoretical methods to provide more detailed structural information.
Ken TERAO, XinYue JIANG, Akiyuki RYOKI, Hirokazu HASEGAWA
Recent developments of synchrotron-radiation small-angle X-ray scattering (SAXS) measurements for dilute polymer solution make it possible to determine dimensional properties and intermolecular interactions quantitatively even in common organic solvents at very low temperatures, and in viscous solvents. This paper reports these characteristics for polystyrene in two solvents at a wide temperature range, molecular conformation and intermolecular interactions for thermochromic polysilanes, and conformational properties of polysaccharides in high viscous solvents including an ionic liquid. This method can also be applied to solutions of cyclic and branched polymers with relatively low molar mass, and we describe dilute solution properties of rigid cyclic polysaccharide derivatives, semiflexible and rigid star polymers, and comb-like complexes of polyelectrolytes and rigid helical polypeptides.
Protein drugs and therapeutic cells are among promising current and future therapies for patients. The importance of these proteins and cells has increased in the clinical field, and protein and cell purification methods, without losing their potency or biological activity, are urgently needed. We prepared thermoresponsive polymer brushes as a new protein and cell separation tool because interactions between the polymer brushes and targeted proteins and cells can be modulated by changing the external solution temperature without using other agents that might contaminate these biologics or disrupt their function. Using these new thermoresponsive polymer brushes, a variety of different bio-separations have been performed by simple temperature changes in aqueous solutions. The present review describes the recent achievement in bioseparation using thermoresponsive polymer brushes.
Polylactides, which were synthesized by renewable sources, can be used as environmental and biomedical materials because they are biodegradable and -absorbable. However, they have low thermal and mechanical strength, and lack specific functionalities. It is known that the stereocomplex formation of polylactides improve their thermal stability and mechanical strength. In this review, we use chain end modification for additional functionalization. We achieved high thermal stability, antibacterial properties, and dynamic interaction functionality. Additionally, we also investigated the selective adhesion by stereocomplex formation due to polymer-polymer interaction with interfacial main chains of polylactide.
The objective of this study is to obtain the fundamental knowledge of mesenchymal stem cells (MSC) cultured in a sandwiched condition with biofunctional hydrogels as a 3-D culture model. The biofunctional hydrogels were prepared through the immobilization of a cell signaling protein on poly(acrylamide) hydrogels with different crosslinking densities. As the cell signaling protein, ephrinB2 of an Eph signal ligand was employed to stimulate the osteoblastic differentiation of MSC. In this study, by making use of the specific interaction between IgG Fc domain and proteinA, the immobilization of ephrinB2-Fc in an orientation-regulated manner was designed to achieve the Eph signaling.
Sonodynamic therapy (SDT) using ultrasound irradiation instead of photoactivation as in photodynamic therapy, has emerged as a promising treatment for various types of cancer. We have focused on titanium dioxide nanoparticles (TiO2 NPs) as a sonosensitizer which can generate reactive oxygen species by sonication. TiO2 NPs-incorporated polyion complex micelles were developed for the delivery into the cells. Here, carmofur being a hydrophobic prodrug was solubilized into the micelles. From in vitro experiments, it was confirmed that carmofur-solubilized micelles effectively suppress the cell viability due to the additive effect of the anticancer effect of 5-fluorouracil produced by hydrolysis of carmofur and the SDT effect.