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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]

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. [ABSTRACT FROM AUTHOR]

In response to nutrients, intestinal L‐ and K‐cells naturally secrete glucagon‐like peptide 1 (GLP‐1). GLP‐1 regulates postprandial blood glucose by increasing insulin secretion, slowing down gastric emptying and inducing satiety. A selection of specifically developed collagen hydrolysates was screened for their ability to enhance natural GLP‐1 production in vitro. The best performing hydrolysate, H80 (Nextida GC), was orally administered at different doses to lean, normoglycemic mice and overweight, prediabetic mice. Lean mice were acutely challenged 45 min before an oral glucose load. While daily supplemented for 6 weeks, prediabetic mice were acutely challenged at day 21 and 34. Oral glucose tolerance, plasma insulin and GLP‐1 levels were assessed, and a gastric emptying assay performed in prediabetic mice. H80 significantly lowered the blood glucose response in lean and prediabetic mice, at a 4 g/kg dose (−25% and −36%, respectively), compared to vehicle. In chronically supplemented, prediabetic mice, acute H80 administration slowed down gastric emptying (−60%) after 21 days and increased plasma insulin (+166%) after 35 days of supplementation. H80 increased plasma active GLP‐1 in lean (+217%) and prediabetic (+860%) mice. Overall, the data indicate that the specific collagen hydrolysate, H80, has significant GLP‐1‐mediated effects on oral glucose tolerance in lean and prediabetic mice. Furthermore, effects on postprandial glucose tolerance were evaluated in a small, human, proof of concept study. H80 reduced the postprandial glucose response at a 5 g dose in healthy, normoglycemic and prediabetic participants. Oral supplementation with H80 might thus be a promising strategy to maintain normal glucose tolerance. [ABSTRACT FROM AUTHOR]

Organogels are polymer networks extended by a liquid organic phase, offering a wide range of properties due to the many combinations of polymer networks, solvents, and shapes achievable through 3D printing. However, current printing methods limit solvent choice and composition, which in turn limits organogels' properties, applications, and potential for innovation. As a solution, a method for solvent‐independent printing of 3D organogel structures is presented. In this method, the printing step is decoupled from the choice of solvent, allowing access to the full spectrum of solvent diversity, thereby significantly expanding the range of achievable properties in organogel structures. With no changes to the polymer network, the 3D geometry, or the printing methodology itself, the choice of solvent alone is shown to have an enormous impact on organogel properties. As demonstrated, it can modulate the thermo‐mechanical properties of the organogels, both shifting and extending their thermal stability range to span from ‐30 to over 100 °C. The choice of solvent can also transition the organogels from highly adhesive to extremely slippery. Finally, the method also improves the surface smoothness of prints. Such advances have potential applications in soft robotics, actuators, and sensors, and represent a versatile approach to expanding the functionality of 3D‐printed organogels. [ABSTRACT FROM AUTHOR]

Lamellae forming polystyrene‐b‐poly‐2‐vinylpyridine diblock copolymer melts are investigated with linear shear rheology and Fourier transformation rheology (FT rheology) to quantify their nonlinear behavior under oscillatory shear via mechanical higher harmonic contributions such as I3/1(ω1, γ0). The determination of the zero‐shear nonlinearity (3Q0(ω)≡limγ0→0I3/1/γ02$^3Q_0(\omega)\equiv \lim _{\gamma _0 \rightarrow 0}I_{3/1}/\gamma _0^2$) by a variation of γ0 is hindered by the increasing domain alignment at increasing γ0. Thus, an approach for determining 3Q0(T) by a variation of the temperature is developed and used. This approach allows obtaining insights on the nonlinear behavior directly at temperature‐dependent phase transitions, such as at the order‐disorder transition temperature TODT of block copolymers. The maximum of 3Q0 is found to be close to TODT. The nonlinearity originating from the connection of the unequal polymer blocks is shown to dominate the overall nonlinearity, and the maximum of 3Q0(T) correlates to domain alignment for T < TODT. [ABSTRACT FROM AUTHOR]

3D printing technologies have matured to produce complex structures, still they are often limited to static materials. Introducing alkoxyamine bonds into 3D printed structures offers unprecedented possibilities for post‐synthetic modification through nitroxide exchange reaction and nitroxide‐mediated polymerization. This study provides a comprehensive molecular and macroscopic characterization of 3D‐printed alkoxyamine‐containing dynamic covalent adaptable networks. The study provides new insights into their dynamic structural and mechanical alterations, making them promising candidates for advanced applications ranging from biomedical engineering to flexible electronics. [ABSTRACT FROM AUTHOR]

Mechanical fatigue under strain controlled tension/tension (T/T) of rectangular un-notched and notched specimens of high density polyethylene and polyamide 6 was performed. Under large amplitude oscillatory elongation, the stress response is nonlinear asymmetric due to a different stress response during loading and unloading and was analyzed via discrete Fourier transform. Dynamic strain ([[epsilon].sub.0]) sweep tests revealed odd ([I.sub.3/1] [alpha] [[epsilon].sub.0.sup.2]) and even ([I.sub.2/1] [alpha] [[epsilon].sub.0.sup.1]) harmonics in the stress, well described by the Neo-Hooke's law. Before crack onset for the Nc specimens, the storage and loss moduli and [I.sub.2/1] are constant, but [I.sub.3/1] increases with fatigue. The first derivative of [I.sub.3/1] (([I.sub.3/1]/dN) and the cumulative nonlinearity [Q.sub.f] parameter (integral of [I.sub.3/1] /[[epsilon].sub.0.sup.2]) were found to be strong criteria predicting fatigue. To break the unnotched specimens in the low and high cycle fatigue regime, large strain amplitudes were applied, resulting for both materials in initial plastic deformation followed by buckling when a critical compression force is exceeded. This results in a different time evolution of the linear and nonlinear parameters, especially as a minimum in the [I.sub.2/1] curve. Finally, a model is proposed to describe the nonlinear viscoelastic specimen response under T/T and the effect of buckling. KEYWORDS buckling, mechanical fatigue, nonlinear stress response, plastic deformation, 1 | INTRODUCTION Failure of a part under a cyclic load or deformation is called mechanical fatigue break-up. It is typically characterized via the average applied stress ([[sigma].sub.0]) or the [...]

The steady-state shear viscosity η(γ̇)\eta (\dot{\gamma }) is required in controlling processing parameters for the extrusion processing of polymer melts. A new method, the so-called ramp test, is investigated in this study to obtain the steady-state shear viscosity with a closed cavity rheometer (CCR). To verify the method and the accuracy of the CCR data, three commercial polyolefin polymers, a low-density polyethylene (LDPE), a linear low-density polyethylene (LLDPE), and a polybutadiene (PBD), were used as model systems. Measurements of the magnitude of the complex viscosity ∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| were compared with the steady-state shear viscosity data obtained by capillary rheometer and CCR. Further, time–temperature superposition master curves of the magnitude of the complex viscosity and steady-state shear viscosity obtained by CCR were developed for LLDPE and PBD. The influence of the cavity sealing on the instrument’s accuracy to obtain the steady-state shear viscosity was investigated using the finite element method simulations. Thus, it was shown that the ramp test performed by CCR is a practical method to determine reliable and reproducible data of the steady-state shear viscosity within a wide range of temperatures (T = 50–180°C) for low and high viscous materials (∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| = 1.6–480 kPa s, M w = 144–375 kg mol−1).

Polymer gels, consisting of cross‐linked polymer network systems swollen by a solvent, show great potential in biomedicine, flexible electronics, and artificial muscles, due to their tissue‐like mechanical properties. Due to the presence of a large amount of solvent, the improvement of the mechanical properties of the polymer gel is a challenge. Moreover, combining high toughness with useful properties, such as 3D printability or shape‐memory, in one polymer gel system is even more challenging. In this study, a simple and efficient method is developed for the fabrication of tough polymer gels by polymerizing 2‐hydroxyethyl methacrylate (HEMA) in a mixture of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). The polymerized elastic networkpresents distinct compatibility with PEG (compatible) and PPG (poorly compatible), resulting in in‐situ phase separation at the microscale. The resulting phase‐separated gel demonstrates high strength (8.0 MPa), favorable fracture strain (430%), and large toughness (17.0 MJ m−3). The separated hard phasewith a high glass transition temperature (75 °C) endows the whole soft polymer gel with the property of shape memory at room temperature. Finally, the fabrication of tunable tough PEGgels is combined with 3D printing as well as with shape memory properties, demonstrating the use of PEGgels for 4D printing. [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]