Thermally stable blue emitting terfluorene block copolymers

Spectroscopic and morphological studies on a series of rod-coil block copolymers containing terfluorene segments as the rigid blocks and polystyrene as the flexible parts demonstrate an increase in the photoluminescence intensity and the exciton lifetime as well as formation of isolated spheres as thin films upon thermal annealing in air (200 degrees C for 30 min). Moreover, no appearance of the low energy emission band centered at 520 nm was found after the same thermal treatment which permits these copolymers to emit pure blue light.     

Synthesis and optoelectronic properties of alternating benzofuran/terfluorene copolymer with stable blue emission

The solution processable alternating benzofuran/terfluorene copolymer bearing side oxadiazole groups ( PBF‐OXD ) was synthesized and its optoelectronic properties and color stability were investigated. Electron‐deficient and stereohindered oxadiazole units were used as pendent groups to compensate for the poor electron‐transporting ability of a p‐type polymer backbone, to depress the intermolecular π‐stacking, and to improve solubility while retaining polymer blue emission. PBF‐OXD showed a glass transition at 135 °C and an onset decomposition temperature of ～345 °C. A simple EL device, with the configuration of ITO/PEDOT:PSS/ PBF‐OXD /Ba/Al, displayed a stable blue emission (λ_max = 434 nm), good color purity (full width half‐maximum = 59 nm), maximum brightness of 1400 cd/m², and a maximum luminance efficiency of 0.95 cd/A. The PL and EL spectra changed slightly on annealing and on increasing the applied voltage. These results show that the as‐synthesized copolymer PBF‐OXD had integrated respective functions of its different building blocks and exhibited good thermal and color stability with improved EL performance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5488–5497, 2009     

New rod-coil block copolymers consisting of terfluorene segments and electron transporting units as the flexible blocks

A series of new rod-coil block copolymers having a well-defined terfluorene unit as the rigid segment with three different electron transporting moieties as the flexible part, such as side chain oxadiazole (TFPOXD), side chain quinoline (TFPQN) and a molecule containing two oxadiazole rings in the side chain (TFPDOXD), were synthesized using the atom transfer radical polymerization (ATRP) technique. All the synthesized copolymers were extensively examined with respect to their optical properties as pristine films, upon thermal annealing (200 °C for 30 min in air) and photo-oxidation treatment in air. Thermal annealing of the block copolymers resulted in stable blue light emission from TFPOXD and TFPDOXD while TFPQN showed the appearance of the undesired 520 nm emission band. In addition, TFPOXD does not exhibit the low-energy emission band at 520 nm after photo-oxidation under prolonged diffuse UV radiation at ambient atmosphere, despite the fluorenone formation on the terfluorene segment, in contrast to all the other copolymers.     

Novel fluorene-carzazole-based conjugated copolymers containing pyrazoline and benzothiazole segments for blue light-emitting materials

A series of novel fluorene-carbazole-based copolymers with pyrazoline and benzothiazole units were synthesized successfully through Suzuki coupling reactions.The molecular structures and thermal properties of these polymers were characterized by FT-IR, ~1H NMR,DSC and TGA.GPC results indicated that the weight-average molecular weight(M_w) and polydispersity of these polymers were in range(12,000-14,000)and(1.8-2.0),respectively.The two resulting polymers have high photoluminescence quantum efficiency implying that they may be promising candidates for polymer light-emitting diodes (PLEDs).     

Synthesis and properties of new poly(terfluorene) derivatives containing spirobifluorene and electron transport groups for stable blue electroluminescence

We have synthesized three new blue‐emitting poly(terfluorene) derivatives containing spirobifluorene and electron transport groups (quinoline or oxadiazole). The strategy is to connect the monomers via positions 2 and 2′ of spirobifluorene, which significantly restricts the interchain interaction and effectively adjusts the conjugation length. The incorporation of electron‐deficient units (quinoline or oxadiazole) into the positions 7 and 7′ of spirobifluorene tunes the emission band and reduces the lowest unoccupied molecular orbital energy level. Blue electroluminescence with narrow emission was achieved in the devices of ITO/PEDOT/polymer/Ca/Al. The maximum luminances are in the range of 102–235 cd/m² and the maximum photometric efficiencies are in the range of 0.17–0.21 cd/A. All the polymers show good spectral stability, and are promising for use as stable blue‐emitting or electron‐transport/injection materials in polymeric light‐emitting diodes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4517–4529, 2005     

Synthesis of conducting block and graft copolymers with polyether segments

Synthesis of block and graft copolymers containing polyether and conducting polypyrrole sequences were described. Pyrrole moieties were incorporated at the chain ends of polytetrahydrofuran and polysiloxane and at the side chains of polyethyl vinylether by ionic polymerization and appropriate chemical reactions. Subsequent electropolymerization with pyrrole through these moities yielded free standing films of the corresponding block and graft copolymers. The formation copolymers was evidenced by FTIR spectroscopy and extraction with solvent of the precursor homopolymers. The thermal and morphological properties were also characterized. The two surface of the copolymer films generally differ in appearance, the surface at the solution side being cauliflowerlike or wrinkled, whereas the surface at the electrode side smooth. Conductivies of the copolymers were comparable with that of the pure polypyrrole.     

Graft and block copolymers with polysiloxane and vinyl polymer segments

A convenient new process to make silicone/organic block and graft copolymers has been recently demonstrated. This dual copolymerization process combines conventional condensation polymerization of the siloxane segments with free radical polymerization of the organic vinyl polymer segments. The copolymerization process is relatively simple and economical compared with other copolymerization techniques as it uses commonly available starting materials and available process equipment. Silicone segments containing alkene side chains or end-groups are prepared in the usual way by polycondensation using an acid or base catalyst. The double bonds of the alkene groups are oxidized to carbonyls which are then used to initiate vinyl monomer polymerization and link the siloxane with the vinyl segments. This initiation step is based on a redox system of copper^(II) salts which generates free radicals on the alpha carbons next to the carbonyl groups. This copolymerization process is relatively fast and proceeds at high yields.     

Heterogeneity parameters by light scattering for statistical copolymers incorporating long side-chain comonomers

Heterogeneity parameters were obtained by light scattering for a series of statistical copolymers incorporating long side-chain comonomers, by employing the method of Bushuk and Benoit. These copolymers were selected to exhibit varied compositional drift as required by copolymerization theory. The magnitude of the parameters found agreed qualitatively with the heterogeneity expected from the drift in composition with conversion. This was calculated using the treatment of Skeist, as modified by Kruse. However, values greater than the limit of unity were found in two instances for the heterogeneity index, Q/Q_max, which relates the compositional drift constant Q to the maximum value obtained for mixtures of homopolymers. These anomalies were attributed to the insensitivity of the method for heterogeneous copolymers having small differences in the refractive increaments of their respective homopolymers. The magnitude and sign of P, which reflects molecular weight effects on composition, was questionable because of experimental error. Both effects appear to be general deficiencies of the method, which limit its practical use. For solvents with high values of dn/dc (≈0.1), the observed weight-average molecular weight approached the true value.     

Wetting of heterogeneous surfaces of block copolymers containing fluorinated segments

 The wetting of well-characterized heterogeneous surfaces of block copolymers has been studied by low-rate dynamic contact angle measurements using axisymmetric drop-shape analysis. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the roughness, the heterogeneity and the chemical composition of the surfaces. By changing the block length of polysulfone and semifluorinated polyester segments in the block copolymers, the surface heterogeneity of thin films prepared on silicon wafers could be controlled. Tapping-mode AFM measurements showed that soft, hydrophobic domains of varying size on the submicrometer length scale were obtained on these surfaces (60–250 nm). The mean roughness was of the order of several nanometers. The results of the contact angle measurements showed that neither roughness nor heterogeneity had a significant effect on the advancing contact angle of water, at the scale of the features present; however, the contact angle hysteresis increased with increasing percentage of the soft domains. We assume that liquid retention by the solid upon retraction of the three-phase line is the main cause for the observed increase in contact angle hysteresis. Concerning the molecular composition of these block copolymer surfaces, angle-resolved XPS analysis showed a surface segregation of fluorine within the surface region. A direct correlation was found between the fluorine content of the block copolymer surfaces and the advancing contact angle of water. Received: 26 May 2000 Accepted: 3 January 2001     

Complex macromolecular structures from stable radical containing block copolymers

A novel synthetic strategy for the synthesis of graft copolymers is reported. Block copolymers containing segments with stable nitroxyl radicals side groups were first prepared by anionic polymerization, which were then used as a precursor for the subsequent nitroxide-mediated radical polymerization (NMRP) of styrene. This way, block–graft copolymers with polystyrene side chains grafted from one of the blocks were successfully synthesized in a controlled manner. In addition, block–graft copolymers with grafted polystyrene chains and a poly(tert-butyl methacrylate) block were subjected to hydrolysis to yield the corresponding amphiphilic polymers. The structures and the molecular weight characteristics of the polymers were characterized by spectral and chromatographic analyses. The surface morphology of thus obtained polymers was also investigated by microscopic techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 62–69     

Synthesis of amphiphilic block copolymers bearing stable nitroxyl radicals

We present here the synthesis of two kinds of amphiphilic block copolymers, a diblock copolymer MPEG‐b‐PTAm and a triblock copolymer MPEG‐b‐PLA‐b‐PTAm, which can self‐assemble into micelles with nitroxyl radicals‐containing PTAm segment in the core. The structure of the block copolymers was characterized by ¹H NMR and GPC. Dynamic laser light scattering and transmission electron microscopy were used to study the micellar behavior of the two block copolymers in aqueous solution. The micelles carrying nitroxyl radicals in the core can generate electron paramagnetic resonance, which is stable for a period of time up to 8 min even in the presence of reducing reagent such as ascorbic acid. The enhanced stability against the reducing agent was ascribed to the inaccessibility of the nitroxyl radical core placed in the interior of the micelles. Combined with the biocompatibility, these micelles were promising to be used as the EPR probes for bioimaging in vivo. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis of a double spiro-polyindenofluorene with a stable blue emission

[reaction: see text] A novel polyindenofluorene containing a double spiro-anthracene structure with solublizing alkyl groups was synthesized. Enhanced spectral stability of the polymer was investigated by heat treatment and photoirradiation in air. The EL spectrum of the polymer showed an enhanced sensitivity to the human eye and good color purity as a blue-emitting material.     

Diffusion and distribution of stable nitroxyl radicals in diene-styrene block copolymers

A method for studying the distribution and migration of additives between the phases of heterophase polymers has been developed. It is based on a photochemical reaction which selectively affects the additive contained in the phase with higher reactivity, thus sharply decreasing additive concentration in this phase. This method was used for studying the distribution of stable nitroxyl radicals between the phases of butadiene- or isoprene-styrene block copolymers and for determining diffusion coefficients of nitroxyl radicals in the polystyrene phase in the room temperature region. Diffusion coefficients for 2,2,6,6-tetramethylpiperidyl-l-oxyl in polystyrene and polybutadiene phases were also determined based on desorption curves for this radical.     

Synthesis and characterization of double hydrophilic block copolymers containing semi-rigid and flexible segments

3-Methyl-(E)-stilbene (3MSti) and 4-(diethylamino)-(E)-stilbene (DEASti) monomers are synthesized and polymerized separately with maleic anhydride (MAn) in a strictly alternating fashion using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The optimal RAFT chain transfer agents (CTAs) for each copolymerization affect the reaction kinetics and CTA compatibilities. Psuedo-first order polymerization kinetics are demonstrated for the synthesis of poly((3-methyl-(E)-stilbene)-alt-maleic anhydride) (3MSti-alt-MAn) with a thiocarbonylthio CTA (methyl 2-(dodecylthiocarbonothioylthio)−2-methylpropionate, TTCMe). In contrast, a dithioester CTA (cumyl dithiobenzoate, CDB) controls the synthesis of poly((4-(diethylamino)-(E)-stilbene)-alt-maleic anhydride) (DEASti-alt-MAn) with pseudo-first order polymerization kinetics. DEASti-alt-MAn is chain extended with 4-acryloylmorpholine (ACMO) to synthesize diblock copolymers and subsequently converted to a double hydrophilic polyampholyte block copolymers (poly((4-(diethylamino)-(E)-stilbene)-alt-maleic acid))-b-acryloylmorpholine) (DEASti-alt-MA)-b-ACMO) via acid hydrolysis. The isoelectric point and dissociation behavior of these maleic acid-containing copolymers are determined using ζ-potential and acid–base titrations, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 219–227     

Synthesis and characterization of polypropylene-based block copolymers possessing polar segments via controlled radical polymerization

A new method to prepare the polypropylene (PP) macroinitiator for controlled radical polymerization was described. Bromination of terminally-unsaturated PP was carried out by using N-bromosuccinimide and 2,2′-azobis(isobutyronitrile) to give a brominated PP (PP-Br), that has allylic bromide moieties at or near the chain ends. Thus, the obtained PP-Br was successfully used as a macroinitiator for radical polymerization of styrene, methyl methacrylate, and n-butyl acrylate using a copper catalyst system. From ¹H NMR analysis, it was confirmed that the chain extension polymerization was certainly initiated from allylic bromide moieties with high efficiency, leading to the PP-based block copolymers linking the polar segment. From differential scanning calorimetry, it was observed that peak melting temperature of block copolymers was higher than that of PP-Br and the obtained PP-PS block copolymers with different compositions of each segment demonstrated the unique morphological features due to the microphase separation between both segments. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 812–823, 2009     

Neutron and light scattering studies of polymer blends and block copolymers

The structure of compatible polymer mixtures and its temperature dependence can be well described in many cases by the mean-field approximation. Deviations with regard to the temperature dependence of the correlation length of concentration fluctuations can be explained by taking into account the spatial structure of the interaction potential. Concentration fluctuations and the microphase separation in diblock copolymers are in good agreement with theories based on the random phase approximation. In the two-phase region the temperature dependence of the scattered X-ray or neutron intensity is governed by the difference in the thermal expansion coefficients of the two components of the diblock copolymer. Photon correlation spectroscopy (PCS) yields valuable information on the concentration dependence of the mutual diffusion coefficient D_AB.     

Fluorene-based copolymers for color-stable blue light-emitting diodes

A series of random conjugated copolymers (PFO-HBT) derived from 9,9-dioctylfluorene (DOF) and 2-hexylbenzotriazole (HBT) is prepared by the palladium-catalyzed Suzuki coupling reaction with the feed HBT molar ratio around 1%, 5% and 15%. By copolymerizing 2-hexylbenzotriazole into the backbone of polyfluorene, an efficient colorfast blue light-emitting polymer system is developed. The device with the structure of ITO (indium tin oxide)/PEDOT/PVK/PFO-HBT1/Ba/Al exhibits the highest external quantum efficiency 1.62% with luminance efficiency of 2.69 cd/A, power efficiency of 1.25 lm/W and the CIE coordinates of (0.15, 0.17). The EL spectra are stable at the increased current density and continuous operation without significant change of CIE.