Search

The determination of molar masses and their distributions is crucial in polymer synthesis and design. This work presents the current performance and limitations of diffusion-ordered spectroscopy (DOSY) on a low-field (benchtop) NMR spectrometer (at 90 MHz) as an alternative to size exclusion chromatography (SEC) for determining diffusion coefficient distributions (DCDs) and molar mass distributions (MMDs). After optimization for narrowly distributed homopolymers, MMDs obtained with inverse Laplace transformation (ILT) and log-normal distribution are compared with average molar masses obtained with mono- and bi-exponential fits, as well as MMDs obtained from SEC. This approach enables ILT to determine DCDs and MMDs even for bimodal homopolymers with fully spectrally overlapping signals and block copolymers with various chemical compositions, for which chemical composition profiles are determined. The feasibility of low-field diffusion NMR with samples dissolved in non-deuterated solvents is further demonstrated and methods for solvent suppression are discussed., (© 2024 The Author(s). Macromolecular Rapid Communications published by Wiley‐VCH GmbH.)

This article presents a fast, straightforward synthesis approach to polymerize alternating multiblock copolymers, ultra-high molecular weight (UHMW) (homo)polymers as well as precursors for complex macromolecular topologies such as comb or barbwire architectures. The one-pot synthesis strategy proposed in this work is based on anionic polymerization via a bifunctional initiator and the subsequent linking of macro dianions with a bifunctional linker, additionally overcoming the limitations associated with the monomer reactivity. Thus, the synthetic route guarantees the repeating size of polymer blocks and an equal distribution of functional groups in precursors for complex topologies. Dianions of polystyrene (PS), polyisoprene-b-polystyrene-b-polyisoprene, and poly-2-vinylpyridine-b-polystyrene-b-poly-2-vinylpyridine are linked with α , α ' -dibromo-para-xylene to UHMW and multiblock copolymers. Multiblock copolymers with on average up to 50 well-defined alternating A and B blocks are accessible within 15 min., (© 2021 The Authors. Macromolecular Rapid Communications published by Wiley-VCH GmbH.)

Online chemically sensitive detectors for size exclusion chromatography (SEC) through coupled setups based on infrared (IR) (or NMR) spectrometers present new possibilities through unprecedented levels of polymer detail with respect to molecular weight and chemical composition. Herein, a new external cavity quantum cascade laser (EC-QCL) mid-IR spectrometer as a chemically sensitive online detector for SEC is custom-designed, built, and tested. This unique spectrometer features multiple broadly tunable EC-QCL sources, which can be operated in continuous wave and pulsed mode, accompanied with balanced liquid nitrogen cooled mercury cadmium telluride (MCT) detectors and a new custom-built transmission flow cell. Automated data analysis is done with a self-written MATLAB code. The limit of detection (LOD) is measured online, coupled with SEC chromatography, where on average, one carbonyl functionality in 530 000 g mol -1 at chromatographic conditions for SEC could be detected. It is possible to detect 0.46 µg (LOD) PMMA, which is approximately a factor of 30 lower than that reported for SEC-Fourier transform infrared., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The determination of molecular weight and correlated chemical composition is of major interest for the advanced analysis of copolymers, blends, or unknown samples. In this work, we present a new way of online coupling IR spectroscopy and SEC to achieve a chemically sensitive, universally applicable SEC detector. Our method overcomes the limitations of existing spectroscopy-SEC combinations. We solved the major problems, like huge intensity of solvent signals (polymer concentration in detector <1 g L(-1) ) and short measuring time (<30 s), by recording the IR spectra with fully optimized sensitivity and by following mathematical solvent suppression. The measuring time for a certain S/N was reduced in several optimization steps by a factor of more than 70 000. The resulting sensitivity allows online coupled IR-SEC measurements., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC-MR-NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table-top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online (1) H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. (1) H NMR spectra of PMMA and PS homopolymers as well as PS-PMMA block copolymers were of sufficient quality to enable detection and de-formulation of unknown polymer compounds. (1) H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC-MR-NMR combination., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The understanding of long chain branched homopolymer melts in shear flow is of significant interest to polymer science and critical to ensure stable processing. We report on the startup shear flow at a constant shear rate of well-defined pom-pom shaped polymer melts. Pom-poms consist of two stars covalently connected by a single backbone. For low-arm numbers and short arms, a single stress overshoot followed by a steady state is observed, similar to linear and star shaped melts. For one highly branched pom-pom with entangled branches, a double stress overshoot during the startup shear flow could be observed before reaching the steady state viscosity. Additionally, we find that the Cox–Merz rule, which relates the complex viscosity η * ω to the steady state shear viscosity η γ ̇ , fails at high-shear rates, if the backbone is not self-entangled. [ABSTRACT FROM AUTHOR]

Strain hardening of long-chain branched polymers in elongational flow occurs due to the stretch of the backbone chain between branch points. With an increasing number of side arms, the length of the backbone chain segment between two branch points of a comb decreases. Of particular interest is the case when the number Nb of arms per entanglement length of the polymer is larger than one. This leads not only to larger strain hardening but also to hyperstretching, i.e., the elongational stress growth shows an enhanced increase with strain. We consider elongational data reported by Abbasi et al. [Macromolecules 50(15), 5964–5977 (2017)] and Faust et al. [Macromol. Chem. Phys. 224(1), 2200214 (2023)] on a series of comb and branch-on-branch polystyrene (PS) melts with the average number Nb of branches per entanglement segment of the backbone ranging from Nb = 0.2 to Nb = 9.5. In addition, we present measurements of the elongational viscosity of two PS combs with Nb = 4.7 as well as of blends consisting of 5 to 50 wt. % of a PS comb and a monodisperse linear PS. Analysis by the hierarchical multimode molecular stress function model shows that while backbone chains of loosely grafted combs with Nb < 1 are stretched affinely in elongational flow, backbone chains of more densely grafted combs with Nb > 1 show increasing hyperstretching with increasing Nb. The elongational data of the comb/linear blends confirm that hyperstretching is an intrinsic property of the comb macromolecule with Nb > 1, independent of its concentration in the blend. While this is of considerable interest from a modeling point of view, hyperstretching causing an enhanced increase of the elongational stress growth can also have a significant impact on the processability of polymers, and quantification of this effect is, therefore, important. [ABSTRACT FROM AUTHOR]

The low melting points of solid polymer electrolytes (SPEs) based on the KTFSI electrolyte salt allow comparatively low operation temperatures (below 50 °C) for K‐ion batteries, unlike their Li or Na counterparts. Unfortunately, for this reason the electrolyte is also rendered mechanically unsuitable in its function to act as a cell separator. Therefore, in this work the use of inorganic nanofillers (Al2O3 and SiO2) is explored with the aim to improve rheological, thermal and cation transport properties of the resulting polymer composite electrolytes. Their electrochemical properties were further examined in K‐metal symmetrical cells and K‐metal/SPE/K2Fe[Fe(CN)6] cells and compared to corresponding liquid electrolyte systems. As a result of particle‐polymer interactions, filler‐containing SPEs showed higher degrees of crystallinity combined with filler polymer interaction and thus improved mechanical integrity in the relevant temperature range of 25–55 °C, while maintaining similar ionic conductivities than a filler‐free sample above the melting temperature. Although plating‐stripping experiments in symmetrical cell setups suggested high cell resistances for various compositions and in some cases even rapid cell failure, Al2O3‐based SPEs generally displayed high capacity retention when cycled against a positive electrode (here Prussian blue analogue K2Fe[Fe(CN)6]) over 100–160 cycles and possibly beyond. [ABSTRACT FROM AUTHOR]

The present study highlights a range of surface and volume extrudate patterns that can be detected during the extrusion flow of long‐chain branched polymers. Thus, four linear low‐density polyethylenes (LDPEs) have been extruded using a single‐screw extruder coupled to an inline optical imaging system. The selected LDPEs are selected to outline the influence of molecular weight and long‐chain branching on the types of melt flow extrusion instabilities (MFEI). Through the inline imaging system, space–time diagrams are constructed and analyzed via Fourier‐transformation using a custom moving window procedure. Based on the number of characteristic frequencies, peak broadness, and whether they are surface or volume distortions, three main MFEI types, distinct from those typically observed in linear and short‐chain branched polymers, are identified. The higher molecular weight, low long‐chain branching LDPEs exhibited all three instability types, including a special type volume instability. Independently of the molecular weight, higher long‐chain branching appeared to have a stabilizing effect on the transition sequences by suppressing volume extrudate distortions or limiting surface patters to a form of weak intensity type. [ABSTRACT FROM AUTHOR]

The nonlinear mechanical behavior of viscoelastic materials is modeled based on the Schapery integral model containing internal variables. In this context, a new approach for the strain‐dependent material properties is introduced considering a one‐dimensional formulation with strain‐dependent nonlinear functions for an oscillatory load case. In addition to the viscoelastic storage and loss modulus, the higher order harmonic oscillations in the stress response are computed and compared to experimental data from Fourier transform rheology of Polyamide 6 (PA6). The comparison reveals a good agreement between the predictions of the nonlinear model and the experimental data for the higher harmonic intensity I2/1. [ABSTRACT FROM AUTHOR]

The inverse vulcanization produces high sulfur content polymers from alkenes and elemental sulfur. Control over properties such as the molar mass or the solubility of polymers is not well established, and existing strategies lack predictability or require large variations of the composition. Systematic design principles are sought to allow for a targeted design of materials. Herein, we report on the inverse vulcanization of norbornenylsilanes (NBS), with a different number of hydrolysable groups at the silicon atom. Inverse vulcanization of mixtures of NBS followed by polycondensation yielded soluble high sulfur content copolymers (50 wt % S) with controllable weight average molar mass (MW), polydispersity (Đ), glass transition temperature (TG), or zero‐shear viscosity (η0). Polycondensation was conducted in the melt with HCl as a catalyst, abolishing the need for a solvent. Purification by precipitation afforded polymers with a greatly reduced amount of low molar mass species. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding polymer gelation over multiple length‐scales is crucial to develop advanced materials. An experimental setup is developed that combines rheological measurements with simultaneous time‐domain 1H NMR relaxometry (TD‐NMR) techniques, which are used to study molecular motion (<10 nm) in soft matter. This so‐called low‐field RheoNMR setup is used to study the impact of varying degrees of crosslinking (DC) on the gelation kinetics of acrylic acid (AAc) and N,N′‐methylene bisacrylamide (MBA) free radical crosslinking copolymerization. A stretched exponential function describes the T2 relaxation curves throughout the gelation process. The stretching exponent β decreases from 0.90 to 0.67 as a function of increasing DC, suggesting an increase in network heterogeneity with a broad T2 distribution at higher DC. The inverse correlation of the elastic modulus G′ with T2 relaxation times reveals a pronounced molecular rigidity for higher DC at early gelation times, indicating the formation of inelastic, rigid domains such as crosslinking clusters. The authors further correlate G′ with the polymer concentration during gelation using a T1 filter for solvent suppression. A characteristic scaling exponent of 2.3 is found, which is in agreement with theoretical predictions of G′ based on the confining tube model in semi‐dilute entangled polymer solutions. [ABSTRACT FROM AUTHOR]

The fatigue behavior of 28 amorphous and semi‐crystalline thermoplastic polymers and elastomers is tested under strain controlled sinusoidal tension‐tension (TT) and torsion (T) at room temperature and analyzed via strain‐life (total strain amplitude versus fatigue lifetime) and crack propagation rate versus total strain amplitude curves, analogous to Paris' law. Investigating fatigue is extremely time‐ and resources consuming, so universal relationships between the exponents of the strain‐life power‐law and material properties are of high importance. For a brittle failure mechanism (I), the strain‐life curves are found to have fixed exponents of BTT,I = −0.27 and BT,I = −0.22, respectively, while the crack propagation versus strain amplitude in TT has an exponent of mda/dN,I = 4. For ductile failure (II), fixed strain‐life curve exponents in TT of BTT,II = −0.35 and in torsion of BT,II = −0.48 with mda/dN,II = 2.8 are obtained. In torsion, most semi‐crystalline polymers show brittle and ductile failure depending on the applied strain amplitude, so the strain‐life curve exponent changes accordingly. The universal exponents for strain‐life and crack growth‐strain amplitude curves offer a significant simplification to rapidly estimate, predict, and simulate the fatigue behavior of polymers. [ABSTRACT FROM AUTHOR]

A Capillary Break-up Extensional Rheometer (CaBER) was modified to enable measurements of the axial force in combination with the related displacement. This makes it possible to determine the separation energy W s e p N , the tackiness, of a polymer solution between two parallel plates with the CaBER. Separation energies of solutions of linear polystyrene, comb polystyrene and linear poly(methyl methacrylate) in dimethylformamide were measured as model systems. For linear polymers at a critical polymer concentration, there was a drastic change in slope of the separation energy W s e p N c . This critical concentration was shown to be the minimum concentration at which continuous bead-free fibers could be electrospun. [ABSTRACT FROM AUTHOR]

The transient shear and extensional properties of ethylene vinyl acetate nanocomposites containing two geometrically different nanoparticles (spheres of CaCO3 and platelet of clay) were investigated experimentally and the data were compared to the rheological predictions of the modified molecular stress function (MSF) theory as recently proposed by Abbasi et al. [Rheol. Acta 51, 163-177 (2012)]. While good agreement was obtained for spherical particles, deviations were observed for platelet particles at concentrations higher than 2.5 wt. %. The limitation of MSF theory for such compositions was related to the domination of the linear rheological response by the presence of particle nanonetworks over polymeric chains' contribution. This particle network contribution was also found to increase nonlinearity under large deformation, a phenomenon which was quantified via Fourier transformed rheology on data obtained under large amplitude oscillatory shear. [ABSTRACT FROM AUTHOR]

Following a theoretical proposal [M. Farhat et al., Phys. Rev. Lett. 103, 024301 (2009)], we design, fabricate, and characterize a cloaking structure for elastic waves in 1 mm thin structured polymer plates. The cloak consists of 20 concentric rings of 16 different metamaterials, each being a tailored composite of polyvinyl chloride and polydimethylsiloxane. By using stroboscopic imaging with a camera from the direction normal to the plate, we record movies of the elastic waves for monochromatic plane-wave excitation. We observe good cloaking behavior for carrier frequencies in the range from 200 to 400 Hz (one octave), in good agreement with a complete continuum-mechanics numerical treatment. This system is thus ideally suited for demonstration experiments conveying the ideas of transformation optics. [ABSTRACT FROM AUTHOR]

Studying the mechanical response of nearly monodisperse linear and comb polystyrene (PS) melts to medium amplitude oscillatory shear (MAOS), Hyun and Wilhelm [Macromolecules 42, 411 (2009)] identified two important scaling relations: (1) The relative intensity I3/1 of the third harmonic compared to the first harmonic scales with the strain amplitude according to γ02. Consequently, a new nonlinear coefficient Q≡I3/1/γ02 as well as the so-called intrinsic nonlinearity Q0≡limγ0→0 Q was introduced. (2) In the terminal relaxation regime, the intrinsic nonlinearity Q0(ω) scales with ω2 and was found to be a very sensitive measure regarding molecular topology by identifying and separating relaxation processes in model branched polymers. A constitutive analysis based on a general single integral constitutive equation, which includes the Doi-Edwards model without (DE) and with (DE IA) independent alignment assumption as well as the molecular stress function (MSF) model, confirms both scaling relations. We show that the nonlinear viscoelastic moduli can be expressed as sums of their linear-viscolelastic counterparts at frequencies of ω, 2ω, and 3ω. The absolute value of Q0(ω) depends on the difference (α-β) between the third order orientational effect (parameter α) according to the DE or DE IA model and the second order isotropic stretching effect (parameter β) according to the MSF model. When comparing MAOS data to constitutive models, the apparent values of Q0(ω) measured in parallel-plate geometry have to be rescaled in order to take the non-uniform shear deformation into account. Both the DE and DE IA models fail to describe the experimental data. The data of four linear PS melts are quantitatively described by the MSF model with nonlinear parameters α=5/21 (corresponding to the DE IA model) and β=0.12 in the terminal relaxation regime. For the comb polymers, with the same orientational parameter of α=5/21, stretch parameters of β=0.14 for a polymer with unentangled branches and of β=0.18 for two polymers with entangled branches are found. However, the model predicts a plateau at the level of the maximum of the experimental data, while the experimental values of Q0 decrease with increasing frequency. For the comb polymers with entangled branches, a minimum in Q0 is observed, and a second increase of Q0 at higher frequencies, which correspond to the terminal relaxation times of the branches. Surprisingly, these features can be modeled quantitatively if only the terminal relaxation modes of the backbone and, if present, the branches are assumed to deforming non-affinely and responding to the nonlinearity. The shorter modes seem to be deforming affinely and are excited only in the regime of finite linear viscoelasticity. We are presently not aware of any molecular mechanism that could explain this behavior. [ABSTRACT FROM AUTHOR]

• Analysis of the stress of fatigue in tension/tension via Fourier transform. • Quantification of mechanical nonlinearity during mechanical fatigue of polymers. • Fatigue criteria and lifetime prediction based on nonlinear mechanical parameters. • Better statistics of the nonlinear fatigue prediction than the Wöhler curves. • Fracture fingerprints in the evolution of the mechanical nonlinearity. The fatigue behavior of polystyrene (PS) and polymethylmethacrylate (PMMA) in tension/tension (T/T) was investigated under strain control measurements. During testing, the stress was continuously analyzed via Fourier transform (FT) and decomposed into linear and nonlinear contributions as higher harmonics were related to fatigue, crack initiation and propagation, as well as failure. Dumbbell and notched rectangular samples were submitted to different deformation ratios and the results showed that the lifetime can be well predicted by the rate of change of the first odd higher harmonic and the cumulative nonlinearity parameter. Fingerprints due to crack initiation and propagation were found in the higher harmonics and correlated to failure analyzed via microscopy, as well as to plastic deformation depending on the deformation ratio. This work shows that fatigue analysis via higher harmonics of the stress obtained by FT can be applied to a wide range of samples and conditions, with a higher predictive power than Wöhler curves, since the standard deviations are lower. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate the global polymer chain motion under large amplitude oscillatory shear (LAOS), the dielectric properties under LAOS are measured by a new rheo-dielectric combination. The design of the rheo-dielectric setup including a new fixture and modified oven is explained in detail. For 1,4-cis-polyisoprene, having type-A dipoles parallel to the backbone, the dielectric dipoles can detect the global polymer chain motion via the end-to-end vector. Thus rheological and dielectric (rheo-dielectric) properties reflect the dynamics of the polymer chain motion under LAOS. In this study, we investigate the rheo-dielectric properties under LAOS with 1,4-cis-polyisoprene as model component. As the strain amplitude was increased under LAOS, the relaxation strength from dielectric properties decreased for the whole spectra without changing the shape of the dielectric spectra. These results are analyzed on the basis of the molecular model of dynamic tube dilation (DTD) induced by the convective constraint release (CCR). It is found that the global chain motion under LAOS flow is affected by both rheological frequency and strain amplitude. It is also observed that segmental motion is affected via the oscillatory frequency under LAOS. This result differs from experiments under steady shear. [Copyright &y& Elsevier]