Novel Fluorinated Polymer by Radiation‐Induced Polyaddition of Bisperfluoroisopropenyl Terephthalate with 1,4‐Dioxane

Radical polyaddition of bis(α‐trifluoromethyl‐β,β‐difluorovinyl) terephthalate [CF₂?C(CF₃)OCOC₆H₄COOC(CF₃)?CF₂] (BFP) with 1,4‐dioxane (DOX) was investigated under γ‐rays radiation from a ⁶⁰Co source to produce higher molecular weight polymers compared to those yielded by benzoyl peroxide initiation. Prior to polyaddition, the addition reactions of 2‐benzoxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅] (BPFP) with tetrahydrofuran (THF) and DOX, and BFP with THF were examined in order to develop probable polyaddition reaction conditions. The polymer bearing 1.5 × 10⁴ as a molecular weight was obtained under the feed molar ratio of DOX/BFP = 16 with an irradiation dose of 2 000 kGy at 40 °C, which is a much higher molecular weight compared to that yielded by benzoyl peroxide.

     

Synthesis and Photovoltaic Properties of 1,8‐Carbazole‐Based Donor–Acceptor Type Conjugated Polymers

1,8‐Diethynylcarbazole‐based conjugated polymers were synthesized by the acetylenic oxidative coupling reaction or Pd‐catalyzed Sonogashira reaction of the newly designed 3,6‐dialkylated 1,8‐diethynylcarbazole monomers. In particular, the Sonogashira polycondensation was effective for the preparation of donor–acceptor type alternating copolymers. The UV‐vis absorption and fluorescence spectra of the polymers revealed the strength of the donor–acceptor interactions as well as their self‐assembling features. The combination of electrochemical redox potentials and optical band gaps enabled the estimation of the polymer energy levels. The bulk‐heterojunction solar cells composed of these promising polymers and PCBM exhibited a photoconversion efficiency (PCE) of 0.24%. It was determined that the partial doping of the bulk‐heterojunction layer increased the open‐circuit voltage (V_oc), but decreased the short‐circuit current (J_sc).     

New Carbazole‐Based Hyperbranched Conjugated Polymer with Good Hole‐Transporting Properties

A copper‐catalyzed Ullmann C–N coupling reaction was used for the preparation of a new carbazole‐based HPU in good yield with a high molecular weight through a facile “AB₂ + A₂ + B₂”‐type approach. The HPU exhibited good solubility, high thermal stability with a T_g of 196 °C, as well as a suitable HOMO level for good hole injection and transporting properties. A two‐layer OLED device, using HPU as hole‐transporting layer (HTL) and Alq₃ as the light‐emitting layer, was fabricated to investigate the hole‐transporting properties of HPU. The luminance efficiency reached 1.14 cd · A^?1 at the maximum current density of 1 240 mA · cm^?2, while the maximum luminance efficiency was 1.65 cd · A^?1, indicating the high morphological and thermal stability of HPU.

     

New Carbazole‐Based Copolymers as Amorphous Hole‐Transporting Materials for Multilayer Light‐Emitting Diodes

New carbazole‐based copolymers, which contain various concentrations of 9‐alkyl‐3,6‐carbazole fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)‐catalyzed Yamamoto‐type aryl‐aryl coupling reactions. Full characterization of the copolymer structure by NMR spectroscopy and elemental analysis is presented. These compounds represent amorphous materials of high thermal stability with glass transition temperatures of 151–162 °C and thermal decomposition starting at temperatures >390 °C. UV‐Vis absorption and photoluminescence emission of the copolymers confirmed that the effectively conjugated segment in the 3,6‐linked carbazole‐type copolymers is limited to dyads (dimeric units). However, copolymers with varying concentrations of the oligocarbazole chromophores demonstrate different charge injection and transport properties in multilayer light‐emitting diodes with the copolymers as the hole transport and Alq₃ as the electroluminescent/electron transport layer. The device based on a copolymer composed of oligocarbazole blocks with an average length of around four carbazoles exhibited the best overall performance with a turn‐on voltage of 3.5 V, a maximal photometric efficiency of 4.1 cd · A^?1 and maximum brightness of about 4 200 cd · m^?2.

     

Recent Progress in Polymer White Light‐Emitting Materials and Devices

In this paper, recent progress in polymer white light‐emitting materials and devices published until April 2012 was reviewed according to the kinds of the materials and devices. The polymer light‐emitting materials were reviewed by the classification of small‐molecule‐doped polymer type, polymer blend type, polymer doped small molecule type, molecule‐dispersed polymer type, dye‐terminated polymer type, and excimer white EL polymer type. The polymer light‐emitting devices were reviewed by the classification of fabricating PWLED through the multilayer device and improving efficiency through the multilayer device. The relationship between the structures of materials or devices and properties was the main content during review. At last, some scientific problems and developing trends on PWLED are discussed.     

Novel Fluorinated Hybrid Polymer by Radical Polyaddition of Bis(α‐trifluoromethyl‐β,β‐difluorovinyl) Terephthalate onto Dialkoxydialkylsilanes

To develop the radical polyaddition of bisperfluoroisopropenyl esters, the reactions of bis(α‐trifluoromethyl‐β,β‐difluorovinyl) terephthalate [CF₂?C(CF₃)OCOC₆H₄COOC(CF₃)?CF₂] (BFP) with dialkoxydialkylsilane were examined to prepare fluorinated hybrid polymers bearing dialkylsilyl groups in the main chain. Prior to polyaddition, the radical addition reaction of 2‐benzoyloxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅] (BPFP) has been investigated to afford the results that diethoxydimethylsilane (DEOMS) or dimethoxydimethylsilane with BPFP initiated by oxo radical are the best combination for the preparation of polymers. The mechanism of the addition reaction was proposed. Radical polyaddition of BFP with DEOMS initiated by benzoyl peroxide or di‐tert‐butyl peroxide has yielded polymers of up to molecular weight 1 × 10⁶ with rather broad molecular weight distribution. A mechanism for the polyaddition reaction is proposed based on the radical addition reaction between BPFP and DEOMS. The step‐growth polymerization is initiated by hydrogen abstraction of DEOMS to add a perfluoroisopropenyl group, followed by a 1,7‐shift of the radical in the intermediate. The relationship between addition reaction mechanism and polyaddition mechanism was also discussed.

     

Novel Carbazole‐Based Ladder‐Type Polymers for Electronic Applications

Summary : New carbazole‐based ladder‐polymers have been prepared utilising a 3,6‐diacyl‐2,7‐dibromocarbazole building block 4 . Suzuki polycondensation of 4 with carbazole‐2,7‐diboronic acid followed by addition of methyl lithium and ring closure with boron trifluoride gave ladder‐polymers 9 with all methine bridges, analogous to ladder‐type poly(para‐phenylene). In very dilute solution, these polymers show blue‐green fluorescence similar to that from the corresponding LPPP. At higher concentrations, a broader red‐shifted emission is seen which suggests that the chains are aggregating in solution. Homopolymerisation of 4 followed by condensation of the carbonyls with boron sulfide produced a novel ladder‐type structure 13 with alternating five‐ and six‐membered rings. This ladder‐polymer displays bright yellow‐green fluorescence. Cyclic voltammetry indicated that these materials have HOMO energy levels comparable to the work function of ITO, making them good candidates for use as hole accepting emissive materials for LEDs.

The ladder polymers synthesised.     

Poly(carbazole)‐Based Copolymers Containing Deep‐Blue Chromophore for Polymer Light‐Emitting Diode Applications

A new series of two poly(carbazole)‐based copolymers (poly(9‐hexyl‐carbazole‐co‐9‐(6‐(3‐(4‐phenylquinolin‐2‐yl)carbazol‐9‐yl)hexyl)carbazole) (PCVz) and poly(9,9‐dioctylfluorene‐co‐9‐(6‐(3‐(4‐phenylquinolin‐2‐yl)carbazol‐9‐yl)hexyl)carbazole) (PFCVz)) containing carbazoylphenylquinoline pendant groups were synthesized via the Suzuki coupling reaction for polymer light‐emitting diode applications. The electro‐optical properties of ITO/PEDOT/Polymer/PBD/LiF/Al devices based on these copolymers were investigated using UV‐visible, photoluminescence, and electroluminescence spectroscopy. The turn‐on voltages of the copolymer devices were found to be 6.0–8.0 V. The maximum brightness and luminescence efficiency of the copolymers device were found to be 230 cd · m^?2 and 0.28 cd · A^?1 at 11 V, respectively.

     

A Binaphthyl–Bithiophene Copolymer for Light‐Emitting Devices

We report the properties of a binaphthyl–bithiophene copolymer (PHBNT₂) used either as an emitter or as a hole transporter in light‐emitting diodes. The polymer has a well‐defined conjugation length between two binaphthyl units that is independent of its polymer chain length. It is easily soluble in common organic solvents and can form high quality thin films by a spin coating technique. The HOMO and LUMO energy levels of the PHBNT₂ were –5.42 and –2.50 eV respectively, as determined by cyclic voltammetry. A single layer device of ITO/PHBNT₂/Al using PHBNT₂ as an emitter, had a turn‐on voltage of 5.7 V and had an orange emission peak at 568 nm. The luminous efficiency for a double‐layer device of ITO/PHBNT₂/Alq₃/Al using PHBNT₂ as the hole transporting layer is 0.57 lm·W^–1.     

Synthesis and Properties of Novel Fluorinated Poly(phenylene‐co‐imide)s

A new class of high‐performance materials, fluorinated poly(phenylene‐co‐imide)s, were prepared by Ni(0)‐catalytic coupling of 2,5‐dichlorobenzophenone with fluorinated dichlorophthalimide. The synthesized copolymers have high molecular weights ( = 5.74 × 10⁴–17.3 × 10⁴ g · mol^?1), and a combination of desirable properties such as high solubility in common organic solvent, film‐forming ability, and excellent mechanical properties. The glass transition temperature (T_gs) of the copolymers was readily tuned to be between 219 and 354 °C via systematic variation of the ratio of the two comonomers. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 66.7–266 MPa, 2.7–13.5%, and 3.13–4.09 GPa, respectively. The oxygen permeability coefficients ( ) and permeability selectivity of oxygen to nitrogen ( ) of these copolymer membranes were in the range of 0.78–3.01 barrer [1 barrer = 10^?10 cm³ (STP) cm/(cm² · s · cmHg)] and 5.09–6.25, respectively. Consequently, these materials have shown promise as engineering plastics and gas‐separation membrane materials.

     

Photocontrolled Living Anionic Polymerization of Silicon‐Bridged [1]Ferrocenophanes with Fluorinated Substituents: Synthesis and Characterization of Fluorinated Polyferrocenylsilane (PFS) Homopolymers and Block Copolymers

Photocontrolled living anionic ring‐opening polymerization (ROP) of strained silicon‐bridged [1]ferrocenophanes Fe(η‐C₅H₄)₂SiMe(CH₂CH₂CF₃) ( 1 ), Fe(η‐C₅H₄)₂SiMe(CH₂CH₂(CF₂)₇CF₃) ( 2 ) and Fe(η‐C₅H₄)₂SiMe(CH₂CH₂CH₂C₆F₅) ( 3 ) with 3,3,3‐trifluoropropyl, heptadecafluoro‐1,1,2,2‐tetrahydrodecyl, and pentafluorophenylpropyl hydrofluorocarbon substituents, respectively, on silicon, have been explored. Thus well‐defined fluorine‐containing homopolymers [Fe(η‐C₅H₄)₂Si(Me)R_F]_n ( 4–6 ) (R_F = hydrofluoro‐ carbon substituents), with controlled molecular weights and narrow molecular weight distributions ( < 1.10) were synthesized from the photocontrolled ROP of the respective [1]ferrocenophanes 1–3 , initiated by Na[C₅H₅] in THF at 5 °C. The sequential living photolytic anionic ROP allowed the synthesis of well‐defined diblock copolymers, polyferrocenylmethylphenyl‐ silane‐block‐polyferrocenylmethyl(3,3,3‐trifluoropropyl)silane (PFMPS‐b‐PFS_F) ( 7a–c ), with different ratios of the two blocks. DSC analysis of the resulting fluorinated diblock copolymers showed the presence of two distinct glass transition temperatures suggesting the immiscibility of the two blocks. The diblock copolymers 7a–c undergo predictable self‐assembly in the bulk as revealed by TEM analyses. The increased hydrophobicity of the fluorinated organometallic homopolymers was also studied by measuring the water contact angles on the homopolymer films.

     

Novel Polymers with Inherent Conductivity and Enhanced Second‐Order NLO Activity

A new polythiophene derivative bearing an azobenzene substituent at the end of a ethylenic side‐chain was synthesized and characterized by FT‐IR spectroscopy, ¹H and ¹³C NMR spectroscopy, DSC, TGA, XRD, and UV‐vis spectroscopy. Its electrical conductivity was measured and its second‐order NLO activity was by SHG. Structure‐property relations were elucidated by comparison with a similar polymer only partially substituted by the NLO‐active chromophore. The molecular design of the chromophoric system allows high and stable non‐linear coefficients d₃₃ to be obtained, making these polymers suitable for the construction of second‐harmonic generators with improved efficiency and life‐time.

     

Novel Amphiphilic Styrene‐Based Block Copolymers for Induced Surface Reconstruction

This paper describes the synthesis of amphiphilic block copolymers by living radical polymerization (NMP) of new styrene‐like monomers. The polar monomers (ethylene oxide side chains and free hydroxyl‐ or amino‐groups after deprotection) were polymerized in a “protected form” to adjust the solubility of the monomers. In this way high molar mass polymers with a narrow polydispersity (around or below 1.2) were accessible. In the bulk state hydrophobic and hydrophilic domains demix. By exposing thin films of these polymers to vacuum (air) or alternatively to water or a hydrophilic surface it becomes possible to switch the surface polarity reversibly between contact angles of about 105° and 83° as a result of surface reconstruction. Through side chains of different length and with different functionalities, it was possible to adjust the glass transition temperatures to values between ?2 °C to 140 °C for the hydrophilic blocks and ?30 °C to 100 °C for the hydrophobic block. The wide range of the glass temperatures allowed it to find a block copolymer system with a slow kinetic concerning the surface reconstruction process, so that a mechanistic examination of the process by AFM was possible. It got, thereby, possible to detect the break‐up of the hydrophobic surface lamella and the upfold of the hydrophilic lamella in contact with water.

     

Synthesis and Optical Properties of a Copolymer of Tetrafluoro‐ and Dialkoxy‐Substituted Poly(p‐phenylenevinylene) with a High Percentage of Fluorinated Units

A copolymer of 2,3,5,6‐tetrafluoro‐1,4‐phenylenevinylene and 2,5‐dioctyloxy‐1,4‐phenylenevinylene [co(TFPV‐DOPV)], containing more than 60% of tetrafluorophenylenevinylene monomeric units, was synthesized by the Stille cross‐coupling reaction. Its linear and nonlinear optical properties were investigated. Linear absorption and photoluminescence measurements performed on thin films and solution indicate interchain migration upon excitation. The Z‐scan technique was used to evaluate the third‐order nonlinear susceptibility at λ = 1064 nm. A very high refractive nonlinearity (n₂ = (?10 ± 2) × 10^?12 cm² · W^?1) was measured with a value one order of magnitude larger than that of the corresponding dialkoxy‐substituted homopolymer.

     

NMR Characterization of Carbazole‐Substituted Norbornene Comonomer 9‐(Bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) and Poly(ethylene‐co‐BHMCZ) Copolymer

Carbazole‐substituted norbornene comonomer 9‐(bicyclo[2.2.1.]hept‐5‐en‐2‐ylmethyl)‐9H‐carbazole (BHMCZ) can be copolymerized with ethylene using the [Ph₂C(Ind)(Cp)ZrCl₂] catalyst and methylaluminoxane (MAO) cocatalyst system. The microstructures of BHMCZ comonomer and of ethylene–BHMCZ copolymer containing 4.6 mol‐% BHMCZ units in the chain were characterized by one‐dimensional ¹³C DEPT and two‐dimensional homonuclear ¹H‐¹H COSY and heteronuclear ¹H‐¹³C HXCO NMR spectroscopy. The BHMCZ comonomer appears as endo and exo stereoisomers, which were identified on the basis of chemical shifts, signal multiplicities, and coupling in the 2D NMR spectra. The NMR information on the BHMCZ isomers was used to assist in the determination of the chemical shifts and microstructure of ethylene–BHMCZ copolymer. The NMR analysis of ethylene–BHMCZ copolymer indicated that exo‐BHMCZ polymerizes with ethylene slightly more readily than does endo‐BHMCZ under the polymerization conditions employed.

Isolated segments of exo(2)‐exo(5)‐exo(6) and endo(2)‐exo(5)‐exo(6) ethylene‐BHMCZ copolymer showing carbon atom numbering.     

Novel Soluble N‐Phenyl‐Carbazole‐Containing PPVs for Light‐Emitting Devices: Synthesis,Electrochemical, Optical,and Electroluminescent Properties

Summary: Novel PPV derivatives (PCA8‐PV and PCA8‐MEHPV) containing N‐phenyl‐carbazole units on the backbone were successfully synthesized by the Wittig polycondensation of 3,6‐bisformyl‐N‐(4‐octyloxy‐phenyl)carbazole with the corresponding tributyl phosphonium salts in good yields. The newly formed and dominant trans vinylene double bonds were confirmed by FT‐IR and NMR spectroscopy. The polymers (with of 6 289 for PCA8‐PV and 7 387 for PCA8‐MEHPV) were soluble in common organic solvents and displayed high thermal stability (T_gs are 110.7 °C for PCA8‐PV and 92.2 °C for PCA8‐MEHPV, respectively) because of the incorporation of the N‐phenyl‐carbazole units. Cyclic voltammetry investigations (onsets: 0.8 V for PCA8‐PV and 0.7 V for PCA8‐MEHPV) suggested that the polymers possess enhanced hole injection/transport properties, which can be also attributed to the N‐phenyl‐carbazole units on the backbone. Both the single‐layer and the double‐layer light‐emitting diodes (LEDs) that used the polymers as the active layer emitted a greenish‐blue or bluish‐green light (the maximum emissions located 494 nm for PCA8‐PV and 507 nm for PCA8‐MEHPV, respectively). Compared with those of the single‐layer devices, the emission efficiencies of the double‐layer devices, in which an electron‐transporting layer (Alq₃) was added, were enhanced by a factor of 10, implying that the better hole‐electron balance is achieved because of the incorporation of the electron‐transporting layer.

The N‐phenyl‐carbazole‐containing polymers synthesized.     

Bis‐Diketopyrrolopyrrole and Carbazole‐Based Terpolymer for High Performance Organic Field‐Effect Transistors and Infra‐Red Photodiodes

Carbazoles constitute one of the most widely used donor moieties for organic semiconductors due to their excellent hole transport and high environmental stability. However, they are seldomly used in recent high performance donor–acceptor (D–A) copolymers. In the present study, a planar regular terpolymer, PCbisDPP, composed of carbazole and thiophene flanked bis‐diketopyrrolopyrrole (bis‐DPP) for application as an active layer for high‐performance organic devices is reported. Organic field‐effect transistors with PCbisDPP as the active layer exhibit field‐effect mobility up to 1.48 cm² v^?1 s^?1, which to the best of the current knowledge corresponds to the highest hole mobility reported to date for carbazole‐based D–A polymers. The high mobility is achieved via a tailored polymer‐design resulting in high crystallinity and a strong aggregating property without sacrificing solubility. PCbisDPP is applied as an active donor material in organic photodiode with fullerene derivative PC₆₁BM as an acceptor in a bulk heterojunction blend. Binary additive combinations (tetralin: 1,8‐diiodooxtane (3:3) v/v%) utilization achieves an impressive performance with an external quantum efficiency of 80%, an average responsivity of 309.1 mA W^?1, and specific detectivity of 4.73 × 10¹¹ Jones in the near infra‐red light region (730 nm) utilizing a simple single layer organic photodiode structure as ITO/PEDOT:PSS/PCbisDPP:PC₆₁BM/LiF/Al.     

Effect of Polymer Network Topology on the Electro‐Optical Performance of Polymer Stabilized Liquid Crystal (PSLC) Devices

Polymer‐stabilized liquid crystal (PSLC) devices can realize fast switching between transparent and scattering state, and have been widely applied as smart windows and optical shutters. It has many advantages such as high transmittance, high haze value, fast response speed, and low driving voltage. The electro‐optical response of PSLC devices depends on the properties of the liquid crystal molecules and the influence of the polymer network on the motion of the liquid crystal molecules. In this paper, the effect of polymer network morphology on the performance of PSLC devices is systematically studied. By adding mono‐acrylate monomer into the liquid crystal di‐acrylate monomers, the polymer network became softer and sparser after photopolymerization. The threshold voltage and response time of PSLC devices decreased with increasing the mono‐acrylate monomer concentration, but changed to increase after the concentration exceeds 1.8 wt%. This study provides guidelines to optimize of PSLC based optical devices and windows.     

Synthesis and Evaluation of Water‐Soluble Fluorinated Dendritic Block‐Copolymer Nanoparticles as a 19F‐MRI Contrast Agent

Well‐defined water‐soluble fluorinated polymer nanoparticles (PNPs) with a high fluorine content and biocompatibility were successfully prepared by living radical polymerization (LRP) of 2,2,3,3‐tetrafluoropropyl methacrylate (TFPMA) from the polyamidoamine dendrimer macroinitiator (PAMAM‐Br), and successive block polymerization of carboxybetaine monomer (CMB). The obtained core–shell type PNPs (PAMAM‐g‐PTFPMA‐b‐PCMB) showed high solubility in water and a sphere‐like structure with a diameter in the range of 15–80 nm in water. The short ¹⁹F‐NMR spin–lattice relaxation time (T₁) (<250 ms) of PAMAM‐g‐PTFPMA‐b‐PCMB allowed the use of fast repetition time. The spin–spin relaxation time (T₂) was evaluated to be as low as 10 ms. ¹⁹F‐MRI in vitro signals can be detectable even at concentrations lower than 1 µM (particle concentration). These results demonstrate that a new type of ¹⁹F‐MRI contrast agent can be developed by the molecular design using the dendrimer‐initiated LRP method.

     

4,5‐Ethylene‐2,7‐Carbazole‐Based Medium‐Bandgap Conjugated Polymers with Low‐Lying HOMO Levels Toward Efficient Polymer Solar Cells with High Open‐Circuit Voltage

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 (V_oc) 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 V_oc.