Macromolecules最新文献

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.

Transforming waste polymers into materials with improved properties offers a compelling strategy for advancing the sustainable use of polymers, echoing the Chinese proverb: “Blue comes from indigo but surpasses it in blueness.” Herein, we report a photo-oxidative deconstruction and upcycling method for unsaturated rubber waste. Under 390 nm LED irradiation at room temperature, in the presence of a nitroarene oxidant, diverse unsaturated polymers─including natural rubber, polybutadiene, nitrile rubber, styrene–butadiene rubber, and even cross-linked nitrile gloves─are selectively converted into carbonyl-terminated oligomers. The aldehyde-functionalized products are cross-linked via dynamic imine chemistry with p-phenylenediamine to yield reprocessable elastomers with markedly improved tensile strength (from 12.9 to 16.7 MPa) and surface hydrophobicity (contact angle from 23 ± 2° to 83 ± 3°). Furthermore, the aldehyde groups on the oligomers can be selectively oxidized to carboxylic acids or reduced to hydroxyl groups, enabling their versatile use as polymeric additives including curing agents, chain extenders, and toughening agents. This strategy demonstrates a versatile route for converting rubber waste into high-value functional materials.

Vitrimers are polymer networks that can rearrange their topology via thermally triggered dynamic covalent bonds. While their versatility offers interesting paths for developing new applications, one needs first to understand how their dynamics depends on the topology of the network to exploit their large potential. These past few years, boronic esters, especially dioxaborolanes, have been widely studied as moieties to create reversible covalent bonds. Recently, dioxazaborocanes, moieties featuring a labile N–B bond, have also been proposed, showing much faster dynamics at high temperatures compared to dioxaborolanes when incorporated in vitrimers. Herein, we study the viscoelastic properties of vitrimers obtained from linear precursors bearing complementary dioxazaborocane and dioxaborolane moieties. By playing with the density of these two different moieties, we can accurately control the proportion of free functional groups present in the vitrimers and therefore study their influence on the dynamics of the reversible network. It is found that the network dynamics can be either slowed down or accelerated in the presence of dioxaborolane or dioxazaborocane free functional groups, respectively, regardless of the total density of functional groups. The results also show a nonmonotonic dependence of the network relaxation time as a function of the cross-linking density, which we attribute to the antagonistic effects of the subdiffusion process of the dynamic moieties and the restricted mobility of the polymer chains within the network.

Boron-based bifunctional catalysts are a novel class that has emerged recently, demonstrating exceptional catalytic activity for the copolymerization of epoxides with CO₂. Nevertheless, the structure-performance relationship of these catalysts has remained inadequately explored. Here, we report a series of highly efficient metal-free catalysts. These catalysts are designed through the strategic integration of a Lewis acidic boron center and a Lewis basic imidazolium cation. Extensive tunability of catalytic activity was achieved by systematically modulating the steric and electronic properties of the imidazolium moiety, achieved through variations in the imidazole substituents and precise optimization of the spatial separation between the boron and nitrogen centers. These catalysts exhibited remarkable efficiency (TOF > 500 h^–1), maintaining >99% polycarbonate selectivity over a wide temperature range (25–120 °C) and under moderate CO₂ pressures (1.0–4.0 MPa). Mechanistic insights were garnered from reaction kinetics studies, control experiments, ¹¹B NMR analysis, polymer MALDI-TOF mass spectrometry of the polymers, and density functional theory (DFT) calculations. These findings support an intramolecular cooperative catalytic mechanism. These results underscore the critical importance of cationic structure optimization in catalyst design and provide a rational pathway for developing advanced metal-free catalysts for future epoxide/CO₂ copolymerization applications.

Ultrasmall nanoparticles (NPs) exhibit solvent-like characteristics, such as induced disentanglement. However, previous studies have observed that adding ultrasmall NPs can either slow down or not affect polymer segmental relaxation. Therefore, the similarities and differences between ultrasmall NPs and solvents when mixed with entangled polymers remain elusive. This study used polyhedral oligomeric silsesquioxane (POSS) NPs with a diameter of 3 nm as model ultrasmall NPs. Using single-molecule fluorescence tracking and microrheology measurements, we investigated their effects on the diffusion and relaxation of polyethylene glycol (PEG) relative to solvents and large silica NPs. Furthermore, coarse-grained molecular dynamics (CGMD) simulations were employed to elucidate the underlying mechanisms. Compared to solvents, we found that athermal POSS NPs more effectively promote chain disentanglement while exhibiting a negligible plasticizing effect. In addition, ultrasmall NPs retain their particulate characteristics and can form an NP network at high volume fraction to constrain the movement of polymer chains─a distinct effect compared to that of solvent molecules. We expect these findings to provide insight into the role of ultrasmall NPs in entangled polymer composites.