Three novel dithieno[3,2‐b:2′,3′‐d]thiophene‐based low‐bandgap polymers are synthesized by a Suzuki–Miyaura coupling reaction or by direct arylation polycondensation. The polymers present a high molecular weight (26–32 kDa) and narrow polydiversity (1.3–1.7). With a highest occupied molecular orbital (HOMO) energy level around ?5.20 eV, these polymers exhibit a narrow bandgap of 1.75–1.87 eV. All the polymers display strong absorption in the range of 350–700 nm. Bulk‐heterojunction (BHJ) solar cells are further fabricated by blending the as‐prepared polymer with (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) at different weight ratios. The best devices contribute a power conversion efficiency (PCE) of 0.73% under AM 1.5 (100 mW cm?2).
Two alternating low‐bandgap conjugated polymers with 10,11‐di(3,7‐dimethyloctyloxy)di‐thieno[2,3‐d:2′,3′‐d′]naphtho[1,2‐b:3,4‐b′]dithiophene (NDT) as electron‐donor moieties and N,N′‐di(2‐hexyldecyl)isoindigo (ID) or bis(thieno‐2‐yl)‐N,N′‐bis(2‐hexyldecyl)‐1,4‐dioxo‐pyrrolo[3,4‐c]pyrrole (DPP) as electron‐acceptor moieties, respectively named as PNDT‐ID and PNDT‐DPP, are firstly synthesized and characterized. The polymers exhibit appropriate energy levels, good solution processabilities and broad light absorption properties; the power conversion efficiencies (PCEs) of 0.16%–0.19% for the photovoltaic solar cells (PVCs) from the blend films of the polymers and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) are very low. The performances of the PVCs from the polymers are remarkably increased when a very small amount of 1,8‐diiodooctance (DIO) or diphenyl sulfide (DPS) is used as solvent additives, and the maximal PCEs of 3.79% and 5.01% are respectively achieved in the PVCs from the blend films of PNDT‐ID/PC71BM (W:W, 1:1.5) and PNDT‐DPP/PC71BM (W:W, 1:1.5), with DPS as solvent additives under 100 mW cm?2 illumination (AM 1.5G).
Copolymerization of carbon dioxide (CO2) and propylene oxide (PO) is employed to generate amphiphilic polycarbonate block copolymers with a hydrophilic poly(ethylene glycol) (PEG) block and a nonpolar poly(propylene carbonate) (PPC) block. A series of poly(propylene carbonate) (PPC) di‐ and triblock copolymers, PPC‐b‐PEG and PPC‐b‐PEG‐b‐PPC, respectively, with narrow molecular weight distributions (PDIs in the range of 1.05–1.12) and tailored molecular weights (1500–4500 g mol?1) is synthesized via an alternating CO2/propylene oxide copolymerization, using PEG or mPEG as an initiator. Critical micelle concentrations (CMCs) are determined, ranging from 3 to 30 mg L?1. Non‐ionic poly(propylene carbonate)‐based surfactants represent an alternative to established surfactants based on polyether structures.
Three medium‐bandgap polymers based on a 4,5‐ethylene‐2,7‐dithienyl carbazole as the electron‐donating unit and different 5,6‐dialkoxy‐2,1,3‐benzothiadiazoles as the electron‐accepting units, are synthesized as polymer donors for photovoltaic applications. The three copolymers possess highest occupied molecular oribital (HOMO) levels around ?5.47 eV and medium bandgaps of about 1.94 eV. The solar cells with polymer:[6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) = 1:4 as the active layer, show an especially high open‐circuit voltage (Voc) of 0.95 V and attain good power conversion efficiency up to 5.91%. The hole mobilities of the active layer films, measured by space‐charge‐limited current (SCLC), are up to 3.5 × 10?4 cm2 V?1 s?1. Given the favorable medium bandgaps, low‐lying HOMO levels, and good hole mobilities, these copolymers are promising candidates for the construction of a highly efficient front cell to harvest the shorter wavelength band of the solar radiation in a tandem solar cell with high Voc.
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%.
Graft polymers with poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as backbones are successfully prepared via two convenient steps. The utilization of semiflexible PPO as backbones offers unique properties for the graft polymers. Thermal, rheological, and phase behaviors of these new graft polymers are well controlled via the precise design of architectural parameters. The disordered microphase separation in melt state and the proper composition of side grafts provide the ease of thermal processing for these graft polymers. The graft density shows impact on the relaxation and mechanical properties of the thermoplastics. This work shows the possibility to use lots of semiflexible engineering polymers as backbones to construct new thermoplastics.
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.
The cationic polymerization of 1,3‐pentadiene using a tert‐butyl chloride (tBuCl)/TiCl4 initiating system in CH2Cl2 at different reaction conditions is reported. It is shown that the reaction rate increases with the increase of the tBuCl/TiCl4 molar ratio, while the molecular weight distribution becomes narrower. Well‐defined oligo(1,3‐pentadiene)s ( ≤ 3500 g mol?1; / ≤ 3.0) are obtained at high tBuCl/TiCl4 molar ratio (340) and low temperature (–78 °C). 1H and 13C NMR spectroscopy studies reveal the presence of tert‐butyl head and –CH2–Cl end groups. The number‐average functionalities (Fns) at the α‐ and ω‐ends are calculated to be Fn(tBu) > 1 and Fn(Cl) < 1, respectively. The general mechanism of 1,3‐pentadiene polymerization is proposed.
Inspired by the well‐known amphiphilic block copolymer platform known as Pluronics or poloxamers, a small library of ABA and BAB triblock copolymers comprising hydrophilic 2‐methyl‐2‐oxazoline (A) and thermoresponsive 2‐n‐propyl‐2‐oxazoline (B) is synthesized. These novel copolymers exhibit temperature‐induced self‐assembly in aqueous solution. The formation and size of aggregates depend on the polymer structure, temperature, and concentration. The BAB copolymers tend to agglomerate in water, with the cloud point temperature depending on the length of poly(2‐n‐propyl‐2‐oxazoline) chain. On the other hand, ABA copolymers form smaller aggregates with hydrodynamic radius from 25 to 150 nm. The dependence of viscosity and viscoelastic properties on the temperature is also studied. While several Pluronic block copolymers are known to form thermoreversible hydrogels in the concentration range 20–30 wt%, thermogelation is not observed for any of the investigated poly(2‐oxazoline)s at the investigated temperature range from 10 to 50 °C.
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.
Melting and reorganization of conformationally disordered crystals (α′‐phase) of poly(l ‐lactic acid) (PLLA) are analyzed as a function of the rate of heating in a wide range between about 10?1 and 103 K s?1. It is found for the first time that the reorganization of conformationally disordered α′‐crystals into stable α‐crystals can be suppressed by fast heating. Heating of α′‐crystals of PLLA at a constant rate, faster than 30 K s?1, leads to its complete melting between 150 and 160 °C and suppression of formation of α‐crystals on continuation of heating. Non‐isothermal reorganization of α′‐crystals into α‐crystals only occurs when heating at a rate slower than 30 K s?1. It is evidenced that isothermal reorganization of α′‐crystals into α‐crystals at 150–160 °C proceeds via melting followed by recrystallization rather than a solid–solid phase transition.
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.
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.
Unsaturated polyesters are synthesized via ring‐opening copolymerization of α‐methylene‐δ‐valerolactone and δ‐valerolactone. These polyesters 4a–c are mixed with ethyl methacrylate (EMA), 2‐hydroxyethyl methacrylate (HEMA), and α‐methylene‐δ‐valerolactone (α‐MVL), respectively. Then, crosslinking is carried out by free radical polymerization initiated by an azo‐initiator. A second glass transition is found with incorporation of HEMA and α‐MVL. These findings indicate the formation of phase‐separated polyester blocks crosslinked with the poly(meth)‐acrylic‐segments, respectively poly(α‐methylene‐δ‐valerolactone) segments.
A family of novel (X‐TATAT)n‐type conjugated polymers based on the carbazole (X), thiophene (T), and benzoxadiazole (A) moieties is designed and explored as electron‐donor materials for organic bulk heterojunction solar cells. Incorporation of the branched side chains of different size and shape affects significantly the optoelectronic properties of the materials, particularly frontier energy levels of polymers translated to the open circuit voltages of the photovoltaic cells. The revealed unprecedented correlation between the parameters of the solar cells (V OC, fill factor (FF), J SC) and bulkiness of the alkyl side chains provides useful guidelines for rational design of novel materials for organic photovoltaics.
Molecular‐recognition‐responsive characteristics of a novel poly(N‐isopropylacrylamide‐co‐benzo‐12‐crown‐4‐acrylamide) (PNB12C4) hydrogel have been investigated. In the prepared PNB12C4 hydrogel, benzo‐12‐crown‐4 (B12C4) groups act as guest molecules and γ‐cyclodextrin (γ‐CD)‐receptors, and poly(N‐isopropylacrylamide) (PNIPAM) networks act as phase‐transition actuators. The formation of stable γ‐CD/B12C4 complexes enhances the hydrophilicity of the PNB12C4 hydrogel networks, and induces positive shift of the volume phase transition temperature (VPTT) of PNB12C4 hydrogel. Moreover, the PNB12C4 hydrogel also shows thermoresponsive adsorption property selectively towards γ‐CD. The γ‐CD‐recognition sensitivity of PNB12C4 hydrogel can be dramatically improved by increasing γ‐CD concentration in solution or B12C4 content in PNB12C4 copolymer networks. The results in this study provide valuable information for developing crown ether‐based smart materials in various applications.
Iron‐mediated atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in N‐methylpyrrolidin‐2‐one (NMP) solution is investigated via online VIS/NIR spectroscopy up to 2500 bar. The activation–deactivation equilibrium constant, KATRP, decreases towards higher NMP content due to the formation of catalytically less active FeII/NMP species. The reaction volume increases from 1 to 15 cm3 mol?1 in passing from 16 to 92 mol% NMP. The same effects are observed for monomer‐free model systems with poly(MMA)–Br as the initiator. Investigations into iron‐catalyzed ATRP of MMA in less polar solvents or even without an additional solvent (i.e., for bulk ATRP) yield KATRP values, which are by two to three orders of magnitude higher than in the presence of NMP.
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.
Poly(spirobifluorene)s and their derivatives with three primary colors are promising for application in efficient and stable polymer light‐emitting diodes (PLEDs). Here, a novel approach is reported to tune the emission colors of blue‐light‐emitting poly(spirobifluorene)s through a charge‐transfer mechanism from the side chain to the main chain. By using the electron‐rich 2,3,6,7‐tetra‐octyloxyfluorene unit as the side chain and incorporating the electron‐deficient dibenzothiophene‐S,S‐dioxide ( SO ) unit into the main chain, a series of polyspirobifluorene derivatives are successfully developed. They all display efficient green photoluminescence and electroluminescence. The observed green emission can be ascribed to both intramolecular and intermolecular charge transfer from the pendant 2,3,6,7‐tetra‐octyloxyfluorene unit to the SO unit in the main chain. Single‐layer PLEDs of these polymers reveal a maximum luminance efficiency of 1.99 cd A?1 and a maximum power efficiency of 1.30 lm W?1 with Commission Internationale de L'Eclairage coordinates of (0.37, 0.54).
Amphiphilic block copolymers based on sucrose methacrylate (SMA) and alkyl methacrylates (alkyl = ethyl, butyl, and hexyl) are synthesized by atom transfer radical polymerization, employing CuBr/CuBr2/2,2,2‐tribromoethanol/1,1,4,7,10,10‐hexamethyltriethylenetetramine as a catalyst/deactivator/initiator/ligand system. Poly(alkyl methacrylate)s with similar polymerization degrees are used as macroinitiators for SMA polymerization. The introduction of PSMA blocks with molar mass varying from 2000 to 12 000 g mol−1 results in changes in the solubility, thermal stability, and water swelling capacity. The copolymers are able to stabilize water/oil emulsion and also to self‐assemble in solution, as verified by gel permeation chromatography and dynamic light scattering, as well as in solid state, as verified by atomic force microscopy.
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