Tuning the solubility of hepta(p-benzamide)s via the monomer sequence

The automated synthesis of hepta(p-benzamide) hetero sequences on solid support using a modified peptide synthesizer is reported. The oligomers are synthesized from 4-aminobenzoic acid and 4-amino-2-(hexyloxy)benzoic acid, the latter carrying a solubilizing hexyl side chain. It is known from previous studies that both the unsubstituted hepta(p-benzamide) and the fully hexyloxy-substituted hepta(p-benzamide) are insoluble in all common organic solvents. Heterosequences in which both types of monomers alternate are, however, soluble in polar organic solvents such as DMSO. The heterosequence heptamers behave as strong organogelators when DMSO solutions are left at room temperature for several hours. Transmission electron microscopic (TEM) investigations revealed that the gelation was due to the oligomers forming long entangled fibers via a non-covalent aggregation mechanism. We explain these phenomena by a heterosequence triggered switch of aggregation mechanism. The unsubstituted oligomers strongly aggregate via a directional hydrogen-bond driven mechanism which changes to a less directional π-interaction driven aggregation mechanism for the substituted oligomers.We thereby demonstrate that designed hetero sequences in non-natural oligoamides can lead to materials with distinctly different conformations which directly affects the intermolecular interactions and their supramolecular organization

Sequence-controlled synthesis of soluble oligo(p-benzamide)s

This work focused on the synthesis of novel monomers for the design of a series of oligo(p-benzamide)s following two approaches: iterative solution synthesis and automated solid phase protocols. These approaches present a useful method to the sequence-controlled synthesis of side-chain and main-chain functionalized oligomers for the preparation of an immense variety of nanoscaffolds. The challenge in the synthesis of such materials was their modification, while maintaining the characteristic properties (physical-chemical properties, shape persistence and anisotropy). The strategy for the preparation of predictable superstructures was devote to the selective control of noncovalent interactions, monodispersity and monomer sequence. In addition to this, the structure-properties correlation of the prepared rod-like soluble materials was pointed. The first approach involved the solution-based aramide synthesis via introduction of 2,4-dimethoxybenzyl N-amide protective group via an iterative synthetic strategy The second approach focused on the implementation of the salicylic acid scaffold to introduce substituents on the aromatic backbone for the stabilization of the OPBA-rotamers. The prepared oligomers were analyzed regarding their solubility and aggregation properties by systematically changing the degree of rotational freedom of the amide bonds, side chain polarity, monomer sequence and degree of oligomerization. The syntheses were performed on a modified commercial peptide synthesizer using a combination of fluorenylmethoxycarbonyl (Fmoc) and aramide chemistry. The automated synthesis allowed the preparation of aramides with potential applications as nanoscaffolds in supramolecular chemistry, e.g. comb-like-hairy- and Janus rods. Additionally, the synthesis of benzamide-aspartic acid amphiphiles was presented and the aggregation properties in water were discussed. Finally, polydisperse homopolymers derived from the hexyl- and glycol- functionalized monomers were prepared via polycondensation through triphenyl phosphite- and N-sulfinylaminobenzoyl chloride activation. Solubility, thermal stability as well as the liquid crystalline properties of the polymers were analyzed.Im Rahmen dieser Arbeit wurden neue Monomere hergestellt und zur Darstellung einer Serie von löslichen Oligo(p-benzamid)en nach zwei Syntheserouten eingesetzt: der iterativen Lösungssynthese und der Festphasensynthese. Diese Strategien stellen einen praktischen und schnellen Zugang zur sequenzkontrollierten Synthese von haupt- und seitenkettenfunktionalisierten Oligomeren für den Einsatz als Nanoobjekte dar. Die besondere Herausforderung bei der Herstellung solcher Moleküle bestand darin, ihre interessanten Eigenschaften (Formtreue, Stabilität, Anisotropie) auch nach der Modifizierung zu erhalten. Zusätzlich wurde die Korrelation zwischen Struktur und Eigenschaften der löslichen benzamid-basierten Materialien aufgezeigt. Ein Ansatz beruhte auf der lösungsbasierten Aramidsynthese mittels Einführung der Dimethoxybenzyl N-Amidschutzgruppe. Hierfür wurde eine iterative Syntheseroute, die über Dimer- und Tetramervorstufen verlief, bis zum löslichen Okta(p-benzamid) entwickelt. Der zweite Ansatz beruhte auf der trägerbasierten Synthese von Oligo(p-benzamid)en mit löslichen niedermolekularen Substituenten am aromatischen Oligomerrückgrad. Das Salicylsäure-Gerüst ermöglichte somit, zum einen die Einführung von Substituenten, die das steife Molekülrückgrad solvatisieren und zum anderen, die Stabilisierung von Rotameren über die Ether-Funktionalisierung. Die Durchführung erfolgte in automatisierter Form an einem Peptidsynthesizer unter Verwendung der Fluorenylmethoxycarbonyl (Fmoc) Amin-Schutzgruppe. Homo- und alternierende Hetero-Oligomere von Hexyloxy-, Triethylenglykol substituierten und unsubstituierten Monomereinheiten, wurden dargestellt, wobei die Sequenzkontrolle durch den Einsatz des Peptidsynthesizers erreicht wurde. Die Automatisierung erlaubte die Herstellung von aromatischen Oligoamiden die potentiell Anwendung als Nanoobjekte (z.B. comb-like rods, hairy rods und Janus rods) in der Supramolekularen Chemie finden können. Im Rahmen dieser Arbeit konnten auch Benzamid-Asparaginsäure Amphiphile komplett automatisiert dargestellt werden. Diese Strukturen unterscheiden sich von den üblichen Peptid-Amphiphilen dadurch, dass die Überstrukturbildung allein durch die selbst-organisierenden Eigenschaften der hydrophoben Aramid-Stäbchen hervorgerufen wird. Polydisperse Homopolymere der Hexyl- und Triethylenglykol-substituierten Monomere wurden durch Polykondensation nach der Triphenylphosphit-Methode und über N-Sulfinylaminobenzoylchlorid-Aktivierung hergestellt. Löslichkeit, thermische Stabilität und flüssigkristalline Eigenschaften der Materialien wurden im Rahmen der Arbeit ebenfalls analysiert

Preparation of Piezo-Resistive Materials by Combination of PP, SEBS and Graphene

The use of polyolefins in structural components requires the simultaneous improvement of stiffness and toughness of the matrix, whilst in the case of sensing components during operation, additional functions are needed such as electrical conductivity. However, providing various desired properties without impairing those intrinsic to the materials can be somewhat challenging. In this study we report the preparation of an isotactic polypropylene (iPP)/styrene–ethylene–butylene–styrene triblock copolymer (SEBS)/graphene system that combines enhanced mechanical properties with electrical conductivity. Blends were prepared by solution mixing (SoM) and solution/solid state mixing (SoM/SSM) formulation routes prior to melt processing. The nanocomposites were characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) and the electrical and mechanical properties were evaluated. The materials prepared via the SoM/SSM route displayed good electrical conductivity while retaining the mechanical properties of iPP, making them attractive materials for low cost and high throughput structural components with sensing capacity

Contents

1. Berichterstatter: 2. Berichterstatter

The role of molecular architecture on the viscoelastic properties of thermoreversible polyurethane adhesives

New polyurethane (PUR) adhesives containing covalent Diels-Alder (DA) bonds that can break and form with temperature have been recently developed for sustainable multilayer packaging. The understanding of the mechanical properties and in particular of creep in terms of molecular architecture appears of outmost importance in view of their applications and potential reutilization. Oscillatory shear rheometry shows a modulus decrease with temperature associated to bond breakage and the enhancement found upon cooling can be associated with network reconstruction. Analysis of storage modulus values above the glass transition and below the retro-DA reaction suggests a lower network crosslinking density with increasing adduct content. Room temperature indentation and shear rheometry tests reveal that DA bonds improve the modulus and reduce the resistance to linear viscoelastic flow. The modulus improvement can be associated to the enhanced chain rigidity introduced by the DA moieties and the reduced creep resistance seems to be related to the decrease of crosslinking density.This project has received funding from the Bio Based Industries Joint Undertaking (BBI-JU) under the European Union’s Horizon 2020 research and innovation program under grant agreement N◦ 837715. The authors wish to thank the MICINN (Ministerio de Ciencia e Innovacion), ´ Spain, for funding under grant PID2019-107710 GB-I00. The TEM-BIOPHYM Service at the IEM-CSIC is acknowledged for granting the use of the rheology facilities

Remotely triggered reversible bonds in adhesives for sustainable multi-layered packaging

Plastic films used in food packaging are multi-layered materials comprising different polymer layers each with a specific function, which makes the packaging very difficult to recycle, ending up in landfills or incineration plants. Innovative approaches are required to resolve this issue and this work focuses on the adhesive layers used to bind the polymer layers together. We report on the development of a new, reusable polyurethane adhesive containing dynamic covalent Diels-Alder bonds that can be reversibly opened and closed by controlling the temperature. The breaking/formation cycle of the thermoreversible bonds in the adhesive can be repeated up to ∼20 times. In addition, the incorporation of radiation-absorbing nanoparticles into the adhesive facilitates bond breaking that can be remotely triggered in tens of seconds using NIR radiation. This new adhesive concept will facilitate the recycling of the individual polymer layers, opening the door to a circular economy solution towards sustainable packaging.This project has received funding from the Bio Based Industries Joint Undertaking (BBI-JU) under the European Union’s Horizon 2020 research and innovation programme under grant agreement N◦ 837715Peer reviewe

Designing New Sustainable Polyurethane Adhesives: Influence of the Nature and Content of Diels–Alder Adducts on Their Thermoreversible Behavior

With a view to the development of new sustainable and functional adhesives, two Diels–Alder (DA) adducts are incorporated as a third component into the curing process of solvent-based and solvent-free polyurethanes in this study. The influence of the nature and content of the DA molecules on the retro-DA (rDA) reaction and its reversibility and cyclability is investigated. It is demonstrated that the bonding/debonding properties of the adhesives are mainly controlled by the concentration of the DA adducts, with a minimum thermoreversible bond (TB) content required that depends on the system and the total ratio between all the diols in the formulation. For the solvent-based system, rDA/DA reversibility can be repeated up to ~20 times without deterioration, in contrast to the solvent-free system where a gradual loss in the DA network reconstruction efficiency is observed. Despite this limitation, the solvent-free system presents clear advantages from an environmental point of view. The changes observed in the physical properties of these new thermoreversible adhesives are of great relevance for recycling strategies and, in particular, their potential for separating multilayered film packaging materials in order to recycle the individual polymer films involved.This research was funded by the Bio Based Industries Joint Undertaking (BBI-JU) under the European Union´s Horizon 2020 research and innovation program under grant agreement N◦ 837715

Continuous flow synthesis of organic electronic materials-case studies in methodology translation and scale-up

The continuous flow synthesis of functional thiophene derivatives was examined. Methodology for the lithiation of thiophene building blocks was developed using a commercial bench-top flow reactor. In addition, the advantages of flow processing were demonstrated in the synthesis of a high performance organic dye in gram scale.close

Single Isomer of Indene‑C₇₀ BisadductIsolation and Performance in Bulk Heterojunction Solar Cells

Indene-C₇₀ bisadduct (IC₇₀BA) is a high performance electron acceptor material consisting of a mixture of regioisomers. A single isomer of the IC₇₀BA was isolated by careful chromatographic separation. The structure of this isomer was confirmed by various analytical techniques including single crystal X-ray analysis. The isomer showed superior performance to other isomer mixtures of IC₇₀BA in bulk heterojunction solar cells using poly­(3-hexylthiophene) as the donor material