Structure Of Polymer Chains Research Articles

Copolymer Randomization by End‐Group Interchain Exchange Reactions

AbstractTheoretical analysis of the kinetic scheme describing formation and randomization of a binary copolymer due to end‐group interchange reactions is presented. Compact analytical expressions are obtained for the transient and equilibrium values of the copolymer degree of blockiness and fractions of active end‐groups of different types. The resulting copolymer is described by the first‐order Markov statistics, which can be rather far from the Bernoullian one. Its structure is determined by the composition of the system and a single combination of the rate constants of four elementary reactions. The kinetics includes fast and slow stages with characteristic time periods independent of and proportional to the average polymerization degree, respectively. During the fast stage, the initial polymers disappear, whereas the copolymer degree of blockiness is still very low. The distribution of units in the copolymer is Markovian, only if the initial polymers possess the most probable molar mass distributions. At the slow stage copolymer randomization gradually progresses, whereas the distribution of end groups may change in the opposite direction compared to the fast stage. The results can be used to analyze the experimental data on the chain structure of condensation, metathesis, and dynamic covalent polymers, where interchange reactions play a significant role.

Mechanochemical Controlled Radical Polymerization: From Harsh to Mild.

Mechanochemistry constitutes a burgeoning field that investigates the chemical and physicochemical alterations of substances under mechanical force. It enables the synthesis of materials which is challenging to obtain via thermal, optical or electrical activation methods. In addition, it diminishes reliance on organic solvents and provides a novel route for green chemistry. Today, as a distinct branch alongside electrochemistry, photochemistry, and thermochemistry, mechanochemistry has emerged as a frontier research domain within chemistry and material science. In recent years, the intersection of mechanochemistry with controlled radical polymerization has witnessed rapid advancements, providing new routes to polymer science. Significantly, we have experienced breakthroughs in methods relying on sonochemistry, piezoelectricity and contact electrification. These methodologies not only facilitate the synthesis of polymers with high molecular weight but also enable precise control over polymer chain length and structure. Transitioning from harsh to mild conditions in mechanochemical routes has facilitated a significant improvement in the controllability of mechanochemical polymerization. From this perspective, we introduce the progress of mechanochemistry in controlled radical polymerization in recent years, aim to clarify the historcial development of this topic.

CROSSLINK DENSITY AND ITS DISTRIBUTION IN HEAT AND OIL RESISTANT ELASTOMERS BY DOUBLE QUANTUM NUCLEAR MAGNETIC RESONANCE

ABSTRACT Double quantum (DQ) nuclear magnetic resonance (NMR) was used to characterize the crosslink density, crosslink density distribution, and defect level in a series of heat and oil resistant elastomers. A wide range of defect levels, crosslink densities, and crosslink density distributions was measured, and results depended on elastomer type and compound formulations, including the vulcanization system. The sol fraction defect level generally correlated with the concentration of added plasticizer in the formulation. The presence of polar side chains appeared to cause additional dynamic contributions to the dangling chain end fraction. The large differences in elastomer composition and rubber formulations prevented meaningful correlation of the measured crosslink densities with the low strain modulus. Fast Tikhonov regularization and log normalization fitting of the corrected DQ build-up curve was extremely useful to provide insight into the modality and widths of the crosslink density distributions. A high degree of heterogeneity of the crosslink network of heat and oil resistant elastomers was found. Crosslink density distributions were explained in terms of the polymer chain structure comprised of monomer sequencing coupled with the position of the crosslinking sites. The type of vulcanization system had a lesser effect of the nature of the crosslink density distribution. The primary polymer chain crosslinking sites may become segregated from the continuous phase due to polarity differences seen in the microstructure of oil and heat resistance elastomers. The development of such micromorphologies can favor curative partitioning. The sole use of DQ NMR can provide valuable insight into the nature of the polymer chain structure and crosslink network in rubber.

-Effects and mechanisms of acrylamide-based polymer containing N-vinylpyrrolidone on drilling fluids at high temperature

The exploration of ultra-deep oil and gas presents higher temperature resistance requirements for water-based drilling fluids. However, the lack of temperature resistance mechanism of drilling fluid polymers limits the development of key materials and drilling fluids. In this paper, by comparing the preparation of acrylamide polymers for drilling fluids, the influence of cyclic monomer N-vinylpyrrolidone (NVP) on the properties of polymers for drilling fluids was investigated, and the mechanism of NVP was deeply discussed. The results show that the NVP-containing copolymer PAAN has superior viscosity enhancement and filtration control in high-temperature drilling fluids. This is mainly due to the fact that PAAN has a more stable and complex polymer chain structure than PAA, the polymer that does not contain NVP, and its thermal stability is improved by 18.6 % up to 268°C. At the same time, NVP provides more adsorption spots, and the high-temperature clay adsorption capacity of PAAN in drilling fluids is increased by more than 66.9 % compared with that of PAA, which improves clay hydration and promotes clay dispersion, and ultimately reduces filtration of drilling fluids and stabilizes drilling fluids at high temperatures by more than 23.7 %. The introduction of NVP and the in-depth analysis of its action mechanism supplemented the anti-temperature mechanism of drilling fluid polymers, aiming to support the research and development of ultra-deep drilling fluid technology.

Role of Annealing with Electric Field Toward Improvement of Ferroelectric and Electroactive Properties of PVDF Copolymer and Terpolymer Thin Films.

The present study elucidates the role of annealing with electric field on lamellar crystalline structure and molecular orientation of polymer chains in ferroelectric copolymer (P(VDF-TrFE)) and ferroelectric terpolymer (P(VDF-TrFE-CFE)) spin-coated thin films. The ferroelectric polymer thin films annealed under an electric field support the growth of nanostructure with an "edge-on" lamellar crystalline structure having in-plane molecular chain orientation. The poled P(VDF-TrFE) thin films have higher remnant polarization (Pr) ≈6.2µCcm-2 and saturation polarization (Ps) ≈8.2µCcm-2 at an applied electric field of 250 MV/m compared to unpoled thin films having Pr ≈4.7 and Ps ≈6.2µCcm-2. Also, poled P(VDF-TrFE) thin films show lower coercive field (Ec) ≈94 MV/m compared to an unpoled thin film having Ec ≈105 MV/m. Similarly, poled PVDF-TrFE-CFE thin film shows better ferroelectric properties having Pr ≈0.4 and Ps ≈5.7µCcm-2 at an applied electric field of 200 MVm-1 compared to unpoled thin films having Pr ≈0.4 and Ps ≈4.1µCcm-2. The storage energy efficiency of unpoled and poled P(VDF-TrFE-CFE) thin films is measured to be ≈75% and 80%. Annealing of ferroelectric P(VDF-TrFE) polymer thin films under an electric field demonstrates improved ferroelectric and electroactive properties.

Motorized chain models of the ideal chromosome

An array of motor proteins consumes chemical energy in setting up the architectures of chromosomes. Here, we explore how the structure of ideal polymer chains is influenced by two classes of motors. The first class which we call "swimming motors" acts to propel the chromatin fiber through three-dimensional space. They represent a caricature of motors such as RNA polymerases. Previously, they have often been described by adding a persistent flow onto Brownian diffusion of the chain. The second class of motors, which we call "grappling motors" caricatures the loop extrusion processes in which segments of chromatin fibers some distance apart are brought together. We analyze these models using a self-consistent variational phonon approximation to a many-body Master equation incorporating motor activities. We show that whether the swimming motors lead to contraction or expansion depends on the susceptibility of the motors, that is, how their activity depends on the forces they must exert. Grappling motors in contrast to swimming motors lead to long-ranged correlations that resemble those first suggested for fractal globules and that are consistent with the effective interactions inferred by energy landscape analyses of Hi-C data on the interphase chromosome.

Advanced electrochemical synthesis and characterization of Al2O3 nanoparticles embedded in polyaniline matrix for optoelectronic applications

Nanocomposite materials, featuring conducting polymers and aluminum oxide nanoparticles (Al2O3-NPs), are revolutionizing various fields including biomedicine, optoelectronic devices, and dye adsorption. In this study, we report on the synthesis of Al2O3 nanoparticles embedded in a Polyaniline (PANI) matrix for the fabrication of Al2O3/PANI nanocomposite films. The electrodeposition method was employed to deposit these films onto ITO-glass substrates, with concentrations ranging from 5 % to 20 %. The optical properties of the nanocomposites were analyzed using UV–Vis spectroscopy, allowing the determination of the refractive index and absorption coefficients. In addition, the Scherrer equation was used to calculate the average crystallite size, providing insight into the microscopic, ordered regions within the material. With increasing nanoparticle concentration in PANI-Al2O3 nanocomposites, Tauc plots revealed an increase in energy band gaps from 3.70 eV to 3.85 eV. Additionally, optical bandgap energies increased in PANI- Al2O3 nanocomposites, while electrical conductivities decreased with higher Al2O3 NPs content. Incorporation of Al2O3 NPs reduced the degree of conjugated π-bonds in PANI and disrupted the ordered structure of polymer chains. Moreover, the SEM analysis confirmed that the nanocomposite films had a dense, fiber-like structure. Further analysis of FTIR and XRD data revealed interactions between Al2O3 nanoparticles and PANI chains. At lower concentrations, minimal interaction was observed, while higher concentrations resulted in enhanced molecular interactions, leading to improved chain stretching, molecular packing, and larger crystallite sizes. As a result of Al2O3 nanoparticle incorporation, the nanocomposites exhibited conductivity values ranging from 0.12 to 0.02 S cm−1. These engineered nanocomposite films, characterized by high crystallinity, varied electrical conductivities, and controlled band gaps, show promising potential as active components in next-generation optoelectronic devices.

IGC investigation of the effect of the length of the n-alkyl substituent in 5-alkylsubstituted norbornenes on solute retention

Polymerization of 5-n-alkyl-substituted 2-norbornenes synthesized a series of polymers having the same structure of the main polymer chain, but differing in the length of the alkyl substituent (up to 14 methylene units). The obtained polymers were studied by the capillary IGC method as a stationary phase during separation of a mixture of normal hydrocarbons C6-C10. Retention data in the form of a logarithm of the retention factor lnk were correlated with the size of the sorbate (via the carbon number of the alkane ZS) and with the size of the n-alkyl substituent in the polymer chain (via the carbon number of the polymer ZP). Correlation of lnk vs. ZS turned out to be linear for all polymers, but the angle of the slope of linear dependence dlnk/dZS increases with a decrease in the carbon number of the polymer ZP. Dependency of dlnk/dZS vs. ZP is not linear and indicates an increase in the retention of sorbates by the stationary phase with a decrease in the length of the alkyl substituent in the polymer chain. The correlation of the retention of lnk analytes with the carbon number of the polymer ZP is not linear and indicates an increase in the sorbate/sorbent interaction with a decrease in the length of the alkyl substituent. Inflection points were found at both correlations with ZP in the region of ZP = 8, which indicates a possible change in the sorption mechanism or a change in the phase state of the polymer. In polymer chemistry, the phase state of a polymer is characterized by the glass transition temperature Tg, the dependence of which vs. ZP turned out to be nonlinear with an inflection point at ZP ∼11. Thus, a decrease in the length of the alkyl substituent leads to the transition of the polymer from a rubbery state to a glassy one at ZP ∼ 11, which in turn, with a further decrease in the carbon number of the polymer to ZP ∼ 8, causes a change in the sorption mechanism from bulk sorption to surface sorption. The change in the sorption mechanism is accompanied by an increase in the interaction of the sorbate with the stationary phase, which manifests itself both in an increase in the retention time of analytes and in an increase in the enthalpy and entropy of sorption. The reason for this increase can be seen in the formation of a microporous structure in 5-alkyl-substituted polynorbornenes in a glassy state.

Unveiling the effect law of carbon dots with polyfunctional groups on interface structure and ion migration in polymer electrolytes for solid lithium battery

Solid polymer electrolyte (SPE) has been considered as promising candidate electrolyte for solid-state lithium metal battery. However, the low ion conductivity and poor interface stability seriously hinder the development of SPE. Introducing the functional filler is a commonly used and effective approach to solving these issues. The poor compatibility and ambiguous mechanism of action are currently the main challenges. In this study, we design and synthesize carbon dots (NSFCDs) with quaternary functional groups, which are introduced into the SPE in the polymerization process of hybrid polymer electrolyte (HPE). The detailed effect law of polyfunctional groups on the polymer chain structure, interface structure of electrolyte/electrode and ion migration is systematically revealed. The dense polymer network endows HPE with enhanced mechanical properties. Through the regulation of polymer segments, the coordination environment of lithium ions is altered, promoting ion transport. The solid electrolyte interface (SEI) induced by NSFCDs and lithium salt anions effectively improves the morphology of lithium ion deposition and alleviates volume strain. As a result, the HPE based on polyethylene oxide (PEO) constructed by free radical polymerization of NSFCDs and polyethylene glycol diacrylate (PEGDA) exhibits excellent comprehensive performance, the assembled Li symmetric battery can cycle stably for 4000 h.

Cholesterol-Bearing Polysaccharide-Based Nanogels for Development of Novel Immunotherapy and Regenerative Medicine.

Novel functional biomaterials are expected to bring about breakthroughs in developing immunotherapy and regenerative medicine through their application as drug delivery systems and scaffolds. Nanogels are defined as nanoparticles with a particle size of 100 nm or less and as having a gel structure. Nanogels have a three-dimensional network structure of cross-linked polymer chains, which have a high water content, a volume phase transition much faster than that of a macrogel, and a quick response to external stimuli. As it is possible to transmit substances according to the three-dimensional mesh size of the gel, a major feature is that relatively large substances, such as proteins and nucleic acids, can be taken into the gel. Furthermore, by organizing nanogels as a building block, they can be applied as a scaffold material for tissue regeneration. This review provides a brief overview of the current developments in nanogels in general, especially drug delivery, therapeutic applications, and tissue engineering. In particular, polysaccharide-based nanogels are interesting because they have excellent complexation properties and are highly biocompatible.

Understanding local interactions in freestanding flexible poly(vinylidene fluoride)/poly(3,4‐ethyelenedioxythiophene):poly(styrelenesulfonate) films using impedance, Raman, and X‐ray absorption spectroscopy

AbstractThe local interaction within poly(vinylidene fluoride)/poly(3,4‐ethyelenedioxythiophene):poly(styrelenesulfonate) (PVDF/PEDOT:PSS) composite films has been explored in this study. Vibrational and impedance spectroscopy were used extensively to investigate the potential interactions within the moieties of PVDF and PEDOT:PSS in the composite. The increased concentration of PEDOT:PSS used as additives enhanced the dielectric constant of the composite films significantly. Both the AC conductivity and the estimated mobility also increased in the composite films with increasing additives. X‐ray absorption spectroscopy gave an insight into the local chain interactions within the polymer composite films. A shift in the C K‐edge toward higher energy confirmed the local interaction of the polymer moieties, suggesting a change in the polymer chain structure due to the possible association of moieties.

Review on Crystallization Strategies for Polymer Single Crystals

Polymer physics has evolved significantly over the past century, transitioning from the early recognition of the chain structure of polymers to a mature field integrating principles from statistical mechanics, thermodynamics, and condensed matter physics. As an important part of polymer physics, polymer single crystals are crucial for understanding molecular structures and behaviors, enhancing material properties, and enabling precise functionalization. They offer insights into polymer crystallization kinetics, serve as templates for nanofabrication, and have applications in electronics, sensors, and biomedical fields. However, due to the complexity of molecular chain movement, the formation of polymer single crystals is still very difficult. Over the decades, numerous researchers have dedicated themselves to unraveling the mysteries of polymer single crystals, yielding substantial findings. This paper focus on the historical evolution and advancements in polymer single crystal research, aiming to offer valuable insights and assistance to fellow researchers in this field.

Poly(β‐amino ester) based solid polymer electrolytes for lithium‐ion batteries

AbstractIn this paper, we present the synthesis of poly(β‐amino ester)‐based solid polymer electrolytes (SPE) from off‐stoichiometric acrylate‐amine formulations using one‐step, catalyst and solvent free aza‐Michael addition. By varying the monomers, the pendant functionality of the polymer chain structure could be altered. All synthesized polymers yield freestanding and easy to handle electrolyte films and hence are evaluated as a new class of SPEs. The SPE with 1,4‐butanediol diacrylate and propylamine showed the highest conductivity of 1.15 × 10−7 S cm−1 at 30°C with 10 wt% lithium bis(trifluoromethanesulfonyl)imide. Because of the presence of the various functional groups in the structure, the polymer chain aids in the movement of both the anion and the cation.

Comparing coupled cluster and composite quantum chemical methods for computing activation energies and reaction enthalpies of radical propagation reactions.

Accurate determination of activation energies and reaction enthalpies is essential for understanding the propagation step in free radical polymerization, as it significantly affects polymer chain length and structure. In this study, we compare DLPNO-CCSD(T) to canonical CCSD(T) for 17 radical addition activation energies and 18 reaction enthalpies from Radom and Fischer's test set. Additionally, we compare the computationally efficient composite methods G3(MP2)-RAD and CBS-RAD against CCSD(T)/aug-cc-pVTZ and DLPNO-CCSD(T)/CBS methods. Compared to the CCSD(T)/aug-cc-pVTZ reference, our results indicate that DLPNO-CCSD(T)/CBS with unrestricted Hartree-Fock (UHF) or UB3LYP reference orbitals and NormalPNO parameters consistently achieves chemical accuracy, with mean absolute deviations of 3.5 kJ mol-1 for activation energies and 1.5 kJ mol-1 for reaction enthalpies. Comparing the two composite methods shows that CBS-RAD agrees most closely with coupled cluster reaction enthalpies, while G3(MP2)-RAD tracks the activation energies most closely.

Sliding dynamics of ring chain on graft polymer in rotaxane

Rotaxane is a mechanically interlocked molecule in which rings are threaded on the axial linear polymer chain, and a characteristic feature of rotaxane is that ring can slide along the axial chain. In this study, molecular dynamics simulations are performed to investigate the sliding dynamics of ring on a regular/random graft polymer with graft density f and side chain length Ns. The mean-square displacement g3(t) of ring exhibits a novel sub-diffusion behavior in the intermediate time range due to the interaction between the branches and ring, and the sub-diffusive regime occurs at g3(t)∼((Nc−1)*b2)2, qualitatively, where Nc is the number of monomers between two adjacent side chains and b is bond length. For ring chain sliding along either a regular graft polymer or a random one, the sliding dynamic of ring relies strongly on the side chain length Ns、graft density f、ring size as well as the distribution of branches in the graft polymer. The diffusion coefficient D of ring decreases with the increase of Ns or f. However, ring slides faster along the regular graft polymer than that random one, because the dense side chains in the random graft polymer greatly hinder the ring's mobility. The effect of regular distribution on the improved diffusion gets most obvious when the side-chain length is middle. These results may provide a fundamental view for the understanding the effect of topological structure of axial graft polymer chain on the sliding dynamics of ring in rotaxane.

Fine-tuning gas separation performance of intrinsic microporous polyimide by the regulation of atomic-level halogen substitution

The molecular structure of polymers is essential to membrane separation performance. However, the inherent relationship between molecular structure and gas separation performance of polymeric membranes is unclear. Herein, the halogen atoms (F, Cl, and Br) were introduced into intrinsic micropore polyimide (PIM-PI) to precisely regulate its interchain cavity and elucidate the structure-property relationship. Based on the pristine BAPI, the halogen atoms were precisely designed at the ortho position of the amino group and synthesized three PIM-PIs, namely BFPI, BCPI, and BBPI, respectively. Then, it can be found that the packing structure of polymer chains and fine-tuning of fractional free volume (FFV) exhibits a regular trend in halogen-containing PIM-PIs. In addition, as the van der Waals volume of halogen atoms increases, the gas permeability of halogen-containing PIM-PIs exhibits an increasing trend. Specifically, compared with BFPI, the CO2 permeability of BCPI and BBPI is increased by 48 % and 100 %, respectively. Our findings may elucidate the structure-property relationship of microporous polymer membranes and provide a brand-new insight to design an advanced high-performance membrane.

Revealing the Role of Chain Conformations on the Origin of the Mechanical Reinforcement in Glassy Polymer Nanocomposites.

Understanding the mechanism of mechanical reinforcement in glassy polymer nanocomposites is of paramount importance for their tailored design. Here, we present a detailed investigation, via atomistic simulation, of the coupling between density, structure, and conformations of polymer chains with respect to their role in mechanical reinforcement. Probing the properties at the molecular level reveals that the effective mass density as well as the rigidity of the matrix region changes with filler volume fraction, while that of the interphase remains constant. The origin of the mechanical reinforcement is attributed to the heterogeneous chain conformations in the vicinity of the nanoparticles, involving a 2-fold mechanism. In the low-loading regime, the reinforcement comes mainly from a thin, single-molecule, 2D-like layer of adsorbed polymer segments on the nanoparticle, whereas in the high-loading regime, the reinforcement is dominated by the coupling between train and bridge conformations; the latter involves segments connecting neighboring nanoparticles.

Effect of composition and structure of ethylene-vinyl acetate copolymer on its alcoholysis kinetics: A combined experimental and DFT study

The alcoholysis process of ethylene–vinyl acetate copolymer (EVA) is both important and complex. In this work, we conduct experimental and computational investigations to examine the alcoholysis kinetics and mechanism of EVA with an ethylene content if less than 50 mol%. Our findings indicate that the overall structure of EVA polymer chain has little effect on the alcoholysis rate. However, the local structure of the acetate group, particularly its association with the ethylene content, significantly affects the overall alcloholysis. To predict the influence of ethylene content on the overall rate constant, we propose an empirical model based on detailed kinetic studies of triads. Additionally, we discover a self-acceleration phenomenon in EVA alcoholysis, although it is less pronounced compared to polyvinyl acetate. Furthermore, we employed quantum chemical calculation using density functional theory (DFT) to confirm the effect of structure on EVA alcoholysis. Notably, we investigate, for the first time, the influence of neighboring hydroxyl group on self-acceleration phenomenon through theoretical calculations. This work offers valuable insight into EVA alcoholysis and may serve as a guide for exploring its mechanism and designing processes for producing EVA related polymer materials.

Facile engineering strategy to control polymer chain structure for enhanced dispersion, electrical and sensing properties of nanocomposites

Preventing the aggregation of nanofillers and inducing uniform filler dispersion are key parameters for improving the electrical conductivity and sensing sensitivity of nanocomposites. Although the viscosity and flow index which are determined by the polymer chain structure can significantly influence the nanofiller dispersion, few systematic structural and physical analyses have been reported. In this study, a facile engineering strategy to control the polymer chain structure was designed and applied using quad-screw extrusion (QSE) capable of transferring high shear stresses. According to the increase in rotation speed of the QSE, low molecular weight polymer chains with relatively uniform chain length were prepared, enabling the fabrication of a nanocomposite with uniform dispersion. Compared to the controls, when the optimized matrix (2000 rpm) was applied to the nanocomposite with 1 wt% multi-walled carbon nanotubes, the improved strain sensor sensitivity of 798.3% were achieved owing to the improved filler dispersion and electrical conductivity.

Molecular‐scale hybrid membranes: Metal‐oxo cluster crosslinked benzimidazole‐linked polymer membranes for superior H2 purification

AbstractHydrogen (H2) purification requires separation membranes with excellent performance and high stability. Here, a few nanometer‐sized Zr‐oxygen clusters (CP‐2) abundant in amino groups were incorporated in benzimidazole‐linked polymers (BILPs) by interfacial polymerization (IP) to fabricate molecular‐scale hybrid membranes for efficient H2/CO2 separation. The amino groups in CP‐2 engage in IP. The structure of the BILPs polymer chains is regulated and more H2 selective channels are created. The hybrid membranes provide an H2/CO2 selectivity of up to 75.2 (with a corresponding H2 permeance of 318 GPU) and a high H2 permeance of up to 1470 GPU (with a corresponding H2/CO2 selectivity of 23.6). In addition, the membranes exhibit satisfactory separation performance and durability under industry‐relevant conditions (573 K, 11 bar, or steam treatment).