Polymer Network Research Articles

Effect of molecular structure on the dynamics and viscoelasticity of vitrimers

Vitrimers are a class of dynamic polymer networks that perform bond-exchange reactions (BERs) under environmental stimuli while preserving network connectivity. The viscoelastic properties of vitrimers are not only dependent on the kinetics of BERs, but also the architectures of polymer matrix. Here, we investigate the influence of polymer architectures on the dynamics and linear viscoelasticity of vitrimers through varying the sticker (reactive bead) distribution in the precursor chain and the BERs energy barrier (Ub) by performing hybrid molecular dynamics-Monte Carlo simulations. Increasing Ub, vitrimers with block and gradient distributions exhibit considerably faster relaxations of chain ends, Rouse mode, and stress and lower zero-shear viscosity than the analogs with random and uniform distributions, in qualitative agreement with the predictions of the sticky Rouse model. In contrast, the distribution of stickers has a small influence on the relaxation of dynamic bonds regardless of the Ub value. By comparing the molecular structures of vitrimers with different distributions of stickers, we find that the molecular defects, especially the relatively longer dangling end in block and gradient distributions, impair the effect of dynamic bonds on the dynamics and viscoelasticity of vitrimers. This suggests that the dangling defects can be leveraged for further development of recyclable and healable materials with fast stress relaxation and improved flowability.

Synthesis of silver nanocomposite semi-interpenetrating polymer network hydrogel based on sodium alginate-g-polyacrylamide for using in Epirubicin anticancer drug release

Synthesis of silver nanocomposite semi-interpenetrating polymer network hydrogel based on sodium alginate-g-polyacrylamide for using in Epirubicin anticancer drug release

Experimental and numerical characterization of a flexible strain sensor based on polydimethylsiloxane polymeric network and MWCNT’s

We demonstrated the feasibility of obtaining a low-cost, flexible strain sensor by spraying a conductive thin layer of MWCNT’s over an S-pattern embedded within a PDMS matrix. The final composite conforms a dog bone-shaped tensile specimen intended to measure the strain associated with a human wrist extension movement. Our sensor works with a combination of different mechanisms, such as piezoresistivity and tunneling, which depend on the level and repetitions of loads applied to the sensor. According to the reported elongation ratios, these sensors can detect large strains, up to 40%, for several uniaxial loading-unloading cycles. This makes them useful for human skin strain measurements.Graphical abstract

Tuning the Mechanical Properties of 3D‐printed Objects by Mixing Chain Transfer Agents in Norrish Type I Photoinitiated RAFT Polymerization

Photoinduced 3D printing via photocontrolled reversible–deactivation radical polymerization (photoRDRP) techniques has emerged as a robust technique for creating polymeric materials. However, methods for precisely adjusting the mechanical properties of these materials remain limited. In this study, we present a facile approach for adjusting the mechanical properties of 3D‐printed objects by adjusting the polymer dispersity within a Norrish type I photoinitiated reversible addition‐fragmentation chain transfer (NTI‐RAFT) polymerization‐based 3D printing process. We investigated the effects of varying the concentrations and molar ratios of trithiocarbonate (BTPA) and xanthate (EXEP) on the mechanical properties of the printed materials. Our findings demonstrate that increased concentrations of RAFT agents or higher proportions of the more active BTPA lead to a decrease in Young's modulus and glass transition temperatures, along with an increase in elongation at break, which can be attributed to the enhanced homogeneity of the polymer network. Using a commercial LCD printer, the NTI‐RAFT‐based 3D printing system effectively produced materials with tailored mechanical properties, highlighting its potential for practical applications.

Large-area preparation of rainbow cholesteric liquid crystal polymer network films using a photoisomerizable chiral dopant

ABSTRACT Since the cholesteric liquid crystal polymer network (CLCN) films with a structural colour have been applied for decoration, those with colourful patterns become more attractive. They have been successfully prepared using photochromic cholesteric liquid crystals with the addition of photoisomerizable chiral dopants. Herein, two isosorbide derivatives with benzoate and cinnamate groups were synthesised using isomannide through chirality inversion and without using protecting groups. CLCN films were prepared using these two isomers as the chiral dopants. The structural colour of the films can be tuned by the photoisomerisation of the chiral dopants. Colourful patterns were also prepared using photomasks, which were suitably applied for decoration and anti-counterfeiting. Although the isomer with a higher melting point tended to induce the crystallisation of the CLC mixtures, the CLC mixtures prepared using the isomer with a lower melting point were stable at room temperature. Rainbow CLCN films were prepared using photomasks on a coating line.

Viscoelastic Adhesive, Super-Conformable, and Semi-Flowable Liquid Metal Eutectogels for High-Fidelity Electrophysiological Monitoring.

Integrating gels with human skin through wearables provides unprecedented opportunities for health monitoring technology and artificial intelligence. However, most conductive hydrogels, organogels, and ionogels lack essential environmental stability, biocompatibility, and adhesion for reliable epidermal sensing. In this study, we have developed a liquid metal eutectogel simultaneously possessing superior viscoelasticity, semiflowability, and mechanical rigidity for low interfacial skin impedance, high skin adhesion, and durability. Liquid metal particles (LMPs) are employed to generate free radicals and gallium ions to accelerate the polymerization of acrylic acid monomers in a deep eutectic solvent (DES), obtaining highly viscoelastic polymer networks via physical cross-linking. In particular, graphene oxide (GO) is utilized to encapsulate the LMPs through a sonication-assisted electrostatic assembly to stabilize the LMPs in DES, which also enhances the mechanical toughness and regulates the rheological properties of the eutectogels. Our optimized semi-flowable eutectogel exhibits viscous fluid behavior at low shear rates, facilitating a highly conformable interface with hairy skin. Simultaneously, it demonstrates viscoelastic behavior at high shear rates, allowing for easy peel-off. These distinctive attributes enable the successful applications of on-skin adhesive strain sensing and high-fidelity human electrophysiological (EP) monitoring, showcasing the versatility of these ionically conductive liquid metal eutectogels in advanced personal health monitoring.

Studies on adsorptive dehydration of pasteurised milk by filled polymeric IPN hydrogel

ABSTRACT Adsorptive dehydration utilising polymeric hydrogels presents an effective technique for removing excess water from pasteurised milk. This study investigated three Interpenetrating Polymeric Network (IPN) hydrogels comprising Polyvinyl Alcohol (PVOH) and Hydroxyethyl Cellulose (HEC) at mass ratios of 90:10, 70:30 and 50:50, respectively, with Maleic Anhydride (MAn) as a cross-linker at concentrations of 2% 4%, and 8% based on total polymer weight. It was observed that the rate of dehydration increased with higher HEC content in the hydrogels. However, the stability decreased due to changes in the structural alignment of polymer chains and weak cross-linking. Among the tested hydrogels, the one with a composition of 70:30 for PVOH and HEC, respectively, cross-linked with 8% MAn (0.096gm), exhibited the best adsorption (569% Swelling) with minimal changes in pH (<10%) and conductivity (<10%) and was, therefore, selected for further study. This selected hydrogel composition was further enhanced by incorporating a hydrophilic nanofiller (Bentonite) at proportions of 2%, 4% and 6% based on total polymer weight during hydrogel synthesis. The hydrogel with 4% nanofiller (0.081 gm) showed the best results in terms of swelling and stability although the 6% filled hydrogel exhibited superior swelling but lower stability. Finally, the dehydration process was optimised using Type 1 fuzzy logic (T1FL), achieving an R2 value of 95.13%.

Direct and Reversible Transformations between Intermolecular Polymer Networks and Single-Chain Nanoparticles Based on Thermally Dissociable Bis(hindered amino)disulfide Linkages

Direct and Reversible Transformations between Intermolecular Polymer Networks and Single-Chain Nanoparticles Based on Thermally Dissociable Bis(hindered amino)disulfide Linkages

Polymer Free Volume‐Controlled Molecular Clock and Emitter for Multicolored Transient Data Display in Advanced Photonic Cryptography

The booming demand on data security has aroused great interest for developing smart materials with temporal display feature and dynamic multicolor fluorescence. However, it remains challenging to implement both features on most responsive molecules. Herein, we construct a polymer free volume‐controlled “molecular clock and emitter” via covalently embedding a multi‐stimuli responsive molecular switch (i.e., spiropyran) into a polymer network (i.e., poly(pentafluorophenyl acrylate)) with programmable crosslink density and free volume. By the aminolysis of pentafluorophenyl ester with different amount of diamine crosslinkers, pPFPA‐co‐SP networks with controllable crosslink densities are generated, which have different confinement effects on the rate constant of SP/MC isomerization, thus leading to time‐dependent photochromism. In addition, PTF1, a fluorescent probe that is sensitive to polymer rigidity, is introduced to further endow pPFPA‐co‐SP system with phototunable dynamic full‐color emission. Therefore, relying on their synergistical responses to the rigidity of the polymer network, we have successfully developed a versatile molecular clock and emitter via an “one stone two birds” manner, which shows time‐dependent data display along with dynamic multicolor fluorescence switching, providing great potential for advanced encryption and anticounterfeiting with a high security level.

Closed-Loop Recyclable and Totally Renewable Liquid Crystal Networks with Room-Temperature Programmability and Reconfigurable Functionalities.

Dynamic covalent liquid crystal networks (DCv-LCNs) with straightforward (re)programmability, reprocessability, and recyclability facilitates the manufacture of sophisticated LCN actuators and intelligent robots. However, the DCv-LCNs are still limited to heat-assisted programming and polymer-to-polymer reprocessing/recycling, which inevitably lead to deterioration of the LCN structures and the actuation performances after repeated programming/processing treatments, owing to the thermal degradation of the polymer network and/or external agent interference. Here, a totally renewable azobenzene-based DCv-LCN with room-temperature programmability and polymer-to-monomers chemical recyclability is reported, which was synthesized by crosslinking the azobenzene-containing dibenzaldehyde monomer and the triamine monomer via the dynamic and dissociable imine bonds. Thanks to the water-activated dynamics of the imine bonds, the resultant DCv-LCN can be simply programmed, upon water-soaking at room temperature, to yield a UV-Vis light-driven actuator. Importantly, the reported DCv-LCN undergoes depolymerization in an acid-solvent medium at room temperature because of the acid-catalyzed hydrolysis of the imine bonds, giving rise to easy separation and recovery of both monomers in high purity, even with tolerance to additives. The recovered pure monomers can be used to regenerate totally new DCv-LCNs and actuators, and their functionalities can be reconfigured by removing old and introducing new additives, by implementing the closed-loop polymer-monomers-polymer recycling.

PH-Sensitive Hydrogels Fabricated with Hyaluronic Acid as a Polymer for Site-Specific Delivery of Mesalamine.

Hydrogels with the main objective of releasing mesalamine (5-aminosalicylic acid) in the colon in a modified manner were formulated in the present work using a free-radical polymerization approach. Different ratios of hyaluronic acid were cross-linked with methacrylic and acrylic acids using methylenebis(acrylamide). The development of a new polymeric network and the successful loading of drug were revealed by Fourier transform infrared spectroscopy. Thermogravimetric analysis demonstrated that the hydrogel was more thermally stable than the pure polymer and drug. Scanning electron microscopy (SEM) revealed a rough and hard surface which was relatively suitable for efficient loading of drug and significant penetration of dissolution medium inside the polymeric system. Studies on swelling and drug release were conducted at 37 °C in acidic and basic conditions (pH 1.2, 4.5, 6.8, and 7.4, respectively). Significant swelling and drug release occurred at pH 7.4. Swelling, drug loading, drug release, and gel fraction of the hydrogels increased with increasing hyaluronic acid, methacrylic acid, and acrylic acid concentrations, while the sol fraction decreased. Results obtained from the toxicity study proved the formulated system to be safe for biological systems. The pH-sensitive hydrogels have the potential to be beneficial for colon targeting due to their pH sensitivity and biodegradability. Inflammatory bowel disease may respond better to hydrogel treatment as compared to conventional dosage forms. Specific amount of drug is released from hydrogels at specific intervals to maintain its therapeutic concentration at the required level.

Retraction Note: Understanding mechanical characteristics of pH-responsive PEG 4000-based polymeric network for colorectal carcinoma: its acute oral toxicity study

Retraction Note: Understanding mechanical characteristics of pH-responsive PEG 4000-based polymeric network for colorectal carcinoma: its acute oral toxicity study

CHARACTERISTICS OF MUTUAL ACTIVATION OF AN INTERGEL SYSTEM BASED ON HYDROGEL POLYMETHACRYL ACID AND POLY-4-VINYL PYRIDINE

The electrochemical properties of mutual activation of polymer networks as a result of remote interaction in an intergel system have been studied. An intergel system consisting of hydrogels of rare crosslinked polymethacrylic acid (hPMAA) and poly-4-vinylpyridine (hP4VP) was chosen as the object of study [1,2]. The purpose of the work is to study the mutual activation features of the intergel system of rare crosslinked hPMAA: hP4VP. The obtained results as the contact time of hydrogels with water increased, zones of maximum and minimum conductivity were observed at the highest points of initial conductivity for different ratios of hPMAA:hP4VP hydrogel systems. In the 6:0 ratio of hPMAA hydrogel, the specific conductivity of the aqueous medium reached its maximum value after one day, and the pH value of the medium decreased relatively to about 4.95. The swelling degree of hPMAA hydrogel was constant at 6:0 different time intervals. In this system, only one polymer, namely hPMAA showed that the hydrogel's water absorption capacity was limited. In the 5:1 ratio of the intergel system, the specific conductivity of the medium reached a high value, and the pH value decreased in the 5:1 ratio. After 2.5 hours of study, a decrease in the conductivity of the aqueous medium was observed at 4:2 hydrogel ratio. After 6 hours, the highest degree of swelling was maintained at 1:5 ratio. In the presence of hP4VP hydrogel at a ratio of 0:6, the pH of the medium increased from 5 to a maximum value of 6.6 within 24 hours. Conclusion. The electrochemical properties of hPMAA:hP4VP hydrogel system were studied by remote interaction. Based on the systematic work, we synthesized the required acidic hydrogel hPMAA:hP4VP and carried out various studies on their properties. To create an intergel system, the obtained hydrogels in seven different proportions were made into an intergel system and their interactions were studied using various physicochemical methods. As a result of the study, the remote interaction of hydrogels in the intergel system leads to conformational changes in their intercellular bonds which undergo additional swelling. As a result of mutual activation, the hydrogels move to a highly ionized state.

A clusteroluminescent supramolecular polymer network constructed by pillararene and its application in information encryption

A clusteroluminescent supramolecular polymer network constructed by pillararene and its application in information encryption

Cobalt-based Polymerized Porphyrinic Network for Visible-light-driven CO2 Reduction.

Visible-light-driven conversion of carbon dioxide to valuable compounds and fuels is an important but challenging task due to the inherent stability of the CO2 molecules. Herein, we report a series of cobalt-based polymerized porphyrinic network (PPN) photocatalysts for CO2 reduction with high activity. The introduction of organic groups results in the addition of more conjugated electrons to the networks, thereby altering the molecular orbital levels within the networks. This integration of functional groups effectively adjusts the levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The PPN(Co)-NO2 exhibits outstanding performance, with a CO evolution rate of 12 268 μmol/g/h and 85.8% selectivity, surpassing most similar photocatalyst systems. The performance of PPN(Co)-NO2 is also excellent in terms of apparent quantum yield (AQY) for CO production (5.7% at 420 nm). Density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL), and electrochemical tests reveal that the introduction of methyl and nitro groups leads to a narrower energy gap, facilitating a faster charge transfer. The coupling reaction in this study enables the formation of stable C-C bonds, enhancing the structural regulation, active site diversity, and stability of the catalysts for photocatalytic CO2 reduction. This work offers a facile strategy to develop reliable catalysts for efficient CO2 conversion.

Chemically Programmed Hydrogels for Spatiotemporal Modulation of the Cardiac Pathological Microenvironment.

After myocardial infarction (MI), sustained ischemic events induce pathological microenvironments characterized by ischemia-hypoxia, oxidative stress, inflammatory responses, matrix remodeling, and fibrous scarring. Conventional clinical therapies lack spatially targeted and temporally responsive modulation of the infarct microenvironment, leading to limited myocardial repair. Engineered hydrogels have a chemically programmed toolbox for minimally invasive localization of the pathological microenvironment and personalized responsive modulation over different pathological periods. Chemically programmed strategies for crosslinking interactions, interfacial binding, and topological microstructures in hydrogels enable minimally invasive implantation and in situ integration tailored to the myocardium. This enhances substance exchange and signal interactions within the infarcted microenvironment. Programmed responsive polymer networks, intelligent micro/nanoplatforms, and biological therapeutic cues contribute to the formation of microenvironment-modulated hydrogels with precise targeting, spatiotemporal control, and on-demand feedback. Therefore, this review summarizes the features of the MI microenvironment and chemically programmed schemes for hydrogels to conform, integrate, and modulate the cardiac pathological microenvironment. Chemically programmed strategies for oxygen-generating, antioxidant, anti-inflammatory, provascular, and electrointegrated hydrogels to stimulate iterative and translational cardiac tissue engineering are discussed. This article is protected by copyright. All rights reserved.

Strong Acid Enabled Comprehensive Training of Poly (Sodium Acrylate) Hydrogel NetworksStrong Acid Enabled Comprehensive Training of Poly (Sodium Acrylate) Hydrogel Networks.

The design of admire hydrogel networks is of both practical and fundamental importance for diverse applications of hydrogels. Herein a general strategy of acid-assisted training is designed to enable multiple improvement of conventional poly (sodium acrylate) networks for hydrogels. Hydrophobic homogeneous crosslinked poly (sodium acrylate) hydrogels are prepared to verify the strategy. The acid-assisted training is simply achieved by immersing the hydrogel networks into 4 M H2SO4 solutions. The introduced acids would induce transformation of poly (sodium acrylate) into poly (acrylic acid) at hydrogel surface, which constructs dynamic hydrogen bonding interactions to tighten the network. The acid-containing poly (sodium acrylate) hydrogels newly generate anti-swelling and self-healing performance, and show mechanical improvement. The internal poly (sodium acrylate) of the pristine acid-containing hydrogels is further fully transformed via acid-infiltration after following cyclic stretch/release training to significantly improve the mechanical performance. The Young's modulus, stress, and toughness of the fully-trained hydrogels are 187.6 times, 35.6 times, and 5.4 times enhanced, respectively. The polymeric networks retain isotropic in fully-trained hydrogels to ensure superior stretchability of 8.6. The acid-assisted training performance of the hydrogels can be reversibly recovered by NaOH neutralization. The acid-assisted training strategy here is general for poly (sodium acrylate) hydrogels.

Performance of magnetic nanocomposite based on xanthan gum-grafted-poly(acrylamide) crosslinked by borax for the effective elimination of amoxicillin from aquatic environments

This study evaluated the effectiveness of using nanocomposite (NCs) of xanthan gum grafted polyacrylamide crosslinked Borax - iron oxide nanoparticle (XG-g-pAAm-CL-Borax-IONP) to remove the amoxicillin antibiotic (AMX) from an aquatic environment. To confirm the structural characteristics of the prepared XG-g-pAAm-CL-Borax-IONP NCs, unique characterization methods (XRD, FT-IR, FE-SEM, EDX, BET, TGA, Zeta, and VSM) were used. Adsorption experimental setups were performed with the influence of solution pH (4–9), the effect of adsorbent dose (0.003–0.02 g), the effect of contact time (5–45 min), and the effect of initial AMX concentration (50–400 mg/L) to achieve the most efficient adsorption conditions. Based on the Freundlich isotherm model, XG-g-pAAm-CL-Borax-IONP NCs provided the maximum AMX adsorption capacity of 1183.639 mg/g. This research on adsorption kinetics also established that the pseudo-second-order model (R2 = 0.991) is outstanding compatibility with the experimental results. AMX adsorption on the NCs may occur through intermolecular hydrogen bonding, diffusion, and trapping into the polymer network. Even after five cycles, these NCs still displayed the best performance. Based on these results, XG-g-pAAm-CL-Borax-IONP NCs may be a viable material for the purification of AMX from contaminated water.

Mechanical properties of co-continuous network polymers packed with thiol-ene thermosets in epoxy monolith

Co-continuous network polymers (CNPs) as the new polymer composites are fabricated by filling the continuous pores of an epoxy monolith with a high glass transition temperature (Tg) using another kind of network polymer with a low Tg. In this study, we prepared sheet-like and cylindrical CNPs using thiol–ene thermosets as the second component with a low Tg. A thiol–ene reaction is suitable for the preparation of thermosets with a controlled network structure. Here, various thiols and acrylates including the different numbers of functional groups and/or oligo(ethylene oxide) spacers with different lengths are used for the fabrication of the second thermosetting component. We investigated the tensile and compression mechanical properties of the produced CNPs. Dynamic mechanical analysis (DMA) of the thiol–ene bulk thermosets (BTs) as the second component was also carried out in order to clarify the influence of the Tg and the crosslinking density on the mechanical and physical properties of the CNPs. The results of the mechanical tests were discussed on the functionality of the used acrylate and thiol compounds. In conclusion, we have revealed that the properties of CNPs are not only dependent on the crosslinking density, but also significantly affected by the detailed network structure of the second component.

Dynamic Covalent Chemistry of Enamine-ones: Exploring Tunable Reactivity in Vitrimeric Polymers and Covalent Organic Frameworks.

Dynamic covalent chemistry (DCC) has revolutionized the field of polymer science by offering new opportunities for the synthesis, processability, and recyclability of polymers as well as in the development of new materials with interesting properties such as vitrimers and covalent organic frameworks (COFs). Many DCC linkages have been explored for this purpose, but recently, enamine-ones have proven to be promising dynamic linkages because of their facile reversible transamination reactions under thermodynamic control. Their high stability, stimuli-responsive properties, and tunable kinetics make them promising dynamic cross-linkers in network polymers. Given the rapid developments in the field in recent years, this review provides a critical and up-to-date overview of recent developments in enamine-one chemistry, including factors that control their dynamics. The focus of the review will be on the utility of enamine-ones in designing a variety of processable and self-healable polymers with important applications in vitrimers and recyclable closed-loop polymers. The use of enamine-one linkages in crystalline polymers, known as COFs and their applications are also summarized. Finally, we provide an outlook for future developments in this field.