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The present work highlights the preparation of the epoxidized natural rubber conjugated spent coffee biocomposites (ENR‐g‐SC) via one‐pot synthesis to control petroleum oil spills. The structural determination of the spent coffee grafted epoxidized natural rubber (ENR‐g‐SC) was confirmed through FTIR and 1H‐NMR spectroscopic analyses. The thermal performance, tensile tests, and morphological properties of the synthesized (ENR‐g‐SC) biocomposites were performed. The data revealed that ENR‐g‐SC biocomposite with 20 phr of spent coffee (SC) exhibited the highest tensile properties due to maximal chemical linkages of spent coffee and epoxide groups in ENR. The epoxidized natural rubber conjugated spent coffee copolymers were evaluated as oil sorbers for oil absorbency applications in chloroform, toluene, and 10% crude petroleum diluted with toluene. The data revealed that the oil absorbency increased slightly with chloroform or toluene instead of 10% crude oil diluted with toluene. Furthermore, swelling and network parameters including the maximum oil absorbency (Qmax), swelling rate constant (k), polymer‐solvent interaction (χ), effective crosslink density (ύe), equilibrium modulus of elasticity (GT), and average molecular weight between crosslinks (Mc) and theoretical crosslink density (ύt) were determined, and correlated to the efficiency of the synthesized epoxidized natural rubber conjugated spent coffee. [ABSTRACT FROM AUTHOR]

This article aims to appraise the effect of microstructure comprising molecular weight distribution and chemical composition distribution on the mechanical properties of high‐density polyethylene (HDPE). HDPE resins were synthesized using several titanium–magnesium‐supported Ziegler–Natta catalysts in the industrial gas phase reactor under the same polymerization condition. Gel permeation chromatography and crystallization elution fractionation (CEF) were conducted on the resins to characterize the molecular weight and comonomer distribution. Crystallization, thermal and rheological behavior were evaluated following differential scanning calorimetry, polarization light microscopy, and rheometric mechanical spectrometry. The resins with higher soluble fraction in trichlorobenzene below 80°C (highly branched low molecular weight chains) exhibited longer crystallization time based on the crystallization kinetic obtained from the Avrami model. Rheological determination of the molecular weight between entanglements (Me) and the average lamella thickness based on the Gibbs–Thomson equation revealed that the entanglement density and impact strength decreased, and the average lamella thickness increased with an increase in the ratio of CEF eluted fraction below 80°C to the crystallizable fraction in the range of 80–90°C. [ABSTRACT FROM AUTHOR]

Vitrimers are promising reprocessable materials. To tune their properties, microphase separated block copolymers as backbones play an essential role in the thermal and mechanical properties of the resulting nanostructured networks. In this study, various narrow disperse di‐ and triblock copolymers containing a hydroxyethyl methacrylate block and, for comparison, random copolymers of the same comonomers are synthesized in a controlled manner by photoiniferter reversible addition‐fragmentation chain transfer polymerization. Subsequently, the copolymers are modified by acetoacetate groups and cross‐linked with diamines. After curing, the di‐ and triblock copolymer‐based vitrimers exhibit excellent thermal and mechanical properties compared to random ones; moreover, their characteristic properties can be adjusted by different types and amounts of diamines. As the transamination reaction is a thermoreversible exchange reaction, the resulting vitrimers are reprocessable and therefore are recyclable materials. The combining of two of these classes of soft materials, namely vitrimers and block copolymers, leads to materials with a broad spectrum of adjustable mechanical properties for various applications with an improved end‐of‐life management, when compared to permanently crosslinked thermosets. [ABSTRACT FROM AUTHOR]

Shear banding in entangled polymer solutions is an elusive phenomenon in polymer rheology. One recently proposed mechanism for the existence of banded velocity profiles in entangled polymer solutions stems from a coupling of the flow to banded concentration profiles. Recent work [Burroughs et al., Phys. Rev. Lett.126, 207801 (2021)] provided experimental evidence for the development of large gradients in concentration across the fluid. Here, a more systematic investigation is reported of the transient and steady-state banded velocity and concentration profiles of entangled polybutadiene in dioctyl phthalate solutions as a function of temperature (T) , number of entanglements (Z), and applied shear rate (W i a p p ), which control the susceptibility of the fluid to unstable flow-concentration coupling. The results are compared to a two-fluid model that accounts for coupling between elastic and osmotic polymer stresses, and a strong agreement is found between model predictions and measured concentration profiles. The interface locations and widths of the time-averaged, steady-state velocity profiles are quantified from high-order numerical derivatives of the data. At high levels of entanglement and large W i a p p , a significant wall slip is observed at both inner and outer surfaces of the flow geometry but is not a necessary criterion for a nonhomogeneous flow. Furthermore, the transient evolution of flow profiles for large Z indicate transitions from curved to "stair-stepped" and, ultimately, a banded steady state. These observed transitions provide detailed evidence for shear-induced demixing as a mechanism of shear banding in polymer solutions. [ABSTRACT FROM AUTHOR]

This article gives an overview of experimental results on dynamics in bulk glass-forming molecular liquids. Rather than looking for phenomenology that is universal, in the sense that it is seen in all liquids, the focus is on identifying the basic characteristics, or "stylized facts," of the glass transition problem, i.e., the central observations that a theory of the physics of glass formation should aim to explain in a unified manner. [ABSTRACT FROM AUTHOR]

We study the translocation of charged star polymers through a solid-state nanopore using coarse-grained Langevin dynamics simulations, in the context of using nanopores as high-throughput devices to characterize polymers based on their architecture. The translocation is driven by an externally applied electric field. Our key observation is that translocation kinetics is highly sensitive to the functionality (number of arms) of the star polymer. The mean translocation time is found to vary non-monotonically with polymer functionality, exhibiting a critical value for which translocation is the fastest. The origin of this effect lies in the competition between the higher driving force inside the nanopore and inter-arm electrostatic repulsion in entering the pore, as the functionality is increased. Our simulations also show that the value of the critical functionality can be tuned by varying nanopore dimensions. Moreover, for narrow nanopores, star polymers above a threshold functionality do not translocate at all. These observations suggest the use of nanopores as a high-throughput low-cost analytical tool to characterize and separate star polymers. [ABSTRACT FROM AUTHOR]

Viscoelastic response in terms of the complex shear modulus G*(ω) of the linear polymers poly(ethylene-alt-propylene), poly(isoprene), and poly(butadiene) is studied for molar masses (M) from 3k up to 1000k and over a wide temperature range starting from the glass transition temperature Tg (174 K-373 K). Master curves G′(ωτα) and G″(ωτα) are constructed for the polymer-specific relaxation. Segmental relaxation occurring close to Tg is independently addressed by single spectra. Altogether, viscoelastic response is effectively studied over 14 decades in frequency. The structural relaxation time τα used for scaling is taken from dielectric spectra. We suggest a derivative method for identifying the different power-law regimes and their exponents along G″(ωτα) ∝ ωε″. The exponent ε″ = ε″(ωτα) ≡ d ln G″(ωτα)/d ln(ωτα) reveals more details compared to conventional analyses and displays high similarity among the polymers. Within a simple scaling model, the original tube-reptation model is extended to include contour length fluctuations (CLFs). The model reproduces all signatures of the quantitative theory by Likhtman and McLeish. The characteristic times and power-law exponents are rediscovered in ε″(ωτα). The high-frequency flank of the terminal relaxation closely follows the prediction for CLF (ε″ = −0.25), i.e., G″(ω) ∝ ω−0.21±0.02. At lower frequencies, a second regime with lower exponent ε″ is observed signaling the crossover to coherent reptation. Application of the full Likhtman-McLeish calculation provides a quantitative interpolation of ε″(ωτα) at frequencies below those of the Rouse regime. The derivative method also allows identifying the entanglement time τe. However, as the exponent in the Rouse regime (ωτe > 1) varies along εeRouse = 0.66 ± 0.04 (off the Rouse prediction εRouse = 0.5) and that at ωτe < 1 is similar, only a weak manifestation of the crossover at τe is found at highest M. Yet, calculating τe/τα= (M/Mo)2, we find good agreement among the polymers when discussing ε″(ωτe). The terminal relaxation time τt is directly read off from ε″(ωτα). Plotting τt/τe as a function of Z = M/Me, we find universal behavior as predicted by the TR model. The M dependence crosses over from an exponent significantly larger than 3.0 at intermediate M to an exponent approaching 3.0 at highest M in agreement with previous reports. The frequency of the minimum in G″(ωτα) scales as τmin ∝ M1.0±0.1. An M-independent frequency marks the crossover to glassy relaxation at the highest frequencies. Independent of the amplitude of G″(ω), which may be related to sample-to-sample differences, the derivative method is a versatile tool to provide a detailed phenomenological analysis of the viscoelastic response of complex liquids. [ABSTRACT FROM AUTHOR]

We derive the effective Flory-Huggins parameter in polarizable polymeric systems, within a recently introduced polarizable field theory framework. The incorporation of bead polarizabilities in the model self-consistently embeds dielectric response, as well as van der Waals interactions. The latter generate a χ parameter (denoted χ ̃ ) between any two species with polarizability contrast. Using one-loop perturbation theory, we compute corrections to the structure factor S k and the dielectric function ϵ ^ ( k ) for a polarizable binary homopolymer blend in the one-phase region of the phase diagram. The electrostatic corrections to S(k) can be entirely accounted for by a renormalization of the excluded volume parameter B into three van der Waals-corrected parameters BAA, BAB, and BBB, which then determine χ ̃ . The one-loop theory not only enables the quantitative prediction of χ ̃ but also provides useful insight into the dependence of χ ̃ on the electrostatic environment (for example, its sensitivity to electrostatic screening). The unapproximated polarizable field theory is amenable to direct simulation via complex Langevin sampling, which we employ here to test the validity of the one-loop results. From simulations of S(k) and ϵ ^ ( k ) for a system of polarizable homopolymers, we find that the one-loop theory is best suited to high concentrations, where it performs very well. Finally, we measure χ ̃ N in simulations of a polarizable diblock copolymer melt and obtain excellent agreement with the one-loop theory. These constitute the first fully fluctuating simulations conducted within the polarizable field theory framework. [ABSTRACT FROM AUTHOR]

Defined, branched polymer architectures with low dispersity and architectural purity are of great interest to polymer science but are challenging to synthesize. Besides star and comb, especially the pom-pom topology is of interest as it is the simplest topology with exactly two branching points. Most synthetic approaches to a pom-pom topology reported a lack of full control and variability over one of the three topological parameters, the backbone or arm molecular weight and arm number. A new, elegant, fast, and scalable synthetic route without the need for post-polymerization modification (PPM) or purification steps during the synthesis to a pom-pom and a broad variety of topologies made from styrene and dienes is reported, with potential application to barbwire, bottlebrush, miktoarm star, Janus type polymers, or multi-graft copolymers. The key is to inset short poly(2-vinyl-pyridine) blocks (<2 mol% in the branched product) into the backbone as branching points. Carb anions can react at the C6 carbon of the pyridine ring, grafting the arms onto the backbone. Since the synthetic route to polystyrene pom-poms has only two steps and is free of PPM or purification, large amounts of up to 300 g of defined pom-pom structures can be synthesized in one batch., (© 2024 The Authors. Macromolecular Rapid Communications published by Wiley‐VCH GmbH.)

This study investigates the effect of adding oligomers on the rheological properties of polymer nanocomposite melts with the goal of enhancing the processability of nanocomposites. The scaling analysis of plateau modulus (G N ) is used in understanding the complex mechanical behavior of entangled poly(methyl acrylate) (PMA) melts upon oligomer addition. Increasing the oligomer amount led to a decrease in G N and an apparent degree of entanglement (Z) in the neat polymer melt. The particle dispersion states at two particle loadings with oligomer addition are examined in transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The dilution exponent is found unchanged at 7 and 17 vol% particle loadings for the well-dispersed PMA-SiO 2 nanocomposites compared to the neat PMA solution. These findings suggest that attractive particles with strong interfacial layers do not influence the tube dilution scaling of the polymer with the oligomer. To the contrary, composites with weak polymer-particle interfaces demonstrate phase separation of particles when oligomers are introduced and its exponent for tube dilution scaling reaches 4 at a particle loading of 17 vol%, potentially indicating that network-forming clusters influence chain entanglements in this scenario., (© 2023 Wiley-VCH GmbH.)

More recently pellet‐based additive manufacturing or so‐called micro‐extrusion has become more popular for final polymeric part production. In the present work, it is evaluated how pellet‐based AM (PBAM) performs for its extrudates and specimens compared to the more established fused filament fabrication technique, considering both commercial acrylonitrile butadiene styrene polymer and poly(lactic acid) pellets and filaments as feedstocks. For benchmarking purposes, a comparison with conventional techniques, that is, single screw extrusion and injection molding, is also included. To support the performance interpretation a theoretical analysis is conducted regarding the melting finalization point as well as void measurements and Fourier transfer infrared spectroscopic analysis for degradation effects are included. It is demonstrated that for the extrudates comparable results are obtained among the different manufacturing techniques, whereas for the specimens the situation is dissimilar. It is highlighted that PBAM/ME has a large market potential implementation, provided that its operating settings are further optimized. [ABSTRACT FROM AUTHOR]

A multiscale simulation method is used to calculate the rheological properties of entangled Nylon 6 melts, including the stress relaxation modulus, storage and loss moduli, and the melt viscosity. The three‐level multiscale approach includes all‐atom, coarse‐grained and slip‐spring models, each operating at different levels of resolution and encompassing a wide range of length scales and over nine orders of magnitude in time. These models are unified by matching the polymer chain structure and dynamics as well as the stress relaxation, and together predict the rheological master curves at various temperatures using time–temperature superposition. The calculated viscosity agrees reasonably with experiment. The effect of polydispersity on rheology is also studied by simulating a polydisperse melt with chain lengths follow the Schulz‐Zimm distribution. Under the same weight‐average molecular weight, the polydisperse melt shows faster stress relaxation and lower viscosity compared to the monodisperse melt. For polymers that undergo rapid degradation at elevated temperatures, such as Nylon, the proposed approach offers a useful means to investigate rheology over a wide range of conditions. Importantly, the approach is fully predictive in that calculations of rheology are generated without relying on experimental information, and it therefore offers potential for design of polymeric materials on the basis of purely molecular models. [ABSTRACT FROM AUTHOR]

We investigate the linear viscoelastic properties of industrial pressure sensitive adhesives comprising double networks with an entangled acrylate-based polymer and two types of intermolecular associations (crosslinking), permanent (epoxide) and reversible (metal-chelate), having different compositions. A combination of shear rheometry and an appropriately modified version of the Time Marching Algorithm (TMA) allows to probe and analyze the behavior of the different double dynamic networks, in particular, the effects of the type and amount of crosslinks on their linear viscoelastic spectra. To this end, the dynamics of the double networks are compared with the respective individual responses of the polymeric component without crosslinks and the single networks (possessing only physical or only chemical crosslinks), in order to quantify their contributions to the relaxation mechanisms, particularly the interplay between disentanglement and bond association/dissociation processes. With the help of the TMA model, we also examine the respective roles of the lifetime of stickers, polydispersity, and molar mass. Triggered by the good comparison between predictions and experimental data, we propose a framework to tune material parameters in order to obtain a desired viscoelastic behavior. [ABSTRACT FROM AUTHOR]

The relationship between the structure and the final properties of materials is an important issue in polymer science. In particular, the properties of polyolefins are impacted by their branching contents. A simple rheological method is presented to estimate the degree of short chain branching (SCB) in linear low‐density polyethylene (LLDPE). A range of ethylene‐1‐hexene copolymers is synthetized using a metallocene catalyst to obtain homogenous LLDPE models with various comonomer contents. The polymers are analyzed by size exclusion chromatography, 13C NMR, and crystallization elution fractionation to determine both their molar masses and their chemical composition distributions. Subsequently, they are measured by rheology to assess the impact of SCB. This work provides calibration curves for rheology and proves that it is possible to predict the SCB content in LLDPE from the melt viscosity analysis. [ABSTRACT FROM AUTHOR]

Copper chloride (CuCl2) is used in sulfur‐cured natural rubber (NR) to regulate disulfide exchange reaction in self‐healing process while factors influencing the healing capability remain unclear. Herein CuCl2 and other additives including zinc oxide and sulfur are used to mediate self‐healing efficiency of NR vulcanizates. For revealing the role of proteins and phospholipids in NR, the mediated self‐healing capability is compared with sulfur‐cured isoprene rubber (IR) vulcanizates. The results reveal that CuCl2 interferes rheological responses and vulcanization dynamics in both rubbers, and it causes intermolecular disassociation in NR gums. As self‐healing capability is closely related to crosslinking density, formulation is adjusted to balance healing efficiency and tensile strength. Healing efficiency of around 70% and the highest tensile strength of about 6 MPa are achieved at crosslinking density about 70 mol/m3 when vulcanizates are healed at 140°C for 30 min. [ABSTRACT FROM AUTHOR]

Self‐healing polymer–carbon composites are seen as promising materials for future electronic devices, which must be able to restore not only their structural integrity but also electrical performance after cracking and wear. Despite multiple reports about self‐healing conductive elements, there is a lack of a broad fundamental understanding of correlation between viscoelasticity of such composites, their electrical properties, and self‐healing of their mechanical as well as electrical properties. Here, it is reported thorough investigation of electromechanical properties of blends of carbon black (CB) as conductive filler and viscoelastic polymers (polydimethylsiloxanes (PDMS) and polyborosiloxane (PBS)) with different relaxation times as matrices. It is shown that behavior of composites depends strongly on the viscoelastic properties of polymers. Low molecular polymer composite possesses high conductivity due to strong filler network formation, quick electrical, and mechanical properties restoration, but for this the ability is sacrificed to flow and ductility at large deformation (material is brittle). In contrary, high relaxation time polymer composite behaves elastically on small time and flows at large time scale due to weak filler network and can heal. However, the electrical properties are worse than that of carbon and viscous polymer and degrade with time. [ABSTRACT FROM AUTHOR]

The introduction of functionality is essential to the surface, bulk and mechanical properties of poly(diene‐styrene). In this work, copolymerizations of hydroxyl (My‐OH) and epoxide (My‐EPO) functionalized myrcenes with styrene by a solvent‐free reversible addition fragmentation chain transfer polymerization route have been performed. In both cases, the copolymerizations were processed with functional diene preferentially inserted (rMy‐OH/rSt, 1.28 ± 0.02/0.81 ± 0.02; rMy‐EPO/rSt, 1.15 ± 0.01/0.91 ± 0.02), providing a series of composition drifted copolymers with controlled functionality degree and molecular weight by feeding ratios of comonomer and chain transfer agent. The copolymers have remarkably low contact angles with water, an indication of potentially good miscibility with polar additives. In addition, the in‐chain included hydroxyl and epoxide groups could further provide a very versatile 'intermediate' that can be used to prepare various functional polymers, block and graft copolymers. © 2022 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The relaxation time of a viscoelastic fluid is an essential parameter for characterizing the degree of elasticity. However, measuring the relaxation time of dilute polymer solutions with low viscosity using conventional rotational rheometers remains challenging because of the low instrument sensitivity. In this study, we demonstrate an efficient microfluidic method for measuring the relaxation time of a dilute polymer solution by utilizing elasticity-driven lateral particle migration in a microchannel. First, the previous theoretical model was refined, based on the Oldroyd-B constitutive equation, in order to predict lateral particle migration in a viscoelastic fluid with constant shear viscosity, considering the inlet and finite particle size effects. This model was utilized to determine the relaxation times of dilute poly(ethylene oxide) (PEO) aqueous solutions. Direct comparison of the measured relaxation times with those obtained from Zimm theory verified the reliability of the proposed method. The current approach is expected to be useful in characterizing the relaxation times of a wide range of polymer solutions. [ABSTRACT FROM AUTHOR]

Recent work arrived at expressions for the complex viscosity of a suspension of star-branched macromolecules [Coombs, Phys Fluids, 33, 093111 (2021)] using general rigid bead-rod theory without hydrodynamic interaction. In this work, we advance the theory by accounting for intramolecular interactions modeled with the interferences of Stokes flow solvent velocity profiles between adjacent beads. We derive the analytical expression for the complex viscosity of a suspension of four-arm star-branched macromolecules as a function of the number of beads in each arm N B and of the hydrodynamic interaction parameter A. We test our comprehensive theory against complex viscosity measurements of a cis-polybutadiene silicon-centered four-arm star suspension. We find the incorporation of hydrodynamic interaction improves the fit to complex viscosity measurements. [ABSTRACT FROM AUTHOR]

An orientation-stretch-coupled constitutive equation is suggested for symmetric Cayley tree-like dendrimers, which can self-consistently describe the linear relaxation spectrum and nonlinear viscoelastic behavior. The molecular stress is determined by orientation-stretch-coupled conformation tensors of all segments. The linear relaxation spectrum is determined according to hierarchical arm retraction with branch point hopping and dynamic tube dilation. Under strong flows, the orientation relaxation time and the stretch relaxation time are affected by the convective constraint release effect and branch point withdrawal. The coupling between segmental orientation and stretch in each generation is represented in the evolution of the coupled conformation tensor, while the possible stretch coupling among different generations is ignored. The predictions on both linear and nonlinear rheological behaviors are consistent with experiments, proving the rationality in treating coupling problems. [ABSTRACT FROM AUTHOR]

We investigate the linear rheology of ultrahigh molecular weight polyethylene (UHMWPE) solutions with the aim of determining the molecular weight distribution of the polymer. The UHMWPE is dissolved in oligo-ethylene in order to avoid issues related to unfavorable interactions with the solvent. To prepare the solutions, UHMWPE, solvent, and a fixed amount of antioxidants are mixed by means of a corotating twin-screw microcompounder. All prepared solutions are within the concentrated regime, as confirmed by the scaling laws of the main rheological parameters (plateau modulus, relaxation time, and zero-shear viscosity) with concentration. Based on the viscoelastic response of the solutions, we adopt a heuristic approach to extrapolate the linear viscoelastic behavior of the melt, according to a time-concentration superposition principle. Such a technique allows us to span many decades of angular frequency, eventually attaining the terminal relaxation regime. The latter is difficult to achieve by direct measurements in the molten state because of experimental issues such as extremely long experimental times and thermal limits. The viscoelastic spectrum of the melt is used to obtain the molecular weight distribution (MWD) according to the time-dependent diffusion/double reptation model. The MWD of UHMWPE evaluated by using this approach agrees well with data obtained from gel permeation chromatography. [ABSTRACT FROM AUTHOR]

Stress overshoot is one of the most important nonlinear rheological phenomena exhibited by polymeric liquids undergoing start-up shear at sufficient flow strengths. Despite considerable previous research, the fundamental molecular characteristics underlying stress overshoot remain unknown. Here, we analyze the intrinsic molecular mechanisms behind the overshoot phenomenon using atomistic nonequilibrium molecular dynamics simulations of entangled linear polyethylene melts under shear flow. Through a detailed analysis of the transient rotational chain dynamics, we identify an intermolecular collision angular regime in the vicinity of the chain orientation angle 73952; ≈ 20° with respect to the flow direction. The shear stress overshoot occurs via strong intermolecular collisions between chains in the collision regime at 73952; = 15°-25°, corresponding to a peak strain of 2-4, which is an experimentally well-known value. The normal stress overshoot appears at approximately 73952; = 10°, at a corresponding peak strain roughly equivalent to twice that for the shear stress. We provide plausible answers to several basic questions regarding the stress overshoot, which may further help understand other nonlinear phenomena of polymeric systems. [ABSTRACT FROM AUTHOR]

Segmental dynamics of a highly entangled melt of linear polyethylene-alt-propylene with a molecular weight of 200 kDa was studied with a novel proton nuclear magnetic resonance (NMR) approach based upon ¹H→²Hisotope dilution as applied to a solid-echo build-up function ISE(t), which is constructed from theNMRspin echo signals arising from the Hahn echo (HE) and two variations of the solid-echo pulse sequence. The isotope dilution enables the separation of inter- and intramolecular contributions to this function and allows one to extract the segmental mean-squared displacements in the millisecond time range, which is hardly accessible by other experimental methods. The proposed technique in combination with time-temperature superposition yields information about segmental translation in polyethylene-alt-propylene over 6 decades in time from 10-6 s up to 1 s. The time dependence of the mean-squared displacement obtained in this time range clearly shows three regimes of power law with exponents, which are in good agreement with the tube-reptation model predictions for the Rouse model, incoherent reptation and coherent reptation regimes. The results at short times coincide with the fast-field cycling relaxometry and neutron spin echo data, yet, significantly extending the probed time range. Furthermore, the obtained data are verified as well by the use of the dipolar-correlation effect on the Hahn echo, which was developed before by the co-authors. At the same time, the amplitude ratio of the intermolecular part of the proton dynamic dipole-dipole correlation function over the intramolecular part obtained from the experimental data is not in agreement with the predictions of the tube-reptation model for the regimes of incoherent and coherent reptation. [ABSTRACT FROM AUTHOR]

Many studies have established a major effect of nanoscale confinement on the glass transition temperature (Tg) of polystyrene (PS), most commonly in thin films with one or two free surfaces. Here, we characterize smaller yet significant intrinsic size effects (in the absence of free surfaces or significant attractive polymer-substrate interactions) on the Tg and fragility of PS. Melt infiltration of various molecular weights (MWs) of PS into anodic aluminum oxide (AAO) templates is used to create nanorods supported on AAO with rod diameter (d) ranging from 24 to 210 nm. The Tg (both as Tg,onset and fictive temperature) and fragility values are characterized by differential scanning calorimetry. No intrinsic size effect is observed for 30 kg/mol PS in template-supported nanorods with d = 24 nm. However, effects on Tg are present for PS nanorods with Mn and Mw = 175 kg/mol, with effects increasing in magnitude with increasing MW. For example, in 24-nm-diameter template-supported nanorods, Tg,rod - Tg,bulk = -2.0 to -2.5 °C for PS with Mn = 175 kg/mol and Mw = 182 kg/mol, and Tg,rod Tg,bulk = ~-8 °C for PS with Mn = 929 kg/mol and Mw = 1420 kg/mol. In general, reductions in Tg occur when d ≤ ; -2Rg, where Rg is the bulk polymer radius of gyration. Thus, intrinsic size effects are significant when the rod diameter is smaller than the diameter (2Rg) associated with the spherical volume pervaded by coils in bulk. We hypothesize that the Tg reduction occurs when chain segment packing frustration is sufficiently perturbed by confinement in the nanorods. This explanation is supported by observed reductions in fragility with the increasing extent of confinement. We also explain why these small intrinsic size effects do not contradict reports that the Tg-confinement effect in supported PS films with one free surface exhibits little or no MW dependence. [ABSTRACT FROM AUTHOR]

The authors here demonstrate some significant benefits of using graft polymers with inner molten block and outer glassy block at the graft chains (Graft‐Block polymer) for thermoplastic elastomers. The synthesis of the target Graft‐Block polymer is made by combining two types of living radical polymerization, reversible addition‐fragmentation chain transfer polymerization and atom transfer radical polymerization. Temperature ramp rheology, tensile tests, and load‐unload cycle tests indicate that the Graft‐Block polymer‐based elastomers have significantly improved thermal stability and mechanical properties when compares to the Triblock copolymer‐based analog. The enhanced properties are discussed in terms of the effective network strands that connected the different glassy hard domains and the presence of abundant junction points in the molten strand matrix. Overall, this research presents clear experimental evidence of such graft polymers' high potential for application as thermoplastic elastomers. [ABSTRACT FROM AUTHOR]

Highly branched polyethylene (HBPE) was developed into practical application as highly efficient sorbent material for oil‐spill cleanup and oil/water separation. To obtain large‐scale production of HBPE, a thermal stable Ni(II)‐α‐diimine catalyst for ethylene polymerization in our previous work has been employed to prepare the polyolefin material in a 10‐liter polymerization reactor with a high activity (>106 gPE/mol[Ni] h). The structure, molecular weight and distribution, thermal and mechanical properties were systematically characterized by NMR, ATR‐FTIR, GPC, DSC, DMA, and TGA, respectively. Through simple but feasible cross‐linking process, the HBPE‐based oil‐absorption materials with contact angles up to 111.5° were directly applied into absorption test using various oil and pure hydrocarbons. Reusability and recovery of the absorption materials and oil or solvents were probed by drying or using the distillation method. Oil/water separation was made to determine the hydrophobic and oleophilic nature of this material. Flory‐Rehner polymer swelling theory is employed to study the structure–property relationship via determining the network structure including cross‐linking density ρc and average molecular weight Mc between two cross‐links. The mixture of sorbent material after absorbing oil was regarded as crude oil component to simulate oil refinery process by thermogravimetric analysis, providing an alternative approach for oil‐collection. [ABSTRACT FROM AUTHOR]

To achieve long‐term and real‐time monitoring of the deformation of isolation bearings, a conductive composite with a natural rubber (NR) matrix modified by multiwalled carbon nanotubes (MWCNTs) is processed by prestrain. The resistance‐strain response of this composite indicates excellent uniformity, linearity, hysteresis, reproducibility and stability due to the prestrain process for the composite before application. To explain the mechanism of the resistance‐strain response for the composite, a theoretical model is developed to analyze the relation between the conductivity and the MWCNT network structure. Mechanical and electrical testing under cyclic loads indicates that the prestrain of the composite could reduce or even eliminate the 'shoulder peak' effect of the resistance‐strain curve. Meanwhile, the resistance‐strain response behavior is independent of the prestrain temperature and discontinuous before and after the interval time. Furthermore, the coarse‐grained molecular dynamics simulation and microstructure testing indicate that the resistance‐strain response is induced by the changing orientation of MWCNT molecules in the rubber matrix under tension loading. All of the results and findings provide potential applications of this MWCNT/NR composite for deformation monitoring. [ABSTRACT FROM AUTHOR]

Crosslinked low‐density polyethylene (XLLDPE) is widely used in several specialty plastics industries. However, the permanent chemical crosslinks cause high‐melt viscosity and poor processability, preventing the material from being reused and recycled effectively. This study investigates solid‐state shear pulverization (SSSP) as a continuous, commercially viable mechanochemical processing technique to initiate the decrosslinking of XLLDPE for mechanical recycling. Post‐industrial XLLDPE scrap material was processed using SSSP with a range of pulverization conditions, which were correlated with universal processing covariants of specific mechanical energy and particle size distribution. The physical properties of SSSP‐processed materials were compared to as‐received XLLDPE and uncrosslinked low‐density polyethylene. While gel content tests confirm a gradual decrease in crosslinking density with a more energy‐intensive SSSP process, melt rheology and dynamic mechanical analysis characterization revealed additional chain architecture modifications such as branching and chain scission. Based on differential scanning calorimetry and thermogravimetric analysis, the SSSP‐processed XLLDPE retained its thermal stability and crystallinity; tensile testing results showed improved stiffness, strength, and toughness. These results indicate that tunable SSSP can transform XLLDPE into a decrosslinked, branched, and melt‐processable recycled polyethylene. [ABSTRACT FROM AUTHOR]

We developed a new data analysis strategy, the so-called micro-rheo-mapping technique, based on multiparticle tracking experiments to obtain an accurate and direct visualization of the microstructure of commercial acrylate thickeners of Carbopol-type with high (Ultrez 10), intermediate (ETD 2020), and low (ETD 2050) degree of crosslinking. At low polymer concentration, aggregates made of several primary Carbopol particles are formed with an average diameter of 43 ± 11, 56 ± 14, and 10 ± 2.5 μm for Ultrez 10, ETD 2020, and ETD 2050, respectively. For ETD 2050, the least crosslinked thickener, the shell of dangling polymer chains covering the aggregate surface is thicker than for ETD 2020 and Ultrez 10. At technically relevant polymer concentrations, our results indicate, for all three thickeners, that the microstructure is highly heterogeneous with regions of different crosslink densities. One region inaccessible for tracer particles corresponding to a mixture of polydisperse aggregates and individual primary particles with a core mesh size less than 200 nm and a second, diluted enough to be accessible and which exhibits both elastic and viscous characteristics. The study of the impact of pH, polymer concentration, and crosslink density on these local structural and viscoelastic heterogeneities as well as macrorheological properties allowed us to establish a correlation between microstructure and macroelasticity. In particular, we found that the bulk shear modulus strongly depends on the fraction of inaccessible areas, making this microscopic parameter most relevant for describing the macroelasticity of Carbopol gels, whereas the local elasticity of the interstitial regions is of minor importance. [ABSTRACT FROM AUTHOR]

Due to their unique topology of having no chain ends, dilute solutions of ring polymers exhibit behavior distinct from their linear chain counterparts. The universality of their static and dynamic properties, as a function of solvent quality z in the thermal crossover regime between θ and athermal solvents, is studied here using Brownian dynamics simulations. The universal ratio U RD of the radius of gyration R g to the hydrodynamic radius R H is determined, and a comparative study of the swelling ratio α g of the radius of gyration, the swelling ratio α H of the hydrodynamic radius, and the swelling ratio α X of the mean polymer stretch X along the x -axis, for linear and ring polymers, is carried out. The ratio U RD for dilute ring polymer solutions is found to converge asymptotically to a constant value as z → ∞ , which is a major difference from the behavior of solutions of linear chains, where no such asymptotic limit exists. Additionally, the ratio of the mean stretch along the x -axis to the hydrodynamic radius, (X / R H) , is found to be independent of z for polymeric rings, unlike in the case for linear polymers. These results indicate a fundamental difference in the scaling of static and dynamic properties of rings and linear chains in the thermal crossover regime. [ABSTRACT FROM AUTHOR]

Chemical composition and architecture are two key factors that control the physical and material properties of polymers. Some of the more unusual and intriguing polymer architectures are the polycatenanes, which are a class of polymers that contain mechanically interlocked rings. Since the development of high yielding synthetic routes to catenanes, there has been an interest in accessing their polymeric counterparts, primarily on account of the unique conformations and degrees of freedom offered by non-bonded interlocked rings. This has lead to the synthesis of a wide variety of polycatenane architectures and to studies aimed at developing structure–property relationships of these interesting materials. In this review, we provide an overview of the field of polycatenanes, exploring synthesis, architecture, properties, simulation, and modelling, with a specific focus on some of the more recent developments. [ABSTRACT FROM AUTHOR]

A set of syndiotactic polypropylene/iron (sPP/Fe) composite samples were manufactured with the extrusion technique to study the impact of iron content on the thermal behavior of sPP/Fe composites in the melt phase. The dosage of iron contents varied from 0 to 8%. Melting point (Tm), crystallization temperature (Tc), and thermal degradation temperature (Td) were measured by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) for each composite sample. Thermal temperatures (Tm, Tc, and Td) increased with increasing the iron contents due to the enhancement of the strength and thermal stability of the sample. This investigation is a validated fact that fillers (iron) alter both the macroscopic and microscopic properties of the polymer composites. [ABSTRACT FROM AUTHOR]

Cyclodextrins are a class of biocompatible and highly water‐soluble oligosaccharide polymers, with vast applications in industries ranging from drug delivery to agriculture. Currently, most fiber production relies on using environmentally unfriendly organic solvents and polymeric additions. Cyclodextrins are seldom used on their own without a carrier polymer, however in this work, (2‐hydroxypropyl)‐β‐cyclodextrin) fibers are successfully produced with water, as the "green" solvent with pressurized gyration and electrospinning, without using a carrier polymer. The average fiber diameter of the pressurized gyration produces fibers ranged between 5.5 and 5.8 µm, while the average fiber diameter of the electrospun fibers ranged between only 183 and 305 nm. These findings show the thinnest diameter of pure cyclodextrin fibers achieved in current literature. Both techniques have specific advantages, such as electrospinning being able to produce nanofibers, while pressurized gyration has productivity of over 1.5 g min−1. Here, a pioneering study into the production of cyclodextrin‐only fibers with two different fiber production techniques and the creation of a cyclodextrin‐super‐mat that combines both types of fibers is presented. [ABSTRACT FROM AUTHOR]

Three subjects in polymer and soft matter physics are outlined in the present article. The first relates to concepts of an ideal glass transition. We describe work on ultra‐stable glass, either a 20‐million‐year‐old amber or a vapor deposited amorphous fluoropolymer, which examines the temperature dependence of the dynamics in a window between a low fictive temperature and the glass transition temperature. From this "finesse" of the problem of the geological time scales in sub‐glass temperature systems strong evidence that the divergence of the relaxation times at finite temperature from WLF‐types of extrapolation is not correct. The second topic is polymer nonlinear viscoelasticity as it relates to dynamic heterogeneity. We show results from mechanical hole burning experiments that suggest that dynamic heterogeneity arises from the nature of specific relaxation mechanisms rather than heterogeneous changes in, for example, the fictive temperature. Included is a discussion of large amplitude oscillatory shear testing and how it relates to characterization of nonlinear viscoelastic materials. The last topic addressed is the rheology of circular macromolecules. Here, we take a historical perspective and describe important new results from several laboratories that seem inconsistent. New works from our own studies on circular DNA are also discussed. [ABSTRACT FROM AUTHOR]

A coarse‐grained (CG) model of cis‐1,4‐polyisoprene (cis‐PI) is developed using systematic coarse‐graining strategy. The bonded interactions of the model are captured using analytical potentials with parameters derived to match structural probability distributions of atomistic system. The nonbonded interactions are presented by Lennard‐Jones potentials with parameters specified to match the density and thermal expansion behavior obtained from experiment. The CG force field is validated through the molecular weight dependence of chain dimension and Flory−Fox scaling relationship for the glass transition temperature of the polymer. The model developed provides much faster chain dynamics and simulation speed compared to the reference atomistic one. [ABSTRACT FROM AUTHOR]

We compute by molecular simulation the energy/entropic partition of the force in a stretched double‐stranded (ds)DNA molecule that is not yet available from the single‐molecule measurements. Simulation using the coarse‐grained wormlike chain (WLC) model predicts a gradual decrease in the internal (bending) energy of DNA at stretching. The ensuing negative energy contribution to force fU is outweighed by the positive entropy contribution fS. The ratio fU/f, used to assess the polymer elasticity, is about −1 at the moderate extension of DNA. At the high extension, the extra energy expenses due to the contour length elongation make the ratio fU/f less negative. The simulation findings of the hybrid energy/entropy nature of DNA elasticity at weak and moderate forces are supported by computations using the thermoelastic method mimicking the polymer experiments in bulk. It is contended that the observation of the negative energy elasticity in DNA can be generalized to other semiflexible polymers described by the WLC model. [ABSTRACT FROM AUTHOR]

The nonlinear response to the uniaxial extension of a series of isotactic polypropylene (iPP) ionomers is studied by melt rheology and ex situ small and wide-angle x-ray scattering measurements. These ionomers bear iPP backbones decorated with pendant aluminum carboxylate groups. Minuscule amounts of ion groups (<0.1 mol. %) are sufficient to produce remarkably high extensional strain hardening ratios of up to 200 and maximum stretch ratios (before breakage) of up to 50. Small and wide-angle scattering measurements from an iPP ionomer sample quenched during an extensional flow reveal monotonic correlations between Hencky strain, crystallinity, and crystal alignment. These results indicate a direct correlation between extensional stress and the chain alignment in the ionomer melt. Intriguingly, the ion clusters in the ionomer show no alignment induced by extensional deformation, suggesting undetermined rearrangements involving cluster dissociation and reassociation that occur during the flow. Slow stress relaxation, after flow cessation, was measured in the ionomers, in sharp contrast to much faster relaxation typically observed in the iPP homopolymer. Stress relaxation is not concomitant with a decrease in crystal alignment, which indicates that chain recoiling is not the stress relaxation mechanism in iPP ionomers. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear behavior of carbon black-filled polybutadiene solutions under large-amplitude oscillatory shear is investigated. The results show that in the nonlinear regime, the third harmonic intensity, as measured by the ratio of the third to the first harmonics I3/I1, decreases significantly above a critical concentration ϕc of the polymer in the matrix, which results in the amplitude stress deviating strongly from the linear dependence of strain, while the time dependence of stress remains sinusoidal. Increasing the filler particle size significantly decreases the critical ϕc. However, increasing the filler loading basically has no effect on the transition to linear-nonlinear dichotomy. This transition happens when the mesh size ξ of the entangled polymer network in the matrix becomes smaller than the primary filler particle size. Above ϕc, the topological hindrance of the entangled polymer chains apparently considerably slows down the recovery speed of the broken filler network in the material. Hence, the quasisinusoidal response in the system that has a strain-dependent modulus is probably due to the restoration of the broken filler network requiring longer than the time scale of a typical dynamic perturbation. [ABSTRACT FROM AUTHOR]

Both entangled and unentangled polymer melts exhibit stress overshoots when subject to shearing flow. The size of the overshoot depends on the applied shear rate and is related to relaxation mechanisms such as reptation, chain stretch, and convective constraint release. Previous experimental work shows that melts subjected to interrupted shear flows exhibit a smaller overshoot when sheared after partial relaxation. This has been shown to be consistent with predictions by constitutive models. Here, we report molecular dynamics simulations of interrupted shear of polymer melts where the shear flow after the relaxation stage is orthogonal to the originally applied flow. We observe that, for a given relaxation time, the size of the stress overshoot under orthogonal interrupted shear is larger than observed during parallel interrupted shear, which is not captured by constitutive models. Differences in maxima are also observed for overshoots in the first normal stress and chain end-to-end distance. We also show that measurements of the average number of entanglements per chain and average orientation at different scales along the chain are affected by the change in shear direction, leading to nonmonotonic relaxation of the off-diagonal components of orientation and an appearance of a "double peak" in the average number of entanglements during the transient. We propose that such complex behavior of entanglements is responsible for the increase in the overshoots of stress components and that models of the dynamics of entanglements might be improved upon by considering a tensorial measurement of entanglements that can be coupled to orientation. [ABSTRACT FROM AUTHOR]

Atomistic simulations of alkanes and polyethylenes have grown in utility and application over a 50-year period beginning at the earliest days of molecular dynamics research. This retrospective covers this period of time, aiming to present a coherent history of the development and implementation of nonequilibrium molecular dynamics simulations to one rather limited but immensely practical subject area, that of shear flows of linear, monodisperse alkane and polyethylene liquids. The development of accurate potential models to describe the energetic interactions between methyl and methylene groups is discussed at length from a historical perspective, as pertaining to the evolution of realistic united-atom models used in contemporary simulations. Molecular dynamics methodology is presented as relevant to the limited subject matter of the Review. Most importantly, the results of simulations tracing back 50 years are summarized for relevant published works known to the authors, building over time a coherent history of the subject and delineating the major impacts of the combined body of work on the field of polymer rheology, 50 years after its inception. [ABSTRACT FROM AUTHOR]

A morphology and viscoelastic behavior of a wide range of in‐reactor blends (RBs) on the base of ultrahigh molecular weight polyethylene (UHMWPE) with Mw = 1000 kg mol−1 and polymer fractions of different microstructure were investigated to develop the understanding of relationships between the structure and properties of polyolefin materials. Linear low‐molecular weight polyethylene of high density (LMWPE) with Mw = 160 kg mol−1 as well as ethylene/1‐hexene copolymers (CEH‐n) containing from 3 to 19 mol% of 1‐hexene were used as the components of RBs. In‐reactor blends UHMWPE/CEH‐n and UHMWPE/LMWPE with a varied content of CEH‐n or LMWPE fractions were prepared in the two‐step polymerization processes of ethylene homo‐ and copolymerization over metallocene catalyst. It was found by the methods of differential scanning calorimetry (DSC) and Wide Angle X ray Scattering (WAXS) methods, that the percentages of crystalline and amorphous phases and the lamella sizes in the materials depend on the nature and amount of modifying polymer fractions. Linear dependences of α‐relaxation temperature on the lamella sizes in crystalline phase and β‐relaxation temperature on the density of butyl branches in copolymer fractions of in‐reactor blends UHMWPE/CEH‐n were found by the method of dynamic mechanical analysis (DMA) method. The mechanisms of the processes of α‐ and β‐relaxations in the in‐reactor blends including polymer fractions with different microstructure are discussed. [ABSTRACT FROM AUTHOR]