Articles in 2023

A buffer solution of dual stimuli-responsive polymer with photodimerizable groups and temperature-responsive moieties undergoes a phase transition from a sol state to a gel state by exposure to ultraviolet light. The resulting gels changed the physical (elastic modulus) and chemical (hydrophilicity) properties by varying UV exposure time and temperature, respectively. Cell adhesion, spreading, and proliferation were strongly influenced by the physical and chemical properties of the polymer gels, which were regulated by varying UV exposure time and temperature.

The aggregation states from the interface to the bulk of the adhesive/adherend is a key to unraveling adhesion at the molecular level. We applied X-ray absorption spectroscopy (XAS) in combination with an Ar gas cluster ion beam (Ar GCIB) to poly(methyl methacrylate) (PMMA) films adsorbed onto a SiO_x/Si(111) surface. GCIB-XAS analysis revealed that the orientation of the C=O group in the side chain of PMMA differs between the region from the SiO_x interface to a distance on the order of 1 nanometer and the bulk PMMA region.

In this review, we show that reversibility of charge storage occurs in polymers with bistable redox-active groups populated in the repeat units of a nonconjugated backbone, especially when an electron self-exchange reaction spreads throughout the polymer. We will also show that extending the idea of electron exchange to electron/proton exchange leads to reversible hydrogen storage based on the bistability of hydrogenated and dehydrogenated states and the equilibrium for hydrogenation.

We added lithium (trifluoromethane sulfonyl) imide (LiTFSI) salt into an immiscible poly(methyl methacrylate) (PMMA)/ethylene-vinyl alcohol copolymer (EVOH) to improve the transparency and tensile properties. The addition of LiTFSI reduced the refractive index of EVOH, which matched the refractive index of PMMA, resulting in high transparency. In addition, LiTFSI interrupted the intra- and intermolecular hydrogen bonds between the OH groups in EVOH, resulting in decreased crystallinity. Consequently, the amorphous and flexible EVOH domains in the PMMA matrix changed the tensile properties from brittle to ductile by suppressing the stress concentration.

The tensile strength of short carbon fiber (SCF)-reinforced plastics (SCFRPs) prepared by injection molding with various functionalized polypropylenes (PPs) using different types and contents of functional groups and crystallinity, depended on interfacial adhesion. Functionalized PP with more functional groups added to the side chains (PP-g- MA1) exhibited higher interfacial adhesion near the SCFRP surface where the SCF filaments and PP chains were highly oriented in parallel than that with fewer functional groups (PP-t-MA).

Although a fundamental problem, the effect of node functionality on network fracture has yet to be clarified. This study performed phantom chain simulations for networks made from star polymer mixtures with different functionalities. The results reveal that the fracture characteristics lie on the master curves if they are plotted as functions of the cycle rank of the network, irrespective of the mixing ratio and the conversion rate.

Electrically conductive porous materials consisting of cellulose nanofiber (CNF) and graphene were prepared with postreduction processes. Porous CNF/graphene oxide (GO) composites were used as precursors and the reduction of the GO under dry conditions was carried out. Both thermal and chemical reduction processes successfully proceeded to obtain the porous CNF/reduced GO (rGO) composites, in which the conductive path was effectively fabricated owing to the good dispersibility of GO sheets. As a result, the porous CNF/rGO exhibited high electrical conductivity of up to 1.39 × 10^–3 S/m.

The characteristic ratios C_∞ of syndiotactic, isotactic, and atactic hydrogenated ring-opened poly(norbornene)s, H-poly(NB)s, were determined in 1,2,4-trichlorobenzene at 140 °C with molecular dynamics simulations and size exclusion chromatography with a multiangle light-scattering online detector (SEC-MALS). The C_∞ results were 11, 14 and 12 for syndiotactic, isotactic and atactic H-poly(NB), respectively, all of which were consistent with the rotational isomeric state model, and definitely larger than those for polyethylene and polypropylenes. The stiffness of the H-poly(NB) chains was induced by the cyclopentane ring in the chains.

To examine the behavior of degradation by a conjugate substitution reaction in aqueous media, the degradation of a poly(conjugated ester), prepared from 1,4-butylene bis[α-(bromomethyl)acrylate] and fluorescein, with aqueous solution of various nucleophiles was investigated using UV‒vis spectrometry and size-exclusion chromatography. At the earliest stage of the degradation, the affinity between the nucleophile and the polymer affected the reaction rate, leading to faster degradation for relatively hydrophobic amines. On the other hand, hydrophilic nucleophiles that produce water-soluble degradation products promoted complete chain scission.

A degradable cross-linked polybutadiene was synthesized using a peptide-based cross-linker. As a degradable cross-linker, we synthesized poly(L-cysteine) (polyCys) by papain-catalyzed chemoenzymatic polymerization. The thiol-ene reaction between polybutadiene and polyCys was conducted in the presence of a radical initiator, resulting in the formation of an insoluble polybutadiene gel. The successful cross-linking and network formation was confirmed by Raman spectroscopy and viscoelastic analysis. Dynamic viscoelastic measurements of the cross-linked polybutadiene revealed the disappearance of slow relaxation mode. The polyCys-linked polybutadiene underwent degradation through acidic hydrolysis, allowing the recovery of soluble polybutadiene.

This study explores enhanced electrical properties in conductive polymers, particularly PEDOT:PSS, by creating multilayered films. Initial findings show a sheet resistance of 1639 Ω□^-1 for a single layer, but applying three additional layers reduces it to 29 Ω□^-1, boosting conductivity from 2.6 to 18.3 Scm^-1. Similar improvements are observed with formulations containing Tween 80. Analysis via X-ray diffraction and Raman spectroscopy indicates increased crystalline order and a benzoid to quinoid shift. Surface profiling reveals growing roughness with additional PEDOT:PSS layers, partially mitigated by Tween 80.

Tributylborane-initiated graft polymerization of methyl methacrylate on a poly(vinylidene fluoride) film was successfully achieved. The reaction was affected by the temperature and concentration of tributylborane, and a 41% graft yield was obtained under the optimized conditions. This value was higher than those obtained with other methods. This method facilitated modifications of only the surface of the poly(vinylidene fluoride) film, which was confirmed by IR spectroscopy and cross-section observations. New physical properties were added to the surface, such as hydrophilicity.

Ester free type trimethylene carbonate derivatives bearing bulky aromatic groups were designed and synthesized, including one or two benzyl groups, diphenylmethyl groups, and triphenylmethyl groups. The mechanical properties of the polymers were estimated by compressive test, resulting in around 0.3MPa at most. The degradation behaviors were also evaluated under Lipase solution and 0.01M NaOHaq. for several weeks, revealing the substituents influenced on the prevention of degradation at most cases. The degradation behavior was slowly observed, which were analyzed by weight loss, SEM images, SEC, TGA, and DSC.

The effect of radiation-induced graft polymerization (RIGP) on abaca fibers was evaluated for composite reinforcement. Using grafted fibers improved composite properties, especially when RIGP was carried out under reversible addition-fragmentation chain transfer (RAFT) mechanism. Controlled chain growth of grafted polymer could be achieved by RAFT-RIGP and this led to the highest improvement in mechanical strength versus pristine fibers and those modified by conventional RIGP. These findings show the capability of RAFT-RIGP to optimize the effectiveness of natural fibers in the composite industry.

In this review article, an overview of recent studies on heat-responsive and photoresponsive adhesive materials and the characteristics of other external stimuli used for dismantlable adhesive systems are described. Then, research on dismantlable adhesive materials using polyperoxides is introduced as an example of early material design. Next, the development of a dual-stimuli responsive dismantlable adhesive material is interpreted as a material design for achieving stability during use and degradability during dismantling. Finally, recent studies on heat-responsive, dismantlable adhesive materials, which are thermally stable during use while responding quickly during disassembly by heating, are described.

Monomer sequence transformation and reversible polymerization–depolymerization control were achieved in the cationic copolymerization of 2-methyl-1,3-dioxepane and γ-butyrolactone by vacuuming or temperature change. The removal of monomers from the polymerization solution with a vacuum pump promoted depolymerization, resulting in a transformation to pseudo-alternating copolymers and subsequent oligomer formation. Heating the polymerization solution also promoted a similar monomer sequence transformation and oligomer formation, while cooling led to the polymerization of monomer molecules generated via depolymerization.

Elastic moduli of nano-dispersed elastomer domains in injection molded isotactic polypropylene (iPP)/ethylene-co-octene elastomer (EO) binary blends were investigated by an atomic force microscopy. The EO domains were highly elongated to the flow direction. The elastic modulus distribution of the EO domains was quite different depending on the annealing conditions.

Poly(dopamine) (PDA) was investigated as a primer to enhance adhesion in flexible optoelectronic devices using the conducting polymer PEDOT:PSS. PDA improved wettability on polypropylene (PP) but reduced it on poly(ethylene terephthalate) (PET). However, PDA enhanced the quality and adhesion of pristine PEDOT:PSS and PEDOT:PSS/Tween 80 films on glass, PP, and PET. Crucially, it did not negatively affect sheet resistance of PEDOT:PSS/Tween 80 films, establishing its suitability as a primer for flexible substrates. This research addresses a key challenge in utilizing PEDOT:PSS in flexible optoelectronics, enhancing its performance on various substrates.

We determined intrinsic viscosity for polystyrene (PS) samples with a wide range of molecular weight in d-limonene, which attracts interest as an environmentally friendly solvent for PS. By analyzing the experimental data obtained in d-limonene using the helical wormlike chain model with and without the excluded-volume effect, solvent quality of d-limonene for PS was quantitatively evaluated. Consequently, it was concluded that d-limonene belongs to the category of medium solvent, which is intermediate between good solvents like toluene and poor solvents like cyclohexane, for PS.