Original Article in 2024

Well-defined temperature-responsive gels with homogeneous network structures were prepared by photogelation of a four-armed star block copolymer composed of N-isopropylacrylamide and allylacrylamide upon visible light exposure. The dynamic lightscattering measurements revealed that the resulting gels had homogeneous networks, influencing the kinetics of temperature-responsiveness.

Liquid crystalline (LC) epoxy thermosets with a cyclic siloxane structure were prepared. The obtained epoxy thermosets formed an LC domain structure and exhibited a high modulus and fracture toughness as a result of the packing structure of the smectic ordered network chains. The introduction of a flexible siloxane structure slightly suppressed the increase in thermal conductivity, and the highly oriented structure resulted in a high thermal conductivity value of 0.28 W/(m K).

A combination of AFM-based AM-FM and nDMA methods evidences the effect of the curing temperature on the structural heterogeneities in epoxy networks: a lower pre-curing temperature provides a less heterogeneous network, which in turn can control the thermal and mechanical properties of resultant epoxy resins.

A novel hydrogel (TempGel(NP)) was synthesized through template polymerization of phenylboronic-acid-coated nanoparticles with tris(hydroxymethyl)methyl acrylamide (THMAAm). This process forms dynamic boronic ester crosslinks, creating a highly dense and uniform three-dimensional network. The innovative structure exhibits reversible thermal responsiveness, enabling rapid bond dissociation and reformation upon temperature changes. The dense packing around nanoparticles minimizes molecular diffusion, ensuring superior self-healing, high thermal hysteresis, and tunable viscoelastic properties. This innovative design provides a robust platform for advanced applications in smart materials, biomedical devices and responsive hydrogels.

In this study, to improve the compatibility of PLA and starch, the hydroxyl groups of the starch were modified with acetoacetic acid, and amine-modified silicone was used as a compatibilizer. PLA/SAA/amine-modified silicone blends were prepared by melt-kneading. The toughness of PLA/SAA was improved by about 15 times by adding 3 wt% amine-modified silicone. This approach can contribute to the widespread use of biodegradable plastics in packaging materials and single-use plastics.

A multiple particle tracking method was used to track probe particles in Tetra-PEG slimes with various network connectivities, revealing that the deviation from the Gaussian distribution of the particle dynamics is greater than the percolation threshold (network connectivity = 0.34). This study is the first to report that the heterogeneity of particle dynamics in transient networks, formed through reversible bonds, exhibits characteristics similar to those observed during sol–gel transitions.

Cellulose nanocrystals (CNCs) bearing densely grafted polymer brushes of different molecular weights (asymmetrically polymer-brush–decorated CNCs; aPB-CNCs) were synthesized via a CNC intermediate possessing two types of dormant moieties for controlled radical polymerization at the reducing end and other surfaces, respectively. The aPB-CNCs exhibited good dispersion in organic solvents and form a monolayer at the air/water interface. The compression of this monolayer induced a phase transition of a long polymer brush at the reducing end and a change in the orientation of the CNC core due to repulsive interactions.

The cross-linking structure and physical properties of epoxy resins cured with amine under off-stoichiometric ratio conditions were examined. As the excess amine increased, some of the amine not only remained as unreacted monomers or low-molecular-weight isolated chains within the cross-linking structure, but also formed dangling chain ends. As a result, the cross-linking density and mass density decreased, as did the glass transition temperature. On the other hand, Young’s modulus increased with the excess amount of amine due to the suppression of the widening distance between phenyl groups.

This study examined the fracture of polymer networks via Brownian simulations with various strain rates. The networks were created from star polymers with different branching degrees and conversion ratios. The results showed that strain and stress at break, plotted against cycle rank, form master curves dependent on strain rate; the fracture characteristics decrease with decreasing strain rate. Despite the interplay of Brownian motion, elongation, and bond scission, the cycle rank dependence is qualitatively similar to that reported previously for energy-minimized networks.

The effect of calcium ion on the swelling structure of polymer brushes bearing phosphorylcholine (PC) and cholinephosphate (CP) groups in aqueous solution were investigated by scanning probe microscopy and neutron reflectivity measurements. The CP-type polymer brushes formed collapsed structure in the aqueous CaCl₂ solution because the phosphate of CP, which is located outside the betaine unit, strongly interacts with calcium ions to form insoluble calcium phosphate. In contrast, no significant change was observed in the swollen thickness of the PC-type polymer brush in the aqueous CaCl₂ solution.

The thermoresponsive behavior of the microgels, the surface properties, and the core region of the microgels were evaluated independently using light scattering, electrokinetic measurements, and high-speed atomic force microscopy. The heterogeneous deswelling behavior of the microgels was revealed by combining these techniques.

The number-average molecular weights (M_ns) of the first and second blocks of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HBV)-b-poly(3-hydroxybutyrate) (P3HB) and P3HB-b-P3HBV block copolymers biosynthesized from Ralstonia eutropha were investigated. The first and second blocks for both P3HBV-b-P3HB and P3HB-b-P3HBV showed a decrease and increase in the M_n, respectively; this indicates that degradation and polymerization proceeded at the initial end of the first block and at the other end of the second block, respectively.

Dynamic bond elastomers are attracting attention because of their self-healing properties and toughness. Using coarse-grained molecular dynamics simulations, we studied how the sequence of binding sites and reaction time before elongation affect their mechanical properties. Our simulations with random, regular, and semiregular sequences indicated that reaction time influences the formation of crosslinking structures. Elastomers with a regular sequence and shorter reaction time had a higher modulus due to more interchain crosslinks. These findings provide new insights into the mechanical behavior of dynamic bond elastomers.

Selective opening and closing reactions of cage-shaped triethanolamine borate (TEAB) at polymer side chains and their effect on the thermal properties of the parent polymers are reported. The conversion of TEAB-pendant polymethacrylates into the triethanolamine (TEA) counterparts was quantitatively achieved by hydrolysis of the pendant TEAB groups. The side chain conversion resulted in a large variation in glass transition temperature (T_g). Regeneration of pendant TEAB group also proceeded in a highly selective manner and almost recover the original T_g, demonstrating the reversible and large modulation of polymer chain flexibility.

The degradation of various thermosetting epoxy resins prepared from bisphenol A diglycidyl ether as a typical epoxy agent and various curing agents, such as diamino arenes, dithiols, and acid anhydrides proceeded smoothly with sodium tert-butoxide in 1,3-dimethyl-2-imidazolidinone (DMI) solvent at 150 °C to form bisphenol A in high yields. Amide solvents effectively promoted depolymerization and allowed insoluble cross-linked thermosetting epoxy resins to undergo the reaction.

Various lengths of alkyl chains, like -C₈H₁₇ to -C₂₀H₄₁, were introduced into trimethylene carbonate (TMC) to enhance the physical properties of ester-free poly(trimethylene carbonate) (PTMC). The resulting polymers were studied for their thermal properties, hydrophobicity, and degradation behavior. Solidified PTMC was achieved with alkyl chains longer than -C₁₆H₃₃ and had melting points above room temperature. PTMC derivative with a -C₁₈H₃₇ group side chain showed 91% and 11% degradation after 9 weeks under organic and aqueous condition, respectively, suggesting that the long alkyl chains influenced its hydrophobic nature and degradation behavior.

The horseradish peroxidase (HRP)/acetone peroxide (ACAC) binary system serves as an initiator to stimulate the generation of free radicals from starch, acrylic acid (AA), and methyl acrylate (MA). Simultaneously, while AA and MA undergo self-polymerization and copolymerization, they also get grafted onto starch chains through self-polymerization and alternating copolymerization. A substantial number of branched small-molecule chains are uniformly grafted onto the primary chain of starch with a low molecular weight.

The intermolecular interactions between polystyrene (PS) and d-limonene were comprehensively studied utilizing both light-scattering experiments and computational simulations. From analyses of the mean-square radius of gyration 〈S²〉 and second virial coefficient A₂ for PS in d-limonene determined by the light-scattering experiments, d-limonene was confirmed as a medium solvent with intermediate solvent quality between good solvents like toluene and poor solvents like cyclohexane for PS. The intermolecular interaction energy between repeat unit of PS and d-limonene, which was obtained from the computational simulations, supported the estimated solvent quality for PS.

We propose a new sheet-type adhesive consisting of a conventional liquid epoxy adhesive and an epoxy monolith sheet with internal continuous pores to avoid stress concentration. We evaluated the adhesion strength for metal bonding using sheet-type epoxy adhesives via lap-shear tensile adhesion tests at various temperatures. The tapered double cantilever beam test revealed that the combination of the epoxy adhesive and the monolith sheet effectively increased the total fracture energy. Furthermore, a heat cycle adhesion test was conducted using two types of metallic materials with different coefficients of thermal expansion to elucidate the effect of the monolith sheet on the improvement of interfacial failure induced by stress concentration.

Normalized relaxation time as a function of the estimated number of interparticle polymer bridges (n_bridge). Images show the molecular dynamics pertaining to n_bridge < 1 and 1 < n_bridge.