A novel type of single white‐light‐emitting copolymers, PF‐DTFOx, derived from poly(9,9‐dioctylfluorene) (PF) in which 2,7‐di‐(2‐thienyl)‐9‐fluorenone (DTFO) is introduced as an orange‐emitting unit, is reported, and their application in white‐light polymer light‐emitting devices (PLEDs) is explored. Because of the very simple structure of DTFO, the synthetic routes to PF‐DTFOx are not complicated, and the raw materials are cheap; these are advantageous in reducing the fabrication cost of white‐light PLEDs. In the fluorescence spectra, PF‐DTFOx in solid powder shows dual peaks at around 460 and 560 nm. In white‐light PLEDs, the color of the white‐light emission is tunable; this can be achieved by changing the content of DTFO in PF‐DTFOx. The light‐emission color varies from blue‐white to pure white and orange‐white when the composition of DTFO increases. All the PLEDs based on PF‐DTFOx exhibit maximum luminance above 1800 cd m?2 and a color rendering index above 80.
The radical copolymerization of N‐substituted maleimides containing polymethylene and poly(ethylene oxide) side chains as the N‐substituent groups with isobutene, styrene, and α‐methylstyrene as the electron‐donating monomers is carried out in order to investigate the structure and thermal properties of the resulting comb‐like copolymers. The obtained copolymers show excellent thermal stability and their glass transition temperatures vary depending on the chain length of the introduced N‐substituents. The main‐ and side‐chain motions of the copolymers are investigated by dynamic mechanical analysis at various frequencies over the temperature range of ?150 to 100 °C.
The application of selenol‐X chemistry in nucleophilic substitution and Se‐Michael addition reactions for polymer chain end modification is presented. Selenol‐labeled polystyrene can easily react with alkyl halides, methyl methacrylate, methyl acrylate, pentafluorostyrene, etc. The mild conditions make it attractive for the synthesis of macromonomers. The resulting polymers are analyzed and characterized by UV, size‐exclusion chromatography (SEC), NMR, and matrix assisted laser desorption/ionization time of flight mass spectroscopy.
Cationic polyelectrolytes find potential applications in electronic device fabrication, biosensing as well as in biological fields. Herein, a series of cationic main‐chain polyelectrolytes with pyridinium‐based p ‐phenylenevinylene units that are connected via alkylene spacers of varying lengths are synthesized by a base‐catalyzed aldol‐type coupling reaction. Their mean average molecular weights range from 15 000 to 32 000 g mol‐1, corresponding to about 16–33 repeat units. Due to the presence of alkyl side‐chains and alkylene spacers as well as cationic hard‐charges the polymers are endowed with amphiphilic character and hence, aggregation of these polyelectrolytes at high concentration leads to thermoreversible physical gel formation in dimethyl sulfoxide accompanied by interchain interactions. Morphological analysis shows spherical aggregates in case of C16‐Poly‐S12 in dimethyl sulfoxide. Dependence of gelation behavior on the length of alkyl side‐chains and alkylene spacers of the polyelectrolytes are addressed.
To study the influence of the spacer between the donor (D) and acceptor (A) units in a side chain on the photophysical and photovoltaic performance, a novel side‐chain D–A conjugated copolymer of PDPAT‐BDT‐BT is made, which contains binary donor units of N,N‐diphenylthiophen‐2‐amine (DPAT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT) in the main chain and an appending benzothiadiazole (BT) acceptor unit in the side chain. Compared with its counterpart of PDPAT‐BDT‐BT, which has an additional phenyl spacer between the DPAT and BT units, this PDPAT‐BDT‐BT exhibits a smaller optical bandgap, a broader absorption range, and a lower highest occupied molecular orbital (HOMO) energy level (?5.42 eV), as well as improved photovoltaic properties in bulk heterojunction polymer solar cells containing [6,6]‐phenyl‐C71‐butyric acid methyl ester as an electron acceptor. A maximum power conversion efficiency of 3.27% with an open circuit voltage of 0.87 V and a fill factor of 49.8% are obtained in the cells. This work indicates that the photophysical and photovoltaic performance of the side‐chain D–A polymers in polymer solar cells can be significantly improved by shortening the phenyl spacer between the D and A units.
Hydrophilic naphthalene diimide based acceptor polymers are prepared by the incorporation of triethylene glycol or poly(ethylene glycol) side chains in the monomers and subsequent nitroxide‐mediated polymerization (NMP). The kinetic investigation of the polymerization reveals a controlled chain growth as well as a narrow molar mass distribution. Due to the utilization of a functional NMP initiator, a single Ru(II) photosensitizer unit is readily attached at the polymers chain terminus by a modular approach to construct water soluble photoredox‐active acceptor–photosensitizer dyads. The analysis of the optical properties by steady‐state absorption and emission spectroscopy reveals preserved optical absorption properties of the individual building blocks, and, more importantly, an efficient quenching of the Ru(II) emission assigned to intramolecular charge transfer from the complex to the acceptor polymer. The results demonstrate the versatility of side chain modifications to prepare water‐processible photoredox‐active architectures under preservation of the modular character known from hydrophobic systems.
A new azobenzene‐group‐containing monomer and several respective functional side‐chain polymers grafted on a methylhydrosiloxane backbone (with two different degrees of polymerization; with and without the addition of a photoreactive benzophenone derivative) are designed, synthesized, and characterized. The resulting materials clearly show self‐assembly behavior and possess a nematic liquid‐crystal phase over a broad temperature range, which extends below 0 °C. The optical properties of these new photochromic liquid‐crystalline materials are determined from the absorbance spectra of oriented samples and by photoinduced birefringence studies. The results indicate a considerable dichroism of the side‐chain liquid‐crystalline polymers (SCLCPs), and hence demonstrate their potential applicability for optical storage.
A convenient one‐pot method for the controlled synthesis of polystyrene‐block‐polycaprolactone (PS‐b‐PCL) copolymers by simultaneous reversible addition–fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) processes is reported. The strategy involves the use of 2‐(benzylsulfanylthiocarbonylsulfanyl)ethanol (1) for the dual roles of chain transfer agent (CTA) in the RAFT polymerization of styrene and co‐initiator in the ROP of ε‐caprolactone. One‐pot polymerizations using the electrochemically stable ROP catalyst diphenyl phosphate (DPP) yield well‐defined PS‐b‐PCL in a relatively short reaction time (≈4 h; = 9600?43 600 g mol?1; / = 1.21?1.57). Because the hydroxyl group is strategically located on the Z substituent of the CTA, segments of these diblock copolymers are connected through a trithiocarbonate group, thus offering an easy way for subsequent growth of a third segment between PS and PCL. In contrast, an oxidatively unstable Sn(Oct)2 ROP catalyst reacts with (1) leading to multimodal distributions of polymer chains with variable composition.
Novel branched polyoxymethylene copolymers are synthesized by cationic copolymerization of 1,3,5‐trioxane (TOX) with 3‐(alkoxymethyl)‐3‐ethyloxetane (ROX) using BF3·Et2O as an initiator. Four oxetane derivatives with different side‐chain lengths (from 1 to 6 carbons) are tested for copolymerization. The copolymer composition is controlled by the feed ratio of ROX, and influenced by the chain length of alkyl group on ROX. The incorporation ratio and side‐chain length of the ROX unit have great influence on the thermomechanical properties and crystallinity of the copolymers.
Polyacrylonitrile (PAN) with high molecular weight and low dispersity is successfully synthesized by visible‐light‐induced metal‐free radical polymerization at room temperature. This polymerization technique uses organic dye Eosin Y as photocatalyst and benzenediazonium tetrafluoroborates as initiator. Gel permeation chromatography‐multiangle laser light scattering shows the absolute molar weight of the PAN more than 1.50 × 105 g mol−1 with a polydispersity index < 1.3 while MALDI‐TOF MS and 19F NMR spectroscopy indicate the F‐chain‐end process. The first‐order kinetic behavior, molecular weight distributions shifting, and “ON/OFF” experiment results suggest this reaction may follow the atom‐transfer‐like radical polymerization mechanism. In addition, this new approach allows for the efficient synthesis of well‐defined random copolymers.
Novel nitrogen‐doped graphene nanoribbons (GNR‐Ns) are synthesized by the coupling reaction between a pyrazine (or benzene) derivative and naphthalene followed by cyclodehydrogenation. The amount of nitrogen doping in the GNR‐Ns is controlled by changing the monomer feed ratio of pyrazine to benzene for polymerization. The electron mobility of the GNR‐Ns increases while the hole mobility decreases, as the amount of nitrogen doping in the GNR increases, indicating that the charge‐transport behavior of GNRs is changed from ambipolar to an n‐type semiconductor. The threshold voltage of the GNR‐Ns also shifts from 20 to ?6 V as the amount of nitrogen doping increases.
High‐temperature thermal gradient interaction chromatography (HT‐TGIC) fractionates polyolefins based on an adsorption–desorption mechanism. Several factors influence the shape and position of HT‐TGIC chromatograms, notably polymer microstructure, analytical conditions, and, to a lesser extent, solvent type. This article investigates the joint influence of chain length and comonomer content of a series of polyethylene and ethylene/1‐octene copolymers having similar 1‐octene fractions (0–13 mol%) and a wide range of molecular weights on HT‐TGIC fractionation. For each series of copolymers having similar 1‐octene fraction, the elution peak temperature decreases exponentially and the profiles become increasingly broader below a critical number average chain length value. The authors use Monte Carlo simulation and Stockmayer distribution to explain the observed behavior, finding that no simple correlation exists between ethylene sequences in the copolymers and peak elution temperature, but that there is strong evidence that axial dispersion is responsible for symmetrical broadening of the HT‐TGIC profiles. The authors also study the HT‐TGIC of binary blends, finding that components with similar 1‐octene contents and dissimilar chain lengths tend to increase co‐adsorption/co‐desorption effects.
The swelling, viscoelastic, and mechanical behavior of phase‐segregated poly(ester urethane) (PEU) block copolymers, composed of 4,4′‐methylenediphenyl diisocyanate, 1,4‐butanediol as a chain extender, and crystallizable poly(1,4‐butylene adipate) (PBA) with molecular weights between 1330 and 4120 g mol?1, are investigated. Wide‐angle X‐ray scattering (WAXS) is employed to study the overall PEU crystallinity, which increases from 8.6 to 13.6% at higher PBA contents. The existence of two crystalline, polymorphic PBA phases, a thermodynamically stable α phase and a metastable β phase, is confirmed by further WAXS measurements. Calorimetric and thermomechanical investigations give evidence for controllable PBA polymorphic behavior. The crystallization conditions, like the cooling rate, affect the emerging polymorphic mixture, whereas the storage conditions either promote or inhibit the polymorphic (β to α) transition. The introduced concepts represent a new approach for gaining control over programmable thermoresponsiveness, which may be transferable to other shape‐memory polymers with polymorphic switching segments.
Interface structure and dynamics properties in an all‐polystyrene composite composed of linear chains and one single‐chain nanoparticle (SCNP) are investigated by using large‐scale molecular dynamics simulations at both coarse‐grained and full atomistic level. It is demonstrated that the SCNP adopts a crumpled globular state in composite; it has layered internal structures especially at low temperatures. When temperature decreases, its interior phenyl rings (iPRs) are parallel to each other and scaffold cross‐linking bonds undergo a “loose‐to‐tight” transition, leading to a “soft‐to‐hard” transition of the SCNP. Such transition provides more interior free volume and therefore results in faster rotational relaxation of inner layer iPRs at low temperature. It also facilitates the infiltration of the matrix monomers, resulting in an enhanced interfacial correlation and therefore a stronger deceleration effect in diffusion of matrix monomers at low temperatures. These results provide new insights into unique structure and dynamics properties at the polymer/SCNP interface region.
Novel self‐healing silicone rubbers are prepared by a two‐step procedure: aminopropyl methyl phenyl polysiloxanes is first reacted with salicylaldehyde and then with copper acetate. The reversible nature of the metal–ligand coordination interaction between polysiloxanes with pendent Schiff‐base groups and Cu2+ has endowed silicone rubbers with superior self‐healing properties. As compared with other self‐healing silicone rubbers based on hydrogen bonds or Diels–Alder reaction, this cross‐linked system shows high healing power. The materials are cut into two parts and put together in a mold for 1 h at 30 °C, observing a macroscopic healing and a strength recovery up to 87.0%.
This paper reports on the effect of a semifluorinated alkyl side chain for achieving a self‐organized nanostructure to facilitate the efficient charge carrier transport. So far, semifluorinated alkyl side chains have rarely been introduced into semiconducting polymers, despite their interesting properties such as hydrophobicity, thermal stability, and solvent resistance, as well as self‐organization. Herein, this study synthesizes the semifluorinated alkyl chain introduced poly(3‐dodecylthiophene), SFA‐P3DT, and demonstrates that self‐organization of SFA‐P3DT is intensely induced in nonfluorous solvent by the so‐called fluorophobic effect, resulting in the formation of nanofibrillar structure. In presence of the semifluorinated alkyl side chain, organic thin film transistor (OTFT) devices exhibit the improved charge carrier mobility than that of poly(3‐dodecylthiophene) with hydrocarbon alkyl chain. Moreover, higher charge carrier mobility can be obtained from the nonfluorous solvent, in comparison to the fluorous solvent, confirming the crucial role of fluorophobic effect. These observations suggest that the introduction of semifluorinated alkyl chains into a conjugated polymer may enhance the performance of OTFTs through the development of a well‐ordered nanostructure via self‐organization by fluorophobic effect, which, in turn, facilitates the efficient charge carrier transport.
Here, the synthesis, characterization, and photovoltaic properties of four new donor–acceptor copolymers are reported. These copolymers are based on 4,4‐difluoro‐cyclopenta[2,1‐b:3,4‐b′] dithiophene as an acceptor unit and various donor moieties: 4,4‐dialkyl derivatives of 4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene and its silicon analog, dithieno[3,2‐b:2′,3′‐d]‐silol. These copolymers have an almost identical bandgap of 1.7 eV and have a HOMO energy level that varies from ?5.34 to ?5.73 eV. DSC and X‐ray diffraction (XRD) investigations reveal that linear octyl substituents promote the formation of ordered layered structures, while branched 2‐ethylhexyl substituents lead to amorphous materials. Polymer solar cells based on these copolymers as donor and PC61BM as acceptor components yield a power conversion efficiency of 2.4%.
A new synthetic strategy is developed for the synthesis of polyphosphazene bearing stable nitroxide radicals as a pendant group. The resulting material is investigated as a cathode‐active material for rechargeable lithium–ion batteries that performs 80 mAh g−1 capacities at a C/2 current density over 50 cycles. Thus, the inorganic–organic hybrid system can be proposed as an alternative cathode‐active material with improved performance.
The crystal structure of poly(4,4′‐diphenylsulfonyl terephthalamide) (pt‐PSA) is studied by X‐ray diffraction and molecular simulation. Although the number of observed reflections is limited to warrant a precise determination of the unit cell structure and symmetry, a reasonable monoclinic unit cell is suggested with dimensions of a = 0.645 nm, b = 0.488 nm, c = 3.010 nm, and γ = 122.5°. A twofold molecule with two monomeric units forming a large zigzag conformation satisfies the X‐ray diffraction data. A layer structure is formed in the crystal phase, which is stabilized by the hydrogen bond between ? NH and ? C?O and the parallel‐displaced π–π stacking from the distortional coplanarity of the benzene rings and amide group.
Novel vanadium‐oxide‐based catalysts supported on alumina, zirconia, or titania‐modified silica, which are able to synthesize ultrahigh molecular weight polyethylene (UHMWPE), are successfully developed. Compared with the unmodified silica supported catalyst, the activities of the modified catalysts are substantially enhanced. By changing the polymerization temperature (T p) from 90 to 60 °C, the molecular weight of the produced UHMWPE can be easily regulated from 2 × 106 to more than 6 × 106 g mol−1. It is the first time that chloride‐free nonsingle site catalysts have been developed to synthesize UHMWPE within such a broad range of T p. Catalyst characterization by NH3‐temperature‐programmed desorption and pyridine‐Fourier transform infrared spectroscopy reveals that the modified catalysts have increased acidity derived from both Lewis and Brønsted acid sites. The X‐ray photoelectron spectroscopy characterization indicates that the vanadium on the modified catalysts is more electron deficient. Thus, the acidity of the catalysts and the electronic state of the vanadium play a critical role in determining the activity of the vanadium active sites for ethylene polymerization.
