Publications by authors named "Rint P Sijbesma"

86 Publications

Dynamic Polyamide Networks via Amide-Imide Exchange.

Macromolecules 2021 Oct 13;54(20):9703-9711. Epub 2021 Oct 13.

Department of Chemical Engineering & Chemistry, Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

The diamide-imide equilibrium was successfully exploited for the synthesis of dynamic covalent polymer networks in which a dissociative bond exchange mechanism leads to high processibility at temperatures above ≈110 °C. Dynamic covalent networks bridge the gap between thermosets and thermoplastic polymers. At the operating temperature, when the network is fixed, dynamic covalent networks are elastic solids, while at high temperatures, chemical exchange reactions turn the network into a processible viscoelastic material. Upon heating a dissociative network, the viscosity may also decrease due to a shift of the chemical equilibrium; in such materials, the balance between processibility and excessive flow is important. In this study, a network is prepared that upon heating to above ≈110 °C dissociates to a significant extent due to a shift in the amide-imide equilibrium of a bisimide, pyromellitic diimide, in combination with poly(tetrahydrofuran) diamines. At room temperature, the resulting materials are elastic rubbers with a tensile modulus of 2-10 MPa, and they become predominantly viscous above a temperature of approximately 110 °C, which is dependent on the stoichiometry of the components. The diamide-imide equilibrium was studied in model reactions with NMR, and variable temperature infrared (IR) spectroscopy was used to investigate the temperature dependence of the equilibrium in the network. The temperature-dependent mechanical properties of the networks were found to be fully reversible, and the material could be reprocessed several times without loss of properties such as modulus or strain at break. The high processibility of these networks at elevated temperatures creates opportunities in additive manufacturing applications such as selective laser sintering.
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http://dx.doi.org/10.1021/acs.macromol.1c01389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8552437PMC
October 2021

Efficient Exchange in a Bioinspired Dynamic Covalent Polymer Network via a Cyclic Phosphate Triester Intermediate.

Macromolecules 2021 Sep 17;54(17):7955-7962. Epub 2021 Aug 17.

Department of Chemical Engineering & Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

Bond exchange via neighboring group-assisted reactions in dynamic covalent networks results in efficient mechanical relaxation. In Nature, the high reactivity of RNA toward nucleophilic substitution is largely attributed to the formation of a cyclic phosphate ester intermediate via neighboring group participation. We took inspiration from RNA to develop a dynamic covalent network based on β-hydroxyl-mediated transesterifications of hydroxyethyl phosphate triesters. A simple one-step synthetic strategy provided a network containing phosphate triesters with a pendant hydroxyethyl group. P solid-state NMR demonstrated that a cyclic phosphate triester is an intermediate in transesterification, leading to dissociative network rearrangement. Significant viscous flow at 60-100 °C makes the material suitable for fast processing via extrusion and compression molding.
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http://dx.doi.org/10.1021/acs.macromol.1c01504DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8444552PMC
September 2021

Elucidating dynamic behavior of synthetic supramolecular polymers in water by hydrogen/deuterium exchange mass spectrometry.

J Polym Sci (2020) 2021 Jun 21;59(12):1151-1161. Epub 2021 Feb 21.

Department of Chemical Engineering and Chemistry Institute for Complex Molecular Systems, Eindhoven University of Technology Eindhoven The Netherlands.

A comprehensive understanding of the structure, self-assembly mechanism, and dynamics of one-dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX-MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX-MS is influenced by the internal order within the supramolecular polymers and by the self-assembly mechanism.
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http://dx.doi.org/10.1002/pol.20210011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8247967PMC
June 2021

Correction: Mechanochemical tools for polymer materials.

Chem Soc Rev 2021 Jun;50(11):6659-6660

Department of Chemical Engineering & Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

Correction for 'Mechanochemical tools for polymer materials' by Yinjun Chen et al., Chem. Soc. Rev., 2021, 50, 4100-4140, DOI: 10.1039/D0CS00940G.
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http://dx.doi.org/10.1039/d1cs90042kDOI Listing
June 2021

Role of Acetate Anions in the Catalytic Formation of Isocyanurates from Aromatic Isocyanates.

J Org Chem 2021 Apr 1;86(8):5651-5659. Epub 2021 Apr 1.

Polymer Performance Materials Group, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

The formation of isocyanurates via cyclotrimerization of aromatic isocyanates is widely used to enhance the physical properties of a variety of polyurethanes. The most commonly used catalysts in industries are carboxylates for which the exact catalytically active species have remained controversial. We investigated how acetate and other carboxylates react with aromatic isocyanates in a stepwise manner and identified that the carboxylates are only precatalysts in the reaction. The reaction of carboxylates with an excess of aromatic isocyanates leads to irreversible formation of corresponding deprotonated amide species that are strongly nucleophilic and basic. As a result, they are active catalysts during the nucleophilic anionic trimerization, but can also deprotonate urethane and urea species present, which in turn catalyze the isocyanurate formation. The current study also shows how quantum chemical calculations can be used to direct spectroscopic identification of reactive intermediates formed during the active catalytic cycle with predictive accuracy.
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http://dx.doi.org/10.1021/acs.joc.1c00119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8154571PMC
April 2021

Mechanochemical tools for polymer materials.

Chem Soc Rev 2021 Mar 5;50(6):4100-4140. Epub 2021 Feb 5.

Department of Chemical Engineering & Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.

Mechanochemistry provides a unique approach to investigate macroscopic deformation, failure and healing of polymer materials. The development of mechanophores - molecular units that respond to mechanical force - has been instrumental in the success of this endeavor. This review aims to provide a critical evaluation of the large variety of mechanophores reported in literature, and to assess the molecular and macroscopic factors that determine their activation. Applications in materials science are highlighted, and challenges in polymer mechanochemistry are discussed.
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http://dx.doi.org/10.1039/d0cs00940gDOI Listing
March 2021

Nanoporous Films with Photoswitchable Absorption Kinetics Based on Polymerizable Columnar Discotic Liquid Crystals.

ACS Appl Mater Interfaces 2021 Jan 12;13(3):4385-4392. Epub 2021 Jan 12.

Laboratory of Supramolecular Polymer Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

A photoresponsive nanoporous polymer film has been produced from the templated self-assembly of a columnar liquid crystal containing azo units. A liquid crystalline complex of polymerizable azobenzoic acid and a tris-benzimidazolyl benzene template molecule was cross-linked via thiol-ene radical copolymerization with dodecanedithiol. Subsequent removal of the template yielded nanoporous polymer films with pores of approximately 1 nm in diameter. Both trans-cis and cis-trans photoisomerizations of azobenzoic acid took place in the porous films. At room temperature, the cis isomer was sufficiently long-lived to establish a difference in dye absorption kinetics of the two isomers. The cationic dye rhodamine 6G was bound to both isomers, but the rate of binding to films enriched in the cis isomer was 8 times faster.
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http://dx.doi.org/10.1021/acsami.0c19180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7844832PMC
January 2021

Pyranine Based Ion-Paired Complex as a Mechanophore in Polyurethanes.

Macromol Rapid Commun 2021 Jan 14;42(1):e2000476. Epub 2020 Oct 14.

Department of Chemical Engineering & Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513 MB Eindhoven, Eindhoven, 5600, The Netherlands.

A new mechanophore for polyurethane thermoplastic elastomers based on ion-paired complexes is developed. 8-(2-hydroxyethoxy)pyrene-1,3,6-trisulfonate (HEPTS) is incorporated into polyurethanes as an end-capper and aggregates in apolar media. Aggregation of the ionic HEPTS end groups in solution depends on concentration solvent polarity. The addition of dimethylformamide to a tetrahydrofuran solution of the polymer results in the dissociation of the aggregates and a significant shift in fluorescence emission from yellow to blue. The same shift in fluorescence emission is induced by stretching the solid polymer at strains larger than 1 and stresses above 7.5 MPa, with a clear increase above 12.5 MPa. Strain induced dissociation of HEPTS aggregates not attached to the polymer chain leads to fluorescence changes that are much less reproducible.
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http://dx.doi.org/10.1002/marc.202000476DOI Listing
January 2021

Suppressing depolarization by tail substitution in an organic supramolecular ferroelectric.

Phys Chem Chem Phys 2019 Jan;21(4):2069-2079

Complex Materials and Devices, Department of Physics, Chemistry and Biology (IFM), Linköping University, 58183 Linköping, Sweden.

Despite being very well established in the field of electro-optics, ferroelectric liquid crystals so far lacked interest from a ferroelectric device perspective due to a typically high operating temperature, a modest remnant polarization and/or poor polarization retention. Here, we experimentally demonstrate how simple structural modification of a prototypical ferroelectric liquid-crystal benzene-1,3,5-trisamide (BTA) - introduction of branched-tail substituents - results in materials with a wide operating temperature range and a data retention time of more than 10 years in thin-film solution-processed capacitor devices at room temperature. The observed differences between linear- and branched-tail compounds are analyzed using density functional theory (DFT) and molecular dynamics (MD) simulations. We conclude that morphological factors like improved packing quality and reduced disorder, rather than electrostatic interactions or intra/inter-columnar steric hindrance, underlay the superior properties of the branched-tailed BTAs. Synergistic effects upon blending of compounds with branched and linear side-chains can be used to further improve the materials' characteristics.
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http://dx.doi.org/10.1039/c8cp06315jDOI Listing
January 2019

Mimicking Active Biopolymer Networks with a Synthetic Hydrogel.

J Am Chem Soc 2019 02 25;141(5):1989-1997. Epub 2019 Jan 25.

SupraPolix BV , Horsten 1 , 5612 AX , Eindhoven , The Netherlands.

Stiffening due to internal stress generation is of paramount importance in living systems and is the foundation for many biomechanical processes. For example, cells stiffen their surrounding matrix by pulling on collagen and fibrin fibers. At the subcellular level, molecular motors prompt fluidization and actively stiffen the cytoskeleton by sliding polar actin filaments in opposite directions. Here, we demonstrate that chemical cross-linking of a fibrous matrix of synthetic semiflexible polymers with thermoresponsive poly( N-isopropylacrylamide) (PNIPAM) produces internal stress by induction of a coil-to-globule transition upon crossing the lower critical solution temperature of PNIPAM, resulting in a macroscopic stiffening response that spans more than 3 orders of magnitude in modulus. The forces generated through collapsing PNIPAM are sufficient to drive a fluid material into a stiff gel within a few seconds. Moreover, rigidified networks dramatically stiffen in response to applied shear stress featuring power law rheology with exponents that match those of reconstituted collagen and actomyosin networks prestressed by molecular motors. This concept holds potential for the rational design of synthetic materials that are fluid at room temperature and rapidly rigidify at body temperature to form hydrogels mechanically and structurally akin to cells and tissues.
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http://dx.doi.org/10.1021/jacs.8b10659DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6367683PMC
February 2019

Strain-Stiffening in Dynamic Supramolecular Fiber Networks.

J Am Chem Soc 2018 12 6;140(50):17547-17555. Epub 2018 Dec 6.

SupraPolix BV , Horsten 1 , 5612 AX , Eindhoven , The Netherlands.

The cytoskeleton is a highly adaptive network of filamentous proteins capable of stiffening under stress even as it dynamically assembles and disassembles with time constants of minutes. Synthetic materials that combine reversibility and strain-stiffening properties remain elusive. Here, strain-stiffening hydrogels that have dynamic fibrous polymers as their main structural components are reported. The fibers form via self-assembly of bolaamphiphiles (BA) in water and have a well-defined cross-section of 9 to 10 molecules. Fiber length recovery after sonication, H/D exchange experiments, and rheology confirm the dynamic nature of the fibers. Cross-linking of the fibers yields strain-stiffening, self-healing hydrogels that closely mimic the mechanics of biological networks, with mechanical properties that can be modulated by chemical modification of the components. Comparison of the supramolecular networks with covalently fixated networks shows that the noncovalent nature of the fibers limits the maximum stress that fibers can bear and, hence, limits the range of stiffening.
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http://dx.doi.org/10.1021/jacs.8b09289DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6302312PMC
December 2018

Physical reality of the Preisach model for organic ferroelectrics.

Nat Commun 2018 10 23;9(1):4409. Epub 2018 Oct 23.

Complex Materials and Devices, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-58 183, Linköping, Sweden.

The Preisach model has been a cornerstone in the fields of ferromagnetism and ferroelectricity since its inception. It describes a real, non-ideal, ferroic material as the sum of a distribution of ideal 'hysterons'. However, the physical reality of the model in ferroelectrics has been hard to establish. Here, we experimentally determine the Preisach (hysteron) distribution for two ferroelectric systems and show how its broadening directly relates to the materials' morphology. We connect the Preisach distribution to measured microscopic switching kinetics that underlay the macroscopic dispersive switching kinetics as commonly observed for practical ferroelectrics. The presented results reveal that the in principle mathematical construct of the Preisach model has a strong physical basis and is a powerful tool to explain polarization switching at all time scales in different types of ferroelectrics. These insights lead to guidelines for further advancement of the ferroelectric materials both for conventional and multi-bit data storage applications.
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http://dx.doi.org/10.1038/s41467-018-06717-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6199281PMC
October 2018

Tracking Local Mechanical Impact in Heterogeneous Polymers with Direct Optical Imaging.

Angew Chem Int Ed Engl 2018 Dec 9;57(50):16385-16390. Epub 2018 Oct 9.

Inorganic Systems Engineering group, Department of Chemical Engineering, Delft University of Technology, 2629, HZ, Delft, The Netherlands.

Structural heterogeneity defines the properties of many functional polymers and it is often crucial for their performance and ability to withstand mechanical impact. Such heterogeneity, however, poses a tremendous challenge for characterization of these materials and limits our ability to design them rationally. Herein we present a practical methodology capable of resolving the complex mechanical behavior and tracking mechanical impact in discrete phases of segmented polyurethane-a typical example of a structurally complex polymer. Using direct optical imaging of photoluminescence produced by a small-molecule organometallic mechano-responsive sensor we observe in real time how polymer phases dissipate energy, restructure, and breakdown upon mechanical impact. Owing to its simplicity and robustness, this method has potential in describing the evolution of complex soft-matter systems for which global characterization techniques fall short of providing molecular-level insight.
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http://dx.doi.org/10.1002/anie.201809108DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6348422PMC
December 2018

Mechanics of elastomeric molecular composites.

Proc Natl Acad Sci U S A 2018 09 28;115(37):9110-9115. Epub 2018 Aug 28.

Laboratoire Sciences et Ingénierie de la Matière Molle, ESPCI Paris, PSL University, Sorbonne Université, CNRS, F-75005 Paris, France;

A classic paradigm of soft and extensible polymer materials is the difficulty of combining reversible elasticity with high fracture toughness, in particular for moduli above 1 MPa. Our recent discovery of multiple network acrylic elastomers opened a pathway to obtain precisely such a combination. We show here that they can be seen as true molecular composites with a well-cross-linked network acting as a percolating filler embedded in an extensible matrix, so that the stress-strain curves of a family of molecular composite materials made with different volume fractions of the same cross-linked network can be renormalized into a master curve. For low volume fractions (<3%) of cross-linked network, we demonstrate with mechanoluminescence experiments that the elastomer undergoes a strong localized softening due to scission of covalent bonds followed by a stable necking process, a phenomenon never observed before in elastomers. The quantification of the emitted luminescence shows that the damage in the material occurs in two steps, with a first step where random bond breakage occurs in the material accompanied by a moderate level of dissipated energy and a second step where a moderate level of more localized bond scission leads to a much larger level of dissipated energy. This combined use of mechanical macroscopic testing and molecular bond scission data provides unprecedented insight on how tough soft materials can damage and fail.
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http://dx.doi.org/10.1073/pnas.1807750115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6140500PMC
September 2018

Pore size dependent cation adsorption in a nanoporous polymer film derived from a plastic columnar phase.

Chem Commun (Camb) 2018 Aug;54(68):9521-9524

Laboratory of Molecular Science and Technology, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.

Self-supporting polymer thin films were obtained by the polymerization of an AB3-type hydrogen-bonded complex in the plastic columnar phase. Porous polymers with pore diameters of ≈1.1 and ≈1.6 nm lined with either -COOH or -COONa groups were fabricated from the polymer thin films. Both the pore size and pore collapse influence the adsorption of cations.
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http://dx.doi.org/10.1039/c8cc03292kDOI Listing
August 2018

Carbon Nanotube Reinforced Supramolecular Hydrogels for Bioapplications.

Macromol Biosci 2019 01 7;19(1):e1800173. Epub 2018 Aug 7.

Laboratory of Macromolecular and Organic Chemistry, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513,, 5600, MB, Eindhoven, The Netherlands.

Nanocomposite hydrogels based on carbon nanotubes (CNTs) are known to possess remarkable stiffness, electrical, and thermal conductivity. However, they often make use of CNTs as fillers in covalently cross-linked hydrogel networks or involve direct cross-linking between CNTs and polymer chains, limiting processability properties. Herein, nanocomposite hydrogels are developed, in which CNTs are fillers in a physically cross-linked hydrogel. Supramolecular nanocomposites are prepared at various CNT concentrations, ranging from 0.5 to 6 wt%. Incorporation of 3 wt% of CNTs leads to an increase of the material's toughness by over 80%, and it enhances electrical conductivity by 358%, compared to CNT-free hydrogel. Meanwhile, the nanocomposite hydrogels maintain thixotropy and processability, typical of the parent hydrogel. The study also demonstrates that these materials display remarkable cytocompatibility and support cell growth and proliferation, while preserving their functional activities. These supramolecular nanocomposite hydrogels are therefore promising candidates for biomedical applications, in which both toughness and electrical conductivity are important parameters.
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http://dx.doi.org/10.1002/mabi.201800173DOI Listing
January 2019

In Situ Network Formation in PBT Vitrimers via Processing-Induced Deprotection Chemistry.

Macromol Rapid Commun 2018 Oct 30;39(19):e1800356. Epub 2018 Jul 30.

Supramolecular Polymer Chemistry group, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, Netherlands.

Although the network dynamics and mechanical properties of poly(butylene terephthalate) vitrimers can to some extent be controlled via chemical and physical approaches, it remains a challenge to be able to process PBT vitrimers with the same processing conditions via, for example, injection molding as neat PBT. Here, it is shown that the use of protected pentaerythritol as a latent cross-linker and the use of a Zn(II) transesterification catalyst allows for the in situ dynamic network formation in PBT during processing, with a delayed onset of gelation. This process can be controlled by adjusting the processing temperature, (protected) cross-linker content, and the type of protection group. This solvent-free deprotection strategy opens the way to high production rates of PBT vitrimer products via injection molding with the combination of low viscosity during processing and vitrimer characteristics in the final product.
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http://dx.doi.org/10.1002/marc.201800356DOI Listing
October 2018

Effects of Surfactant and Urea on Dynamics and Viscoelastic Properties of Hydrophobically Assembled Supramolecular Hydrogel.

Macromolecules 2018 Jul 25;51(13):4813-4820. Epub 2018 Jun 25.

Laboratory of Macromolecular and Organic Chemistry, Department of Chemical Engineering and Chemistry, Institute for Complex Molecular Systems, and Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

Physically associated hydrogels based on strong hydrophobic interactions often have attractive mechanical properties that combine processability with elasticity. However, there is a need to study such interactions and understand their relation to the macroscopic hydrogel properties. Therefore, we use the surfactant sodium dodecyl sulfate (SDS) and urea as reagents that disrupt hydrophobic interactions. The model hydrogel is based on a segmented copolymer between poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA). We show that both agents influence viscoelastic properties, dynamics, and relaxation processes of the model hydrogel. In particular, the relaxation time is significantly reduced by urea, as compared to SDS, whereas the surfactant causes a decrease of the modulus of the hydrogel more efficiently. The reversibility of the effects of SDS and urea can be exploited, for instance, by using an injectable sol that solidifies when the SDS or urea diffuses out of the sample. Surfactant-induced processability may be advantageous in future applications of hydrophobically assembled physical hydrogels.
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http://dx.doi.org/10.1021/acs.macromol.8b00892DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6041769PMC
July 2018

Homeotropic Self-Alignment of Discotic Liquid Crystals for Nanoporous Polymer Films.

ACS Nano 2018 Jul 10;12(7):6714-6724. Epub 2018 Jul 10.

Institute for Complex Molecular Systems , Eindhoven University of Technology , P.O. Box 513, Eindhoven , Netherlands 5600 MB.

Nanostructured polymer films with continuous, membrane-spanning pores from polymerizable hexagonal columnar discotic liquid crystals (LCs) were fabricated. A robust alignment method was developed to obtain homeotropic alignment of columns between glass surfaces by adding a small amount of a tri(ethylene glycol) modified analogue of the mesogen as a dopant that preferentially wets glass. The homeotropic LC alignment was fixated via a photoinitiated free radical copolymerization of a high-temperature tolerant trisallyl mesogen with a divinyl ester. Removal of the hydrogen-bonded template from the aligned columns afforded a nanoporous network with pores of nearly 1 nm in diameter perpendicular to the surface, and without noticeable collapse of the nanopores. The effect of pore orientation was demonstrated by an adsorption experiment in which homeotropic film showed a threefold increase in the initial uptake rate of methylene blue compared to planarly aligned films.
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http://dx.doi.org/10.1021/acsnano.8b01822DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6060402PMC
July 2018

Strain Stiffening Hydrogels through Self-Assembly and Covalent Fixation of Semi-Flexible Fibers.

Angew Chem Int Ed Engl 2017 07 19;56(30):8771-8775. Epub 2017 Jun 19.

Department of Chemical Engineering and Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.

Biomimetic, strain-stiffening materials are reported, made through self-assembly and covalent fixation of small building blocks to form fibrous hydrogels that are able to stiffen by an order of magnitude in response to applied stress. The gels consist of semi-flexible rodlike micelles of bisurea bolaamphiphiles with oligo(ethylene oxide) (EO) outer blocks and a polydiacetylene (PDA) backbone. The micelles are fibers, composed of 9-10 ribbons. A gelation method based on Cu-catalyzed azide-alkyne cycloaddition (CuAAC), was developed and shown to lead to strain-stiffening hydrogels with unusual, yet universal, linear and nonlinear stress-strain response. Upon gelation, the X-ray scattering profile is unchanged, suggesting that crosslinks are formed at random positions along the fiber contour without fiber bundling. The work expands current knowledge about the design principles and chemistries needed to achieve fully synthetic, biomimetic soft matter with on-demand, targeted mechanical properties.
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http://dx.doi.org/10.1002/anie.201704046DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5519929PMC
July 2017

Tough Supramolecular Hydrogel Based on Strong Hydrophobic Interactions in a Multiblock Segmented Copolymer.

Macromolecules 2017 Apr 5;50(8):3333-3346. Epub 2017 Apr 5.

Laboratory of Macromolecular and Organic Chemistry, Department of Chemical Engineering and Chemistry, Institute for Complex Molecular Systems, and Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75-92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 10 to 6 × 10 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required.
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http://dx.doi.org/10.1021/acs.macromol.7b00319DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5406785PMC
April 2017

Tailoring Pore Size and Chemical Interior of near 1 nm Sized Pores in a Nanoporous Polymer Based on a Discotic Liquid Crystal.

Macromolecules 2017 Apr 23;50(7):2777-2783. Epub 2017 Mar 23.

Laboratory of Molecular Science and Technology and Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB, Eindhoven, The Netherlands.

A triazine based disc shaped molecule with two hydrolyzable units, imine and ester groups, was polymerized via acyclic diene metathesis in the columnar hexagonal (Col) LC phase. Fabrication of a cationic nanoporous polymer (pore diameter ∼1.3 nm) lined with ammonium groups at the pore surface was achieved by hydrolysis of the imine linkage. Size selective aldehyde uptake by the cationic porous polymer was demonstrated. The anilinium groups in the pores were converted to azide as well as phenyl groups by further chemical treatment, leading to porous polymers with neutral functional groups in the pores. The pores were enlarged by further hydrolysis of the ester groups to create ∼2.6 nm pores lined with -COONa surface groups. The same pores could be obtained in a single step without first hydrolyzing the imine linkage. XRD studies demonstrated that the Col order of the monomer was preserved after polymerization as well as in both the nanoporous polymers. The porous anionic polymer lined with -COOH groups was further converted to the -COOLi, -COONa, -COOK, -COOCs, and -COONH salts. The porous polymer lined with -COONa groups selectively adsorbs a cationic dye, methylene blue, over an anionic dye.
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http://dx.doi.org/10.1021/acs.macromol.7b00013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5391558PMC
April 2017

Ferroelectric switching and electrochemistry of pyrrole substituted trialkylbenzene-1,3,5-tricarboxamides.

J Polym Sci B Polym Phys 2017 04 18;55(8):673-683. Epub 2017 Feb 18.

Laboratory of Macromolecular and Organic Chemistry Eindhoven University of Technology PO Box 513 Eindhoven MB 5600 The Netherlands.

We explore a new approach to organic ferroelectric diodes using a benzene-tricarboxamide (BTA) core connected with C10 alkyl chains to pyrrole groups, which can be polymerized to provide a semiconducting ferroelectric material. The compound possesses a columnar hexagonal liquid crystalline (LC) phase and exhibits ferroelectric switching. At low switching frequencies, an additional process occurs, which leads to a high hysteretic charge density of up to ∼1000 mC/m. Based on its slow rate, the formation of gas bubbles, and the emergence of characteristic polypyrrole absorption bands in the UV-Vis-NIR, the additional process is identified as the oxidative polymerization of pyrrole groups, enabled by the presence of amide groups. Polymerization of the pyrrole groups, which is essential to obtain semiconductivity, is limited to thin layers at the electrodes, amounting to ∼17 nm after cycling for 21 h. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. , , 673-683.
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http://dx.doi.org/10.1002/polb.24318DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5347932PMC
April 2017

Mechanoluminescent Imaging of Osmotic Stress-Induced Damage in a Glassy Polymer Network.

Macromolecules 2017 Mar 2;50(5):2043-2053. Epub 2017 Mar 2.

Laboratory of Macromolecular and Organic Chemistry and the Institute for Complex Molecular Systems, Eindhoven University of Technology , P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.

A chemiluminescent mechanophore, bis(adamantyl-1,2-dioxetane), is used to investigate the covalent bond scission resulting from the sorption of chloroform by glassy poly(methyl methacrylate) (PMMA) networks. Bis(adamantyl)-1,2-dioxetane units incorporated as cross-linkers underwent mechanoluminescent scission, demonstrating that solvent ingress caused covalent bond scission. At higher cross-linking densities, the light emission took the form of hundreds of discrete bursts, widely varying in intensity, with each burst composed of 10-10 photons. Camera imaging indicated a relatively slow propagation of bursts through the material and permitted analysis of the spatial correlation between the discrete bond-breaking events. The implications of these observations for the mechanism of sorption and fracture are discussed.
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http://dx.doi.org/10.1021/acs.macromol.6b02540DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5352978PMC
March 2017

Easily Accessible Thermotropic Hydrogen-Bonded Columnar Discotic Liquid Crystals from Fatty Acid- Tris-Benzoimidazolyl Benzene Complexes.

ChemistryOpen 2016 Dec 24;5(6):580-585. Epub 2016 Oct 24.

Laboratory of Macromolecular and Organic Chemistry and the Institute for Complex Molecular Systems Eindhoven University of Technology P. O. Box 513 5600 MB Eindhoven The Netherlands.

We report the formation of easily accessible hydrogen-bonded columnar discotic liquid crystals (LCs) based on tris-benzoimidazolyl benzene () and commercially available fatty acids. By increasing the length of the fatty acid, the temperature range of liquid crystallinity was tuned. Introducing double bonds in octadecanoic acid lowered the crystallization temperature and increased the temperature range of the mesophase. Surprisingly, dimerized linoleic acid also forms an LC phase. When using branched aliphatic acids with the branching point close to the acid moiety, the mesophase was lost, whereas phosphonic acid or benzenesulfonic acid derivatives did have a mesophase, showing that the generality of this approach extends beyond carboxylic acids as the hydrogen-bond donor. Furthermore, a polymerizable LC phase was obtained from mixtures of with a methacrylate-bearing fatty acid, providing an approach for the fabrication of nanoporous polymer films if the methacrylate groups are polymerized. Finally, the higher solubility of methyl- was used to suppress phase separation in stoichiometric mixtures of the template molecule with fatty acids.
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http://dx.doi.org/10.1002/open.201600078DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5167330PMC
December 2016

Probing Force with Mechanobase-Induced Chemiluminescence.

Angew Chem Int Ed Engl 2016 Jan 9;55(4):1445-9. Epub 2015 Dec 9.

Laboratory of Macromolecular and Organic Chemistry and the Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands.

Mechanophores capable of releasing N-heterocyclic carbene (NHC), a strong base, are combined with triggerable chemiluminescent substrates to give a novel system for mechanically induced chemiluminescence. The mechanophores are palladium bis-NHC complexes, centrally incorporated in poly(tetrahydrofuran) (pTHF). Chemiluminescence is induced from two substrates, adamantyl phenol dioxetane (APD) and a coumaranone derivative, upon sonication of dilute solutions of the polymer complex and either APD or the coumaranone. Control experiments with a low molecular weight Pd complex showed no significant activation and the molecular weight dependence of the coumaranone emission supports the mechanical origin of the activation. The development of this system is a first step towards mechanoluminescence at lower force thresholds and catalytic mechanoluminescence.
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http://dx.doi.org/10.1002/anie.201508840DOI Listing
January 2016

Mechanochemical Reactions Reporting and Repairing Bond Scission in Polymers.

Top Curr Chem 2015 ;369:209-38

Laboratory of Supramolecular Polymer Chemistry, Department of Chemical Engineering and Chemistry, Institute for Complex Molecular Systems, Eindhoven University of Technology, 513, 5600 MB, Eindhoven, The Netherlands.

The past 10 years have seen a resurgence of interest in the field of polymer mechanochemistry. Whilst the destructive effects of mechanical force on polymer chains have been known for decades, it was only recently that researchers tapped into these forces to realize more useful chemical transformations. The current review discusses the strategic incorporation of weak covalent bonds in polymers to create materials with stress-sensing and damage-repairing properties. Firstly, the development of mechanochromism and mechanoluminescence as stress reporters is considered. The second half focuses on the net formation of covalent bonds as a response to mechanical force, via mechanocatalysis and mechanically unmasked chemical reactivity, and concludes with perspectives for the field.
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http://dx.doi.org/10.1007/128_2015_641DOI Listing
February 2016

Dioxetane scission products unchanged by mechanical force.

Chemphyschem 2014 Nov 21;15(16):3565-71. Epub 2014 Aug 21.

Laboratory of Macromolecular and Organic Chemistry, Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (The Netherlands).

Dioxetane-based force-induced light emission from polymers, or mechanoluminescence, is a powerful new way of characterizing the behavior of polymeric materials under stress. Here, we reveal that breaking the dioxetane mechanically gives strikingly similar products to those formed on thermal activation, with a singlet/triplet ratio of 1:9.9 and a total quantum yield of 9.8%. A sensitized relay scheme ensured high reproducibility in the detection of the short-lived triplet products. In addition to guiding the design of more sensitive mechanoluminescent probes, the similarity in the scission products indicates that once mechanical force releases the steric lock between the adamantyl groups, the dioxetane undergoes scission in a pathway that resembles the thermal process. Excited states are formed only after the main transition state in a region in which the excited- and ground-state surfaces are nearly degenerate, which, thus, accounts for the remarkable similarity in the scission products.
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http://dx.doi.org/10.1002/cphc.201402365DOI Listing
November 2014

Increasing the maximum achievable strain of a covalent polymer gel through the addition of mechanically invisible cross-links.

Adv Mater 2014 Sep 17;26(34):6013-8. Epub 2014 Jul 17.

Department of Chemistry, Duke University, Durham, NC, 27708-0346, USA.

Hydrogels and organogels made from polymer networks are widely used in biomedical applications and soft, active devices for which the ability to sustain large deformations is required. The strain at which polymer networks fracture is typically improved through the addition of elements that dissipate energy, but these materials require extra work to achieve a given, desired level of deformation. Here, the addition of mechanically "invisible" supramolecular crosslinks causes substantial increases in the ultimate gel properties without incurring the added energetic costs of dissipation.
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http://dx.doi.org/10.1002/adma.201401570DOI Listing
September 2014
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