Organo-soluble phosphinated polyimides from asymmetric diamines

Two new asymmetric diamines (1-2) were prepared via a facile, one-pot procedure. Based on diamine (1-2), a series of asymmetric polyimides (3-4) were prepared in NMP/xylene by high-temperature solution polymerization. The resulting polyimides are readily soluble in some organic solvents, and can be solution casted into flexible and creasable films. An intramolecular charge complex mechanism was proposed to the structure-optical transparency relationship. Polyimides 3-4 display high-Tg (319-401 °C), high moduli (2.40-7.20 GPa), moderate coefficient of thermal expansion (38-53 ppm/°C), and excellent flame retardancy. These results show that the introduction of the asymmetric structure is an effective way to improve organo-solubility while maintaining thermal properties. Because of these properties, polyimides 3-4 can be considered as excellent high-Tg and flame-retardant materials for microelectronic applications.     

Synthesis, characterization and properties of tetramethyl stilbene-based epoxy resins for electronic encapsulation

Two novel tetramethyl stilbene-based novolac (II and IV) were synthesized from 2,6-dimethyl phenol and chloroacetaldehyde dimethylacetal or chloroacetone, and then the resulted novolacs were epoxidized to tetramethyl stilbene-based epoxy resins (III and V). The proposed structures were confirmed by FTIR, elemental analysis, mass spectra, NMR spectra and epoxy equivalent weight titration. The synthesized tetramethyl stilbene-based epoxy resins were cured with 4,4-diaminodiphenyl methane (DDM) and 4,4-diaminodiphenyl sulfone (DDS). Thermal properties of cured epoxy resins were studied using dynamic mechanical analyzer, differential scanning calorimeter, thermal expansion analyzer and thermal gravimetric analyzer (TGA). These data were compared with that of the commercial tetramethyl biphenol (TMBP) epoxy system. According to the experimental data, the order of T_g for cured epoxy system is III>TMBP>V. The order of moisture absorption for cured epoxy system is V<III<TMBP. According to TGA, the 5% degradation temperatures in nitrogen atmosphere were in the range 370-377 and 397-412 °C for DDM and DDS curing systems, respectively. In air atmosphere, the 5% degradation temperatures were in the range 372-385 and 410-411 °C for DDM and DDS curing systems, respectively. The CTE is in inverse order with T_g, therefore, III/DDS<TMBP/DDS<V/DDS.     

Colorless and high organosoluble polyimides from 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride and aromatic bis(ether amine)s bearing pendent trifluoromethyl groups

A series of polyimides III_a-h characterized by colorlessness, high transparency, high solubility, and good mechanical property, was synthesized from the aromatic dianhydride, 2,5-bis(3,4-dicarboxyphenoxy)-t-butylbenzene dianhydride (I), and various aromatic diamines (II_a-h) with pendent trifluoromethyl group via polyaddition, chemical imidization, and direct cast films. The III series showed more colorless than the polyimides (V and VI series) of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) contained, the VI series was synthesized from the II with 6FDA. These films III had cut-off wavelengths between 371 and 376 nm, as well as b* value (a yellowness index) ranging from 3.0 to 4.7. In fact, it is so far the most colorless aromatic polyimide in our systematical researches. The III series had inherent viscosity ranging from 0.72 to 1.33 dL/g and showed excellent solubility in a variety of organic solvents. They were soluble in a concentration of 5-10% in the amide polar solvent, ether solvent, and chlorinated solvent. These films showed strength tensile of 97-123 MPa, dielectric constants of 2.78-3.28 (1 MHz), and moisture absorptions of 0.11-0.36 wt%. The glass transition temperature of the III series was recorded at 214-259 °C, the 10% weight loss temperature was over 468 °C, and the residue was more than 47% at 800 °C in nitrogen.     

Effect of side chain structure of polyimides on a pretilt angle of liquid crystal cells

A series of poly(amic acid)s had been synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA) and 4,4′-diaminodiphenyl methane (DDM) and functional diamines with various side chain structures. The functional diamines, like 3,5-diamino benzoic acid hexadecane-1-yl ester which had long alkyl or rigid alicyclic side chains with different flexibility had been synthesized. Pretilt angles of liquid crystal cell fabricated with the poly(amic acid)s were measured and investigated factors affecting on the pretilt angles. The pretilt angles of the liquid crystal on the polyimide (5a) with rigid side group was 0.6°, on the other hand, the pretilt angle on the polyimide (5b) and (5c) with flexible side chains were very high above 89.6°. Furthermore, the pretilt angle of liquid crystal on the polyimide (5c) film having rigid cylindrical structure with 6-methylheptyl at the chain end was still high above 86.0° even after the rubbing process.     

Aromatic diamine-based benzoxazines and their high performance thermosets

Four high-purity aromatic diamine-based benzoxazines (13-16), which could not easily be synthesized by traditional approaches, were successfully synthesized by a facile, widely useful three-step synthetic method using four typical aromatic diamines - 4,4′-diamino diphenyl methane (1), 4,4′-diamino diphenyl sulfone (2), 2,2-bis(4-(4-aminophenoxy)phenyl)propane (3), and bis(4-(4-aminophenoxy)phenyl)ether (4), respectively, as starting materials. The structures of the monomers (5-16) were confirmed by ¹H, ¹³C, ¹H-¹H and ¹H-¹³C NMR spectra. Their high performance thermosets, P(13-16), were obtained by thermal curing of benzoxazines (13-16), and their properties were studied and compared with polymer derived from bis(3,4-dihydro-2H-3-phenyl-1,3-benzoxazinyl)methane (F-a), a typical aromatic biphenol-based benzoxazine. Among the benzoxazines, 13 and F-a are constitutional isomers, but the T_g value and 5% decomposition temperature of P(13) are 53 and 111 °C, respectively, higher than those of P(F-a), demonstrating the power of the molecule-approach to enhance the thermal properties. Because of the large varieties of aromatic diamines, this approach can increase the molecule-design flexibility of benzoxazines.     

Non-catalytic Oppenauer oxidation of alcohols in supercritical water

Non-catalytic Oppenauer oxidation was applied for alcohols, such as benzyl alcohol (4) and benzhydrol (1), in the presence of an excess amount of carbonyl compound, formaldehyde (5a), as an oxidant with and without water. Oppenauer oxidation took place in both reactions of 4 and 1 to afford the oxidation products, benzaldehyde (6) (95%) and benzophenone (2) (64%), concomitant with relatively small amounts of reduction products, toluene (7) (1%) and diphenylmethane (3) (13%), respectively, at 400 °C for 10 min without water in an SUS 316 batch-type tubular reactor. Lower yields of oxidation products 6 (68%) and 2 (30%) were obtained in supercritical water under the conditions of 400 °C, 10 min, and 0.35 g/mL water density, while the formation of the reduction products 7 and 3 was completely suppressed. Thus, water was indispensable for the clean and highly selective Oppenauer oxidation of 4 and 1 to yield 6 and 2.     

Synthesis and properties of novel organosoluble polyimides derived from 1,4-bis[4-(3,4-dicarboxylphenoxy)]triptycene dianhydride and various aromatic diamines

A novel triptycene-based dianhydride, 1,4-bis[4-(3,4-dicarboxylphenoxy)]triptycene dianhydride, was prepared from 4-nitro-N-methylphthalimide and potassium phenolate of 1,4-dihydroxytriptycene (1). The aromatic nucleophilic substitution reaction between 4-nitro-N-methylphthalimide and 1 afforded triptycene-based bis(N-methylphthalimide) (2), which hydrolyzed and subsequently dehydrated to give the corresponding dianhydride (3). A series of new polyimides containing triptycene moieties were prepared from the dianhydride monomer (3) and various diamines in m-cresol via conventional one-step polycondensation method. Most of the resulting polyimides were soluble in common organic solvents, such as chloroform, THF, DMAc and DMSO. The polyimides exhibited excellent thermal and thermo-oxidative stabilities with the onset decomposition temperature and 10% weight loss temperature ranging from 448 to 486 °C and 526 to 565 °C in nitrogen atmosphere, respectively. The glass transition temperatures of the polyimides were in the range of 221-296 °C. The polyimide films were found to be transparent, flexible, and tough. The films had tensile strengths, elongations at break, and tensile moduli in the ranges 95-118 MPa, 5.3-16.2%, and 1.03-1.38 GPa, respectively. Wide-angle X-ray diffraction measurements revealed that these polyimides were amorphous.     

Synthesis of sulfonated poly(arylene-co-naphthalimide)s as novel polymers for proton exchange membranes

A series of novel sulfonated poly(arylene-co-binaphthalimide)s (SPPIs) were successfully synthesized via Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and bis(chloronaphthalimide)s. Bis(chloronaphthalimide)s were conveniently prepared from 5-chloro-1,8-naphthalic anhydride and various diamines. Tough and transparent SPPI membranes were prepared and the electrolyte properties of the copolymers were intensively investigated as were the effects of different diamine structures on the copolymer characterisitics. The copolymer membrane Ia-80, with an ion exchange capacity (IEC) of 2.50 meq g⁻¹, displayed a higher proton conductivity, i.e. 0.135 S cm⁻¹ at 20 °C, as compared to Nafion 117 (0.09 S cm⁻¹, 20 °C). The copolymer membrane Id-70, containing 3,3′-dimethyl-4,4′-methylenedianiline (DMMDA) units, exhibited excellent stability toward water and oxidation due to the introduction of hydrophobic methyl groups on the ortho-position of the imido bond in the copolymer. The mechanical property of Id-70 remained virtually unchanged after immersing membrane in pressured water at 140 °C for 24 h. Furthermore, the introduction of aliphatic segment a hexane-1,6-diamine (HDA) in copolymer led to a significant increase in proton conductivity and water uptake with increasing temperature; the proton conductivity of the Ic-70 membrane reached 0.212 S cm⁻¹ at 80 °C, which was higher than Nafion 117 as well as of the membranes based on aromatic diamines at equivalent IEC values. Consequently, these materials proved to be promising as proton exchange membranes.     

Copolymerisation of 1,9-decadiene and propylene with binary and isolated metallocene systems

1,9-Decadiene/propylene copolymers were obtained with isolated metallocenes and with a binary metallocene catalyst system activated by methylaluminoxane. The metallocenes under investigation were syndiospecific diphenylmethyl(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (1) and isospecific rac-dimethylsilylbis(4-tert-butyl-2-methyl-cyclopentadienyl)zirconium dichloride (2). A copolymer structure, in which 1,9-decadiene linked isotactic and syndiotactic polymer chains, was obtained when copolymerisation was started with catalyst 2 at 80 °C followed by injection of catalyst 1 and instantaneous lowering of polymerisation temperature to 40 °C after 15 min of polymerisation. The copolymer was also shown to work as a compatibiliser in a blend of syndiotactic and isotactic polypropylene. We propose that catalyst 2 incorporates 1,9-decadiene into the isotactic main chain without any significant crosslinking within the first 15 min of polymerisation at 80 °C and the produced isotactic macromonomers are further incorporated at 40 °C into the syndiotactic main chain in polymerisation with catalyst 1.     

Syndiotactically enriched 1,2-selective polymerization of 1,3-butadiene initiated by iron catalysts based on a new class of donors

A series of phosphoryl (PO) contained compounds: triethylphosphate (a), diethylphenylphosphate (b), ethyldiphenylphosphate (c) triarylphosphates (d and h-m), triphenylphosphine oxide (e), phenyl diphenylphosphinate (f) and diphenyl phenylphosphonate (g) have been prepared. Iron catalysts, which are generated in situ by mixing the compounds with Fe(2-EHA)₃ and AlⁱBu₃ in hexane, are tested for butadiene polymerization at 50 °C. Phosphates donated catalysts have been, unprecedently, found to conduct extremely high syndiotactically (pentad, rrrr = 46.1-94.5%) enriched 1,2-selective (1,2-structure content = 56.2-94.3%) polymerization of butadiene. Introduction of electron withdrawing substituents on phenyl rings oftriphenylphosphate (k-m) remarkably promotes catalytic activity, while bulky substituent isopropyl at 2-position (h) has beneficial influence on regioselectivity. Employment of e, f or g as donor, results in a suppressed monomer conversion, accompanied by deteriorated 1,2-regioselectivity. The effects of polymerization conditions such as reaction temperature, types of cocatalysts and polymerization medium are also investigated by using catalyst system with tri(2,4-difluorophenyl)phosphate (m) as donor. Highly tolerance to polymerization temperature up to 80 °C is observed for the first time in the iron-based catalyst.     

Effects of internal linkage groups of fluorinated diamine on the optical and dielectric properties of polyimide thin films

To investigate the difference of the trifluoromethyl (CF₃) group and ether group affecting the optical property of fluorinated polyimides (PIs), we prepared 4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl ether (4) with three ether groups and 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane (5) with four CF₃ groups with 2-chloro-5-nitrobenzotrifluoride and 4,4′-dihydroxydiphenyl ether or 2,2-bis(4-hydroxyphenol)hexafluoropropane. Two series of organosoluble and light-colored PIs (4a-4c, 5a-5c) were synthesized from 4 and 5 with various aromatic dianhydrides: 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA) (a), 4,4-oxydiphthalic anhydride (ODPA) (b), and 4,4-hexafluoroisopropylidenediphthalic anhydride (6FDA) (c), prepared through a typical two-step polymerization method. These PIs were soluble in amide polar solvents and even in less polar solvents. The glass-transition temperatures (T_g) of 4a-5c were 221-249 °C and the 10% weight-loss temperatures were above 530 °C. Their films had cutoff wavelengths between 339 and 399 nm and yellowness index ranges from 1.95 to 42.60. The dielectric constants estimated from the average refractive indices are 2.59-2.93 (1 MHz). In a comparison of the PI series based on 4, 5, and 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6), we found that the CF₃ group and ether group on the diamine had almost same effect in lowering the color, but the ether group had better thermal stability. The color intensity of the three PI series was lowered in the following order: 6 > 4 > 5. The PI 5c, synthesized from diamine 5 and dianhydride c, had six CF₃ groups in a repeated segment and ether group at the same time, so it exhibited the lightest color among the three series.     

Synthesis and characterization of luminescent copolyethers with alternate stilbene derivatives and aromatic 1,3,4-oxadiazoles

New copoly(aryl ether)s containing alternate stilbene (P1), distyrylbenzene (P2), or distyrylstilbene (P3) chromophores and aromatic 1,3,4-oxadiazole were prepared by nucleophilic polycondensation. The copolyethers are basically amorphous materials with decomposition temperature greater than 250 °C. Introduction of side hexyloxy groups to distyrylbenzene chromophores in P2 significantly enhanced its solubility in common organic solvents such as toluene, THF, and chloroform. UV/visible and fluorescence spectrometers were employed to investigate their optical properties both in solution and in film state, whereas cyclic voltammograms were used to estimate their band diagrams. Photoluminescence maxima of P1, P2 and P3 are 442, 540 and 528 nm, respectively. Oxadiazole chromophores in backbone enhance electron affinity, whereas pendant hexyloxy groups decrease ionization potential. The threshold voltage and luminance of ITO/P2 (100 nm)/Al single layer device are 17 V and 950 cd/m², respectively.     

New amphiphilic fluorescent CBABC-type pentablock copolymers containing pyrene group by two-step atom transfer radical polymerization (ATRP) and its self-assembled aggregation

A series of novel amphiphilic fluorescent CBABC-type pentablock copolymers (Py-PMMA-PEG4600-PMMA-Py) were prepared from BAB-type amphiphilic triblock copolymer (PMMA-PEG4600-PMMA) as macroinitiator with various contents of 1-(methacryloyloxyethylamino-carboxylmethyl) pyrene (PyMOI) by atom transfer radical polymerization (ATRP) in toluene using CuBr/2,2-bipyridine as catalyst system. Triblock copolymer (PMMA-PEG4600-PMMA) was prepared by ATRP and obtained from Br-PEG4600-Br as macroinitiator with methyl methacrylate in tetrahydrofuran using the same catalyst. The molecular weights of pentablock copolymers which were reinitiated by PMMA-PEG4600-PMMA macroinitiator were calculated from ¹H NMR spectra up to 42,400 gmol⁻¹. The polydispersity of pentablock copolymers obtained from GPC analysis was narrow between 1.10 and 1.38. The crystallinity of triblock copolymer (PMMA-PEG4600-PMMA) was decreased slightly with incorporating PMMA segment. Introducing the bulky pyrene substituent into pentablock copolymer, the melting temperature was not observed and all pentablock copolymers showed amorphous patterns in wide-angle X-ray scattering (WAXS) due to decrease in the degree of crystallinity of polymer chain because of disturbing regular packing. The temperatures at 10% weight loss (Td₁₀), examined by TG analysis, showed values ranging from 265 to 323 °C in nitrogen and 264 to 313 °C in air. Fluorescence spectra of Py-PMMA-PEG4600-PMMA-Py exhibited stronger excimer emission at ca. 480 nm due to the aggregations of pyrene group formed via interaction of the hydrophobic chains. The more content of PyMOI segment in pentablock copolymers can obtain the higher emission intensity ca. 480 nm. When there were higher PyMOI contents (84.9 wt% PyMOI) in pentablock copolymers, they formed larger aggregates (210 nm) in SEM micrographs. On the other hand, while increasing the concentration of the polymer solution in THF, the morphology was changed from spherical (0.1 mg/mL) to chainlike (1.0 mg/mL) aggregates.     

Synthesis, optical and electrochemical properties of luminescent polymers containing 1,2-diphenylmaleimide and thiophene segments

In an attempt to balance energy barriers of hole and electron injection we prepared and characterized homopolymer containing electron-transporting 1,2-diphenylmaleimide chromophores (P1) and copolymers consisting of 1,2-diphenylmaleimide and hole-transporting 2,5-thiophene moieties (P2, P3) via dehalogenation polycondensation. The copolymers are amorphous materials with decomposition temperature greater than 450 °C. Absorption and fluorescence spectra were employed to investigate their optical properties both in solution and film state. Photoluminescence maxima of P1, P2 and P3 films are 564, 559 and 558 nm, respectively. The HOMO and LUMO energy levels have been estimated from their cyclic voltammograms. The HOMO levels of P1, P2, and P3 were readily raised with increasing thiophene content (−5.99, −5.59, and −5.43 eV, respectively), whereas their LUMO levels were very similar (−3.61 to −3.65 eV). Double-layer light-emitting diodes (Al/PEDOT:PSS/P1-P3/ITO) were fabricated to evaluate their optoelectronic characteristics. Incorporation of thiophene units successfully reduced the turn-on electric field from 11.0×10⁵ to 2.9×10⁵ V/cm, but it decreased the luminescent efficiency and the maximum brightness.     

Novel red-emitting thieno-[3,4-b]-pyrazine derivatives suitable for vacuum evaporation and solution method to fabricate non-doped OLEDs

Two novel red-emitting thieno-[3,4-b]-pyrazine-cored molecules with phenyls (TP) or polyphenyls (Müllen type dendron, DTP) as peripheral groups were designed and synthesized. They have large Stokes shifts over 100 nm. DTP is thermally stable with decomposition temperature up to 458 °C. More importantly, it is amorphous with a remarkably high glass transition temperature of 262 °C. DTP can be made into thin films either by solution method or vacuum evaporation. Red OLEDs were fabricated using either spin coated or vacuum evaporated DTP film as emitting layer. The evaporated device exhibited a maximum brightness of 1753 cd m⁻² and a luminous efficiency of 0.74 cd A⁻¹, which are among the best data ever reported for thieno-[3,4-b]-pyrazine derivatives so far. In contrary, TP failed to produce satisfied red emission in its evaporated OLEDs.     

Synthesis and characterization of alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units

A series of soluble alternating fluorene-based copolymers containing diaryl- and non-substituted bithiophene units are synthesized by palladium-catalyzed Suzuki coupling reaction. All polymers demonstrate green colors of photoluminescence (PL) in chloroform, good thermal stability (with decomposition temperatures above 436 °C), and high glass transition temperatures (in the range of 120-144 °C). Owing to the large steric hindrance of diaryl substituents on bithiophenes in the polymers (P2-P4), the aggregation of solids is reduced as well as the solubility is improved, so the performance of their PLED devices are superior to that of the non-substituted polymer (P1). Compared with P1, the introduction of substitutents at 3,3′-position of bithiophene in P2-P4 has significant effects on the photophysical properties of resulting polymers in solution and solid states. Though the PL quantum yield of P1 is much higher than those of diaryl-substituted polymers (P2-P4), the PLED device of P1 has the worst electroluminescence (EL) properties due to the poor solubility of P1. Consequently, among these polymers, the device made of P3 as an emitter has the highest luminance of 2590 cd/m² at 9.5 V. For optimum device performance, a device of P3 blended with PVK can be further enhanced to a brighter luminance of 4284 cd/m² at 18 V.     

Highly optically transparent/low color polyimide films prepared from hydroquinone- or resorcinol-based bis(ether anhydride) and trifluoromethyl-containing bis(ether amine)s

Two series of novel polyimides (5a-g and 6a-g) containing flexible ether linkages and pendent trifluoromethyl (CF₃) groups were synthesized from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3a) and 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride (3b) with various CF₃-substituted aromatic bis(ether amine)s (4a-g) via ring-opening polyaddition to poly(amic acid)s, followed by thermal or chemical imidization. These polyimides were readily soluble in a variety of organic solvents and could be solution-cast into flexible and tough films. The cast films exhibited high optical transparency and almost no color, with a UV-vis absorption edge of 368-382 nm and a very low b^∗ value (a yellowness index) of 6.2-15.5. They had good thermal stability with glass-transition temperatures of 186-288 °C, and most of them did not show significant decomposition before 500 °C. Moreover, these polyimide films also possessed low dielectric constants of 2.79-3.49 (at 1 MHz) and low water uptakes (<0.65 wt%).     

Ring-opening polymerization of six-membered cyclic esters catalyzed by tetrahydroborate complexes of rare earth metals

Catalytic behavior of tetrahydroborate complexes of rare earth metals, Ln(BH₄)₃(THF)_x (1: Ln = La, x = 3; 2: Ln = Pr, x = 2; 3: Ln = Nd, x = 3; 4: Ln = Sm, x = 3; 5: Ln = Y, x = 2.5; 6: Ln = Yb, x = 3), for ring-opening polymerization (ROP) of six-membered cyclic esters, δ-valerolactone (VL) and d,l-lactide (d,l-LA), was studied. The controlled polymerization of VL with 1-6 proceeded in THF at 60 °C. The catalytic activities of these complexes for the ROP of VL were observed to be in order of the ionic radii of the metals: 1(La) ≥ 2(Pr) ≥ 3(Nd) > 4(Sm) > 5(Y) > 6(Yb). The obtained polymers were demonstrated to be hydroxy-telechelic by ¹H NMR and MALDI-TOF MS spectroscopy. The controlled ROP of d,l-LA also proceeded by these complexes. The activities of these complexes for the d,l-LA ROP were also in order of the ionic radii of the metals.     

Cyclopolymerization. Part XXXII radical polymerization of α-(2-phenylallyloxy)methylstyrene: synthesis of highly cyclized polymers with high glass transition temperatures and thermal stability

A new 1,6-diene, α-(2-phenylallyloxy)methylstyrene (1), was synthesized and its radical cyclopolymerizations were studied, since 1 is expected to yield highly cyclized polymers with thermal stability and high glass transition temperatures. A low homopolymerization tendency of the monofunctional counterpart of 1 can be assumed reasonably, because it is a derivative of α-methylstyrene with a low ceiling temperature. This means that intermolecular propagation leading to pendant unsaturations is hard to occur during the polymerization of 1, which results in the formation of highly cyclized polymers. In fact, the degree of cyclization of poly(1) obtained at 180 °C attained the value 99%. Structural studies using a monomeric cyclic compound obtained by the telomerization of 1 permitted to assign main repeating cyclic units of poly(1) to a six-membered ring. The poly(1)s with a higher degree of cyclization were found to be stable up to 300 °C on thermogravimetric analyses and their glass transition temperatures were detected at temperatures over 250 °C.     

Synthesis, electroluminescence, and photovoltaic properties of dendronized poly(p-phenylene vinylene) derivatives

Two dendronized poly(p-phenylene vinylene) (PPV) derivatives, ED-PPV and BB-PPV, have been successfully synthesized according to the Gilch route. The obtained polymers possess excellent solubility in common solvents, good thermal stability with 5% weight loss temperature of more than 340 °C. The weight-average molecular weight (M_w) and polydispersity index (PDI) of ED-PPV and BB-PPV are in the range of (1.26-2.34)×10⁵ and 1.37-1.45, respectively. Polymer light-emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al devices were fabricated, and the PLEDs emitted green-yellow light. The turn-on voltages of the PLEDs based on ED-PPV and BB-PPV were approximately 4.3, and 4.5 V, respectively. The PLED devices of ED-PPV exhibited the maximum luminance of about 157 cd/m² at 10.5 V. Photovoltaic cells with the configuration of ITO/PEDOT:PSS/polymer:C₆₀ (1:1)/Al were also fabricated, and the energy conversion efficiency of the devices based on ED-PPV and BB-PPV was measured to be 0.58, and 0.014%, respectively, under the white light at 75 mW/cm².