Dibromomaleimide Derivative as an Efficient Polymer Coupling Agent for Building Topological Polymers

The dibromomaleimide derivative, N‐(4‐bromobutyl)‐dibromomaleimide (dBMIB), is found to be a highly efficient coupling agent to dimerize thiol‐terminated hydrophilic polymers by substituent reaction. When mono‐thiol poly(ethylene oxide) (PEO₄₅‐SH) is mixed with dBMIB in an equivalent molar feed in water, a dimer of PEO₄₅ with a maleimide unit located at the chain center, (PEO₄₅)₂MIB, is obtained quantitatively. The dBMIB is also used to dimerize thiol‐ terminated poly(N‐(2‐acryloyloxyethyl) pyrrolidone) and poly(N,N‐dimethyl acrylamide). Moreover, the butylene bromide of (PEO₄₅)₂MIB is transferred into a butylene azide, which is allowed to react with alkynyl‐terminated polystyrene to give a A₂B miktoarm star polymer via a copper‐catalyzed azide–alkyne cycloaddition coupling reaction.     

Synthesis and Photopolymerization of Thiol‐Modified Triazine‐Based Monomers and Oligomers for the Use in Thiol‐Ene‐Based Dental Composites

Thiol‐ene photopolymerizations combine the unique features of step‐growth reactions and photoinitiated polymerizations, so that they experience a growing interest for applications such as coatings or dental restoratives. Most studies have making use of a relatively flexible ester and the hydrolytically labile derivative pentaerythritoltetra(3‐mercaptopropionate) ( PETMP ) as the thiol component in common. In this study, the performance of hydrolytically stable 1,3,5‐tris(3‐mercaptopropyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4a ), 1,3,5‐tris(2‐methyl‐3‐mercapto‐propyl)‐1,3,5‐triazine‐2,4,6‐trione ( 4b ), and oligomers thereof in thiol‐ene photopolymerizations is investigated. The oligomers are prepared via thiol‐Michael or thiol‐isocyanate additions by using 4a and suitable diacrylates or diisocyanates containing a rigid core structure. Compared with PETMP , the thiol derivative 4a shows better flexural strength and modulus of elasticity in thiol‐ene photopolymerizations with 1,3,5‐triallyl‐1,3,5‐triazine‐2,4,6‐trione ( TATATO ) as the‐ene derivative. This phenomenon becomes especially evident after storage in water at 37 °C for 24 h. Furthermore, the performance regarding the flexural strength, the Young's modulus of elasticity, the polymerization shrinkage stress of 4a , and the polyadducts thereof in dental filling composites is evaluated and discussed.

     

Thiol‐Functionalized Organic Porous Polymers as a Support for Gold Nanoparticles and Its Catalytic Applications

In this work, a novel synthesis approach of gold nanohybrid materials (Au/SH‐OPPs) is demonstrated using the thiol‐functionalized organic porous polymers (SH‐OPPs) as a support by a combination of hyper‐cross‐linking and molecular templating of functionalized bottlebrush copolymers. HAuCl₄ as the gold source is in situ reduced to produce Au nanoparticles based on the strong action of gold with the thiol groups. The monodispersed Au nanoparticles are anchored on the SH‐OPPs with the small average particle size (3.0 ± 1.0 nm) and the high loading about 18%. Moreover, the resultant Au/SH‐OPPs exhibit excellent catalytic performance for the selective oxidation of benzyl alcohol.

     

Thieno[3,4‐c]pyrrole‐4,6‐dione‐Based Polymers for Optoelectronic Applications

Over the last decade, great progress has been made in the field of organic electronics. Advancements in organic syntheses as well as in device engineering enabled preparation of polymer solar cells with power conversion efficiency (PCE) exceeding 8%–9%. In search for new polymers suitable for photovoltaic applications, push–pull polymers containing thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) motif as an electron deficient (pull) unit emerged as very promising candidates. This Trend Article summarizes research on TPD‐based polymers with a special emphasis on the structure–property relationships.     

Photoluminescence of Self‐organized Perylene Bisimide Polymers

Summary: Three polymers consisting of alternating perylene bisimide chromophores and flexible polytetrahydrofuran segments of different length have been studied using absorption and (time‐resolved) photoluminescence spectroscopy. In o‐dichlorobenzene, the chromophores self organize to form H‐like aggregates. The photoluminescence spectra of the self‐organized polymers consist of vibronically resolved monomeric perylene bisimde fluorescence (λ_max = 538 nm, τ = 3.9 ns) and unstructured excimer‐type emission (λ_max = 635 nm, τ = 17 ns). An additional short‐lived (τ ≈ 2 ns) luminescence component is observed and ascribed to the dynamic deactivation of the monomeric photoexcited state via excimer formation or energy transfer.

Structure of alternating perylene bisimide – polyTHF copolymers.     

Application of Nitroxide‐Terminated Polymers Prepared by Sonochemical Degradation in the Synthesis of Block Copolymers

Summary: The ultrasonic irradiation of a polymer solution results in the breakage of macromolecular C? C bonds. In the presence of radical scavengers the formed macroradicals are prevented from termination reactions as combination or disproportionation. Using nitroxides as trapping agents the polymer is transformed into a macroinitiator, which can be used in controlled free‐radical polymerization to synthesize block copolymers. In this work several polymers were exposed to sonochemical degradation and terminated with various nitroxides, e.g. OH‐TEMPO and TIPNO. In a second reaction step the prepared polymer‐nitroxide‐adducts were applied as macroinitiators in controlled free‐radical polymerizations with styrene. The obtained products were mixtures of block copolymer and the corresponding homopolymers. The visco‐elastic properties were investigated by rheological analysis. A special separation technique with selective solvents was applied to determine the content of block copolymer.

Synthesis of block copolymers with sonochemically prepared macroinitiators.     

Anionic Grafting to Strategies for Functional Polymethacrylates: Convenient Preparation of Stimuli‐Responsive Block Copolymer Architectures

Functional block copolymers (BCP) are promising candidates for many important applications in fields of separations technologies, drug delivery, or (nano)lithography. Here, a universal strategy is described for the preparation of functional poly(methacrylate)s grafted (PMA) to polystyrene‐block‐polyisoprene (PS‐b‐PI) BCPs via a convenient postmodification strategy. PS‐b‐PIs are functionalized by means of hydrosilylation protocols for the introduction of chlorosilane moieties. Subsequent anionic grafting‐to polymerization of different functional PMA macro anions leads to grafted BCP. Various functional and non‐functional homopolymers, that is, poly(di(ethylene glycol) methyl ether methacrylate), poly(methacrylic acid), and poly(3‐methacryloxypropyl)heptaisobutyl‐T8‐silsesquioxane as well as poly(methyl methacrylate), poly(n‐butyl methacrylate), poly(iso‐propyl methacrylate), poly(tert‐butyl methacrylate), and poly(2‐hydroxy ethyl methacrylate) are block‐selectively incorporated into the PI segment. Applied grafting strategies for the non‐functional PMA derivatives, which feature different sizes of the alkyl substituent, reveal a strong influence on the grafting‐to efficiency. The grafted BCP architectures are capable of undergoing microphase separation in the bulk state, while the resulting morphology is significantly influenced by the introduction of PMA segments as shown by transmission electron microscopy measurements. Additionally, the structure formation and pH‐switching capability of the poly(methacrylic acid)‐grafted BCP is studied by dynamic light scattering, proving the feasibility for the herein investigated synthesis strategy.     

Asymmetric Aldol Polymerization: Synthesis of Optically Active Polymers Based on the Asymmetric Mukaiyama Aldol Reaction

Repetitive asymmetric aldol reactions between bis(trimethylsilyl thioketene acetal) 2 and dialdehyde ( 3 , 4 ) proceeded smoothly in the presence of enantiopure N‐tosyl oxazaborolidinone 1 as a chiral Lewis acid catalyst. Optically active poly(β‐hydroxy thioester)s ( 10 , 11 ) having main‐chain configurational chirality were obtained by the asymmetric aldol polymerization. Precise model reaction studies supported the idea that asymmetric aldol polymerization should occur in a stereoselective manner. Degradation of the optically active polymers followed by chiral HPLC analysis of the degraded products was found to be a useful method to estimate the optical purity of the polymers.     

Design of Random and Semi‐Random Conjugated Polymers for Organic Solar Cells

Significant effort has been devoted to the improvement of organic solar cell performance via the optimization of polymer structure. The expanding scope of conjugated polymer design extends from novel monomers to side‐chain and backbone engineering. These efforts target desired properties for optimal organic photovoltaic performance, including electronic aspects such as optical band gaps, frontier orbital levels, and charge carrier mobilities, as well as physical aspects such as surface energy. Perfectly alternating, donor‐acceptor copolymers represent the state‐of‐the‐art, having low band gaps and demonstrating record efficiencies. However, recent reports indicate significant potential by introducing some degree of randomization to donor‐acceptor copolymers. Specifically, semi‐random copolymers have demonstrated promising photovoltaic performance through incorporation of small ratios of acceptor monomers into a donor‐dominant polymer backbone. Semi‐random polymers have also been found uniquely suited to the optimization of ternary blend solar cells, which benefit from highly tunable randomized structures by means of energy level matching, complementary optical absorption, and directed polymer‐polymer miscibility via surface energy tuning. In this trend article the scope of random and semi‐random polymers, many based on poly(3‐hexyl thiophene), is explored, primarily in the context of solar cell applications. Distinctions between regimes of random copolymers are also defined and discussed.     

Tailored Semiconducting Polymers: Living Radical Polymerization and NLO‐Functionalization of Triphenylamines

This paper describes the preparation of various polymers with triarylamine side groups. High molecular weight materials were obtained by free radical polymerization utilizing the gel effect. Polymers with a narrow polydispersity and a predetermined molecular weight could be prepared by living radical polymerization. The T_g could, thereby, be controlled between 50 and 140°C either by using different monomers or by varying the molecular weight. Living radical polymerization allowed in addition the preparation of block copolymers. The triarylamine side groups could be transformed into NLO‐chromophores by reaction with tetracyanoethylene. This leads to the incorporation of tricyanoethylene acceptor groups. As this reaction can be performed selectively on one block in block copolymers, microphase separated structures are accessible, which possess charge transport moieties in one phase and NLO‐chromophores in the other phase.     

Recent Advances in the Design of Ionenes: Toward Convergence with High‐Performance Polymers

Ionenes, condensation polymers wherein the charge (typically cationic) lies directly within the polymer backbone, have been known for over 85 years. Historically, ionenes have been synthesized from 3^o diamines and α,ω‐dihaloalkanes, forming chains of ammonium cations tethered by flexible hydrocarbon linkages with “free” halide anions. However, the requisite building blocks of ionenes are by no means limited only to such molecules. In recent years, ionenes with more sophisticated backbone chemistries have been produced, with a trend toward the use of functionalities associated with classical “high‐performance” condensation polymers such as polyimides and polyarylamides. The expansion of ionenes is also catalyzed by the rapid growth of research in imidazolium‐based ionic liquids (ILs), wherein the combination of ionenes with ILs can yield unexpected behaviors. Furthermore, when considering the largely unexplored experimental space in anionic ionenes, the opportunities for new materials are virtually endless. This review primarily focuses on developments in ionenes published in the scientific literature since 2010, but also includes some older examples that may not have received sufficient attention at the time of their original publication yet can provide some key lessons for the future of ionene design.     

Azobenzene‐Containing Triblock Copolymer Adhesive Based on Light‐Induced Solid–Liquid Phase Transition: Application to Bonding for Various Substrates

Azobenzene‐containing block copolymers have been previously developed as light‐induced reworkable adhesives that can undergo repeatable bonding/debonding on demand, based on photoisomerization of the azobenzene moiety and concomitant softening/hardening of the azo polymer block. For practical use, the applicability of such adhesives to various types of substrates is important and is thus studied as one of their most fundamental properties in this work. Ultraviolet (UV)‐transparent acrylic resin as well as non‐transparent polycarbonate resin, polyethylene ones, and metallic aluminum substrates are utilized as substrates. UV‐transparent acrylic resin is used as one of two substrates to investigate the photoisomerization process. The bonding/debonding process is successful for these substrates, and single lap shear tests show typical adhesion strengths of 1.5–2.0 MPa for the substrates investigated. UV irradiation induced a decrease in the adhesion strength to 0.03 MPa irrespective of the substrate type, indicating that the mechanism of the detachability is flow of the softened adhesive. Facile removal of the residual adhesive on the substrate is successfully demonstrated after detachment without any damage to the substrates by wiping the substrate with laboratory‐grade disposable wipes wet with ethanol.     

Synthesis and Characterization of Functional Triphenylphosphine‐Containing Microporous Organic Polymers for Gas Storage and Separation

Two kinds of novel triphenylphosphine‐containing microporous organic polymers are designed and synthesized via palladium‐catalyzed Sonogashira−Hagihara coupling condensation reaction of triphenylphosphine oxide‐ and sulfide‐based monomers with different arylethynylene linkers. The gas adsorption isotherms reveal that these polymers have strong binding affinity for CO₂ with high CO₂ adsorption capacity, although they have moderate Brunauer−Emmett−Teller surface area ranging from 684 to 883 m² g⁻¹. Among the resulting polymers, triphenylphosphine oxide–tris(4‐ethynylphenyl)amine exhibits the highest CO₂ uptake capacity of 2.61 mmol g⁻¹ at 273 K and 1.13 bar with relatively high gas selectivity of 60.2 for CO₂ over N₂ at 273 K.     

Click Functionalization of Aromatic Polymers for Organic Electronic Device Applications

The [2 + 2] cycloaddition–retroelectrocyclization between electron‐rich alkynes and tetracyanoethylene (TCNE)/7,7,8,8‐tetracyanoquinodimethane (TCNQ), yielding the tetracyanated donor–acceptor (D–A) chromophores, is a new class of click chemistry reactions, due to the high efficiencies, no byproducts, and applicability to polymer syntheses. As compared to the conventional click reactions represented by the Cu(I)‐catalyzed azide–alkyne cycloaddition (CuAAC), these new click reactions provide fascinating optoelectronic properties originating from the D–A chromophore structures formed. A series of π‐conjugated aromatic polymers containing electron‐rich alkynes were successfully functionalized by these click reactions, producing novel organic or organometallic materials featuring conducting and photovoltaic properties in thin film electronic devices. This review article describes the recent results of the author's research group. The power of click chemistry is highlighted by the polymer synthesis using CuAAC. This is followed by the alkyne–TCNE/TCNQ postfunctionalization to produce high‐performance aromatic polymers for use as active components in organic electronic devices, such as thin film transistors, organic solar cells and polymer memory devices.

     

Block Copolymer‐Directed Synthesis of Conjugated Polyimine Nanospheres with Multichambered Mesopores

Conjugated polyimines constructed from aromatic amines and aromatic aldehydes have attracted enormous attention because of their excellent and fascinating properties. However, the structure of these materials constructed by building blocks or linkers is usually confined to a scope of microporosity and small mesopores (less than 5 nm), which largely impedes their applications in many fields. Here, a facile self‐assembly strategy is developed to controllably fabricate conjugated polyimines nanospheres with multichambered mesoporous architecture by using polystyrene‐b‐poly(acrylic acid) diblock copolymer as a soft template. Given the wide availability of amines and aldehydes, it is expected to open new avenues for designing diverse polyimine‐based materials with controlled mesostructure toward applications.     

Bioinspired Functional Gradients for Toughness Augmentation in Synthetic Polymer Systems

In nature, load‐bearing polymeric materials that do not present significant trade‐off between elongation and elastic modulus are often found, but are rare in synthetic systems. One mechanism for emulating these natural systems is with functionally graded materials (FGMs). The development of synthetic FGM systems with varying moduli gradient using tuned poly(meth)acrylate multilayers is shown. Such localized tuning of crosslink density is shown as a mechanism to increase rigidity without significant compromise to maximum strain. The toughest FGM shows 43% higher tensile strength and 9% higher stiffness than copolymer elastomers with similar maximum strain (ε_max ≈ 110%), increasing toughness by 25%. These improved tensile mechanical properties can be due to beneficial interlayer crack deflection and delamination. This gradient approach provides potential to improve toughness of various load‐bearing polymeric materials.     

Photoinduced Charge Separation of Self‐Organized Semiconducting Superstructures Composed of a Functional Polymer–TiO2 Hybrid

The incorporation of TiO₂ nanoparticles into long (several micrometers) fibers of a gel‐forming poly(para‐phenylene vinylene) (PPV) derivative is described. For that purpose, a PPV‐block‐dopamine polymer is synthesized, which is used to coat TiO₂ nanoparticles leading to well‐dispersed nanoparticles and fluorescence quenching of the polymer. Independently, the homopolymer gels in various organic solvents are observed to form long fibers. By mixing the PPV homopolymer with the TiO₂‐PPV hybrid, we are able to incorporate the nanoparticles into the fibrous network, as shown in transmission electron microscopy (TEM) images. Photoinduced charge separation is measured by Kelvin probe force microscopy. Upon illuminating the polymer fibers, positive charges are observed, even at distances of around 300 nm. From these results, charge transport along the polymer fibers is inferred.

     

The Process of Functional Conjugated Organic Polymers Derived from Triple‐Bond Building Blocks

Polyacetylenes, poly(p‐phenyleneethynylenes), and polydiacetylenes, as conjugated polymers derived from triple‐bond containing building blocks, attain considerable attention because of their electronic and photoconduction properties. In this review, recent studies on the design and synthesis of conjugated polymers derived from triple‐bond building blocks are summarized with an emphasis on the developments in our group in recent years. Our intense attention is focused on constructing different molecular systems with enhanced light‐harvesting efficiency, and determining the functional properties of conjugated organic polymers. The conjugated organic polymers that appear in this review are useful candidates for various potential applications because of their extraordinary optical and electronic properties. The potential applications of the conjugated polymer‐containing systems are explored.

     

Ultrasound‐Induced Disruption of Amphiphilic Block Copolymer Micelles

Ultrasound‐induced disruption of PEO‐b‐PTHPMA, PEO‐b‐PIBMA, PEO‐b‐PTHFEMA, and PEO‐b‐PMMA block copolymer micelles in aqueous solution was investigated. Fluorescence change of loaded NR, DLS, IR, AFM, and SEM show that those micelles could be disrupted differently by 1.1 MHz high‐intensity focused ultrasound beams. The micelles of PEO‐b‐PIBMA and PEO‐b‐PTHPMA appear to be more sensitive to ultrasound irradiation, resulting in a more severe micellar disruption, and IR spectra show evidence of ultrasound‐induced chemical reactions, most likely hydrolysis. PEO‐b‐PMMA appear to resist HIFU irradiation better, and IR analysis found no evidence of chemical reactions. This study provides new evidence for the prospect of ultrasound‐responsive BCP micelles for controlled delivery applications.

     

Influence of Smectic Liquid Crystallinity on Lamellar Microdomain Structure in a Main‐Chain Liquid Crystal Block Copolymer Fiber

The microlamellar and smectic liquid crystal (LC) structures of a block copolymer of a main‐chain LC polyester connected at both ends with poly(ethyl methacrylate) are investigated by fiber X‐ray scattering. In the as‐spun fiber, the lamellae are parallel to the fiber axis, while the smectic layers are perpendicular to it. Annealing the as‐spun fiber at a temperature higher than the isotropization temperature (T_i) of the LC segment preserves the lamellae, but the LC structure disappears. Further annealing the fiber at T < T_i improves the lamellar stacking coherence and aligns the smectic layers parallel to the lamellae. In contrast, annealing the as‐spun fiber at T < T_i conserves the smectic layers and arranges the lamellae in parallel to the smectic layers. Thus, the liquid crystallinity affects the lamellar ordering and orientation.