Macromolecules最新文献

Owing to their biocompatibility and thermal responsiveness, Agar hydrogels are extensively applied in chemistry and biology fields. However, their fixed water content and rigid sugar ring structure normally exhibit limited mechanical strength, while introducing additional networks possibly deteriorates the intrinsic thermoreversible cross-linking properties of Agar hydrogel. In this work, we achieve the mechanical enhancement and tunability of Agar-based single-network hydrogels based on the Hofmeister effect via a preforming postimmersion method without the need for supplementary networks. After being immersed in different solutions of the Hofmeister salt series, the tensile strength and toughness of Agar hydrogels can be regulated between 54.7–412.1 kPa and 5.5–94.1 kJ m^–3. Macroscopic and microscopic analyses via SEM and SAXS, together with molecular dynamics simulations, were employed to reveal the systematic mechanisms from the number of hydrogen bonds to the aggregation state and ultimately to the mechanical properties. Since the gelation of Agar relies on double-helix formation, the Hofmeister series and regulation behaviors are different from typical synthetic polymer hydrogels. These results further promoted the elucidation of the water state regulation in the hydration layer of Agar hydrogels. This work provides an understanding of the correlation between the cross-linking state of molecular chains and the resultant Agar hydrogel properties based on the Hofmeister effect, which inspires research on the mechanical regulation mechanisms of natural polysaccharide-based hydrogels.

Confined assembly of chiral block copolymers (BCPs*) affords an effective approach to preparing controllable chiral nanostructures, yet the interplay among molecular hydrophilicity, assembled morphology, and chiroptical properties remains unclear. In this study, we reported hydrophilicity-mediated three-dimensional (3D) confined assembly of poly(2-vinylpyridine)-block-poly(L-lactide) (P2VP-b-PLLA) and P2VP-block-poly(D-lactide) (P2VP-b-PDLA) in evaporative emulsion droplets. The assembled morphology and the chiral transfer from a molecular configuration to a microphase-separated structure was found strongly dependent on the molecular mass (M_n) and the PLA volume fraction (f_PLA) due to the amphiphilic feature of the P2VP block. Specifically, BCPs* with M_n ≥ 17.7 kDa and f_PLA between 17 and 28% possessed relatively high hydrophobicity and formed solid spheres with an internal helical structure. In contrast, BCPs* with lower M_n and hence higher hydrophilicity gave rise to hollow assemblies lacking an evident chiral morphology. Moreover, the addition of protonic species such as H⁺ further enhanced the hydrophilicity of BCP* chains via the protonation of P2VP, thus modulating the assembly behavior of BCPs*. Similar manipulation could be achieved by the addition of Lewis acidic species, such as Cu²⁺ and Fe³⁺, which hydrolyzed and released H⁺. Chiroptical measurements revealed that the dissymmetry factor (g-factor) strongly depended on the assembled morphology: solid spheres with an internal helical structure exhibited significantly stronger circular dichroism responses than hollow morphologies. This work demonstrated hydrophilicity as a governing parameter for confined chiral assembly and chiroptical modulation and provided new insights into the development of functional chiral materials via hydrophilicity-mediated self-assembly.

Catenated “Olympic” networks of ring polymers are emerging as versatile platforms in biology-inspired materials and MOF-catenane hybrids, yet how their pore dimensions are regulated by topology remains poorly understood. Here we use coarse-grained molecular dynamics to investigate two idealized two-dimensional Olympic networks: a square-lattice (SQR) and a hexagonal-lattice (HEX) membrane of interlocked rings. We introduce a pore-size definition based on the largest rigid sphere that can pass through a lattice pore. By varying all chain bending stiffness and a topological tension of the catenated membrane, we map out the pore-size landscape and identify two competing mechanisms: conformational entropy, which favors ring compaction and larger pores, and ring rotational degrees of freedom, allow stiff rings to invade the pore cross-section and create smaller apertures. Their competition yields a bimodal pore-size distribution in the SQR network under intermediate conditions. Using Maxwell counting and topological mechanics, we show that the isostatic SQR lattice exhibits strong nearest neighbor correlations in pore size. For hypostatic HEX lattice, with additional zero modes. This structure largely suppresses such correlations. These results establish a physical picture linking catenane topology, chain mechanics, and pore size, and provide design principles for topologically engineered polymer networks with tunable porosity and dynamic gating of guest transport.

Direct fluorination of polymer films using F₂ gas efficiently alters their surface chemical composition and thereby modifies their physical properties. However, this process can sometimes generate environmentally undesirable low-molar-mass compounds, highlighting the need for milder approaches to expand the applicability of this technique. This study investigates direct fluorination in liquid media using an ethylene–tetrafluoroethylene (ETFE) copolymer film as a benchmark material. By optimizing the fluorination conditions, complete fluorination of the outermost layer was achieved. Fluorination induced a nonmonotonic change in static water contact angle, accompanied by a significant increase in contact angle hysteresis attributed to enhanced chemical heterogeneity on the film surface. Furthermore, neither liquid- nor gas-phase fluorination of ETFE released detectable amounts of low-molar-mass compounds. These findings advance the understanding of direct fluorination in liquid media and its impact on the molecular structure and surface properties of polymers.

High-fidelity bioelectric signal acquisition is crucial for wearable precision medicine, but traditional poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes struggle to balance conductivity, stretchability, and skin compatibility, particularly under perspiration or physical activity. To address this challenge, we developed a PEDOT-based functional system doped with PSS-co-poly(acrylic acid)/poly(acrylamide) binary copolymers (PSA/PSM). Through multiscale characterization, molecular simulations, and in vitro testing, we systematically investigated the unique roles of carboxyl (−COOH) and amide (−CONH₂) groups in regulating microstructure, electrical and interfacial properties, and hydrogen bond network dynamics. Key findings reveal that −COOH groups enhance π-π stacking interactions and charge doping effects in PEDOT. The PSA 3:1 sample exhibits the highest conductivity, surpassing pure PEDOT:PSS, but displays severe swelling and poor adhesion owing to strong electrostatic interactions. In contrast, −CONH₂ groups in PSM form a hydrogen bond network with distinct static structural features characterized by uniform bond length and angle distributions and a homogeneous network structure. This optimizes interfacial performance with only a minor conductivity loss (≤10%). The PSM 3:1 electrode demonstrates strong adhesion, low contact impedance (62.8 kΩ at 10 Hz), swelling resistance, and high electromechanical stability. Molecular dynamics simulations confirm that the static structural advantages of the PSM hydrogen bond network, including stable distribution of bonding sites and moderate fluctuations in bond length and angle, are critical to enhancing electromechanical stability and wet performance. In practical electrocardiogram (ECG)/electromyogram (EMG) monitoring, the PSM 3:1 electrode achieves low noise (ECG RMS: 10.3 μV) and high signal fidelity during both resting and exercise states. Under a 25 kg grip force, it reaches an EMG peak-to-peak voltage of 0.32 mV, outperforming commercial Ag/AgCl electrodes. This study provides a molecular-level synergistic multiperformance optimization strategy for conductive polymers, advancing the development of high-fidelity wearable bioelectronics.

Crystallizing atactic polystyrene (a-PS), the archetypal amorphous polymer, has remained a long-standing challenge in polymer science. Here, we demonstrate the formation of one-dimensional (1-D) extended-chain crystals from a-PS via a rapid thermal quenching (RTQ) process using benzoic acid (BA) as an entropy diluent. Spectroscopic and structural analyses reveal that these crystals are dominated by a β-like zigzag conformation, a highly extended ordered structure previously considered inaccessible for atactic chains. This unique molecular architecture translates into a dramatic enhancement in mechanical properties. The resulting a-PS_RTQ films exhibit a storage modulus approximately three times higher than that of pristine a-PS, a level of reinforcement that far surpasses the modest improvements seen in conventionally crystallized syndiotactic polystyrene (s-PS). This exceptional performance is attributed to the high fraction of load-bearing, extended-chain structures. Furthermore, the induced crystals exhibit unique metastable thermal behavior, including a reversible β-to-α solid-state transition not observed in conventional s-PS. This study challenges the long-held paradigm that stereoregularity is a prerequisite for polymer crystallization, demonstrating that kinetic control via polymer-diluent interactions can effectively guide atactic chains into high-performance, ordered structures. Our findings open a new pathway for transforming low-cost, commodity amorphous polymers into high-strength, semicrystalline materials with tailored properties.

The dynamics and structure were investigated for polyelectrolyte-rich liquids across the high-salt region of the complex coacervation phase diagram of high molecular weight poly(4-styrenesulfonate), PSS, and poly(diallyldimethylammonium), PDADMA. The total concentration of polyelectrolytes (W_PE) was increased at different added KBr concentrations ([KBr]) to obtain liquid complex coacervates (CC) and single-phase, saline polyelectrolyte solutions. The dynamic response of these entangled polymer liquids was found to be self-similar at each [KBr], allowing a time–polyelectrolyte superposition using only a polyelectrolyte concentration-dependent horizontal shift factor, a_P. This self-similarity was further found among all the samples at different [KBr], allowing the construction of a universal master curve unifying the dynamics of all the samples by applying a second, salt-dependent horizontal shift factor, a_S. The CC dynamics were found to have a very strong dependence on the experimentally determined PE concentration with a_P ∝ W_PE,real¹¹, while salty solutions of noninteracting PE behaved as polymers in good solvent with a_P ∝ W_PE,real^4.1. The extreme scaling in the case of the CC defies the predictions for entangled associating polymers, probably due the large number of stickers per chain. Despite the absence of effective stickers in the salty solutions of fully doped polyelectrolytes, they can mimic the viscoelastic response of the CC up to the solubility limit of the PE. We called these materials quasi-complex coacervates (quasi-CC) to distinguish them from both CC and individual-polyelectrolyte solutions. Small-angle X-ray scattering revealed that PSS/PDADMA CC, their quasi-CC, and a PSS solution at the same total polymer and salt concentration all have different nanostructures. Unifying the dynamics of viscoelastic liquids across the high-salt region of the phase diagram, time–PE–salt superposition extends the classical time–salt and time–temperature superposition principles to PE systems, marking a step forward in understanding associative polymer dynamics.

The effect of halogen type in dual-catalyzed photoinduced atom transfer radical polymerization (photoATRP) of methyl acrylate (MA) and methyl methacrylate (MMA) was systematically investigated under green LED irradiation (λ ∼ 527 nm) using rhodamine 6G (RD-6G) as a photocatalyst. Poly(methyl acrylate) and poly(methyl methacrylate) with ω-bromo and ω-chloro chain ends were synthesized via CuX₂/ligand (X = Br, Cl) complexes with excess ligand as an electron donor. Kinetic analyses revealed that Br-based systems exhibited significantly faster activation and allowed controlled polymerizations at markedly lower copper and photocatalyst loadings than their Cl-based counterparts. MA polymerizations were faster than MMA despite the latter’s larger ATRP equilibrium constants, attributed to the higher propagation rate constant of acrylates and similar rates of reduction of CuX₂/ligand deactivators. Optimal ligand selection (Me₆TREN for MA, TPMA for MMA) was important for control of the polymerization rate and low dispersity. Chain-extension experiments confirmed high chain-end fidelity, and temporal control studies demonstrated efficient light-mediated regulation. These findings provide detailed design guidelines for halogen- and monomer-dependent optimization in dual-catalyzed photoATRP.

This study examines how the segmental and chain dynamics of poly(methyl methacrylate) (PMMA) depend on tacticity. Dielectric response spectroscopy reveals a much stronger β-relaxation peak, more clearly separated from the α-relaxation process at T < T_g, for syndiotactic PMMA (sPMMA) than for isotactic PMMA (iPMMA). Linear viscoelastic measurements show similar rubbery plateaus for sPMMA and iPMMA, suggesting comparable entanglement molecular weights. In contrast, nonlinear extensional rheology exhibits substantially weaker strain hardening in sPMMA than in iPMMA. We propose that locally stiffer and more curved chain conformations in sPMMA reduce packing efficiency at T < T_g, facilitating flipping of planar ester groups that manifests as an enhanced β-relaxation in dielectric response spectroscopy. The same local stiffness probably leads to lower stretchability of the sPMMA chains, thereby leading to the weaker strain hardening at Weissenberg number much higher than one.

Main-chain liquid crystal elastomers (LCEs) are synthesized to investigate the interplay of the composition and network structure on LCE nematic-to-isotropic (N–I) transitions. We focus on networks synthesized from liquid crystalline oligomers reacted with tri- or tetrafunctional nonmesogenic cross-linker molecules. We find that coupling between mesogens and the polymer backbone increases with the degree of cross-linking. However, this enhanced coupling competes with mesogenic dilution arising from the cross-linker molecules to determine the N–I transition temperature (T_NI). When cross-linker molecules are dilute, the degree of cross-linking directly correlates to the change in T_NI from the oligomer to LCE (ΔT_NI) through mesogen–backbone coupling. In this regime, ΔT_NI ranges from 2.9 to 12.2 °C and 2.9–13.9 °C for tri- and tetrafunctional cross-linkers, respectively. At high cross-linker concentrations, deviations from this linear relationship appear. Further, the fractional mesogen content within an oligomer chain induces molecular weight-dependent mesogenic dilution effects arising from the flexible spacer molecules. Analysis of the N–I transition peak reveals a maximum latent heat per gram of mesogen (ΔH_NI,mes) for this system.