| 1. |
- Allushi, Andrit, et al.
(author)
-
Polyfluorenes Bearing N,N-Dimethylpiperidinium Cations on Short Spacers for Durable Anion Exchange Membranes
- 2023
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:3, s. 1165-1176
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Journal article (peer-reviewed)abstract
- Alicyclic quaternary ammonium cations having all the β-protons in a strain-free ring structure are in general highly base resistant, and are thus very attractive to employ for anion exchange membrane (AEM) applications. However, tethering cations such as N,N-dimethylpiperidinium (DMP) to polymer backbones without introducing any weak links is quite challenging. In the present study, we have attached pairs of piperidine rings in their 4-position to fluorene and 2,7-diphenylfluorene via methylene bridges using straightforward SN2 reactions. These fluorenes were subsequently utilized as monomers in polyhydroxyalkylations to prepare poly(fluorene alkylene)s with different contents of the piperidine groups. AEMs were cast after quaternizing the piperidine groups to introduce DMP and spirocyclic 6-azonia-spiro-[5,5]undecane-6-ium (ASU) cations, respectively. The AEMs reached very high hydroxide ion conductivities, 100-156 mS cm-1 at 80 ºC, in the ion exchange capacity (IEC) range 1.8-2.4 mequiv. g-1. X-ray scattering showed ionomer peaks indicating ionic clustering with a characteristic distance d = 2.0-2.9 nm depending on IEC. The AEMs displayed high thermal stability, up to ~250 ºC, and 1H NMR data indicated no degradation after storage in 5 M aq. NaOH during 168 h at 90 ºC. However, degradation started under very severe conditions (10 M, 90 °C) with ~75% of the total ionic loss in all the AEMs assigned to Hofmann β-elimination. The overall results show that fluorene-based AEMs carrying DMP and ASU cations via methylene bridges display an attractive combination of ionic phase separation, thermal and chemical stability, and hydroxide conductivity.
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| 2. |
- Antlauf, Mathis, et al.
(author)
-
Thermal Conductivity of Porous and Dense Networks of Cellulose Nanocrystals
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:13, s. 5326-5331
-
Journal article (peer-reviewed)abstract
- Cellulose is a crystalline polymer with intriguing, amorphous-like, temperature dependence of thermal conductivity κ. To determine its origin, we have studied κ of cellulose nanocrystals (CNCs) derived from cotton by sulfuric acid hydrolysis, in both porous and nonporous states by pressure densification; κ increases weakly with increasing temperature and density, like in a fully amorphous material, and it is remarkably similar to that of cellulose fibers (CFs) and cellulose nanofibers (CNFs). For a powder derived from a natural material, like cellulose, amorphous-like κ may originate from poor thermal contact between particles or a high amorphous content, but the latter is not the case for CNCs. Moreover, the amorphous-like behavior is unaffected by densification and, therefore, improved thermal contacts. Instead, we attribute the behavior to CNCs' nanometer-sized fibrils, which limit the phonon mean free path to a few nanometers in a network of randomly oriented CNCs. This explains why κ is essentially the same in networks of CNCs, CFs, and CNFs, which are materials with the same structural unit-elementary fibrils of 3-5 nm in diameter. We obtain κ = (0.60 ± 0.01) W m-1 K-1 for a nonporous network of randomly oriented CNCs at 295 K and atmospheric pressure, and κ increases by only 14% GPa-1, which is unusually weak for a polymer. By using a model for such a network, we find κ = 1.9 W m-1 K-1 along a CNC and argue that this is a good estimate also along a CNF and a CF at room temperature.
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| 3. |
- Cederholm, Linnea, et al.
(author)
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Design for Recycling : Polyester- and Polycarbonate-Based A-B-A Block Copolymers and Their Recyclability Back to Monomers
- 2023
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:10, s. 3641-3649
-
Journal article (peer-reviewed)abstract
- Chemical recycling to monomers (CRMs) of A-B-Ablockcopolymers is governed by the chemical structure and thereby the thermodynamicbehavior of different block constituents. Here, we show how a thermodynamictoolkit based on a cyclic monomer structure and solvent propertiescan be utilized in the design of recyclable A-B-A blockcopolymers with varying material properties. By combining four cyclicmonomers lactide, epsilon-decalactone, 2,2-diethyltrimethylene carbonate,and trimethylene carbonate, three different block copolymers werecreated, suitable for different CRM scenarios. The chemical structureof the soft midblock (epsilon-decalactone or trimethylene carbonate)appeared to have a critical impact both on the ring-closing depolymerizationbehavior and mechanical properties, where changing from a polyesterto a polycarbonate soft block increased Young's modulus from14 to 200 MPa. Hence, this work demonstrates the complexity as wellas the opportunities in the design of macromolecular structures fora circular economy.
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| 4. |
- Chen, Yongzhen, et al.
(author)
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In Situ Spectroscopic and Electrical Investigations of Ladder-type Conjugated Polymers Doped with Alkali Metals
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:16, s. 7294-7302
-
Journal article (peer-reviewed)abstract
- Ladder-type conjugated polymers exhibit a remarkable performance in (opto)electronic devices. Their double-stranded planar structure promotes an extended pi-conjugation compared to inter-ring-twisted analogues, providing an excellent basis for exploring the effects of charge localization on polaron formation. Here, we investigated alkali-metal n -doping of the ladder-type conjugated polymer (polybenzimidazobenzophe-nanthroline) (BBL) through detailed in situ spectroscopic and electrical characterizations. Photoelectron spectroscopy and ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy indicate polaron formation upon potassium (K) doping, which agrees well with theoretical predictions. The semiladder BBB displays a similar evolution in the valence band with the appearance of two new features below the Fermi level upon K-doping. Compared to BBL, distinct differences appear in the UV-vis-NIR spectra due to more localized polaronic states in BBB. The high conductivity (2 S cm(-1)) and low activation energy (44 meV) measured for K-doped BBL suggest disorder-free polaron transport. An even higher conductivity (37 S cm(-1)) is obtained by changing the dopant from K to lithium (Li). We attribute the enhanced conductivity to a decreased perturbation of the polymer nanostructure induced by the smaller Li ions. These results highlight the importance of polymer chain planarity and dopant size for the polaronic state in conjugated polymers.
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| 5. |
- Delavari, Najmeh, et al.
(author)
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Water Intake and Ion Exchange in PEDOT:Tos Films upon Cyclic Voltammetry: Experimental and Molecular Dynamics Investigation
- 2021
-
In: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 54:13, s. 6552-6562
-
Journal article (peer-reviewed)abstract
- Conductive polymer PEDOT:Tos (3,4-ethylenedioxythiophene doped with molecular tosylate) gained considerable attention in various devices for bioelectronic applications, such as organic transistors and sensors. Many of these devices function upon oxidation/reduction processes in contact with aqueous electrolytes. So far, theoretical insight into morphological changes, ion injection, and water intake during these processes was rather limited. In the present work, we combined experiments and molecular dynamics simulations to study the water intake, swelling, and exchange of ions in the PEDOT:Tos film during cyclic voltammetry. We showed that the film underwent significant changes in morphology and mass during the redox processes. We observed both experimentally and in simulations that the film lost its mass during reduction, as tosylate and Na were expelled and gained mass during oxidation mainly due to the uptake of anions, i.e., tosylate and Cl. The results were in line with the UV-VIS-NIR absorption measurements and X-ray photoelectron spectroscopy (XPS) measurements, which revealed that during the redox process a portion of Tos was replaced by Cl- as the counterion for PEDOT. Also, the relative mass change between the most oxidized and reduced states was similar to 10 to 14% according to both experiments and simulations. We detected an overall material loss of the film during voltammetry cycles indicating that a portion of the material leaving the film during reduction did not return to the film during the consecutive oxidation. Our combined experimental/simulation study unraveled the underlying molecular processes in the PEDOT:Tos film upon the redox process, providing the essential understanding needed to improve and assess the performance of bioelectronic devices.
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| 6. |
- Ebadi, Mahsa, et al.
(author)
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Restricted Ion Transport by Plasticizing Side Chains in Polycarbonate-Based Solid Electrolytes
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:3, s. 764-774
-
Journal article (peer-reviewed)abstract
- Increasing the ionic conductivity has for decades been an overriding goal in the development of solid polymer electrolytes. According to fundamental theories on ion transport mechanisms in polymers, the ionic conductivity is strongly correlated to free volume and segmental mobility of the polymer for the conventional transport processes. Therefore, incorporating plasticizing side chains onto the main chain of the polymer host often appears as a clear-cut strategy to improve the ionic conductivity of the system through lowering of the glass transition temperature (T-g) This intended correlation between Tg and ionic conductivity is, however, not consistently observed in practice. The aim of this study is therefore to elucidate this interplay between segmental mobility and polymer structure in polymer electrolyte systems comprising plasticizing side chains. To this end, we utilize the synthetic versatility of the ion-conductive poly(trimethylene carbonate) (PTMC) platform. Two types of host polymers with side chains added to a PTMC backbone are employed, and the resulting electrolytes are investigated together with the side chain-free analogue both by experiment and with molecular dynamics (MD) simulations. The results show that while added side chains do indeed lead to a lower Tg, the total ionic conductivity is highest in the host matrix without side chains. It was seen in the MD simulations that while side chains promote ionic mobility associated with the polymer chain, the more efficient interchain hopping transport mechanism occurs with a higher probability in the system without side chains. This is connected to a significantly higher solvation site diversity for the Li+ ions in the side-chain-free system, providing better conduction paths. These results strongly indicate that the side chains in fact restrict the mobility of the Li+ ions in the polymer hosts.
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| 7. |
- Eriksson, Therese, 1992-, et al.
(author)
-
Carbonyl-Containing Solid Polymer Electrolyte Host Materials : Conduction and Coordination in Polyketone, Polyester, and Polycarbonate Systems
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:24, s. 10940-10949
-
Journal article (peer-reviewed)abstract
- Research on solid polymer electrolytes (SPEs) is now moving beyond the realm of polyethers that have dominated the field for several decades. A promising alternative group of candidates for SPE host materials is carbonyl-containing polymers. In this work, SPE properties of three different types of carbonyl-coordinating polymers are compared: polycarbonates, polyesters, and polyketones. The investigated polymers were chosen to be as structurally similar as possible, with only the functional group being different, thereby giving direct insights into the role of the noncoordinating main-chain oxygens. As revealed by experimental measurements as well as molecular dynamics simulations, the polyketone possesses the lowest glass transition temperature, but the ion transport is limited by a high degree of crystallinity. The polycarbonate, on the other hand, displays a relatively low coordination strength but is instead limited by its low molecular flexibility. The polyester performs generally as an intermediate between the other two, which is reasonable when considering its structural relation to the alternatives. This work demonstrates that local changes in the coordinating environment of carbonyl-containing polymers can have a large effect on the overall ion conduction, thereby also showing that desired transport properties can be achieved by fine-tuning the polymer chemistry of carbonyl-containing systems.
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| 8. |
- Giubertoni, Giulia, et al.
(author)
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Strong reduction of the chain rigidity of hyaluronan by selective binding of Ca2+ ions
- 2021
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:3, s. 1137-1146
-
Journal article (peer-reviewed)abstract
- The biological functions of natural polyelectrolytes are strongly influenced by the presence of ions, which bind to the polymer chains and thereby modify their properties. Although the biological impact of such modifications is well recognized, a detailed molecular picture of the binding process and of the mechanisms that drive the subsequent structural changes in the polymer is lacking. Here, we study the molecular mechanism of the condensation of calcium, a divalent cation, on hyaluronan, a ubiquitous polymer in human tissues. By combining two-dimensional infrared spectroscopy experiments with molecular dynamics simulations, we find that calcium specifically binds to hyaluronan at millimolar concentrations. Because of its large size and charge, the calcium cation can bind simultaneously to the negatively charged carboxylate group and the amide group of adjacent saccharide units. Molecular dynamics simulations and single-chain force spectroscopy measurements provide evidence that the binding of the calcium ions weakens the intramolecular hydrogen-bond network of hyaluronan, increasing the flexibility of the polymer chain. We also observe that the binding of calcium to hyaluronan saturates at a maximum binding fraction of ∼10–15 mol %. This saturation indicates that the binding of Ca2+ strongly reduces the probability of subsequent binding of Ca2+ at neighboring binding sites, possibly as a result of enhanced conformational fluctuations and/or electrostatic repulsion effects. Our findings provide a detailed molecular picture of ion condensation and reveal the severe effect of a few, selective and localized electrostatic interactions on the rigidity of a polyelectrolyte chain.
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| 9. |
- Guiver, Michael D., et al.
(author)
-
Gas Transport in a Polymer of Intrinsic Microporosity (PIM-1) Substituted with Pseudo-Ionic Liquid Tetrazole-Type Structures
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:20, s. 8951-8959
-
Journal article (peer-reviewed)abstract
- We report a side group modification strategy to tailor the structure of a polymer of intrinsic microporosity (PIM-1). PIM-1 with an average of similar to 50% of the repeat units converted to tetrazole is prepared, and a subsequent reaction then introduces three types of pseudo-ionic liquid tetrazole-like structures (PIM-1-ILx). The presence of pseudo-ionic liquid functional groups in the PIM-1 structure increases gas selectivities for O-2/N-2 and CO2/N-2, while it decreases pure-gas permeabilities. The overall gas separation performance of PIM-1-ILx is close to the 2008 Robeson upper bound. Since the tetrazoles are versatile groups for building a wide variety of ionic liquids, the modification method can be expanded to explore a broad spectrum of functional groups.
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| 10. |
- Huang, Jin, et al.
(author)
-
Correlation between Polymerization Rate, Mechanism, and Conformer Thermodynamic Stability in Urea/Methoxide-Catalyzed Polymerization of Macrocyclic Carbonates
- 2023
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:18, s. 7496-7504
-
Journal article (peer-reviewed)abstract
- A combined experimental and theoretical investigation revealed mechanistic differences in the ring-opening polymerization (ROP) behavior of macrocyclic carbonates (MCs, 11-membered to 15-membered MCs). The study employs urea and potassium methoxide as the catalytic system for ROP. Besides the polymerization rate correlating with the ring size, where smaller rings have a faster polymerization rate, both the thermodynamic stability of the conformer and the stability of the transition state affect the polymerization rate. An experimental kinetic evaluation revealed a deviation between the polymerization rate of the 11-membered MC and the rest of the MCs. Computational investigation using density functional theory showed that the thermodynamic stability of the 11-membered MC differs from others, with a population distribution more toward the usually less energetically disfavored (E,Z)conformer, while the larger rings showed a preference for the Z,Z-conformation. In the transition state, the (E,Z)-conformer was found to be lower in energy compared to the (Z,Z)-conformation, which leads to a lower Gibbs free energy of activation for nucleophilic attack on the (E,Z)-conformation (Delta G(+/-) = 18.3 kcal center dot mol(-1)) compared to macrocycles with the more stable (Z,Z)-conformation (19.8 kcal center dot mol(-1)). The rate-determining step for the 11-membered MC with (E,Z)-conformation relates to the nucleophilic addition, while the rate-limiting step for the larger 15-membered MC corresponds to the ring-opening step. Linking the thermodynamic conformer stability of cyclic monomers to their inherent polymerization behavior is essential for the future design of selective catalysts for ROP.
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| 11. |
- Huang, Jin, et al.
(author)
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Simple Approach to Macrocyclic Carbonates with Fast Polymerization Rates and Their Polymer-to-Monomer Regeneration
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:2, s. 608-614
-
Journal article (peer-reviewed)abstract
- Designing polymeric materials for closed-loop material streams is the key to achieving a circular society. Here, a library of macrocyclic carbonates (MCs) was designed by a facile and direct one-pot, two-step synthesis approach without the use of a solvent at a 10 g scale. We demonstrate that anionic polymerization with tert-butoxide enables the ultrafast ring-opening polymerization (ROP) of MCs with high conversion (>97%) within seconds (3-10 s) at ambient temperature. The polymerization rate depends on the odd or even number of methylene groups between the carbonate linkages in the MCs, and not the overall ring size, yielding an "odd-even" effect. This polymerization rate is related to the difference in molecular conformation of the MCs, as determined by X-ray crystallography. The polymers (polypenta-, hexa-, heptamethylene carbonate) were subsequently regenerated back to their original MCs at a high selectivity (95-99 mol %) and good yields (70-85%), hence taking a step toward closing the loop on these long alkyl chain polycarbonates.
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| 12. |
- König, Nico, et al.
(author)
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Spherical Micelles with Nonspherical Cores : Effect of Chain Packing on the Micellar Shape
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; , s. 10686-10698
-
Journal article (peer-reviewed)abstract
- Self-assembly of amphiphilic polymers into micelles is an archetypical example of a "self-confined"system due to the formation of micellar cores with dimensions of a few nanometers. In this work, we investigate the chain packing and resulting shape of Cn-PEOx micelles with semicrystalline cores using small/wide-angle X-ray scattering (SAXS/WAXS), contrast-variation small-angle neutron scattering (SANS), and nuclear magnetic resonance spectroscopy (NMR). Interestingly, the n-alkyl chains adopt a rotator-like conformation and pack into prolate ellipses (axial ratio ϵ ≈ 0.5) in the "crystalline"region and abruptly arrange into a more spheroidal shape (ϵ ≈ 0.7) above the melting point. We attribute the distorted spherical shape above the melting point to thermal fluctuations and intrinsic rigidity of the n-alkyl blocks. We also find evidence for a thin dehydrated PEO layer (≤1 nm) close to the micellar core. The results provide substantial insight into the interplay between crystallinity and molecular packing in confinement and the resulting overall micellar shape.
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| 13. |
- Liu, Chun-Yan, et al.
(author)
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Massively Parallel Aligned Poly(vinylidene fluoride) Nanofibrils in All-Organic Dielectric Polymer Composite Films for Electric Energy Storage
- 2023
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:4, s. 1481-1491
-
Journal article (peer-reviewed)abstract
- It is a formidable challenge to combine the perform-ance advantages of linear and nonlinear polymer dielectrics for developing all-organic film capacitors with high energy density and low loss. In this work, massively parallel aligned poly(vinylidene fluoride) (PVDF) nanofibrils were in situ fabricated for the first time in the polyethylene (PE) matrix via a multistage stretching technology involving hot stretching and solid-state stretching at an elevated temperature. The largely enhanced interfacial area of PVDF nanofibrils could effectively induce interfacial polarization, imparting PE composite films with a high dielectric constant of 4.50. More interestingly, the nanoconfinement effect of PVDF nanofibrils greatly restricted the migration of free electrons and impurity ions, and an impressive breakdown strength of 624 MV m-1 was obtained. As a result, the as-prepared PE/PVDF composite films exhibited an attractive discharged energy density of as high as 6.4 J cm-3, which was more than 10 times of the conventional counterparts, and outperformed the current linear dielectric polymers. The ingenious structure design of in situ nonlinear dielectric nanofibrils provides a promising approach to maximize the advantageous polarizations and minimize the disadvantageous polarizations in the linear and nonlinear polymer dielectric blends, achieving all-organic polymer dielectric composite films with high energy density and low loss.
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| 14. |
- Modarresi, Mohsen, et al.
(author)
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Microscopic Understanding of the Granular Structure and the Swelling of PEDOT:PSS
- 2020
-
In: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 53:15, s. 6267-6278
-
Journal article (peer-reviewed)abstract
- The conjugated polymer poly(3,4-ethylenedioxythiophene) polymerized and stabilized in the presence of polystyrenesulfonate (best known as PEDOT:PSS) is a working horse of organic electronics and bioelectronics and one of the most important conductive polymers. While its morphology is complex and depends on the details in synthesis and post-treatment, its distinctive and common feature is a two-phase granular structure attributed to PEDOT- and PSS-rich regions. Yet, there is still no well-established consensus concerning the precise nature of PEDOT- and PSS-rich regions as well as their chemical composition and structure. In this study we perform coarse-grained MARTINI molecular dynamics simulations of PEDOT:PSS focusing on understanding its two-phase morphology as well as water intake and ion exchange. We demonstrate that PEDOT:PSS is an essentially three-component system consisting of positively charged PEDOT chains, PSS chains with mostly deprotonated sulfonate groups, and protonated PSS chains. PEDOT-rich regions are predominantly composed of PEDOT and deprotonated PSS chains, whereas PSS-rich regions are composed of protonated PSS chains. Our calculations unravel how PEDOT-and PSS-rich regions are formed from the solution phase during the drying process. We show that when the dry polymer film is immersed in water, its swells by nearly 60%, and we demonstrate that the origin of swelling is related to deprotonation of the sulfonate groups in the PSS-rich regions. It is mostly PSS-rich regions that swell while the PEDOT-rich regions remain rather unchanged. We demonstrate that swelling of the film is rather insignificant during reduction/oxidation within the cyclic voltammetry (CV) conditions. We show that during CV experiments each counterion brings on overage approximate to 4 water molecules into the polymer region. Our simulations of swelling, CV experiments, and pi-pi stacking formation in PEDOT and PSS match well the experimental results. Our theoretical studies unravel the most important morphological aspects of one of the most important polymers for organic electronics, providing the essential insight needed for the material and device design and improvements.
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| 15. |
- Motezakker, Ahmad Reza, et al.
(author)
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Effect of Stiffness on the Dynamics of Entangled Nanofiber Networks at Low Concentrations
- 2023
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:23, s. 9595-9603
-
Journal article (peer-reviewed)abstract
- Biopolymer network dynamics play a significant role in both biological and materials science. This study focuses on the dynamics of cellulose nanofibers as a model system given their relevance to biology and nanotechnology applications. Using large-scale coarse-grained simulations with a lattice Boltzmann fluid coupling, we investigated the reptation behavior of individual nanofibers within entangled networks. Our analysis yields essential insights, proposing a scaling law for rotational diffusion, quantifying effective tube diameter, and revealing release mechanisms during reptation, spanning from rigid to semiflexible nanofibers. Additionally, we examine the onset of entanglement in relation to the nanofiber flexibility within the network. Microrheology analysis is conducted to assess macroscopic viscoelastic behavior. Importantly, our results align closely with previous experiments, validating the proposed scaling laws, effective tube diameters, and onset of entanglement. The findings provide an improved fundamental understanding of biopolymer network dynamics and guide the design of processes for advanced biobased materials.
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| 16. |
- Mousa, Maryam, et al.
(author)
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Biobased Lactones-Exploring Their Free-Radical Polymerization and Polymer Properties
- 2021
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:13, s. 6127-6134
-
Journal article (peer-reviewed)abstract
- Herein, we report the free-radical polymerization of the biobased alpha-methylene-gamma-butyrolactone and alpha-methylene-gamma-valerolactone, either into homopolymers or together with fossil-based (meth)acrylate monomers, methyl acrylate and methyl methacrylate in different ratios. The polymerization was thermally initiated by 2,2'-azobisisobutyronitrile or lauroyl peroxide to investigate their effect on the polymerization behaviors. Polymerizations were monitored by monomer conversion, and the final polymers were characterized with respect to molecular weight, composition, glass transition temperature, and thermal degradation. NMR showed significant differences in conversion rates of each monomer in the copolymerizations which suggest differences in reactivity ratios, sometimes to such an extent that the polymers exhibited a substantial compositional drift as corroborated by assessed thermal properties. Tailored T-g's and increased thermal stability were achieved by copolymerizing the lactones and the (meth)acrylates.
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| 17. |
- Murto, Petri Henrik, 1984, et al.
(author)
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Highly Stable Indacenodithieno[3,2-b]thiophene-Based Donor-Acceptor Copolymers for Hybrid Electrochromic and Energy Storage Applications
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 53:24, s. 11106-11119
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Journal article (peer-reviewed)abstract
- Stable doping of indacenodithieno[3,2-b]thiophene (IDTT) structures enables easy color tuning and significant improvement in the charge storage capacity of electrochromic polymers, making use of their full potential as electrochromic supercapacitors and in other emerging hybrid applications. Here, the IDTT structure is copolymerized with four different donor-acceptor-donor (DAD) units, with subtle changes in their electron-donating and electron-withdrawing characters, so as to obtain four different donor-acceptor copolymers. The polymers attain important form factor requirements for electrochromic supercapacitors: desired switching between achromatic black and transparent states (L*a*b∗ 45.9, -3.1, -4.2/86.7, -2.2, and -2.7 for PIDTT-TBT), high optical contrast (72% for PIDTT-TBzT), and excellent electrochemical redox stability (Ired/Iox ca. 1.0 for PIDTT-EBE). Poly[indacenodithieno[3,2-b]thiophene-2,8-diyl-alt-4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-(2-hexyldecyl)-2H-benzo[d][1,2,3]triazole-7,7′-diyl] (PIDTT-EBzE) stands out as delivering simultaneously a high contrast (69%) and doping level (>100%) and specific capacitance (260 F g-1). This work introduces IDTT-based polymers as bifunctional electro-optical materials for potential use in color-tailored, color-indicating, and self-regulating smart energy systems.
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| 18. |
- Olsson, Joel, et al.
(author)
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Functionalizing polystyrene with N-alicyclic piperidine-based cations via Friedel-Crafts alkylation for highly alkali-stable anion-exchange membranes
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:12, s. 4722-4732
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Journal article (peer-reviewed)abstract
- Different anion-exchange membranes (AEMs) based on polystyrene (PS) carrying benzyltrimethyl ammonium cations are currently developed for use in alkaline fuel cells and water electrolyzers. However, the stability of these state-of-the-art cations needs to be further improved. Here, we introduce highly alkali-stable mono- and spirocyclic piperidine-based cations onto PS by first performing a superacid mediated Friedel-Crafts alkylation using 2-(piperidine-4-yl)propane-2-ol. This is followed by quaternization of the piperidine rings either using iodomethane to produce N,N-dimethylpiperidinium cations or cyclo-quaternizations using 1,5-dibromopentane and 1,4-dibromobutane, respectively, to obtain N-spirocyclic quaternary ammonium cations. Thus, it is possible to functionalize up to 27% of the styrene units with piperidine rings, and subsequently achieve complete quaternization. The synthetic approach ensures that all the sensitive β-hydrogens of the cations are present in ring structures to provide high stability. AEMs based on these polymers show high alkaline stability and less than 5% ionic loss was observed by 1H NMR spectroscopy after 30 days in 2 M aq. NaOH at 90 °C. AEMs functionalized with N,N-dimethylpiperidinium cations show a higher stability than the ones carrying N-spirocyclic quaternary ammonium. Careful analysis of the latter revealed that the rings formed in the cyclo-quaternization are more prone to degrade via Hofmann elimination than the rings introduced in the Friedel-Crafts reaction. AEMs with an ion exchange capacity of 1.5 meq g-1 reach a hydroxide conductivity of 106 mS cm-1 at 80 °C under fully hydrated conditions. The AEMs are further tuned and improved by blending with polybenzimidazole (PBI). For example, an AEM containing 2 wt% PBI shows reduced water uptake and much improved robustness during handling, and reaches 71 mS cm-1 at 80 °C. The study demonstrates that the critical alkaline stability of PS-containing AEMs can be significantly enhanced by replacing the benchmark benzyltrimethyl ammonium cations with N-alicyclic piperidine-based cations.
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| 19. |
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| 20. |
- Raghuwanshi, Vikram Singh, et al.
(author)
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Deuterated Bacterial Cellulose Dissolution in Ionic Liquids
- 2021
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:14, s. 6982-6989
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Journal article (peer-reviewed)abstract
- Understanding the dissolution mechanism of deuterated bacterial cellulose (DBC) is important to engineer advanced material applications such as in quantifying and visualizing biomolecules at the cellulose interface for diagnostics. Small-angle neutron scattering (SANS) is applied to evaluate the distribution and volume fraction of dissolved DBC chains in 1-ethyl-3-methylimidazolium acetate (EMIM-Ac) ionic liquid (IL-h) solvent in three different ways: (i) DBC in IL-h, (ii) DBC in a mixture of N,N-dimethylformamide (DMF) with IL-h (IL-h/DMF), and (iii) modified DBC by dissolution in IL-h with dichloromethane (DCM), (DCM-DBC). EMIM-Ac is a highly viscous solvent, and the incorporation of DMF reduces its viscosity. DCM incorporation into EMIM-Ac leads to partial acetylation of the cellulose chains. The DBC dissolves differently in all the modified solvents studied. The DBC and DCM-DBC dissolution in IL-h shows the presence of surface fractals (power law relation of intensity to a scattering vector, q, of q-3.4) indicating compact aggregated DBC structures. The DBC structure is more open in the DMF/IL-h solvent, which is reflected in the SANS curve mass fractal analysis with a power law of q-2.5. At intermediate values of the scattering vector, a q-1 power law is observed, indicative of rigid segments of dissolved DBC chains. Analysis of the intensity in this range provides insights as to the dissolution mechanism. The observed higher intensity measured in the solutions of DBC and DCM-DBC in IL-h can be attributed to the tight binding adsorption of the acetate ions on the DBC surface. Moreover, the unique aspect of this experiment, using deuterated cellulose in a mixture of deuterated DMF with protiated EMINM-Ac, provides direct proof for formation of a shell layer of IL-h surrounding the DBC surface. The results obtained shed light on the dissolution mechanism of cellulose in EMIM-Ac, highlighting its potential application in engineering biosensors and bio-diagnostics.
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| 21. |
- Saha, Ekata, 1992, et al.
(author)
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Dual Role of Boronic Acid Modification in Enhancing Rheological and Photophysical Properties of Supramolecular Gels
- 2024
-
In: Macromolecules. - 1520-5835 .- 0024-9297. ; 57:7, s. 3183-3189
-
Journal article (peer-reviewed)abstract
- Supramolecular gels derived from functionalized gelators offer diverse applications, and modifying the properties of existing organogels using guest molecules presents an attractive approach for designing functional gel materials with targeted properties. In this study, we investigated a method to enhance the mechanical and photophysical properties of readily prepared low molecular weight gels (LMWGs) through the incorporation of boronic acid derivatives. The leveraging of dynamic covalent bonding interactions between the hydroxyl groups of oxotriphenylhexanoates (OTHO) gelator and the boronic acid derivatives gave rise to a boronate adduct along with enhanced intermolecular aromatic stacking interactions between gelators and thereby reinforced the rheological and thermal stability of the doped OTHO gels. In an effort to probe the aforementioned aromatic interactions, we used a pyrene boronic acid dopant, which revealed that the spatial proximity between the aromatic groups of the boronic acid was close enough to display excimer formation. Our findings provide valuable insights into the regulation of mechanical strength, self-healing ability, and photophysical properties of supramolecular gels. Furthermore, this approach holds promise for broad applications in hydroxyl-containing LMWGs, enabling the development of functional gel materials with enhanced properties.
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| 22. |
- Shin, Young-hun, et al.
(author)
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Synthesis and Aggregation Behavior of a Glycolated Naphthalene Diimide Bithiophene Copolymer for Application in Low-Level n-Doped Organic Thermoelectrics
- 2020
-
In: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 53:13, s. 5158-5168
-
Journal article (peer-reviewed)abstract
- The synthesis of a naphthalene diimide bithiophene copolymer P(EO-NDIT2) with branched, base-stable, and purely ether-based side chains is presented. Stille polycondensation leads to high molecular weights that are limited by methyl transfer and eventually T2 homocouplings. While extensive solution aggregation hampers molecular weight determination by conventional methods, NMR spectroscopy allows identification of both T2- (H and methyl) and NDI-related (methyl) end groups, enabling the determination of absolute number average molecular weights larger than M-n,M- NMR similar to 100 kg/mol. Solvent- and temperature-dependent aggregation in solution is investigated by NMR and UV-vis spectroscopy. These results are used for solution doping of P(EONDIT2) with N-benzimidazole-based n-dopants. Spin coating from heated chlorobenzene solutions and using 4-(2,3-dihydro-1,3dimethyl-1H-benzoimidazol-2-yl)-N,N-diisopropylaniline (N-DiPrBI) as the dopant leads to homogeneous films with highest conductivities up to 10(-2) S/cm. Generally, N-DiPrBI concentrations as low as similar to 5 wt % are sufficient to increase conductivity by orders of magnitude. Strikingly, maximum power factors up to 0.11 mu W/mK(2), although limited by conductivity, are achieved for the highest molar mass sample at a low dopant concentration of 2 wt % N-DiPrBI only.
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| 23. |
- Stegerer, Dominik, 1988, et al.
(author)
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Organogels from Diketopyrrolopyrrole Copolymer Ionene/Polythiophene Blends Exhibit Ground-State Single Electron Transfer in the Solid State
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 55:12, s. 4979-4994
-
Journal article (peer-reviewed)abstract
- Acceptor copolymers with low lowest unoccupied molecular orbital (LUMO) energy levels are key materials for organic electronics. In the present work, quaternization of pyridine-flanked diketopyrrolopyrrole (PyDPPPy) is used to lower the LUMO energy level of the resulting monomer (MePyDPPPy) by as much as 0.7 eV. The drastically changed electronic properties of MePyDPPPy hinder a second methylation step even in an excess of trimethyloxonium tetrafluoroborate and thereby give access to the asymmetric functionalization of N-heterocycle-flanked DPP building blocks. The corresponding n-type polymeric ionene PMePyDPPPyT2 with bithiophene as comonomer forms thixotropic organogels with the p-type polythiophene P(g42T-TT), indicative of specific cross-interactions between this couple of copolymers. Gelation of polymer blend solutions, which is absent for other couples of p-type/ n-type polymers, is of general interest for (co)processing and orientation of different electronic polymers simultaneously into films or filaments. Detailed optical and electronic characterization reveals that films processed from organogels exhibit ground-state electron transfer (GSET) enabled by suitably positioned highest occupied molecular orbital (HOMO) and LUMO energy levels of P(g42T-TT) (-4.07 eV) and PMePyDPPPyT2 (-4.20 eV), respectively. Furthermore, molecular interactions related to gelation and GSET do not appear to significantly influence the morphology of the polymer blend films.
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| 24. |
- Sunny, Sonu, et al.
(author)
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Microscopic Insights of Electrochemical Switching of Poly(benzimidazobenzophenanthroline) (BBL) Thin Film: A Molecular Dynamics Study
- 2024
-
In: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 57:11, s. 5155-5165
-
Journal article (peer-reviewed)abstract
- The ladder-type benzimidazobenzophenanthroline (BBL) polymer is one of the most important and most studied n-type conducting polymers. It is also an organic mixed ion-electron conductor (OMIEC), which can undergo electrochemical switching in electrolyte solutions by accommodating opposite ions. The extensive morphological changes of the OMIEC material during operation affect the transport properties and, hence, the device performance. However, molecular insights into the dynamic structural changes during the electrochemical switching are limited, as they are difficult or impossible to access in experiments. The computational microscope based on molecular dynamics (MD) calculations can provide us with complete insights into the detailed dynamic morphological changes that are currently missing, to a large extent, for the BBL polymer. In the present study, using atomistic MD simulations, we obtained microscopic insights into the electrochemical switching of BBL film in two different electrolytes, namely, single-atom counterion K+ (potassium) in water and molecular counterion DMBI+ (dimethyl-3-butyl imidazolium) in chloroform. For both cases, the maximum crystallinity is found up to a moderate reduction level. Beyond that, ion intercalation initiates a structural phase transition and causes a decrease in the crystalline order of the film. At the higher reduction levels, the single-atom K+ counterions are stabilized within the lamellar stacked BBL chains; in contrast, the DMBI+ counterions with higher molecular weights are stabilized within the BBL pi-pi stacks, forming pi-pi stacking between BBL and DMBI+. Our findings substantiate how molecular dopants can improve the thermomechanical stability of the material and why smaller single-atom counterions are preferred for maintaining better crystallinity. The detailed microscopic insights into the morphological changes during the electrochemical switching of BBL film, which cannot be directly accessed experimentally, can definitely help design n-type OMIEC-based devices made of BBL.
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| 25. |
- Tsourtou, Flora D., et al.
(author)
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Molecular Dynamics Simulation of Amorphous Poly(3-hexylthiophene)
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 53:18, s. 7810-7824
-
Journal article (peer-reviewed)abstract
- Molecular dynamics (MD) simulations are employed to study the effect of chain length and temperature on the density and conformational properties of regioregular poly(3-hexylthiophene), also denoted as RR-P3HT, in its pure amorphous phase. First, several widely used all-atom force fields (FFs) currently available in the literature are evaluated by comparing their predictions for the density, mean-square chain end-to-end distance, mean-square chain radius-of-gyration, and persistence length of RR-P3HT oligomers at temperatures above their melting point with the limited available experimental data in the literature. Then, with one of the most promising from these FFs, we extend the MD simulations to higher-chain-length P3HT systems (containing up to 150 monomers per chain) at various temperatures. The MD results indicate that the density and persistence length of amorphous P3HT increase slightly with chain length approaching limiting asymptotic values equal to 0.788 +/- 0.003 g cm(-3) and 21 +/- 0.4 angstrom, respectively, at temperature T = 700 K and pressure P = 1 atm. This is attributed to excess chain end free volume effects that are significant at low molecular weights. On the contrary, the effective conjugation length, which is found to become larger than the persistence length only above a certain molecular weight, shows a stronger dependence on chain length. Both of these characteristic lengths are found to increase with decreasing temperature due to the increasing relative population of planar (cis and trans) conformational states of the inter-ring torsion angle. The probability distribution of the maximum length of conjugated segments along a P3HT chain coincides with the theoretical distribution of a longest run of "heads" in a coin-flip experiment. Our MD results suggest that short-chain-length RR-P3HT chains in their bulk amorphous phase are semiflexible but, as their molecular weight increases, they adopt more and more random coil conformations, especially at higher temperatures.
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| 26. |
- Untilova, Viktoriia, et al.
(author)
-
High Thermoelectric Power Factor of Poly(3-hexylthiophene) through In-Plane Alignment and Doping with a Molybdenum Dithiolene Complex
- 2020
-
In: Macromolecules. - : American Chemical Society (ACS). - 1520-5835 .- 0024-9297. ; 53:15, s. 6314-6321
-
Journal article (peer-reviewed)abstract
- We report a record thermoelectric power factor of up to 160 μW m-1 K-2 for the conjugated polymer poly(3-hexylthiophene) (P3HT). This result is achieved through the combination of high-temperature rubbing of thin films together with the use of a large molybdenum dithiolene p-dopant with a high electron affinity. Comparison of the UV-vis-NIR spectra of the chemically doped samples to electrochemically oxidized material reveals an oxidation level of 10%, i.e., one polaron for every 10 repeat units. The high power factor arises due to an increase in the charge-carrier mobility and hence electrical conductivity along the rubbing direction. We conclude that P3HT, with its facile synthesis and outstanding processability, should not be ruled out as a potential thermoelectric material. ©
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| 27. |
- Wang, R., et al.
(author)
-
Unexpected Gelation Behavior of Cellulose Nanofibers Dispersed in Glycols
- 2022
-
In: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 55:21, s. 9527-9536
-
Journal article (peer-reviewed)abstract
- In this study, the gelation behavior of TEMPO-oxidized wood-based cellulose nanofiber (CNF) suspensions in two different glycols, ethylene glycol (EG) and propylene glycol (PG), was investigated near the overlap concentration and compared with that of aqueous CNF suspensions. The flow property of these non-aqueous and aqueous CNF suspensions was characterized by rheological, UV-vis, and rheo-optical techniques. It was found that the CNF(PG) suspensions exhibited stirring-reversible gelation behavior, where gelation could be induced simply by resting (i.e., prolonged holding time). However, this behavior was not observed for CNF(EG) and CNF(aq) suspensions. Higher temperature and higher CNF concentration could accelerate the gelation process of CNFs in PG, but no large-scale phase separation was detected by the optical techniques. Our study suggests that the reduced hydrophilic attraction between CNFs in PG is the main driving force for forming CNF-rich micro-domains, yielding a physically crosslinked network. This study suggests that the choice of solvent can be used to tailor and control the flow behavior of CNF suspensions, leading to designs of new cellulose-enabled nanocomposites for varying applications.
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| 28. |
- Wang, Xiaohan, et al.
(author)
-
Skin-Inspired Healable Conductive Elastomers with Exceptional Strain-Adaptive Stiffening and Damage Tolerance
- 2021
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:23, s. 10767-10775
-
Journal article (peer-reviewed)abstract
- Stretchable conductive elastomers play an irreplaceable role in flexible electronic devices. However, stretchable conductive elastomers are usually soft and susceptible to damage. In this study, inspired from skin, highly stretchable and elastic conductive elastomers integrated with damage resistance, damage tolerance, and healability are fabricated by loading ionic liquids (ILs) within the polyurethane (PU) elastomers of the multiblock polymers of poly(dimethylsiloxane) (PDMS)/polycaprolactone (PCL) coordinated with Zn2+ ions. The mechanically robust conductive elastomer, with a tensile strength of ∼15.2 MPa and a stretchability of ∼2668%, has a satisfactory ionic conductivity of 2.9 × 10–4 S cm–1. The conductive elastomer exhibits exceptional strain-adaptive stiffening, with an ∼100-fold increase in modulus when being fully stretched. The strain-adaptive stiffening endows the elastomer with excellent damage resistance. Meanwhile, the conductive elastomer has a record-high fracture energy of ∼33.8 kJ m–2. The notched conductive elastomer can prevent the propagation of the notch up to a strain of ∼2400%. The exceptional strain-adaptive stiffening and damage tolerance originate from the in situ formed phase-separated domains, which are deformable and disintegrable under an external force to significantly strengthen the elastomer and dissipate energy. Furthermore, the conductive elastomer can be conveniently healed under heating to restore its original conductivity and mechanical properties.
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| 29. |
- Yang, Philip B., et al.
(author)
-
Comparison of Cyclic and Linear Poly(lactide)s Using Small-Angle Neutron Scattering
- 2022
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 55:24, s. 11051-11058
-
Journal article (peer-reviewed)abstract
- Small-angle neutron scattering (SANS) experiments were conducted on cyclic and linear polymers of racemic and l-lactides (PLA) with the goal of comparing chain configurations, scaling, and effective polymer–solvent interactions of the two topologies in acetone-d6 and THF-d8. There are limited reports of SANS results on cyclic polymers due to the lack of substantial development in the field until recently. Now that pure, well-defined cyclic polymers are accessible, unanswered questions about their rheology and physical conformations can be better investigated. Previously reported SANS experiments have used cyclic and linear polystyrene samples; therefore, our work allowed for direct comparison using a contrasting (structurally and sterically) polymer. We compared SANS results of cyclic and linear PLA samples with various microstructures and molecular weights at two different temperatures, allowing for comparison with a wide range of variables. The results followed the trends of previous experiments, but much greater differences in the effective polymer–solvent interaction parameters between cyclic and linear forms of PLA were observed, implying that the small form factor and hydrogen bonding in PLA allowed for much more compact conformations in the cyclic form only. Also, the polymer microstructure was found to influence polymer–solvent interaction parameters substantially. These results illustrate how the difference in polymer–solvent interactions between cyclic and linear polymers can vary greatly depending on the polymer in question and the potential of neutron scattering as a tool for identification and characterization of the cyclic topology.
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| 30. |
- Yang, Song, et al.
(author)
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Regulating the Tautomerization in Covalent Organic Frameworks for Efficient Sacrificial Agent-Free Photocatalytic H2O2 Production
- 2024
-
In: Macromolecules. - 0024-9297 .- 1520-5835. ; 57:5, s. 2039-2047
-
Journal article (peer-reviewed)abstract
- The efficiency of photocatalytic production of H2O2 is constrained by the low selectivity toward oxygen reduction, and the active sites are still under debate. Herein, analogous covalent organic framework photocatalysts were synthesized from triformylphloroglucinol (Tp) and predesigned diamines, in which a molecular engineering strategy was employed to manipulate the energy barrier for the targeted proton transfers. The tautomerization of enol-imine to keto-enamine introduced abundant alkene bonds (C═C), which serve as the primary adsorption sites and have a lower energy barrier for the reduction of the O2 reduction. DHAA-Tp COF displayed a remarkable photocatalytic H2O2 production rate of 219.5 μmol h–1 g–1 without any sacrificial reagent, which stands out among the structure-related materials. A switch from a concerted one-step 2e– to a two-step single e– process in O2 reduction was observed in TCNAQ-Tp COF, which is presumably ascribed to the suppressed tautomerization mediated by the strong electron-withdrawing cyano groups. The results demonstrate a novel concept for the photocatalytic production of H2O2 using an efficient, stable, and recyclable metal-free photocatalytic system.
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| 31. |
- Yang, Xuan, et al.
(author)
-
Polymer Films from Cellulose Nanofibrils-Effects from Interfibrillar Interphase on Mechanical Behavior
- 2021
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:9, s. 4443-4452
-
Journal article (peer-reviewed)abstract
- Dense polymeric films based on network-forming cellulose nanofibrils (CNFs) have excellent mechanical properties but are limited by moisture sensitivity. Here, interfibrillar effects from CNF surface properties are investigated. TEMPO-oxidized CNFs and two native CNFs are prepared with a similar length and width, to exclude geometrical effects. The CNFs have different surface properties in terms of sorbed hemicellulose content, hemicellulose molar mass, and surface charge. Moisture sorption, structural changes, and mechanical properties at different relative humidities are characterized. The presence of sorbed hemicelluloses in the interfibrillar interphase has favorable effects on the mechanical tensile properties. Surface-charged carboxyls increased moisture sorption and film thickness swelling and reduced the mechanical properties. A comparison with biaxially oriented polyethylene terephthalate films provides a perspective into the structure and properties of CNF films. The present study shows the importance of the interfibrillar interface and interphase region for mechanical film properties, including moisture effects.
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| 32. |
- Zhuang, Wenliu, 1979, et al.
(author)
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Synthesis and Electronic Properties of Diketopyrrolopyrrole-Based Polymers with and without Ring-Fusion
- 2021
-
In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 54:2, s. 970-980
-
Journal article (peer-reviewed)abstract
- Diketopyrrolopyrroles (DPP) have been recognized as a promising acceptor unit for construction of semiconducting donor-acceptor (D-A) polymers, which are typically flanked by spacers such as thiophene rings via a carbon-carbon single bond formation. It may suffer from a decrease in the coplanarity of the molecules especially when bulky side chains are installed. In this work, the two N atoms in the DPP unit are further fused with C-3 of the two flanking thiophene rings, yielding a p-expanded, very planar fused-ring building block (DPPFu). A novel DPPFu-based D-A copolymer (PBDTT-DPPFu) was successfully synthesized, consisting of a benzo[1,2-b:4,5-b]dithiophene (BDTT) unit as a donor and a DPPFu unit as an acceptor. For comparison, the unfused DPP-based counterpart PBDTT-DPP was also synthesized. Two dodecyl alkyl chains were attached to thiophene rings of DPP moieties to ensure good solubility of the DPPFu-based polymer. The influence of the ring-fusion effect on their structure, photophysical properties, electronic properties, molecular packing, and charge transport properties is investigated. Ring-fusion enhances the intermolecular interactions of PBDTT-DPPFu polymer chains as indicated by density functional theory calculation and analysis of electrostatic potential and van der Waals potential and results in significantly improved molecular packing for both the in-plane and out-of-plane directions as suggested by X-ray measurements. Finally, we correlate the molecular packing to the device performance by fabricating field-effect transistors based on these two polymers. The charge carrier mobility of the ring-fused polymer PBDTT-DPPFu is significantly higher as compared to the PBDTT-DPP polymer without ring-fusion, although PBDTT-DPPFu exhibited a much lower number-average molecular weight of 17 kDa as compared to PBDTT-DPP with a molecular weight of 108 kDa. The results from our comparative study provide a robust way to increase the interchain interaction by ring-fusion-promoted coplanarity.
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| 33. |
- Zozoulenko, Igor, et al.
(author)
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Electronic, Optical, Morphological, Transport, and Electrochemical Properties of PEDOT: A Theoretical Perspective
- 2021
-
In: Macromolecules. - : AMER CHEMICAL SOC. - 0024-9297 .- 1520-5835. ; 54:13, s. 5915-5934
-
Journal article (peer-reviewed)abstract
- Among all conducting polymers, PEDOT or poly(3,4-ethylenedioxythiophene) has a special place within the field of organic electronics due to its outstanding conductivity, stability, and processability. Since PEDOT was first synthesized in the late 1980s, a massive amount of knowledge has been accumulated about its morphological, structural, electrical, and optical properties, along with its applications in various devices. Notably, however, is that the vast majority of the reports in the field are purely experimental, without any theoretical support from simulation and modeling. In many other fields of material science, molecular modeling has already become a standard tool for guiding the experimental work. For PEDOT, the lack of the theoretical understanding of many important aspects of the material properties and device functionality leads to misconceptions and controversial issues hindering the progress in the field. The purpose of this Perspective is to fill the knowledge gaps and to present the current state-of-the art of the theoretical understanding of PEDOT. As theoretical understanding is essential to correctly interpretate experimental results and for the design of materials and devices with better performance, this Perspective targets equally experimental and theoretical communities working on PEDOT and related materials. We also hope that this Perspective will attract further attention of the computational community, which would help to bring the theoretical understanding of PEDOT to the levels already achieved in many other fields of material science.
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| 34. |
- Hazra, Nabanita, et al.
(author)
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Structure of Responsive Microgels down to Ultralow Cross-Linkings
- 2024
-
In: Macromolecules. - 0024-9297. ; 57:1, s. 339-355
-
Journal article (peer-reviewed)abstract
- Although microgels have been widely used as model systems for soft colloids, their properties are still far from being completely understood. This stems from their heterogeneous structure strongly differing from that of an idealized polymeric network. Indeed, microgels synthesized by conventional precipitation polymerization exhibit not only a fuzzy structure with respect to the difference of reactivity between monomers and cross-linker molecules but also static heterogeneities related to the distribution in the length of the chains constituting their network. These features can be reproduced in computer simulations using the so-called in silico synthesis. Hereby, a designing force acting on the cross-linkers during the in silico synthesis allows us to finely adjust the radial density distribution and, thus, to reproduce both the fuzziness and local heterogeneities present in real microgel systems. In this study, poly(N-isopropylacrylamide) (PNIPAM) microgels were synthesized with different degrees of cross-linking ccross down to cross-linker free conditions corresponding to so-called ultralow cross-linked microgels (ULC microgels). The experimental characterization was accompanied by numerical simulations at different ccross with the same designing force, which is found to be independent of the cross-linker concentration, as well as the size of the microgels. For the ULC microgels, it was found that no designing force is needed, but the number density of the network is much smaller. The number of effective cross-linkers in this case is found to be ∼0.1%. The form factors of all microgels were measured at different temperatures across their volume phase transition with both static light scattering and small-angle X-ray scattering, favorably comparing them to the simulated ones. Furthermore, the swelling behavior was experimentally determined by dynamic light scattering and viscosimetry and also compared to the simulated results. Finally, experimental and simulated results indicate that the cross-linking dependence of the swelling is well-described by theoretical predictions for the isotropic swelling of an ideal network despite the highly heterogeneous character of real microgels.
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| 35. |
- Lovegrove, Jordan T., et al.
(author)
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Assembly of Multicompartment Glycopolymer Worms in Aqueous Solution
- 2023
-
In: Macromolecules. - 0024-9297. ; 56:8, s. 3195-3203
-
Journal article (peer-reviewed)abstract
- Hierarchical self-assembly is a versatile technique that allows the formation of many complex architectures on the nano- and microscale. However, many of these structures are formed in harsh organic solvents with nonbiocompatible polymers. Here, we investigate in more detail a synthetic path to produce biologically compatible, crosslinked, multicompartment worms (MCWs) in aqueous solution by incorporating thermoresponsive poly-N-isopropylacrylamide (PNIPAM) to direct assembly above the lower critical solution temperature (LCST). As the self-assembly into MCWs can be controlled externally by adjusting the temperature, we can provide new insight into the mechanism of hierarchical self-assembly. The growth of MCWs starting from primary micelles was observed above the LCST using in situ small-angle neutron scattering, dynamic light scattering, atomic force microscopy, and phase contrast microscopy.
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| 36. |
- Valsange, Nitin G., et al.
(author)
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Semi-Crystalline and Amorphous Polyesters Derived from Biobased Tri-Aromatic Dicarboxylates and Containing Cleavable Acylhydrazone Units for Short-Loop Chemical Recycling
- 2024
-
In: Macromolecules. - 0024-9297. ; 57:6, s. 2868-2878
-
Journal article (peer-reviewed)abstract
- Recycling polymers by site-specific scission into short-chain oligomers/polymers, followed by recoupling these to form the original polymer presents an energetically more favorable shorter-loop chemical recycling in comparison to recycling into monomers. Here, we present the synthesis and polymerization of triaromatic diesters to prepare polyesters with acylhydrazone units as weak structural links. Two diester monomers were prepared by combining methyl 5-chloromethyl-2-furoate, obtained from 5-chloromethylfurfural (CMF), with potentially biobased hydroquinone and resorcinol, respectively. The two diesters having a central phenyl ring flanked by two furan rings were polymerized with 1,6-hexanediol and 1,4-butanediol, respectively, together with controlled amounts of monofunctional ethyl levulinate to form telechelic ketone-terminated polyesters. Subsequent reactions of these telechelic polyesters with adipic dihydrazide yielded corresponding chain-extended polyesters with increased molecular weights ([η] = 0.29−0.52 dL g−1) with acylhydrazone units in the backbone. Thermogravimetric analysis showed a high thermal stability of the polyesters with thermal decomposition only above 275 °C. The polyesters containing the linear hydroquinone units were found to be semicrystalline materials with melting points at 158 and 192 °C, respectively, while those containing the kinked resorcinol units were fully amorphous with glass transition temperatures at 35 and 44 °C, respectively. Initial investigations of the chemical recyclability of the polyesters demonstrated that acylhydrazone units could be selectively cleaved to recover the original telechelic ketone-terminated polyesters, which could again be chain-extended to obtain a recycled polymer with molecular weights and properties very similar to those of the original polymer.
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