Articles in 2024

We have discovered that strain-induced crystallization (SIC) of the polymer chains occurs in homogeneous polymer gels, such as slide-ring gels and Tri-/Tetra-PEG gels, with sufficiently high polymer concentrations. SIC significantly improves the mechanical toughness of homogeneous gels. Polymer crystals form and dissolve immediately after the polymer gels are stretched and unstretched. The quick formation and dissolution of the strain-induced crystals leads to elastic mechanical responses with minimal hysteresis under cyclic stretching. Tough and elastic polymer gels have potential applications in biomedical materials and soft electric devices under repeated deformation.

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 facile and versatile one-shot synthetic method for preparing bilayer gels was developed through photoinduced radical polymerization using a phase-separated binary solvent system. The use of an amphiphilic crosslinker soluble in both phases was particularly important for forming a sufficiently adhesive interface. This synthetic method provides a wide variety of bilayer structures due to its broad applicability in various solvents and monomers. The resulting bilayer gels exhibited unique functions, such as selective swelling behavior, mechanical properties, and anisotropic deformation derived from the properties of each polymer layer.

This review highlights recent MD simulation studies focusing on subcontinuum heterogeneities in polymers from the perspective of their mechanical properties. The theoretical framework for rationally distributing the stress tensor to individual molecular components is revisited, and the key achievements made via this approach are summarized.

The surface aggregation states of the amphiphilic diblock copolymer films, which are consistent with polyacrylates and polystyrene, were examined. The hydrophilic polyacrylates presented a lower surface free energy (γ) at room temperature, resulting in surface segregation. A perpendicular microdomain orientation was achieved after thermal annealing above the glass transition temperature of both components. As the annealing temperature increased, the surface became hydrophobic while maintaining this orientation due to polystyrene segregation. The key to this process is appropriate thermal annealing, considering the entropic contribution to γ from differences in molecular motion between the two components.

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 Poisson's ratio (μ) of natural rubber undergoing strain-induced crystallization was studied across a broad stretch range. Below the crystallization onset stretch (\({\lambda }_{{||}}\)* ≈ 4.1), μ remains near 0.5, indicating incompressibility. Beyond \({\lambda }_{{||}}\)*, μ decreases with increasing crystallinity, reaching 0.33 at fracture (\({\lambda }_{{||}}\) ≈ 7.1), as the matrix transforms from amorphous to semicrystalline. The true stress at fracture, accounting for lateral contraction, is approximately 85% of the estimated value assuming μ = 0.5. These insights are vital for modeling the mechanical behavior of strain-crystallizing elastomers.

This rapid communication reports the first successful clarification of the difference in the crosslink inhomogeneity at the nanometer scale for two types of structurally identical epoxy resins cured with a phenolic hardener under organophosphine catalysts.

Bioderived materials are value-added by recycling excessive residues to gain a new life for themselves. Biodegradable materials can address increasing environmental issues via recycling approaches and reprocessing products. Concerning these attractive advantages, in the first part of this review, commodity polymers from biosources and their recycling and biodegradable pathways are described. The second part summarizes the recent advances of bioderived and biodegradable block copolymers in biomedical and electronic applications, including drug carriers, field-effect transistors, and nonvolatile memory. This review sheds light on the bright perspective of bioderived and biodegradable polymers.

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.

Polymer surfaces have notably different properties and dynamic behaviors from bulk materials. The properties and structure at the polymer surface and interface strongly depend on the chemical structure, conformation and dynamics of the polymer chains. In this review, the impacts of the structure and dynamics of designed polymer side chains on the surface and interface properties and their mechanism are described. In particular, the control of the molecular conformation and dynamics leads to their characteristic surface and interface properties.

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.