Abstract
Wir beobachteten eine effiziente Induktion von Chiralität in dünnen Polyfluoren‐Copolymer‐Dünnschichten durch Mischen mit chiralen Additiven vom Helicen‐Typ basierend auf dem Dibenzo
c
,
h
...acridin‐Motiv. Bilder, die mittels Circulardichroismus (CD)‐ und zirkular polarisierter Lumineszenz (CPL)‐Mikroskopie erhalten wurden, liefern Informationen zu den chiralen Anordnungen in den dünnen Schichten mit beugungsbegrenzter Auflösung. Das CD‐Signal zeigt eine charakteristische Abhängigkeit von der Filmdicke, was für einen supramolekularen Ursprung der starken chiralen Antwort des Copolymers spricht. Insbesondere demonstrieren wir die Unterscheidung zwischen Filmen mit entgegengesetzter Chiralität auf Basis ihrer ultraschnellen transienten chiralen Antwort mit Hilfe von Femtosekunden‐Breitband‐CD‐Spektroskopie und einem neu entwickelten Aufbau für die transiente CPL‐Spektroskopie mit 28 ps Zeitauflösung. Eine systematische Variation des Enantiomeren‐Überschusses des chiralen Additivs zeigt, dass das “Feldwebel und Soldaten”‐Konzept und die “Mehrheitsregeln” nicht eingehalten werden.
Herein, the synthesis of a new monomer containing a protected thiol group, 2-(acetylthio)ethyl methacrylate (AcSEMA), is introduced. The monomer has been copolymerized viaatom transfer radical ...polymerization (ATRP) with 2-(2-methoxyethoxy)ethyl methacrylate (MEO sub(2)MA) to obtain a series of well-defined hidden-thiol functionalized thermosensitive polymers. The new system exhibits a sharp lower critical solubility temperature (LCST) and after hydrolysis of the acetyl group, the thiolated copolymers exhibit pH responsiveness. Moreover, to show the versatility of AcSEMA, P(MEO sub(2)MA-co-AcSEMA) copolymers were in situhydrolyzed and modified by thiol-ene Michael addition with some acrylate compounds. The click reaction was successfully performed as revealed by NMR and the change in the LCST. We finally demonstrate that the addition of these polymer coatings onto gold nanoparticles (AuNPs) results in the formation of stable, colloidal thermosensitive polymeruNP complexes due to bridge formation between the thiol groups of AcSEMA and the metallic NP surfaces. The formation of temperature responsive polymer coated plasmonic nanoparticles shows the promise of P(MEO sub(2)MA-co-AcSEMA) copolymers for building multifunctional nanostructures for drug-delivery, diagnosis, tagging, catalysis and organic electronics systems.
Radical Ring‐opening polymerization (RROP) of cyclic ketene acetals (CKAs) emerges to be a valuable polymerization technique. In attracting more attention, RROP has seen a new spike in publications, ...which the authors will put into perspective. This review will hence address the progress made on the number of available CKAs and the synthetic strategies to get them. In grouping, the available monomers into distinct categories, the enormous variety of available CKAs will be highlighted. Polymerizations of CKAs without vinylenes have the potential to yield fully biodegradable polymers, which is why this kind of polymerization is the focus of this review. Detailing the current understanding of the mechanism, the various side reactions will be noted and also their effect on the overall properties of the final polymers. Current attempts to control the ring‐retaining and branching reactions will be discussed as well. In addition to the polymerization itself, the available materials will be discussed as well as homopolymers, copolymers of CKAs, and block‐copolymers with pure CKA‐blocks have significantly widened the range of possible applications of materials from RROP. Altogether this review highlights the progress in the entire field of RROP just of CKAs to give a holistic overview of the field.
Cyclic ketene acetals (CKAs) polymerize into polyesters through radical ring‐opening polymerization. A large number of CKAs are now available through a multitude of synthetic routes. The polyesters then have distinct structural irregularities like ring‐retaining and branching units, which affect the macroscopic properties of the materials. This review addresses the points mentioned and looks at possible applications as amphiphilic block‐copolymers.
Thermoplastic elastomers (TPEs) combine the features of vulcanized thermoset rubbers and thermoplastic materials in their phase-separated microdomain structure. As a consequence soft, flexible and ...resilient materials are obtained, which can be high-speed processed from the melt state. In the last decades, a variety of polymerization strategies has been proven successful to synthesize block copolymers for TPE materials on an industrial scale. Motivated by the outstanding properties of natural rubber (cis-1,4-polyisoprene), the alkyllithium initiated anionic polymerization of isoprene and butadiene plays a key role for the flexible block of TPEs. The synthesis of ABA-type triblock copolymers based on styrene and 1,3-dienes leads to phase-segregated systems which do not require chemical crosslinking. The living character of the carbanionic chain end was utilized in numerous studies to synthesize complex, defined comonomer sequences by multi-step synthesis. Systematic variation of numerous parameters, e.g., block size and sequence allowed to correlate the resulting mechanical and morphological properties with polymer structure. In this review the focus is placed on multiblock structures and gradient copolymers, addressing key parameters of the molecular architecture to enable a general concept for the design of TPE materials with tailor-made properties. The choice of monomers, also bio-based diene structures such as β-myrcene or β-farnesene is another parameter. The major focus is put on the direct, i.e. statistical anionic copolymerization kinetics as the method of choice to synthesize rather complex multiblock sequences in a one-pot reaction. On-line spectroscopic methods are presented that enable to monitor the monomer consumption during the copolymerization, which directly translates to the comonomer incorporation and gradient formation. To enable precise insight into the comonomer composition of the formed chains, an overview of the theory of copolymerization and the determination of reactivity ratios is given. Kinetic Monte Carlo simulation (kMC) is a versatile tool. Based on experimentally determined kinetic rate constants, the copolymerization can be performed in silico. This enables access to relevant parameters, as for example the conversion as a function of the time as well as the composition and monomer sequence in individual chains, which allow rational design and evaluation of synthetic experiments.
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Previous studies have demonstrated that films of sequence‐controlled amphiphilic copolymers display contact angles that depend on microblock size. This suggests that microblock length may provide a ...means of tuning surface and interfacial properties. In this work, the interfacial rheology of a series of sequence‐controlled copolymers, prepared through the addition of bicyclo4.2.0oct‐1(8)‐ene‐8‐carboxamide (monomer A) and cyclohexene (monomer B) to generate sequences up to 24 monomeric units composed of (AmBn)i microblocks, where m, n, and i range from 1 to 6. Interfacial rheometry is used to measure the mechanical properties of an air–water interface with these copolymers. As the microblock size increases, the interfacial storage modulus, G′, increases, which may be due to an increase in the size of interfacial hydrophobic domains. Small‐angle X‐ray scattering shows that the copolymers have a similar conformation in solution, suggesting that any variations in the mechanics of the interface are due to assembly at the interface, and not on solution association or bulk rheological properties. This is the first study demonstrating that microblock size can be used to control interfacial rheology of amphiphilic copolymers. Thus, the results provide a new strategy for controlling the dynamics of fluid interfaces through precision sequence‐controlled polymers.
The viscoelasticity and stress relaxation dynamics of fluid interfaces can be controlled through the microblock length of precision amphiphilic copolymers.
Concurrent with the rapid development of both dendrimers and hyperbranched polymers, a novel class of block copolymer architectures has emerged from the combination of these dendritic architectures ...with linear chains, the “
linear–
dendritic block copolymers” (LDBCs). This review gives a comprehensive summary of the state of the art in this rapidly developing field from pioneering early work to promising recent approaches.The different strategies leading to these hybrid architectures with either perfect dendrimer/dendron building blocks or imperfect, yet more conveniently accessible hyperbranched segments, are reviewed and compared. The consequences of the unusual polymer topology for supramolecular structures both in solution and in the solid state are summarized, and important differences in comparison with classical linear block copolymer structures are highlighted. Current challenges in the area of block copolymers, nanotechnology and potential applications of linear–dendritic block copolymers are also considered.
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Gradient copolymers are members of a unique class of copolymer in which the monomer composition changes gradually from one end of the polymer chain to the other. In general, the ...properties of copolymers are strongly dependent on composition and sequence distribution, and hence gradient copolymers can exhibit unique properties compared to those of block and statistical copolymers. This review presents an overview of the methods of synthesis of gradient copolymers using the range of available polymerization techniques, and compares and contrasts the properties of gradient copolymers with properties of the analogous block and statistical copolymers.
New thiazolothiazole‐dithienosilole copolymer semiconductors bearing side chains of different type, size, and topology were synthesized and used to demonstrate the influence of side chains on ...morphology, charge transport and photovoltaic properties. The field effect mobility of holes varied from 0.01‐0.03 cm2V−1s−1 in PSOTT and PSEHTT to 0.12 cm2V−1s−1 in PSOxTT. The average power conversion efficiency of solar cells under 1.0 sun illumination could be varied from 2.1% in PSOxTT and 4.1% in PSOTT to 5.0% in PSEHTT. The highest photovoltaic efficiency achieved in PSEHTT, that has all‐branched alkyl side chains and face‐on π‐stacking orientation, was corroborated by its enhanced charge photogeneration observed by transient absorption spectroscopy.
New copolymer semiconductors, based on thiazolothiazole and dithienosilole moieties (PSOTT, PSEHTT and PSOxTT), were synthesized and used to demonstrate effects of side chains on the performance of solar cells. Solar cells under one sun illumination showed an average power conversion efficiency of 2.1% (PSOxTT), 4.1% (PSOTT) and 5.0% (PSEHTT), demonstrating the dramatic effects of the type and topology of side chains.
The graft‐through synthesis of Janus graft block copolymers (GBCPs) from branched macromonomers composed of various combinations of homopolymers is presented. Self‐assembly of GBCPs resulted in ...ordered nanostructures with ultra‐small domain sizes down to 2.8 nm (half‐pitch). The grafted architecture introduces an additional parameter, the backbone length, which enables control over the thermomechanical properties and processability of the GBCPs independently of their self‐assembled nanostructures. The simple synthetic route to GBCPs and the possibility of using a variety of polymer combinations contribute to the universality of this technique.
Independently tunable polymer properties: Janus graft block copolymers were synthesized with different backbone length, which serves as a handle for tuning of the thermomechanical properties of the polymer. Simultaneously, the size of the ultra‐small nanodomains is controlled by the side chain length. A broad range of monomers can be used.
Two novel wide‐bandgap copolymers, PBDT‐TDZ and PBDTS‐TDZ, are developed based on 1,3,4‐thiadiazole (TDZ) and benzo1,2‐b:4,5‐b′dithiophene (BDT) building blocks. These copolymers exhibit wide ...bandgaps over 2.07 eV and low‐lying highest occupied molecular orbital (HOMO) levels below −5.35 eV, which match well with the typical low‐bandgap acceptor of ITIC, resulting in a good complementary absorption from 300 to 900 nm and a low HOMO level offset (≤0.13 eV). Compared to PBDT‐TDZ, PBDTS‐TDZ with alkylthio side chains exhibits the stronger optical absorption, lower‐lying HOMO level, and higher crystallinity. By using a single green solvent of o‐xylene, PBDTS‐TDZ:ITIC devices exhibit a large open‐circuit voltage (Voc) up to 1.10 eV and an extremely low energy loss (Eloss) of 0.48 eV. At the same time, the desirable high short‐circuit current density (Jsc) of 17.78 mA cm−2 and fill factor of 65.4% are also obtained, giving rise to a high power conversion efficiency (PCE) of 12.80% without any additive and post‐treatment. When adopting a homotandem device architecture, the PCE is further improved to 13.35% (certified as 13.19%) with a much larger Voc of 2.13 V, which is the best value for any type of homotandem organic solar cells reported so far.
Two novel 1,3,4‐thiadiazole‐based wide‐bandgap copolymers, PBDT‐TDZ and PBDTS‐TDZ, are developed for efficient nonfullerene organic solar cells. The single‐junction devices processed by a green solvent of o‐xylene exhibit a high power conversion efficiency (PCE) of 12.80% with a low energy loss of 0.48 eV. The PCE is finally improved to 13.35% when using a homotandem device architecture.
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