Research articles

Inspired by the natural spinning process, we developed an aqueous spinning system with a citrate/polyethylene glycol buffer for highly extensible silk fibers. This system enabled tuning of the induction of crystallization through the buffer conditions.

Carboxylated butyl rubber derivatives were obtained by reacting the isoprene units in the isobutylene copolymer with alkylmercaptanoic acids comprising alkyl spacers of different lengths. The yield of the reactions varied from 80 to 90% for direct reaction of the copolymer containing 1,4-isoprene units, but increased to 90–98% if the 1,4-units were isomerized to terminal alkenes prior to the reactions.

A series of ester-functionalized polythiophenes (P3OETs) with precisely controlled head-to-tail (HT) ratios was synthesized via palladium-catalyzed direct arylation polycondensation (DArP). The ionization potentials and optical bandgaps of P3OETs decreased as their HT ratios increased because of the increased backbone coplanarity and extensive π-electron delocalization. The method of precisely controlling the regioregularity and HT ratio can contribute to the design of new polythiophene derivatives with enhanced electronic functionality.

RAFT aqueous emulsion polymerization of vinyl acetate (VAc) was performed using poly[di(ethylene glycol) vinyl ether] (PDEGV) macromolecular chain transfer agents. The emulsion polymerization directly induced PDEGV-b-PVAc diblock copolymer assemblies in water. Owing to the characteristic PDEGV as a highly hydrophilic steric stabilizer, this facile formulation enables the production of various particle morphologies, such as spheres, rods (ellipsoids), and vesicles, depending on the composition of the block copolymer. Each morphology change in the nanoparticles via RAFT aqueous emulsion polymerization owes its success to the recent RAFT polymerizations of vinyl ethers.

Amine-containing microgel particles (GPs), which capture CO₂ at a low temperature and desorb it upon a mild heating, are attractive materials for capturing CO₂. In this paper, the effect of pK_a of ammonium ions in the GPs on the amount of CO₂ desorption upon heating was investigated at various CO₂ concentrations by experiments and thermodynamic predictions. A guideline for designing thermoresponsive amine absorbents for various applications including direct air capture and carbon recycling in closed spaces, such as space stations and submarines, is provided.

We chose an autoinduction (IPTG-independent) system for overexpression of recombinant proteins using E. coli as the expression host. In autoinduction, glucose and lactose are used as main carbon sources for cell growth. When the glucose is almost completely consumed as the first growth of E. coli., the carbon source turns to lactose, accompanied by regioselective chemical transformation of lactose to allolactose, which acts as the trigger for activation of transcription by releasing the repressor. Using this system, we achieved marked overexpression of the biosynthesized GFP and aECM-CS5-ELF.

Poly(γ-glutamic acid) (PGA) is a biopolymer produced by Bacillus spp. via the γ-amide linkages of d- and/or l-glutamate. PgsB, PgsC, and PgsA are the minimum protein set required for PGA production in B. subtilis, and PgsE improves PGA productivity. Analysis by size-exclusion chromatography combined with multiangle laser light scattering revealed that the molecular weight of PGA was M_w = 2,900,000 g mol⁻¹ or predominantly M_w = 47,000 g mol⁻¹ in preparations derived from B. subtilis cells with or without pgsE, respectively. PgsE may be required to increase the apparent molecular weight of PGA.

The present study described a new method with one step to fabricate silk fibroin nano- and microspheres, with the size of spheres and crystalline structure being controllable during processing. Silk microspheres prepared in the presence of salts were less porous and more homogeneous in size than those prepared in the absence of salts (Control). These properties are important not only for the stabilization of particles but also for the controlled release of entrapped drug molecules.

A highly random terpolymer of CO₂, styrene oxide (SO), and propylene oxide (PO) was realized by using a tetraphenylporphyrinatocobalt(III) chloride ((TPP)CoCl)/4-dimethylamino pyridine (DMAP) catalyst system. In contrast, gradient terpolymers were formed in the cases of CO₂, cyclohexylethylene oxide (CyEO), tert-butylethylene oxide (^tBuEO) or 1-adamantylethylene oxide (AdEO), and PO. The glass transition temperatures (T_gs) of these terpolymers are tunable between that of the copolymer of CO₂ with PO (34 °C) and that of the copolymers of CO₂ with the corresponding epoxide with bulky side groups.

Latex films typically suffer from poor mechanical strength compared to solution-cast latex films. In the present study, to obtain tougher latex films, we investigated the relationship between the mechanical properties and the nanostructures of films prepared at different film-formation temperatures (FFTs), i.e., FFTs above and below the glass-transition temperatures (T_g) of the microspheres. Tensile tests revealed that the films showed the highest fracture energies when the film was formed at a temperature higher than the T_g of the microspheres and followed by annealing.

We prepared the chemically crosslinked, cylindrical thermoresponsive poly(N-isopropylacrylamide) gels with changing the contents of reversible addition-fragmentation chain transfer (RAFT) agent. The environment in the gel was estimated by using a hydrophobic fluorescence probe. While the equilibrium swelling ratios were comparable, the deswelling response became fast as the content of RAFT agent increased with the formation of “bubble pattern”. This result indicates that the PNIPAAm gels prepared by RAFT still have spatial defects. In addition, the cooperative diffusion coefficients in swelling process of the gels prepared by RAFT polymerization were estimated.

Natural rubber-grafted-polyaniline with nanomatrix structure was prepared through graft-copolymerization. The effect of parameters on the graft-copolymerization was investigated using factorial experimental design and univariate experiments. The structural characterization of the resulting materials through NMR spectroscopy confirmed that aniline was grafted on the natural rubber. As observed in TEM image, polyaniline, which covered the natural rubber particles, formed the nanomatrix, and natural rubber particles formed the dispersed phase. The thermal properties and electrical conductivity of natural rubber-grafted-polyaniline were improved by the formation of nanomatrix structure.

Poly(vinyl butyral) (PVB) is accepted as an adhesive to glass substrates. The PVB was prepared through butyralization of poly(vinyl alcohol) under supercritical carbon dioxides. The Young’s modulus and tensile strength of the PVB prepared under supercritical carbon dioxides were higher than those of the PVBs in the preparation method in solution and swollen states. In addition, the PVB under supercritical carbon dioxide possessed higher adhesive strength to glass substrates even under high humid condition, compared with the other PVBs.

Two novel supramolecular norbornene monomers were prepared according to β-cyclodextrin–ferrocene (/adamantane) host–guest interactions and exhibited both the “living” and “controlled” ROMP characteristics with the aid of the third-generation Grubbs’ catalyst for the construction of corresponding supramolecular homopolymers and diblock copolymers.

Plasticized poly(ethylene carbonate) (PEC)/LiPF₆ electrolytes were prepared and evaluated their ion-conductive and dielectric relaxation behavior using broadband electric spectroscopy (BES). The BES results indicated that the plasticizer accelerates segmental motion of PEC and improve the dc conductivity, and the plasticizing effect of ionic liquid (EMImTFSI) on the PEC electrolyte is larger than that of glycerol. From the results of the Walden plot and fragility analysis, it was revealed that the degree of decoupling and the value of fragility increase by the addition of plasticizer, and these plasticizers weaken interactions between PEC chains and Li ions in the electrolyte.

Photocontrolled ring-opening polymerization of lactones with the advantages of being inexpensive, green, and noninvasive, is still rarely reported. In this work, we developed a series of composite photoacid generators containing a common photocatalyst and an onium salt to induce the living/controlled cationic ring-opening polymerization of lactones using alcohol compound as an initiator under visible light. The wavelength of the light could be easily adjustable by applying different photocatalysts. Moreover, simultaneous living/controlled cationic ring-opening polymerization of lactones and reversible addition–fragmentation chain transfer radical (RAFT) polymerization of methyl acrylate can be performed using hydroxy group capped trithiocarbonate to produce hybrid block copolymers in one step.

The effect of the ionic liquid content in tough inorganic/organic double-network (DN) ion gel membrane on the CO₂ permeability was investigated. By optimizing the composition of the inorganic and organic networks, the mechanical strength of the DN ion gel was significantly increased, and the DN ion gel membrane with more than 95 wt% of an ionic liquid was successfully prepared. With the increase in the ionic liquid content, the CO₂ permeability of the DN ion gel membrane exponentially increased up to ~67% of the theoretical maximum CO₂ permeability.

The synthesis of 100% ¹³C-labelled poly(propylene carbonate) from the completely alternating copolymerization of propylene oxide (rac-PO and R(+)PO) and ¹³CO₂ is reported. The prepared copolymers were shown to be regioselective with predominately head-to-tail (HT) connectivity. The infrared absorption of the polycarbonate in the \(v_{{\mathrm{co}}_{\mathrm{3}}}\) region is red-shifted by 45 cm⁻¹ from the polymer prepared from ¹²CO₂. This shift in frequency allows for the observation of v_NO modes of incorporated dinitrosyl metal complexes.

The generation of singlet oxygen (¹O₂) by sonicating a water-soluble complex of fullerene/poly(2-methacryloyloxyethyl phosphorylcholine) (C₆₀/PMPC) was investigated for sonodynamic therapy (SDT). ¹O₂ was generated from C₆₀/PMPC under ultrasonic irradiation, and the amount of ¹O₂ increased with increasing solubilized C₆₀ concentration and irradiation time. In cell viability tests, after 3 h of incubation, the cell viabilities were 10% and 84% in the presence of C₆₀/PMPC with and without sonication, respectively. This result suggests that C₆₀/PMPC shows a sonodynamic effect, which demonstrates its potential application in SDT.

Polymer micelles with a tunable drug release are promising carriers for drug delivery system. It is very important to clarify the correlation between micellar dissociation kinetics and drug release profile on a stimuli-induced deformation of polymer micelles. In this study, photo-cleavable o-nitrobenzyl ester-based amphiphilic block copolymer was successfully designed and prepared by mechanochemical solid-state copolymerization without any solvents and initiators. The self-assembled block copolymer micelles containing anticancer drugs showed sigmoidal decrease of micellar size and released the corresponding drugs depending on the photo-irradiation time.