Linear Polymer Chains Research Articles

Impact-Resistant Adhesive Based on the Shear-Stiffening Effect via Dynamic B-O Linkages.

The occurrence of adhesive failure under impact poses significant risks, including property damage, structural collapse, and even loss of life. Herein, we have developed a series of impact-resistant adhesives by incorporating dynamic B-O linkages into linear polymeric chains. These adhesives not only possess broad-area adhesion and superior adhesive strength compared to 3 M commercial products but also exhibit a shear-stiffening effect. The shear-stiffening effect provided by the B-O linkages endows the adhesives with remarkable impact resistance, achieving a force attenuation efficiency of 84.3-86.3%. Additionally, when they are bonded to target materials, the resulting sandwich structures retain their excellent impact resistance. Therefore, this class of impact-resistant adhesives with a shear-stiffening effect shows significant potential for applications in protecting precision instruments and buildings.

Sliding on Slide-Ring Gels

Recent investigations have pointed to physical entanglements that greatly outnumber chemical crosslinks as key sources of energy dissipation and low friction in hydrogel networks. Slide-ring gels are an emerging class of hydrogels described by their mobile crosslinks, which are formed by rings topologically constrained to slide along linear polymer chains within the network. These materials have enjoyed decades of study by polymer chemists but have been underexplored by the tribology community. In this work, we synthesized a pseudo-rotaxane crosslinker from poly(ethylene glycol) diacrylate (PEG-diacrylate) and α-cyclodextrin-acrylate followed by hydrogel networks by connecting the sliding crosslinks with polyacrylamide chains. The mechanical and tribological properties of slide-ring hydrogels were investigated using a custom-built microtribometer. Slide-ring hydrogels exhibit unique behavior compared to conventional covalently crosslinked polyacrylamide hydrogels and offer a vast design space for future investigations.Graphical

Langevin Dynamics Study on the Driven Translocation of Polymer Chains with a Hairpin Structure.

The hairpin structure is a common and fundamental secondary structure in macromolecules. In this work, the process of the translocation of a model polymer chain with a hairpin structure is studied using Langevin dynamics simulations. The simulation results show that the dynamics of hairpin polymer translocation through a nanopore are influenced by the hairpin structure. Hairpin polymers can be classified into three categories, namely, linear-like, unsteady hairpin, and steady hairpin, according to the interaction with the stem structure. The translocation behavior of linear-like polymers is similar to that of a linear polymer chain. The time taken for the translocation of unsteady hairpin polymers is longer than that for a linear chain because it takes a long time to unfold the hairpin structure, and this time increases with stem interaction and decreases with the driving force. The translocation of steady hairpin polymers is distinct, especially under a weak driving force; the difficulty of unfolding the hairpin structure leads to a low translocation probability and a short translocation time. The translocation behavior of hairpin polymers can be explained by the theory of the free-energy landscape.

Synthesis of High Mechanical Strength and Thermally Recyclable and Reversible Polyurethane Adhesive by Diels–Alder Reaction

AbstractRecyclability of polyurethane materials is significant to relieve environmental problems caused by damaged polymers. Inspired by plenty of self‐healing properties based on dynamic covalent bonds. A high mechanical strength and thermally reversible polyurethane adhesive are acquired through co‐polymerization of poly‐1,4‐butylene adipate glycol (PBA), soybean oil‐based polyol (MESO), and toluene diisocyanate (TDI) whose linear polymer chains are constructed by Diels–Alder reaction between furfuryl alcohol (FA) and bismaleimide (BMI), named DAPU. Further, the obtained polyurethane adhesives show great recyclability, mechanical performance (Whose tensile strength can reach 91.7 MPa), and appropriate self‐healing ability through the thermally reversible Diels–Alder covalent bonds and hydrogen bonds between urethane groups, which may pave a way for further development of recyclable materials.

Stably Grafting Polymer Brushes on Both Active and Inert Surfaces Using Tadpole-Like Single-Chain Particles with an Interactive "Head".

We report a "grafting to" method for stably grafting high-molecular-weight polymer brushes on both active and inert surfaces using tadpole-like single-chain particles (TSCPs) with an interactive "head" as grafting units. The TSCPs can be efficiently synthesized through intrachain cross-linking one block of a diblock copolymer; the "head" is the intrachain cross-linked single-chain particle, and the "tail" is a linear polymer chain that has a contour length up to micrometers. When grafted to a surface, the "head", integrating numerous interacting groups, can synergize multiple weak interactions with the surface, thereby enabling stable grafting of the "tail" on both active and traditionally challenging inert surfaces. Because the structural parameters and composition of the "heads" and "tails" can be separately adjusted over a wide range, the interactivity of the "heads" with the surface and properties of the brushes can be controlled orthogonally, accomplishing surface brushes that cannot be achieved by existing methods.

Mesoscale modeling of random chain scission in polyethylene melts

Polyolefins account for more than half of global primary polymer production, however only a small fraction of these polymers are currently being recycled. Fragmentation of polymer chains into shorter chains with a targeted molecular weight distribution with the goal of reusing these fragments in subsequent chemical synthesis can potentially introduce an alternative approach to polyolefins recycling. Herein we develop a mesoscale framework to model degradation of polyethylene melts at a range of high temperatures. We use the dissipative particle dynamics approach with modified segmental repulsive potential to model the process of random scission in melts of linear polymer chains. We characterize the fragmentation process by tracking the time evolution of the distribution of degrees of polymerization of chain fragments. Specifically, we track the weight average and the number average degrees of polymerization and dispersity of polymer fragments as a function of the fraction of bonds broken. Furthermore, we track the number fraction distribution and the weight fraction distribution of polymer fragments with various degrees of polymerization as functions of the fraction of bonds broken for a range of high temperatures. Our results allow one to quantify to what extent the distribution of polymer chain fragments during random scission can be captured by the respective analytical distributions for the range of conversions considered. Understanding the thermal degradation of polyolefins on the mesoscale can result in the development of alternative strategies for recycling a range of thermoplastics.

Progressive polymer deformation induced by polar activity and the influence of inertia

Polar activity is shown here to induce a progressive local deformation of linear polymer chains, making a clear distinction between head and tail, while the overall chain conformation gets more compact. This breakdown of self-similarity, provoked by the accumulated tension on the polymer backbone induced by the activity, is shown to occur both in the absence and presence of inertia, although it is stronger in the latter case. Other properties like the relaxation time and diffusion are also largely influenced by the presence of a polar activity. Published by the American Physical Society 2024

Synthesis, characterization, and structural analysis of hetero Ni(II)–Na(I) and Homo Ni(II)–Ni(II) dinuclear complexes with a flexible tridendate schiff base ligand

Two different novel [Ni(II)–Na(I)]n and Ni(II)–Ni(II)] complexes have been synthesized successfully using a flexible tridentate Schiff base ligand. These complexes are characterized by IR and single crystal X–ray analysis and the optical properties of these complexes have been studied by UV spectroscopy (solution and solid). The [Ni(II)–Na(I)]n complexes are repeatedly connected with another Ni(II)–Na(I) unit to yield a linear polymeric chain. The Ni(II)–Ni(II) complex shows the nature of supramolecular dimeric cluster. These results are evidenced by x-ray structural analysis. Both as-obtained complexes are shown in different structures, such as hetro metal [Ni(II)–Na(I)]n] and homo metal [Ni(II)–Ni(II)]coordination environments with the same ligand. The first one forms a linear polymeric structure whereas the second one forms a cluster. The more intense band at 2104 cm1 is assigned to the NCS ligand of compound 1. A sharp band at 1068 cm1 together with a band at 625 cm1 in compound 2 is assigned to the ClO4 stretching vibrations and these bands are evidence for the presence of ionic perchlorate (non–coordinated). The electronic spectra of compounds 1 and 2 are recorded in ACN solvent to exhibit a broad peak around 380 nm due to d-d transition.

Cyclodextrins-Based Polyrotaxanes: From Functional Polymers to Applications in Electronics and Energy Storage Materials.

The concept of polyrotaxane comes from the rotaxane structure in the supramolecular field. It is a mechanically interlocked supramolecular assembly composed of linear polymer chains and cyclic molecules. Over recent decades, the synthesis and application of polyrotaxanes have seen remarkable growth. Particularly, cyclodextrin-based polyrotaxanes have been extensively reported due to the low-price raw materials, good biocompatibility, and ease of modification. Hence, it is also one of the most promising mechanically interlocking supramolecules for wide industrialization in the future. Polyrotaxanes are widely introduced into materials such as elastomers, hydrogels, and engineering polymers to improve their mechanical properties or impart functionality to the materials. In these materials, polyrotaxane acts as a slidable cross-linker to dissipate energy through sliding or assist in dispersing stress concentration in the cross-linked network, thereby enhancing the toughness of the materials. Further, the unique sliding-ring effect of cyclodextrin-based polyrotaxanes has pioneered advancements in stretchable electronics and energy storage materials. This includes their innovative use in stretchable conductive composite and binders for anodes, addressing critical challenges in these fields. In this mini-review, our focus is to highlight the current progress and potential wider applications in the future, underlining their transformative impact across various domains of material science.

Prediction of the Bubble Growth Behavior by Means of the Time-, Temperature-, Pressure- and Blowing Agent Concentration-Dependent Transient Elongational Viscosity Function of Polymers.

Bubble growth processes are highly complex processes, which are not only dependent on the foaming process parameters (temperature, pressure and blowing agent concentration) but also on the type and structure of the polymer used. Since the elongational viscosity at the bubble wall during bubble growth also depends on these influencing factors, the so-called transient elongational viscosity plays a key role in describing the gas bubble growth behavior in polymer melts. The model-based description of the transient elongational viscosity function is difficult due to its dependence on time, Hencky strain and strain rate. Therefore, representative viscosities or shear viscosity models are usually used in the literature to predict the bubble growth behavior. In this work, the transient equibiaxial elongational viscosity function at the bubble wall during bubble growth is described holistically for the first time. This is achieved by extending the so-called molecular stress function (MSF) model by superposition principles (temperature, pressure and blowing agent concentration) and by using the elongational deformation behavior (Hencky strain and strain rate) at the bubble wall during the initial, and thus viscosity-driven, bubble growth process. Therefore, transient uniaxial elongational viscosity measurements are performed and the non-linear MSF model parameters of the two investigated polymers PS (linear polymer chains) and PLA (long-chain branched polymer chains) are determined. By applying the superposition principles and by changing the strain mode parameter to the equibiaxial case in the MSF model, the transient equibiaxial viscosity master curve is obtained and used to describe the bubble growth process. The results show that the extended MSF model can fully predict the transient equibiaxial elongational viscosity function at the bubble wall during bubble growth processes. The bubble growth behavior over time can then be realistically described using the defined transient equibiaxial elongational viscosity function at the bubble wall. This is not possible, for example, with a representative viscosity and therefore clearly demonstrates the influence and importance of knowing the transient deformation behavior that prevails at the bubble wall during bubble growth processes.

Influence of solvent quality on the swelling and shear modulus of polymer gels chemically cross-linked in solution

The effect of temperature (T) is studied on the swelling of model poly(vinyl acetate) (PVAc) gels in isopropyl alcohol. The theta temperature Θ of these gels, at which the second osmotic virial coefficient A2 vanishes, is close to that of the corresponding high molecular mass polymer solution without cross-links so that solvent quality may be defined in the same way as the corresponding precursor polymer solution. We quantified the swelling and deswelling of PVAc gels relative to their size at the theta temperature, and also determined the effect of T on the shear modulus of these gels. It was found that both swelling and deswelling data could be reduced to a universal scaling equation of the same general form as derived from renormalization group (RG) theory for flexible linear polymer chains in solutions.Graphical abstractVariaton of the volumetric swelling factor as a function of the reduced temperature for PVAc gels swollen in isopropyl alcohol.

Supramolecular architecture of sodium heterocyclic dithiocarbamate salt: Insights from spectral analysis and bond valence sum characterization

The hydrated sodium salt of 1,2,3,4-tetrahydroquinolinedithiocarbamate (1) has been successfully synthesized and characterized using IR, NMR, and X-ray single crystal analysis. The υC–S and thioureide υC–N bands appeared at 1484 cm−1 and 968 cm−1, respectively, in Na(H2O)3+(thqdtc)– • H2O. The notable NCS2 carbon signal emerged at 212 ppm, credited to unique nitrogen and sulfur-induced deshielding effects. Compound 1 crystallizes in the monoclinic system, P21/c space group, with dimensions a = 14.4297(4) Å, b = 6.1534(2) Å, c = 17.6701(4) Å, β = 108.7340(10)°, V = 1485.83(7) Å3, and Z = 4. The structure of 1 exhibits a supramolecular architecture through secondary interactions, such as weak intermolecular interactions that link the molecules into a linear polymeric chain. The incorporation of heterocyclic rings in the dithiocarbamate ligands leads to the formation of an intriguing supramolecular architecture, as confirmed by BVS analysis results. The BVS value of sodium does not agree well with the formal oxidation state due to the interactions of anions, cations, coordinated and uncoordinated water molecules.

Polymer translocation: Effects of confinement.

We investigate the influence of varying confinement on the dynamics of polymer translocation through a cone-shaped channel. For this, a linear polymer chain is modeled using self-avoiding walks on a square lattice. The cis side of a cone-shaped channel has a finite volume, while the trans side has a semi-infinite space. The confining environment is varied either by changing the position of the back wall while keeping the apex angle fixed or altering the apex angle while keeping the position of the back wall fixed. In both cases, the effective space ϕ, which represents the number of monomers in a chain relative to the total number of accessible sites within the cone, is reduced due to the imposed confinement. Consequently, the translocation dynamics are affected. We analyze the entropy of the confined system as a function of ϕ, which exhibits nonmonotonic behavior. We also calculate the free energy associated with the confinement as a function of a virtual coordinate for different positions of the back wall (base of the cone) along the conical axis for various apex angles. Employing the Fokker-Planck equation, we calculate the translocation time as a function of ϕ for different solvent conditions across the channel. Our findings indicate that the translocation time decreases as ϕ increases, but it eventually reaches a saturation point at a certain value of ϕ. Moreover, we highlight the possibility of controlling the translocation dynamics by manipulating the solvent quality across the channel. Furthermore, our investigation delves into the intricacies of polymer translocation through a cone-shaped channel, considering both repulsive and neutral interactions with the channel wall. This exploration unveils nuanced dynamics and sheds light on the factors that significantly impact translocation within confined channels.

All-Atom Molecular Dynamics Simulations of Uncharged Linear Polymer Bottlebrushes: Effect of the Brush Sizes and the Number of Side-Chain Monomers.

Bottlebrush polymers (BBPs), characterized by grafted polymer side chains on linear backbone polymer chain, have emerged as a unique and versatile class of macromolecules with extensive applications in the fields of material science, electronics, battery materials, self-healing technology, etc. In this paper, we employ all-atom molecular dynamics (MD) simulations to present a comprehensive study of poly(methyl methacrylate)-g-poly(2-ethyl-2-oxazoline) (PMMA-g-PEtOx) BBP and its structural and hydration properties for varying number of backbone monomers (NBB) and side chain monomers (NSC), as well as properties of water molecules supported by the BBP. We find that the radius of gyration follows a scaling of Rg ∼NSC0.36 for smaller grafts and Rg ∼ NSC0.52-0.58 for longer grafts. We also find that the overall shape of the bottlebrush goes from a rod to sphere-like shape with the increase in NSC. Both the hydration per side chain monomer and hydrogen bonds (HBs) per oxygen and nitrogen of the side chain monomer reduce with an increase in NSC, caused by a corresponding enhancement in localization of the side chain monomers in the interior of the BBP. Furthermore, steric influences ensure the number of water-oxygen HBs is much more than the number of water-nitrogen HBs (with oxygen and nitrogen atoms belonging to the monomer side chains). Also, the BBP-supported water molecules demonstrate two distinctly ordered domains with one more structured and one less structured. The more structured domain disappears with an increase in NSC that causes more side chain monomers to localize in the interior of the BBPs. Finally, we observe that despite the highly negative partial charges of the oxygen and nitrogen atoms (of the side chain monomers), the dipole orientation distributions of water molecules around these atoms exhibit the presence of a neutral environment rather than an anionic environment. Overall, we anticipate that our study will generate significant interest in probing the various BBP systems in greater atomistic detail.

Supramolecular Polymers: Inherently Dynamic Materials.

ConspectusSince its inception in the early 1990s, the field of supramolecular polymers (SPs) has grown into an interdisciplinary field of chemistry. It expanded from the self-assembly of molecular building blocks based on H-bonding into the realm of complex dynamic material, encompassing both supramolecular noncovalent and molecular covalent regimes. It has paved the path for a more diverse field of research into a new class of polymeric materials, coined dynamic polymers or dynamers. Dynamers are bringing a paradigm shift not only in material science research but also in a broad field of applications from self-healing materials to biocompatible polymeric materials. The present Account presents the evolution of supramolecular polymer chemistry from simple linear polymeric chains to complex dynamic polymers imparting novel functional properties, such as component exchange and self-healing. We explore how SPs led to materials of increasing complexity, starting from simple main-chain polymers to the formation of more complex columnar SPs and lateral SPs. The field has experienced three partially overlapping periods. The main goal was first the generation of polymeric entities from various molecular components connected through noncovalent interactions, especially complementary hydrogen bonding recognition patterns as well as stacked columnar SPs. Thereafter, attention was directed in parallel to the exploration of the properties of SPs and their applications as novel materials. In a third period, the dynamic properties of supramolecular polymers were explored, taking advantage of the lability of noncovalent interactions to perform component rearrangement and exchange. We illustrate how the field of SPs has emerged as a multidisciplinary field of chemistry, biology, and materials science with selected examples from the literature. The SPs, specifically dynamic owing to their inherent reversibility, also pave the path to easier sorting and recycling, as desired in the plastics industry.One of the biggest challenges that the plastics industry is facing today is the end-of-life fate of plastics. Plastics that cannot be recycled end up in landfills or are improperly disposed of in rivers and oceans, polluting and damaging the environmental balance irreversibly. Dynamic polymeric materials presenting inherent dynamicity could pave the way for addressing this long-standing challenge of nonrecyclability of plastics. Dynamers formed via noncovalent interactions or reversible covalent bonds can be broken into components that could be easily recycled and reused. Therefore, dynamers could play a pivotal role toward closing the loop for the plastics industry and provide a solution to an elusive circular economy with plastics being an integral part.

Synthesis and crystal structure of a cadmium(II) coordination polymer based on 4,4′-(1H-1,2,4-triazole-3,5-diyl)dibenzoate

The asymmetric unit of the title compound, catena-poly[[[aquabis(pyridine-κN)cadmium(II)]-μ2-4,4′-(1H-1,2,4-triazole-3,5-diyl)dibenzoato-κ4 O,O′:O′′,O′′′] 4.5-hydrate], {[Cd(C16H9N3O4)(C5H5N)2(H2O)]·4.5H2O} n or {[Cd(bct)(py)2(H2O)]·4.5H2O} n (I), consists of a Cd2+ cation coordinated to one bct2– carboxylate dianion, two molecules of pyridine and a water molecule as well as four and a half water molecules of crystallization. The metal ion in I possesses a pentagonal–bipyramidal environment with the four O atoms of the two bidentately coordinated carboxylate groups and the N atom of a pyridine molecule forming the O4N equatorial plane, while the N atom of another pyridine ligand and the O atom of the water molecule occupy the axial positions. The bct2– bridging ligand connects two metal ions via its carboxylic groups, resulting in the formation of a parallel linear polymeric chain running along the [1\overline{1}1] direction. The coordinated water molecule of one chain forms a strong O—H...O hydrogen bond with the carboxylate O atom of a neighboring chain, leading to the formation of double chains with a closest distance of 5.425 (7) Å between the cadmium ions belonging to different chains. Aromatic π–π stacking interactions between the benzene fragments of the anions as well as between the coordinated pyridine molecules belonging to different chains results in the formation of sheets oriented parallel to the (\overline{1}01) plane. As a result of hydrogen-bonding interactions involving the water molecules of crystallization, the sheets are joined together in a three-dimensional network.

Shock and spallation behavior of ultrahigh molecular weight polyethylene

We investigate dynamic compression and fracture of ultra-high molecular weight polyethylene (UHMWPE) with plate impact experiments, high-speed velocimetry, and postmortem X-ray computed tomography. The Hugoniot equation of state of UHMWPE up to peak shock stress of ∼2.0 GPa is obtained via reverse impact. Spall strength and corresponding tensile strain rates are determined via symmetric impact. With increasing impact velocity, spall strength is nearly a constant (∼70 MPa) up at first, and then decreases continuously as a result of competition between increasing tensile strain rate, shock heating and strain softening; the damage degree increases first and then decreases rapidly at the expense of more damage nucleation sites. The void size distributions follow a power law. The small voids are closer to spheres and voids/cracks becomes flatter as void volume increases, likely because of the rearrangement and breakage of linear polymer chains of UHMWPE.

Supramolecular nanoarchitectonics of propionylated polyrotaxanes with bulky nitrobenzyl stoppers for light-triggered drug release.

Cyclodextrin (CD)-based polyrotaxanes (PRXs) are supramolecular polymers comprising multiple CDs mechanically interlocked onto a linear polymer chain by capping the polymer ends with bulky stoppers. Among various PRX derivatives, propionylated PRXs (Pr-PRXs) composed of propionylated α-CD and high molecular-weight poly(ethylene glycol) (PEG) form self-assembled nanoparticles in aqueous solution through hydrophobic interactions. Although Pr-PRX nanoparticles can encapsulate hydrophobic drugs in their hydrophobic domains, their release rate is limited. To improve the efficiency of drug release from Pr-PRX nanoparticles, ultraviolet (UV) light-dissociable Pr-PRXs were designed using 4,5-dimethoxy 2-nitrobenzyl groups as UV-cleavable bulky stopper molecules to facilitate UV-induced drug release. Photodegradable Pr-PRX (Pr-PD-PRX) was synthesized, and its UV-induced dissociation was examined. Pr-PD-PRX was completely dissociated via UV irradiation (365 nm) for 30 min. Additionally, Pr-PD-PRX nanoparticles encapsulating hydrophobic drugs collapsed upon UV irradiation, which promoted the release of the encapsulated drugs compared to non-degradable Pr-PRX nanoparticles. UV irradiation of drug-loaded Pr-PD-PRX nanoparticles resulted in higher cytotoxicity than non-irradiated Pr-PD-PRX and non-degradable Pr-PRX. Consequently, designing photodegradable PRX-based nanoparticles provides new insights into developing photoresponsive drug carriers and smart biomedical materials.

Optically transparent and mechanically tough glass with impact resistance and flame retardancy enabled by covalent/supramolecular interactions.

Exploring glass materials beyond inorganic components represents a new direction in the development of artificial transparent materials. Inspired by the successes of polymeric and supramolecular glasses, we shifted our attention to the preparation of a transparent glass through the polymerization of low-molecular-weight monomers that are naturally tailored with noncovalent recognition motifs. In this work, an imidazolium unit bearing a vinyl group and a tetrafluoroborate counter anion was selected to construct an artificial glass. Experimental and theoretical investigations revealed that the cross-linking behavior of anions effectively transformed linear polymeric chains into three-dimensional networks. The polymeric-supramolecular glass exhibits a tough tensile strength (61.31 MPa), high Young's modulus (1.17 GPa), and good optical transparency (>90%), which are comparable to those of polymethyl methacrylate. Moreover, the obtained glass maintains excellent mechanical toughness and optical transparency over a wide temperature range (from -150 to 150 °C). The material shows a superior impact resistance (18.34 kJ m-2) and flame retardancy (V0 rating), which are barely achieved by supramolecular materials.

Polymer translocation: effects of periodically driven confinement.

We study the influence of confinement on the dynamics of translocation of a linear polymer chain in a good solvent through a cone-shaped pore. Using the Langevin dynamics simulations, we calculate both the first attempt time and translocation time as a function of the position of the back wall and apex angle α. As the in vivo confining environment is inherently dynamic, we extended the present study to explore the consequences of a periodically driven back wall and apex angles on the translocation dynamics. Our findings reveal that the translocation time initially decreases as the driving frequency increases, but increases after a certain frequency. The frequency at which the translocation time is found to be minimum is referred to as the resonance activation. Analyzing the distribution of translocation times around this frequency renders interesting information about the translocation process. We further explore the translocation dynamics by calculating the residence time of individual monomers, shedding light on the microscopic aspects of the process.