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Methylaluminoxane (MAO) activates various transition metal catalysts for coordination polymerization reactions and exists as a counter anion that can interact with cationic metal species in a polymerization medium. The structural modifications to MAO would therefore provide a new direction for controlling the polymerization behavior. In this review, our recent work about the modification, the composition control, and a new preparation method of MAO is summarized. The application of modified MAO for the synthesis of stereoblock polydienes is also described.
To establish effective chemical transformations, catalytic systems with advantages such as high activity, recyclability, durability, and operability have attracted considerable attention. One of the strategies for the development of high-performance catalytic systems is the use of polymer hydrogels. In this focus review, an overview of our research using poly(N-isopropyl acrylamide)-based hydrogel particles and macroporous monoliths as molecular catalysts and loading matrices for palladium catalysts is summarized.
Temperature-responsive (or thermoresponsive) polymers belong to the most studied class of smart polymers and are mainly classified into two types based on their temperature-responsive behavior: lower critical solution temperature (LCST) and upper critical solution temperature (UCST). Based on polymeric design, when more than two temperature-responsive segments are connected through a covalent bond, the block copolymers are expected to show a multi-temperature-responsive property upon conformational changes. This review focuses on current multi-temperature-responsive polymeric materials and their future applications such as drug-delivery carriers, sensors in solvents, model proteins, and memory storage.
When light is shined on semiconducting polymers, singlet excitons are promptly generated in organic solar cells. At a donor–acceptor heterojunction, excitons separate into holes on the donor and electrons on the acceptor as a result of the energetic offset of the molecular orbital. If the electron and hole separate further, they become free from Coulombic attraction and hence survive up to nano- or microseconds, long enough to be transported to each electrode. Otherwise, the geminate electron–hole pairs are likely to recombine to the ground state.
The performance of organic optoelectronic materials is strongly affected by the three-dimensional (3D) alignment of π-electronic systems. This focus review describes several methods for aligning π-electronic systems to achieve various functionalities in both solution and the solid phase. Cyclic oligomers, acting as tethering units, can facilitate precise design of the nanoarchitecture of π-electronic systems in diluted solutions. In the solid state, charged π-electronic systems exhibit nanoarchitectures based on electrostatic interactions. These methods for controlling the arrangements of π-electronic systems can produce fascinating molecular systems.
Double network (DN) gel - hydroxyapatite (HAp) composite achieves robust fixation to bone tissue accompanied by spontaneous osteogenesis penetration into the gel matrix. In addition, the HAp-DN gel composite can be used as a simplified model of bone tissues because of their similarity in terms of components. The HAp orientation is regulated by the anisotropy of the polymer network of gel, implying that the collagen matrix is oriented in the earliest stage of biomineralization in vivo.
Design of an N-phenyl maleimide derivative bearing an activated NHS ester for radical copolymerization with tert-butoxystyrene to achieve both precise alternating sequence control and functionalization.
To obtain functionalization of super-engineering plastic, poly(ether ether ketone) (PEEK) substrate, photoinduced self-initiated graft polymerization of several kinds of functional methacrylate was carried out. Graft polymerization proceeded well, and 50–250 nm in thickness graft polymer layers were generated on the PEEK substrate. Surface characteristics such as surface free energy and surface ζ potential on the polymer-grafted PEEK substrate were corresponded to the chemical structure of the graft polymers. Cell attachment on the polymer-grafted PEEK substrate was examined. The surface ζ potentials of the polymer-grafted PEEK substrates governed the cell adhesion density.
The present work focuses on the development of a system enable to modulate, upon an external stimuli, the amount of metal ions uptake. A photoresponsive compound was used as a functional monomer for the preparation, for the first time, of a photoresponsive ion-imprinted polymer (PIIP) for Pd(II) uptake. The photoisomerization capability of the submicroparticles of PIIP, with conformational changes of the polymer, was demonstrated and an improved binding capacity versus Pd(II) was observed after UV exposure of the polymer with maximum binding capacity near to 22 mg g−1.
Polylactide (PLA) exhibits various types of crystal modifications depending on the preparation conditions, including the components. To solve the open question, a reliable calculation method for crystallinity, crystal forms and composition in neat PLA and PLA composites was developed on the basis of temperature-dependent synchrotron wide-angle X-ray diffraction results. The relative composition of amorphous, α-form, and α’-form phases of PLA and its composites filled with halloysite nanotubes during heating was successfully obtained.
With the aim of gaining more insight into the heat capacity of amorphous polymers and considering that there are more than a dozen types of data on the absolute value of the heat capacity of polymer compounds, we evaluated the heat capacity of 16 main-chain-type amorphous polymers composed of a carbon backbone using a combination of the Tarasov equation, Einstein equation, and the (Cp − CV) correction term by taking into account the degree of freedom of monomer units. We found that the heat capacity of the analyzed amorphous polymers could be reproduced using only three fitting parameters from a combination of the Tarasov and Einstein equations below glass transition temperature.
Long-term storage of isotactic polypropylene caused a dramatic loss of ductility, as manifested by the mechanical tensile and impact behavior. The embrittlement was accompanied by an increase in the crystallinity. A comparison of static and dynamic mechanical data suggests the development of structural heterogeneities upon aging that serve as fracture loci under mechanical stress. Subsequent annealing of the aged samples reversed the loss of ductility. This indicates healing of the hypothetical irregularities by the thermal treatment.
Electrochromic properties of covalently bonded polyaniline-reduced graphene oxide/single walled carbon nanotubes nanocomposites. A high performance electrochromic material was prepared using polyaniline (PANI) and two different dimensional carbon nanostructures, single-walled carbon nanotubes (SWCNTs) and reduced graphene oxide (rGO) as the components. The covalent bond was introduced to interface between PANI and two carbon nanostructures to form a three-dimensional conductive network. Owing to the high electron conduction through directly connected covalent bond and loose molecular chain aggregation brought by two various dimensional carbon nanostructure, PANI-rGO/SWCNTs nanocomposites exhibit superior electrochemical and electrochromic properties (high optical contrast and short switching time) compared with PANI.
Injectable inclusion complex for cerebral aneurysm treatment were prepared by α-cyclodextrin (α-CD) and hydrophobically modified poly(vinyl alcohol) (hm-PVA). The α-CD/hm-PVA inclusion complex with thixotropic properties can easily be injected into the cerebral aneurysm site using a catheter. Due to the recovery of physical crosslinks (hydrophobic and hydrogen bonding interactions), the α-CD/hm-PVA inclusion complex can stably fill in cerebral aneurysms. Finally, stable hm-PVA gel formation enabled embolization of the cerebral aneurysm after α-CD release.
Utilization of chemical modification of M13 phage with oligo(ethylene glycol) to improve its solubility and resistance to organic solvents successfully expands the applicability of M13 phage-based thermally conductive assemblies. The high thermal diffusivity of the assemblies composed of M13 phage modified with longer ethylene glycol chains was maintained when the assemblies were prepared using a mixed solvent of water and tetrahydrofuran. Our results will contribute to construction of novel thermally conductive soft materials composed of biomacromolecular assemblies using organic solvents on substrates with complex surface morphologies and/or hydrophobic surfaces.
Chitin nanofibers were prepared from purified crab-shell chitin particles by repeated high-pressure homogenization in water. AFM images showed that the chitin nanofibers had heterogeneous network structures. X-ray diffraction patterns showed that both the crystallinity index and crystal width of the original α-chitin decreased by nanofibrillation. Solid-state 13C-NMR spectra showed that all C6–OH groups had the gauche–gauche conformation. The degree of N-acetylation increased from 0.83 to 0.98 by nanofibrillation, while the weight-average molar masses of the original chitin and chitin nanofibers were 271,200 and 165,500, respectively.