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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 elongational rheology of blends of a polystyrene (PS) Pom-Pom with two linear polystyrenes was recently reported by Hirschberg et al. (J. Rheol. 2023, 67:403–415). The Pom-Pom PS280k-2x22-22k with a self-entangled backbone (Mw,bb = 280 kg/mol) and 22 entangled sidearms (Mw,a = 22 kg/mol) at each of the two branch points was blended at weight fractions from 75 to 2 wt% with two linear polystyrenes (PS) having Mw of 43 kg/mol (PS43k) and 90 kg/mol (PS90k), respectively. While the pure Pom-Pom shows strong strain hardening in elongational flow (SHF > 100), strain hardening (SHF > 10) is still observed in Pom-Pom/linear blends containing only 2 wt% of Pom-Pom. The elongational start-up viscosities of the blends with Pom-Pom weight fractions above 10 wt% are well described by the Molecular Stress Function (MSF) model, however, requiring two nonlinear fit parameters. Here we show that quantitative and parameter-free modeling of the elongational viscosity data is possible by the Hierarchical Multi-mode Molecular Stress Function (HMMSF) model based on the concepts of hierarchical relaxation and dynamic dilution. In addition, we investigated the elongational viscosity of a blend consisting of 20 wt% Pom-Pom PS280k-2x22-22k and 80 wt% of a PS star with 11 arms of Mw,a = 25 kg/mol having a similar span molecular weight as PS43k and similar Mw,a as the Pom-Pom. This work might open up possibilities toward polymer upcycling of less-defined polymers by adding a polymer with optimized topology to gain the intended strain hardening, e.g., for film blowing applications. [ABSTRACT FROM AUTHOR]

The influence of topology on the strain hardening in uniaxial elongation is investigated using monodisperse comb and dendrigraft model polystyrenes (PS) synthesized via living anionic polymerization. A backbone with a molecular weight of Mw,bb = 310 kg mol−1 is used for all materials, while a number of 100 short (SCB, Mw,scb = 15 kg mol−1) or long chain branches (LCB, Mw,lcb = 40 kg mol−1) are grafted onto the backbone. The synthesized LCB comb serves as precursor for the dendrigraft‐type branch‐on‐branch (bob) structures to add a second generation of branches (SCB, Mw,scb ≈ 14 kg mol−1) that is varied in number from 120 to 460. The SCB and LCB combs achieve remarkable strain hardening factors (SHF) of around 200 at strain rates greater than 0.1 s−1. In contrast, the bob PS reach exceptionally high SHF of 1750 at very low strain rates of 0.005 s−1 using a tilted sample placement to extend the maximum Hencky strain from 4 to 6. To the best of the authors' knowledge, SHF this high have never been reported for polymer melts. Furthermore, the batch foaming with CO2 is investigated and the volume expansions of the resulting polymer foams are correlated to the uniaxial elongational properties. [ABSTRACT FROM AUTHOR]

Polymer topology highly impacts rheological melt and foaming properties. Grafting sidechains onto a linear polymer typically results in shear thinning and strain hardening in elongation flow. To study the influence of an increasing number of covalently connected polystyrene (PS) stars s with a linear PS chain (Mw,PS = 90 kg mol−1), low‐disperse branched polymers with s ranging from one to four are synthesized. Each star contains approximately 12 sidechains with a length of Mw,a≈ 25 kg mol−1. Oscillatory shear measurements indicated that the zero‐shear viscosity η0 scales with η0 ≈ Mw,t3.9$M_{w,t}^{3.9}$ at Tref = 180 °C. Moreover, uniaxial elongation rheology allows determining the strain hardening factor SHF, which varies between SHF = 2–135, with increasing s. Foaming experiments revealed that combining viscosity reduction with the improvement of stretchability promotes higher volume expansion ratios (VER = 3.21–10.41) and the formation of larger cells (D = 4.8–14.8 µm). [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]

ABSTRACT: This study proposes a new concept for the lifetime prediction of solid polymers under mechanical fatigue. The time evolution of linear and nonlinear mechanical parameters was studied using polystyrene (PS), polymethylmethacrylate (PMMA), and styrene‐acrylonitrile (SAN) samples in strain controlled (large amplitude) oscillatory shear (torsion). Higher harmonics of the stress were detected and quantified via Fourier transform (FT). Besides storage and loss modulus (G′, G″), the ratio of the third (I3) harmonic over the fundamental one, I1 (I3/1), was analyzed. After an initial transient period (regime I), the three parameters (G′, G″, and I3/1) linearly de/increase with the cycle number (N) (regime II) before failure onset (regime III) occurs. In regime II, the absolute values of the rates of change (derivative) of G′, G″, and I3/1 (dG′/dN, dG″/dN, and dI3/1/dN) were correlated with the lifetime (Nf). An inverse proportionality between the rate of change and lifetime was found allowing better prediction while testing. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46634. [ABSTRACT FROM AUTHOR]

The fatigue behavior of polystyrene (PS) in strain controlled torsion rectangular oscillatory tests was analyzed via Fourier transform (FT) to better understand the time evolution of linear and nonlinear mechanical parameters, and to establish fingerprints related to failure onset. The tests were performed under large amplitude oscillatory shear (LAOS), so the stress response was no longer perfectly sinusoidal and higher harmonics could be detected and quantified in the FT spectra as a function of time or number of cycles N . A linear parameter, the storage modulus ( G′(N) ), was analyzed, as well as nonlinear parameters of the ratios of the second ( I 2 (N) ) and the third ( I 3 (N) ) harmonics over the fundamental one ( I 1 (N) ). The nonlinear parameter I 2/1 (N) is very low for undamaged samples, but its intensity was found to increase when defects were created in the structure to a point where cracks became visible in the sample. On the other hand, the I 3/1 (N) parameter increased steadily during a test up to a local maximum where a macroscopic crack occurs in the sample. Both parameters I 2/1 (N) and I 3/1 (N) are proposed as new criteria to detect the onset of part failure under the conditions tested and can be used as safety limits for partial damage. [ABSTRACT FROM AUTHOR]

Polystyrene solutions in CDCl3 were examined by different NMR techniques. Diffusion measurements and spectrally resolved frequency-dependent 1H longitudinal relaxation studies give some insight into the complex molecular motional modes and their frequency dependence, that is, the dispersion of the longitudinal relaxation rate. The newly available spectral resolution at low magnetic field around 20 MHz 1H-Larmor frequency additionally allows the differentiation of aliphatic and aromatic spectral contributions and, therefore, a more detailed description of the molecular mobility in the frequency range of several MHz compared to the well-known time-domain or field-cycling NMR studies. [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]

polystyrene- b-poly-4-vinypyridine (PS- b-P4VP) diblock copolymer is modified with a gold precursor to obtain an organic-inorganic (hybrid) block copolymer in bulk with gold nanoparticles selectively incorporated in the P4VP block. In the linear viscoelastic regime, temperature sweep tests over a series of these hybrid block copolymer systems revealed consistent shifts (Δ T) in the glass transition temperatures (both T $_{\rm g\text{-}PS}$ and T $_{\rm g\text{-}P4VP}$) of the hybrid materials in comparison to the pristine polymers. Studying different volume fractions of the pyridine block, a level-off point was found for block copolymers with f > 0.26, where the shifts in T $_{\rm g\text{-}P4VP}$ consistently increased up to Δ T = 25°C. By artificially increasing the volume fraction of the pyridine block, the nanoparticles reduce the transition regime determined in master curves. At higher volume fractions of the pyridine block, crossover frequencies were not detected after the entanglement regime, indicating that the material does not relax from topological constraints (entanglements and nanoparticles) into the terminal regime. Above a specific volume fraction of nanoparticles ( Φ = 0.05), the flow behaviour of the hybrid materials becomes increasingly elastic, exhibiting wall-slip from the geometry at lower strain values in comparison to the pristine material. In the non-linear viscoelastic regime, Fourier-transformed rheology was used to analyse the raw signals from strain sweep experiments. It was clearly demonstrated the nanoparticle effect by following the second and third harmonic ( I, I) of the stress response. Comparing the behaviour of the third and second harmonics provided an unambiguous fingerprint for the effect of the nanoparticles. [ABSTRACT FROM AUTHOR]

Linear and nonlinear rheological properties of model comb polystyrenes (PS) with loosely to densely grafted architectures were measured under small and medium amplitude oscillatory shear (SAOS and MAOS) flow. This comb PS set had the same length of backbone and branches but varied in the number of branches from 3 to 120 branches. Linear viscoelastic properties of the comb PS were compared with the hierarchical model predictions. The model underpredicted zero-shear viscosity and backbone plateau modulus of densely branched comb with 60 or 120 branches because the model does not include the effect of side chain crowding. First- and third-harmonic nonlinearities reflected the hierarchy in the relaxation motion of comb structures. Notably, the low-frequency plateau values of first-harmonic MAOS moduli scaled with M w − 2 (total molecular weight), reflecting dynamic tube dilution (DTD) by relaxed branches. Relative intrinsic nonlinearity Q0 exhibited the difference between comb and bottlebrush via no low-frequency Q0 peak of bottlebrush corresponding to backbone relaxation, which is probably related to the stretched backbone conformation in bottlebrush. [ABSTRACT FROM AUTHOR]

The effect of the molecular architecture of a series of anionically synthesized linear and comb atactic polystyrenes (PS) on their foam properties including cell size, cell density, and volume expansion ratio (V.E.R.) was investigated. The comb-PS had the same molecular weight of the backbone, M w,bb ≈ 290 kg/mol, Z bb ≈ 20 entanglements, and branches, M w,br ≈ 44 kg/mol, Z br ≈ 3 entanglements, but different numbers of branches, 3 ≤ N br ≤ 190. Batch foaming of well-purified linear and comb-PS using CO 2 resulted in cell densities about 109 and 4 × 109 cell/cm3, respectively, which shows that LCB has no distinct effect on the cell density, whereas a small amount of residual impurity in linear PS reduced the cell density to ~108 cell/cm3. For a comb-PS series with the same entangled backbone, M w,bb ≈ 290 kg/mol, Z bb ≈ 20 entanglements, and similar branches, M w,br ≈ 44 kg/mol, Z br ≈ 3 entanglements, but different numbers of branches, 3 ≤ N br ≤ 190, an increase in the N br to 120 with densely grafted comb conformation gradually increased the highest achievable V.E.R. close to a theoretical limit given by the CO 2 solubility. The further increase of N br to 190 with a bottlebrush conformation reduced the V.E.R. of the foam. From a rheological point of view, this optimum N br was related to a comb-PS which showed the maximum strain hardening factor (SHF ≈ 200) in uniaxial extension, and simultaneously the minimum in the zero shear viscosity, η 0. The optimum N br = 120 for this comb-PS series corresponds to an average spacing distance between two neighbor branch points of about Z s ≈ 0.2 entanglements. Image 1 • Long chain branched comb-PS improve foamability at elevated temperatures. • Maximum strain hardening factor is related to highest achievable volume expansion. • Low zero shear viscosity does not affect foamability in case of strain hardening. • Strain hardening in later foaming stage outweighs the effect of low viscosity. • Densely grafted comb conformation achieve 90% foaming efficiency up to V.E.R. = 40. [ABSTRACT FROM AUTHOR]

The effect of the molecular architecture of anionically synthesized linear and comb atactic polystyrenes (PS), as well as lab-scale emulsion polymerized PS and commercial PS on the cell density of foam (number of cells per unit volume of neat polymer) was investigated using CO 2 as foaming agent in a batch foaming setup. The effects of molecular weight, M w , dispersity (Ð), low molecular weight components, i.e. oligomers and residual surfactant, and the number of long chain branches per molecule, N br , in a series of comb-PS with the same entangled backbone, M w,bb ≈ 290 kg/mol, Z bb ≈ 20 entanglements, and similar branches, M w,br ≈ 44 kg/mol, Z br ≈ 3 entanglements, but different numbers of branches, 3 ≤ N br ≤ 190, on the cell density were investigated. Specimens for foaming have been prepared with three different methods, which resulted in non-purified, treated, and purified samples. Well-purified samples produced foams with cell density above 109 cell/cm3, while foams out of the non-purified PS had one to three orders of magnitude lower cell density. However, artificial addition of 6 wt% oligomer PS or 3 wt% surfactant to the purified samples did not reduce the cell density significantly. Treated samples prepared by only dissolving the PS in a solvent followed by removing the solvent, produced a foam with slightly lower cell density, ~5 × 108 cell/cm3, than the purified PS. Lower cell density in non-purified PS was supposed to be related to the formation of a continuous ionic thin film layer (e.g. surfactant) rather than only the presence of low molecular weight components as impurity in the polymer. In the absence of such low molecular weight components, other molecular parameters, i.e. M w , Ð , and N br in these series of comb-PS had surprisingly no distinct effect on the cell density. Image 1 • Low cell density in commercial PS is related to formation of ionic thin film layer. • Presence of low molecular weight components has little effect on cell density. • Treatment and purification of commercial PS results in higher cell density. • Molecular weight and dispersity has no effect on cell density of final foam. • Long chain branching in synthesized model comb PS slightly increases cell density. [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]

This paper investigates the influence of molecular properties (molecular weight, polydispersity (PDI) and molecular weight distribution (MWD)) on the mechanical fatigue of model systems of anionic synthesized polystyrene (PS, low PDI), their blends (bimodal MWD) and commercial PS (broad PDI) under strain-controlled oscillatory shear (torsion). A power-law relation between lifetime N f and strain amplitude γ 0 (Wöhler curve) was found, with the exponent independent, but the pre-factor highly dependent on molecular characteristics. Additionally, nonlinear changes of the stress response, due to ongoing fatigue, were quantified via Fourier Transform (FT), to analyze besides the storage modulus G′ , the intensities of the second ( I 2 ) and third ( I 3 ) harmonics over the fundamental one ( I 1 ). The behavior of G′ and I 3/1 was found to depend on molecular properties, with I 3/1 being more sensitive to failure onset than G′ , while an increase of I 2 / 1 above the noise level could be correlated with the occurrence of macroscopic cracks. [ABSTRACT FROM AUTHOR]

Monodisperse comb polystyrenes (comb-PS) with loosely to densely grafted architectures up to loosely grafted bottlebrush structures were synthesized via anionic polymerization. This comb-PS series, named PS290-Nbr-44, had the same entangled backbone, Mw,bb = 290 kg/mol, corresponding to a number of entanglements along the backbone Zbb ≅ 20, and similar branch length, Mw,br ≅ 44 kg/mol or Zbr ≅ 3, but varied in the number of branches per molecule, Nbr, from 3 to 190 branches. Consequently, the average number of entanglements between two consecutive branch points along the backbone (branch point spacing), Zs, ranged from well entangled, Zs ≅ 5, to values that were far less than one entanglement, Zs ≅ 0.1. Linear viscoelastic data including the zero-shear rate viscosity, η0, diluted modulus, GN,s0, and a new diluted modulus extracted from the van Gurp-Palmen plot, |G*| at δ = 60°, were analyzed as a function of the Mw of the combs. Scaling of η0 versus Mw revealed three different regions for increasing Nbr or decreasing Zs: (1) loosely grafted combs with Zbr < Zs and η0 ~ exp(Mw), (2) densely grafted combs with 1 < Zs < Zbr and η0 ~ Mw-3.4 followed by η0 ~ Mw-1 for 0.2 < Zs < 1, and (3) loosely grafted bottlebrushes with Zs < 0.2 and η0 ~ Mw5. The relative maximum in η0 corresponded to a comb-PS with Zs ≅ Zbr, and the relative minimum resulted from a comb-PS with Zs ≅ 0.2, which displayed almost the same η0 as the linear PS290. Strain hardening factors, SHF ≡ ηE,max/ηDE,max, measured in extensional experiments increased with increasing Nbr and reached SHF > 200 for Hencky strains below εH = 4, which is tremendously high and has to the best of our knowledge not been observed yet. Such a high strain hardening is of great fundamental and technical importance in extensional processes, e.g., foaming, film blowing, or fiber spinning. [ABSTRACT FROM AUTHOR]

• Comparative characterization of SPEs with ATFSI (A = Li, Na and K) is provided. • Microphase-separated copolymer with polystyrene block yields a rigid polymer matrix. • Total ionic conductivities in Li-, Na- and K-SPEs approached similar values. • Reliable transference numbers (T A +) are difficult to quantify for Na- and KTFSI-SPEs. • KTFSI-SPE retains 94% of capacity over 100 cycles in K-metal/SPE/cathode cell. Liquid electrolytes (LEs) commonly show severe side reactions at the electrode-electrolyte interface, especially with alkali metal anodes, leading to rapid capacity fade of metal-ion batteries. Solid polymer electrolytes (SPEs), however, contribute to the suppression of side reactions due to their inherent inertness and high mechanical strength, providing long-term stable battery operation. Herein, we investigated physical and electrochemical properties of SPEs based on our previously reported microphase-separated poly(vinyl benzyl methoxy poly(ethylene oxide) ether)- block -polystyrene block copolymer (PVBmPEO- b -PS) with different alkali metal ions (A + = Li+, Na+ or K +) and their use in the respective metal batteries, showing the potential for the transition from lithium to post-lithium batteries. Rheological and thermal properties as well as ion transport in the SPEs with different bis(trifluoromethanesulfonyl)imide (TFSI) salts concentrations revealed similar shear storage moduli (G') for the investigated SPEs, while the lowest glass transition temperatures (T g) were found for KTFSI-based films. By contrast, the highest total ionic conductivity was found for the LiTFSI-based SPEs. To quantify the A + transference numbers (T A +), the Bruce-Vincent method and pulsed-field gradient (PFG) NMR were conducted, revealing significant challenges for T A + determination of post-Li systems. Further, the examination of the interfacial stability of SPE/A interfaces by conducting plating/stripping experiments revealed significantly higher resistances for sodium- and potassium-based systems in comparison to their lithium-based counterpart. Nonetheless, A-metal/SPE/cathode cells with PVBmPEO- b -PS-based Na- and K-SPEs with the Prussian Blue analogues (PBAs, Na 2- x Fe[Fe(CN) 6 ] and K 2- x Fe[F e (CN) 6 ]) positive electrodes and the respective alkali metal negative electrodes enabled cycling at elevated temperature of 55 °C. Herein, both sodium and potassium metal batteries exhibited stable cycling with capacity retentions of 73% over 100 cycles for the Na-cell, and 94% over the same cycle number for the K-cell, (and a high coulombic efficiency (CE) of 98% at the 100th cycle). [Display omitted] [ABSTRACT FROM AUTHOR]

The bead to bead-free fibers transition for electrospun filaments was investigated for well-defined linear and comb homopolymers. A series of monodisperse model comb structures with well-defined backbone and side chains was synthesized using anionic polymerization of polystyrene (PS). All model combs had the same backbone and a similar total molecular weight. The length and number of branches was varied, but the total number of monomers in the side chains was nearly constant. Solutions of these polystyrenes in N,N-dimethylformamide (DMF) were electrospun under identical conditions to determine the effect of molecular topology on the morphology of the fibers. The morphology and fiber diameter for all PS model polymers depended on the zero shear viscosity, η 0 . The comb solutions generally formed fibers at lower η 0 and the fibers had larger diameters compared with linear polystyrene. The bead to fiber transition occurred at substantially lower polymer concentrations for combs with fewer, but longer branches. [ABSTRACT FROM AUTHOR]

Well-defined, monodisperse homopolymercomb architectures withvaried number and length of the branches under linear and nonlineardeformation were synthesized and examined to determine the effectof branching on different rheological properties. The correlationof the rheological properties with the comb topology is of specialinterest for the determination of the degree of branching. Therefore,well-defined polystyrene-based comb polymers with systematically variednumber and molecular weight of the branches, narrow polydispersities,and a controlled, but low, number of branches (typically 0.1–1mol % branches per backbone) were synthesized and compared with datafrom polystyrene combs of the Roovers series that have a higher numberof branches (>1 mol % branches per backbone). To investigate therheologicalproperties in detail, various linear and nonlinear techniques wereapplied. Within the linear regime, the reduced van Gurp–Palmenplot (δ vs |G*|/GN0) was used to identify critical points that illustrated the influenceof the branch molecular weight and number of branches on the resultingrheological properties. In the nonlinear regime large amplitude oscillatoryshear (LAOS) measurements were performed to obtain the nonlinear parameter Q0(ω) via a quadratic scaling law fromFT-rheology. An intrinsic nonlinear master curve based on the Q0(ω) parameter reflected the relaxationhierarchy and was shown to be a sensitive method to extract informationon the different relaxation time scales. The nonlinear shear measurementswere complemented by uniaxial extensional measurements to quantifythe strain hardening effect and how the strain hardening was affectedby branch relaxation. The results obtained from the uniaxial extensionalmeasurements could be correlated to relaxation times obtained fromthe intrinsic nonlinear master curve Q0(ω). Pom-pom constitutive model predictions were performedfor the comparison with experimental data for extensional rheologywith focus on the strain hardening behavior and for LAOS with focuson the nonlinear parameter Q0(ω)as a function of increasing number and molecular weight of the branchesin the pom-pom molecule. A comparison of the applied rheological methods(1)small amplitude oscillatory shear (SAOS) in the linear regime, (2)LAOS in combination with FT-rheology, and (3) extensional rheologyin the nonlinear regimeillustrated the detection limits aswell as the advantages and disadvantages of each technique towardthe investigation of rare, but entangled branched comb polymer topologies. [ABSTRACT FROM AUTHOR]