Synthesis and characterization of highly stable blue‐light‐emitting hyperbranched conjugated polymers

Polyfluorene homopolymer ( P1 ) and its carbazole derivatives ( P2 – P4 ) have been prepared with good yield by Suzuki coupling polymerization. P2 is an alternating copolymer based on fluorene and carbazole; P3 is a hyperbranched polymer with carbazole derivative as the core and polyfluorene as the long arms; P4 is a hyperbranched polymer with carbazole derivative as the core and the alternating fluorene and carbazole as the long arms. These polymers show highly thermal stability, and their structures and physical properties are studied using gel permeation chromatography, ¹H NMR, ¹³C NMR, elemental analysis, Fourier transform infrared spectroscopy, thermogravimetry, UV–vis absorption, photoluminescence, and cyclic voltammetry (CV). The influence of the incorporation of carbazole and the hyperbranched structures on the thermal, electrochemical, and electroluminescent properties has been investigated. Both carbazole addition and the hyperbranched structure increase the thermal and photoluminescent stability. The CV shows an increase of the HOMO energy levels for the derivatives, compared with polyfluorene homopolymer ( P1 ). The EL devices fabricated by these polymers exhibit pure blue‐light‐emitting with negligible low‐energy emission bands, indicating that the hyperbranched structure has a strong effect on the PLED characteristics. The results imply that incorporating carbazole into polyfluorene to form a hyperbranched structure is an efficient way to obtain highly stable blue‐light‐emitting conjugated polymers, and it is possible to adjust the property of light‐emitting polymers by the amount of carbazole derivative incorporated into the polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 790–802, 2008     

Design,synthesis, photophysical,and electrochemical properties of DCM‐based conjugated polymers for light‐emitting devices

A series of conjugated hyperbranched polymers, hyperbranched copolymers, and linear polymers containing 2‐pyran‐4‐ylidenemalononitrile (acceptor) and triphenylamine/fluorene (donor) units were synthesized and characterized by FTIR, ¹H NMR, thermogravimetric analyses, differential scanning calorimetry, gel permeation chromatography, UV–visible, photoluminescence, and cyclic voltammetry measurements. All the polymers show red‐light emission in the range of 566–656 nm both in solution and in solid state. The quantum efficiency of the polymers was in the range of 56–82%. Among the six polymers synthesized, only polymers containing fluorene units show T_g and polymers based on triphenylamine not exhibit T_g. The band gap of these polymers were found to be reasonably low; hyperbranched copolymer containing fluorene unit shows lowest band gap of 2.18 eV due to the stabilization of LUMO energy level by the electron withdrawing ? CN groups. The thermal and solubility behavior of the polymers were found to be good. All the EL spectra of the devices (indium‐tin oxide/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)/polymer/2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline/tris(8‐hydroxyquinoline)aluminum)/LiF/Al) show red‐light emission, and the device fabricated with P3 and P4 shows maximum luminance and luminous efficiency of 4104 cd m^?2 and 0.55 cd Å^?1 and 3696 cd m^?2 and 0.47 cd Å^?1, respectively, indicates that they had the best carrier balance. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Tuning the optical properties of hyperbranched polymers through the modification of the end groups

Dye‐capped, hyperbranched, conjugated polymers were prepared by the modification of the peripheral bromo end groups of the hyperbranched polymer core with a palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction. The dye‐modified, hyperbranched polymers had high molecular weights and displayed good solubility in common organic solvents such as tetrahydrofuran, toluene, and chloroform. The structure of the dye‐modified, hyperbranched polymers was characterized by ¹H and ¹³C NMR and elemental analysis. The thermal properties of five kinds of hyperbranched polymers were investigated with thermogravimetric analysis and differential scanning calorimetry. The optical properties of the dye‐capped, hyperbranched polymers were investigated with ultraviolet‐absorption and fluorescence spectroscopy. The hyperbranched structure could effectively reduce the aggregation of the peripheral dyes. The emission colors of the hyperbranched polymers could be easily tuned by end‐group modification. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 111–124, 2007     

Synthesis of a novel one‐pot approach of hyperbranched polyurethanes and their properties

A new method for the synthesis of hyperbranched polymers involving the use of AB_x macromonomers containing linear units have been investigated. Two types of novel hyperbranched polyurethanes have been synthesized by a one‐pot approach. The structures of monomers and polymers were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. The hyperbranched polymers have been proven to be extremely soluble in a wide range of solvents. Polymer electrolytes were prepared with hyperbranched polymer, linear polymer as the host, and lithium perchlorate (LiClO₄) as the ion source. Analysis of the isotherm conductivity dependence of the ion concentration indicated that these hyperbranched polymers could function as a “solvent” for the lithium salt. The conductivity increased with the increasing concentration of hyperbranched polymers in the host polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 344–350, 2002     

Synthesis and electro‐optical properties of light‐emitting polymers containing oxadiazole derivatives for light‐emitting diodes applications

Two PPV‐based bipolar polymers containing 1,3,4‐oxadiazole pendant groups were synthesized via the Gilch polymerization reaction for use in light‐emitting diodes (LEDs). The resulting polymers were characterized using ¹H and ¹³C NMR, elemental analysis, DSC, and TGA. These polymers were found to be soluble in common organic solvents and are easily spin‐coated onto glass substrates, producing high optical quality thin films without defects. The electro‐optical properties of ITO/PEDOT/polymer/Al devices based on these polymers were investigated using UV‐visible, PL, and EL spectroscopy. The turn‐on voltages of the OC₁Oxa‐PPV and OC₁₀Oxa‐PPV devices were found to be 8.0 V. The maximum brightness and luminescence efficiency of the OC₁Oxa‐PPV device were found to be 544 cd/m² at 19 V and 0.15 cd/A, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1098–1110, 2008     

Synthesis,characterization, and optoelectronic properties of hyperbranched polyfluorenes containing pendant benzylether dendrons

Linear polyfluorenes with low generation of side benzylether dendrons ( PLG0 , PLG1 ) and hyperbranched polyfluorenes with 1,3,5‐benzene branch unit ( PHG0 and PHG1 ) were prepared by the Suzuki coupling reaction to investigate the structural effect on optoelectronic properties. Their optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. The excimer emission of polyfluorene at about 530 nm, induced by thermal annealing, was completely suppressed by the hyperbranched structure, but the suppression was not obvious by the side benzylether dendrons. The optoelectronic performance of the EL devices (ITO/PEDOT:PSS/polymer/Ca/Al) was strongly dependent upon chemical structures of the emitting polyfluorenes. The hyperbranched PHG0 with zero generation of benzylether side groups revealed the best device performance, with maximal luminance and maximal luminance efficiency of 2350 cd/m² and 0.33 cd/A, respectively. The results suggest that incorporation of branch units with low generation of benzylether dendrons is an effective way to improve annealing stability and EL performance of the polyfluorenes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5945–5958, 2008     

Facile synthesis and characterization of hyperbranched poly(ether amide)s generated from Michael addition polymerization of in situ created AB2 monomers

A new straightforward strategy for synthesis of novel hyperbranched poly (ether amide)s from readily available monomers has been developed. By optimizing the reaction conditions, the AB₂‐type monomers were formed dominantly during the initial reaction stage. Without any purification, the AB₂ intermediate was subjected to further polymerization in the presence (or absence) of an initiator, to prepare the hyperbranched polymer‐bearing multihydroxyl end‐groups. The influence of monomer, initiator, and solvent on polymerization and the molecular weight (MW) of the resultant polymers was studied thoroughly. The MALDI–TOF MS of the polymers indicated that the polymerization proceeded in the proposed way. Analyses of ¹H NMR and ¹³C NMR spectra revealed the branched structures of the polymers obtained. These polymers exhibit high‐moderate MWs and broad MW distributions determined by gel permeation chromatography (GPC) in combination with triple detectors, including refractive index, light scattering, and viscosity detectors. In addition, the examination of the solution behavior of these polymers showed that the values of intrinsic viscosity [η] and the Mark–Houwink exponent α were remarkably lower compared with their linear analogs, because of their branched nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4309–4321, 2007     

Triazatruxene-containing hyperbranched polymers: Microwave-assisted synthesis and optoelectronic properties

Hyperbranched polymer structures represent a class of high-functionality building blocks with excellent three-dimensional topology for the construction of highly substituted conjugated polymers. In this contribution, an efficient microwave synthesis protocol toward the synthesis of conjugated hyperbranched polymers is presented. A novel series of soluble hyperbranched polyfluorenes (PTF1-PTF3) incorporating triazatruxene moiety as the branch units with various branching degrees have thus been successfully constructed with good yields and high molecular weight via a facile “A2+B2+C3” approach. The structures of the hyperbranched polymers were confirmed by NMR and GPC. Their thermal, optical, and electrochemical properties of the hyperbranched polymers were also investigated. The results showed that introduction of triazatruxene units into the hyperbranched structure endowed the polymer with good thermal stability and highly amorphous properties. Photophysical investigation of PTFx revealed strong blue emission in both solution and solid states. Hyperbranched polymers with higher degree of branching and proper content of linear fluorene units exhibited better photophysical properties in terms of narrow emission spectra and relatively high quantum efficiency as well as improved thermal spectral stability. The triazatruxene branching unit also played a role in raising the HOMO energy levels relative to those of polyfluorenes that would help to improve the charge injection and transport properties. The incorporation of triazatruxene unit into hyperbranched polymers has thus explored an effective avenue for constructing optoelectronic polymers with improved functional characteristics.     

Phenothiazine‐S,S‐dioxide‐ and fluorene‐based light‐emitting polymers: Introduction of e−‐deficient S,S‐dioxide into e−‐rich phenothiazine

A novel series of poly(10‐hexyl‐phenothiazine‐S,S‐dioxide‐3,7‐diyl) and poly(9,9′‐dioctyl‐fluorene‐2,7‐diyl‐alt‐10‐hexyl‐3,7‐phenothiazine‐S,S‐dioxide) (PFPTZ‐SS) compounds were synthesized through Ni(0)‐mediated Yamamoto polymerization and Pd(II)‐catalyzed Suzuki polymerization. The synthesized polymers were characterized by ¹H NMR spectroscopy and elemental analysis and showed higher glass transition temperatures than that of pristine polyfluorene. In terms of photoluminescence (PL), the PFPTZ‐SS compounds were highly fluorescent with bright blue emissions in the solid state. Light‐emitting devices were fabricated with these polymers in an indium tin oxide/poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate)/polymer/Ca/Al configuration. The electroluminescence (EL) of the copolymers differed from the PL characteristics: the EL device exhibited a redshifted greenish‐blue emission in contrast to the blue emission observed in the PL. Additionally, this unique phenothiazine‐S,S‐dioxide property, triggered by the introduction of an electron‐deficient SO₂ unit into the electron‐rich phenothiazine, gave rise to improvements in the brightness, maximum luminescence intensity, and quantum efficiency of the EL devices fabricated with PFPTZ‐SS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1236–1246, 2007     

Hyperbranched copolyfluorene from a 2,4,7‐trifunctional fluorene monomer

A new hyperbranched ( P1 ) and linear copolyfluorene ( P2 ) were prepared from 2,4,7‐trifunctional (branching) and 2,7‐bifunctional fluorene monomer, respectively, by the Wittig reaction, followed with end‐capping by aromatic oxadiazole groups, to study the effect of hyperbranch structure. The weight‐average molecular weights (M_w) of P1 and P2 , determined by gel permeation chromatography using polystyrene as standard, were 33,000 and 25,700, respectively. The polymers were readily soluble in common organic solvents and exhibited good thermal stability (T_d > 400 °C). Optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. In film state, the absorption and PL spectra peaked at 401–425 nm and 480–495 nm, respectively. The P1 showed energy funnel effect and enhanced fluorescence efficiency owing to hyperbranched structure and terminal oxadiazole groups. The HOMO and LUMO levels of P1 ( P2) , estimated from cyclic voltammograms, are ?5.34 (?5.25) eV and ?2.94 (?2.94) eV, respectively. Two‐layer polymer light‐emitting diodes devices (ITO/PEDOT/ P1 /Ca/Al) exhibited maximal luminance and luminous efficiency of 3630 cd/m² and 0.78 cd/A, respectively, which are superior to its linear counterpart P2 (598 cd/m², 0.11 cd/A). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5541–5551, 2007     

Synthesis and properties of new orange red light‐emitting hyperbranched and linear polymers derived from 3,5‐dicyano‐2,4,6‐tristyrylpyridine

Two new orange red light‐emitting hyperbranched and linear polymers, poly(pyridine phenylene)s P1 and P2, were prepared by the Heck coupling reaction. In particular, an A₂ + B₃ approach was developed to synthesize conjugated hyperbranched polymer P2 via one‐pot polycondensation. The polymers were characterized by NMR, Fourier transform infrared, ultraviolet–visible, and elemental analysis. They showed excellent solubility in common solvents such as tetrahydrofuran, CH₂Cl₂, CHCl₃, and N,N‐dimethylformamide and had high molecular weights (up to 6.1 × 10⁵ and 5.8 × 10⁵). Cyclic voltammetry studies revealed that P2 had a low‐lying lowest unoccupied molecular orbital energy level of ?3.22 eV and a highest occupied molecular orbital energy level of ?5.43 eV. The thin film of P2 emitted strong orange‐red photoluminescence at 595 nm. A double‐layer light‐emitting diode fabricated with the configuration of indium tin oxide/P2/tris(8‐hydroxy‐quinoline)aluminum/Al emitted orange‐red light at 599 nm, with a brightness of 662 cd/m² at 7 V and a turn‐on voltage of 4.0 V; its external quantum efficiency was calculated to be 0.19% at 130.61 mA/cm². This indicated that this new electroluminescent polymer (P2) based on 3,5‐dicyano‐2,4,6‐tristyrylpyridine could possibly be used as an orange‐red emitter in polymer light‐emitting displays. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 493–504, 2005     

Synthesis of hyperbranched poly(ether nitrile)s by one‐step polycondensation of an AB2 monomer

Hyperbranched poly(ether nitrile)s were prepared from a novel AB₂ type monomer, 2‐chloro‐4‐(3,5‐dihydroxyphenoxy)benzonitrile, via nucleophilic aromatic substitution. Soluble and low‐viscous hyperbranched polymers with molecular weights upto 233,600 (M_w) were isolated. According to the ¹H NMR and GPC data, the unique polymerization behavior was observed, which implies that the weight average molecular weight increased after the number average molecular weight reached plateau region. Model compounds were prepared to characterize the branching structure. Spectroscopic measurements of the model compounds and the resulting polymers, such as ¹H, DEPT ¹³C NMR, and MS, strongly suggest that the ether exchange reaction and cyclization are involved in the propagation reaction. The side reactions would affect the unique polymerization behavior. The resulting polymers showed a good solubility in organic solvents similar to other hyperbranched aromatic polymers. The hydroxy‐terminated polymer was even soluble in basic water. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5835–5844, 2009     

Hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s: Synthesis,characterization, end‐group modification,and optical properties

Novel AB₂‐type monomers such as 3,5‐bis(4‐methylolphenoxy)benzoic acid ( monomer 1 ), methyl 3,5‐bis(4‐methylolphenoxy) benzoate ( monomer 2 ), and 3,5‐bis(4‐methylolphenoxy)benzoyl chloride ( monomer 3 ) were synthesized. Solution polymerization and melt self‐polycondensation of these monomers yielded hydroxyl‐terminated hyperbranched aromatic poly(ether‐ester)s. The structure of these polymers was established using FTIR and ¹H NMR spectroscopy. The molecular weights (M_w) of the polymers were found to vary from 2.0 × 10³ to 1.49 × 10⁴ depending on the polymerization techniques and the experimental conditions used. Suitable model compounds that mimic exactly the dendritic, linear, and terminal units present in the hyperbranched polymer were synthesized for the calculation of degree of branching (DB) and the values ranged from 52 to 93%. The thermal stability of the polymers was evaluated by thermogravimetric analysis, which showed no virtual weight loss up to 200 °C. The inherent viscosities of the polymers in DMF ranged from 0.010 to 0.120 dL/g. End‐group modification of the hyperbranched polymer was carried out with phenyl isocyanate, 4‐(decyloxy)benzoic acid and methyl red dye. The end‐capping groups were found to change the thermal properties of the polymers such as T_g. The optical properties of hyperbranched polymer and the dye‐capped hyperbranched polymer were investigated using ultraviolet‐absorption and fluorescence spectroscopy. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5414–5430, 2008     

One‐pot synthesis and characterization of hyperbranched poly(ester‐amide)s from commercially available dicarboxylic acids and multihydroxyl secondary amines

A convenient and cost‐effective strategy for synthesis of hyperbranched poly(ester‐amide)s from commercially available dicarboxylic acids (A₂) and multihydroxyl secondary amine (CB₂) has been developed. By optimizing the conditions of model reactions, the AB₂‐type intermediates were formed dominantly during the initial reaction stage. Without any purification, the AB₂ intermediate was subjected to thermal polycondensation in the absence of any catalyst to prepare the aliphatic and semiaromatic hyperbranched poly(ester‐amide)s bearing multi‐hydroxyl end‐groups. The FTIR and ¹H NMR spectra indicated that the polymerization proceeded in the proposed way. The DBs of the resulting polymers were confirmed by a combination of inverse‐gated decoupling ¹³C NMR, and DEPT‐135 NMR techniques. The DBs of the hyperbranched poly(ester‐amide)s were in the range of 0.44–0.73, depending on the structure of the monomers used. The hyperbranched polymers exhibited moderate molecular weights with relatively broad distributions determined by SEC. All the polymers displayed low inherent viscosity (0.11–0.25 dL/g) due to the branched nature. Structural and end‐group effects on the thermal properties of the hyperbranched polymers were investigated using DSC. The thermogravimetric analysis revealed that the resulting polymers exhibit reasonable thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5077–5092, 2008     

Preparation and properties of novel thermotropic liquid crystalline hyperbranched polyesters composed of five‐membered heterocyclic mesogen by A2 + B3 approach

New thermotropic liquid crystalline (LC) hyperbranched (HB) polyesters containing 2,5‐diphenyl‐1,3,4‐thiadiazole (DTD) unit as mesogen in the interiors were prepared at various mole ratios (A₂/B₃) by melt and solution polycondensations of a dioxydiundecanol of DTD (A₂) and 1,2,3‐propanetricarboxylic acid (B₃) via the A₂ + B₃ approach and their LC and optical properties were investigated. FTIR and ¹H‐NMR spectroscopies indicated that all the expected HB polyesters, which show good solubilities in organic solvents, are produced without gelation during the polymerization. Among them, the HB polymer prepared in the mole ratio of A₂/B₃ = 3/2 by the solution polycondensation had the highest inherent viscositiy. DSC measurents, polarizing microscope observations of optical textures, and X‐ray analyses suggested that the LC properties of HB polymers depend on the polymerization methods and the feed mole ratios. In the HB polymers prepared using the melt polycondensation, only the polymer prepared in the mole ratio of A₂/B₃ = 3/1 formed a highly‐ordered, tilted, crystal‐like smectic phase, but all the polymers prepared by the solution polycondensation formed highly‐ordered, tilted, smectic phases. Solution and solid‐state UV‐vis and photoluminescent (PL) spectra indicated that the HB polymers show maximum absorbances and blue‐light emission on the basis of the DTD unit, where the Stokes‐shifts were observed, probably because of intermolecular aggregation effects © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2998–3008, 2007     

Monochromatic‐red‐light emission of novel copolymers containing carbazole units and europium–acrylate complexes

Nearly monochromatic‐red‐light‐emitting polymers with pendant carbazole and europium (Eu) complex were synthesized and characterized by Fourier transform infrared, elemental analysis (EA), ¹H NMR, ¹³C NMR, UV, and gel permeation chromatography. The photoluminescence and electroluminescence (EL) properties of these polymers were investigated. A single‐layer light‐emitting‐diode device of the structure (indium tin oxide/polymer P4/Al) was fabricated, showing the characteristic bright‐red EL of the Eu³⁺ complex at 614 nm at a turn‐on voltage of about 17 V. The EL spectrum, current–voltage, and emission‐intensity–voltage characteristics of the device were measured. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3405–3411, 2000     

Effect of molecular architecture and size of mesogen on phase behavior and photoactive properties of photoactive liquid crystalline hyperbranched polyester epoxies containing benzylidene moiety

A series of photoactive liquid crystalline linear and hyperbranched polyester epoxies were synthesized by polyaddition of photoactive bis benzylidene alkanone diol monomers and terephthalic acid and trimesic acid respectively with good yield. The effect of molecular architecture (linear and hyperbranched), size of mesogenic unit (cyclic and acyclic units) on the physicochemical, thermal, mesogenic, and photoactive properties of hyperbranched polymers were studied and compared. Degree of branching of hyperbranched polymers was found to be in the range of 0.46–0.49. Monomers containing cyclic moieties only exhibited nematic mesophase, while all polymers exhibited typical nematic mesophase. Intermolecular photo cycloaddition reaction was studied by ultraviolet–visible spectra (UV–vis) and NMR spectroscopy and photo viscosity measurement of UV irradiated polymer solutions. Faster photo induced behavior of hyperbranched polymers containing acyclic alkanone moiety, as compared to polymers containing cycloalkanone moieties, was observed. The change in the refractive index was found to be in the range of 0.02–0.024. Substantial variation of refractive index indicates that this polymer could be used for optical recording. All the polymers were also found to be fluorescent in nature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 552–563, 2008     

Hyperbranched luminescent polyfluorenes containing aromatic triazole branching units

Using a new aromatic 1,2,4‐triazole branching monomer (4.8–13.3 mol %), three hyperbranched polyfluorenes ( P2 – P4 ) were synthesized by the Suzuki coupling reaction to investigate the structural effect on optoelectronic properties. Poly(9,9‐dihexylfluorene) ( P1 ) was also prepared for comparative investigation. Their weight‐average molecular weights and polydispersity indices are in the range of 1.16 × 10⁴ to 5.9 × 10⁴ and 1.49–2.25, respectively. Optical properties, both in solution and film state, were investigated using absorption and photoluminescence (PL) spectra. In film state, the absorption and PL spectra peaked at 377–392 and 424–425 nm, respectively, blue‐shift with increasing triazole concentration. Furthermore, a linear relationship between 1/λ_max,abs and 1/(1 ? n_triazole) is correlated (n: molar fraction), indicating a smooth decrease in conjugation length by incorporation of the branch unit. The P4 containing 13.3 mol % triazole reveals stable blue emission even at 150 °C (in air). The HOMO and LUMO levels of P2 – P4 , estimated from cyclic voltammograms, are ?5.69, ?5.73, ?5.78 eV and ?2.63, ?2.64, ?2.63 eV, respectively. The maximal brightness (current efficiency) of the electroluminescent devices (ITO/PEDOT:PSS/ P2 – P4 /Ca/Al) improves from 828 cd/m² (0.19 cd/A) to 2054 cd/m² (0.46 cd/A) with increasing triazole concentration. The results suggest that incorporation of aromatic 1,2,4‐triazole branch units is an effective way to improve annealing stability and EL performance of polyfluorenes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4465–4476, 2007     

The thermal polymerization of amino acids revisited; Synthesis and structural characterization of hyperbranched polymers from L‐lysine

This contribution reports on the synthesis of hyperbranched polylysines via thermal polymerization of L ‐lysine hydrochloride. Polymerization of L ‐lysine hydrochloride in the presence of one equivalent KOH at 150 °C resulted in polymers with a number‐average molecular weight of 4600 g/mol and a polydispersity of 2.6 after 48 h. The rate of polymerization could be significantly enhanced and the polymer molecular weight improved by carrying out the polymerization with 3 mol % of an amidation catalyst. Among the different catalysts that were investigated Zr(OⁿBu)₄ was found to be the most effective. Unequivocal support for the branched architecture of the polymers was obtained from ¹H NMR spectroscopy, which allowed the identification and quantification of the four different structural units that constitute the polymer, viz. N^α and N^ε linked linear units, dendritic units and terminal units. The structure of the polymers was found to be relatively independent of the reaction conditions. The degree of branching and the average number of branches varied between 0.35–0.45 and 0.15–0.25, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5494–5508, 2007     

Synthesis and properties of hyperbranched poly(ether sulfone)s prepared by self‐polycondensation of novel AB2 monomer

Hyperbranched poly(ether sulfone)s were prepared by the self‐polycondensation of the novel AB₂ monomer, 4‐(3,5‐hydroxyphenoxy)‐4′‐fluorodiphenylsulfone. The high‐molecular‐weight polymers were isolated in good yields. The degree of branching (DB) of the resulting polymers was investigated by the preparation of dendritic and linear model compounds. The DB determined by gated decoupling ¹³C NMR measurements was in the range 0.17–0.41 and was dependent on the base used for the self‐polycondensation. It was found that cesium fluoride was an effective base to form the polymer having the DB of 0.41. The resulting hyperbranched poly(ether sulfone)s showed good solubility in organic solvents. The solubility and the glass transition temperature of the polymers were influenced by the terminal functional groups. The unique thermal crosslinking phenomenon was observed during the DSC measurements of the hydroxyl‐terminated hyperbranched poly(ether sulfone) under air condition. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012