Proton-conducting electrolyte membranes based on hyperbranched polymer with a sulfonic acid group for high-temperature fuel cells

The hyperbranched polymers (HBP-SA-Acs) with both a sulfonic acid group as a functional group and an acryloyl group as a cross-linker at terminals in different ratios of sulfonic acid group/acryloyl group (SO₃H/Ac) were successfully synthesized as a new thermally stable proton-conducting electrolyte. The cross-linked hyperbranched polymer electrolyte membranes (CL-HBP-SAs) were prepared by thermal polymerizations of the HBP-SA-Acs using benzoyl peroxide, and their ionic conductivities under dry condition and thermal properties were investigated. The ionic conductivities of the CL-HBP-SAs were found to be in the range of 2.2 × 10⁻⁴ to 3.3 × 10⁻⁶ S/cm, depending upon the SO₃H unit contents, at 150 °C under dry condition, and showed the Vogel-Tamman-Fulcher (VTF) type temperature dependence, indicating that proton transfer is cooperated by local polymer chain motion. All CL-HBP-SAs were thermally stable up to 260 °C, and they had suitable thermal stability as electrolyte membranes for the high-temperature fuel cells under dry condition. Fuel cell measurement using a single membrane electrode assembly cell with a cross-linked electrolyte membrane was successfully performed under non-humidified condition. It was demonstrated that applying the concept of dry polymer system to proton conduction is one possible approach toward high-temperature fuel cells.     

High lithium conductivities in weakly-ionophilic low-dimensional block copolymer electrolytes

The structure of amphiphilic low-dimensional copolymer electrolytes I of similar overall composition but prepared by different synthetic procedures X and Y are described. I are copolymers of poly[2,5,8,11,14-pentaoxapentadecamethylene(5-alkyloxy-1,3-phenylene)] (CmO5) and poly[2,-oxatrimethylene(5-alkyloxy-1,3-phenylene)] (CmO1) where the alkyl side chains having m carbons are hexadecyl or mixed dodecyl/octadecyl (50/50). ¹H NMR shows that the copolymers have 50% (m = 16) or only 18 and 13% of CmO5 units and DSC indicates that the copolymers have ‘block’ sequencing of CmO1 and CmO5 segments. Molecular dynamics modelling indicates that in CmO5 Li⁺ and BF₄⁻ ions are separated by Li⁺ encapsulation in tetraethoxy segments but in ionophobic CmO1 units the salt is mostly present as neutral aggregates decoupled from the polymer. Conductivities of these microphase-separated mixtures with salt-bridge amphiphilic polyethers II and III of each system are similar. They have low temperature dependence over the range 20 °C to 110 °C at ∼10⁻³ S cm⁻¹. ⁷Li NMR linewidth measurements confirm high lithium mobilities at −20 °C. A conduction mechanism is proposed whereby Li⁺ hopping takes place along rows of decoupled aggregates (dimers/quadrupoles) within an essentially block copolymer structure. Subambient measurements to −10 °C gave a conductivity of 4 × 10⁻⁵ S cm⁻¹.     

Synthesis and electrochemical characterisation of benzylmercapto and dodecylmercapto tetra substituted cobalt, iron, and zinc phthalocyanines complexes

The work reports on cyclic voltammetry (CV), square wave voltammetry and spectroelectrochemistry of the following complexes: tetrakis (benzylmercapto) phthalocyanine complexes of Zn(II) (ZnTBMPc, 4a), Co(II) (CoTBMPc, 5a), and Fe(II) (FeTBMPc 6a); tetrakis (dodecylmercapto) phthalocyanine complexes of Zn(II) (ZnTDMPc, 4b), Co(II) (CoTDMPc, 5b), and Fe(II) (FeTDMPc, 6b). More reversible CV couples were observed for complexes 4a, 5a, and 6a containing thiol phenyl ring substituents. Complexes 4b, 5b, and 6b containing long chain thiol substituents showed less reversible couples. Complexes 6a and 6b showed a relatively large number of redox processes (5 for 6a and 6 for 6b) within the potential window employed in this work. The processes for FePc derivatives (6a) are assigned to Fe^IIIPc⁻¹/Fe^IIIPc⁻², Fe^IIIPc⁻²/Fe^IIPc⁻², Fe^IIPc⁻²/Fe^IPc⁻², Fe^IPc⁻²/Fe^IPc⁻³, and Fe^IPc⁻³/Fe^IPc⁻⁴ and for the CoPc derivative (5a) to Co^IIIPc⁻¹/Co^IIIPc⁻², Co^IIIPc⁻²/Co^IIPc⁻², Co^IIPc⁻²/Co^IPc⁻², and Co^IPc⁻²/Co^IPc⁻³.     

‘Living’ radical polymerization of styrene mediated by spiro ring-substituted piperidinyl-N-oxyl radicals. The effect of the spiro rings on the control of polymerization

The bulk radical polymerizations of styrene (St) at 80-120 °C in the presence of 6-aza-7,7-dimethyl-9-hydroxyspiro[4.5]decane-6-yloxyl (1) and 1-aza-2,2-dimethyl-4-hydroxy[5.5]undecane-1-yloxyl (2) were studied. At 100 and 120 °C, the polymerizations were well controlled by those nitroxides to give poly(St)s with narrow polydispersities. On the other hand, the polymerization mediated by 2 at 80 °C showed a good ‘livingness’ of polymerization, but 1 had a poor ability to control the polymerization to give poly(St) with a broad polydispersity of 1.52. The rate constants (k_act) for the homolysis of the NO-C bond of the alkoxyamines prepared from 1 and 2 were measured at 333-373 K, and the A_acts and E_acts values were determined to be 2.8×10¹³ s⁻¹ and 128 kJ mol⁻¹ (1) and 4.0×10¹³ s⁻¹ and 125 kJ mol⁻¹ (2), respectively, from the Arrhenius plots. These results are compared with those for the structurally related piperidinyl-N-yloxyl radicals including TEMPO.     

Synthesis of a pyridine substituted polycarbodiimide and its use as a solid support for chemical reagents

Optically active, polycarbodiimides 3(a, b & c) with pyridine pendant groups were synthesized using [(R) - 2,2′- binaphthoxy] (di-isopropoxy) titanium(IV) catalyst. The polymers were characterized by ¹H and ¹³C NMR, and IR. Thermal stability of these polymers (up to 162 °C by TGA), allows thermally demanding chemical transformations on their side chains without decomposition. Advantages include fine-tunability of the other pendant group of the carbodiimide monomer. This allows one to optimize the properties of the polymer without undergoing copolymerization or further post-polymerization modifications. Borane (BH₃) was coordinated to poly 3 (a & b) to prepare the functional polymers 4 (a & b) respectively. A strong IR signature peak at 2368 cm⁻¹ supports BH₃ coordination. Gravimetric analysis indicates 97-99% borane complexation of the pyridine units. In addition, the thermal stability increased to 194 °C in poly 4a is consistent with the incorporation of BH₃ to the pendant pyridine of the helical polycarbodiimide 3a. Poly 4 (a & b) can be used as supported reagents and successfully reduced the carbonyl compounds (5 a-e) in moderate to excellent yields (60-100%) and are shown to be efficient, non-volatile, stable, and mild supported-reducing reagents. Upon completion of the reduction reaction, the polymer support was quantitatively recycled as required for a green solid catalyst support.     

Crown ether bridged homo- and heterodinuclear copper(II) and nickel(II) cyclidene complexes: Interaction with anions

Homodinuclear (3CuCu, 3NiNi) and heterdionuclear (3CuNi) cyclidene complexes linked by two 1,10-diaza-18-crown-6 ethers were synthesized and their properties characterized. For the 3CuCu in the negative potential range the mixed-valence state Cu^I-Cu^II was observed and the comproportionation constants were determined. The redox potentials of M^II/III showed a good correlation with DN of the solvent. In acetonitrile solution containing 0.1 mol dm⁻³ Bu₄NPF₆ reversible M^II/III redox processes were observed. However, in the presence of stronger ion pairing anions (e.g. BF₄⁻ and ClO₄⁻) the “potential inversion” occurred. Redox potentials of dinuclear complexes were compared with mononuclear cyclidene complexes. The influence of selected anions (Cl⁻ and NO₃⁻) on the redox process M^II/III was studied. The effect of Cl⁻ anion was different for 3CuCu and 3NiNi. In 3CuCu coordination of two chloride anions took place after oxidation of copper centers. In the 3NiNi complex two Cl⁻ anions were coordinated to one of the nickel(II) centers facilitating oxidation, at different potentials, of both nickel(II) cations. The behaviour of heteronuclear complex with Cl⁻ anions was similar to 3NiNi. All dinuclear complexes interacted with NO₃⁻ anions and the observed potential shifts were larger for nickel(II) than for copper(II) cations.     

Highly efficient electroluminescent biphenylyl-substituted poly(p-phenylenevinylene)s through fine tuning the polymer structure

A series of novel biphenylyl-substituted PPV derivatives, polymers 1-4, with different substitution patterns, has been synthesized and characterized. These polymers possess excellent solubilities, good thermal stabilities, and high-photoluminescent efficiencies. ¹H NMR measurements indicated that the polymers contain negligible tolane-bisbenzyl (TBB) structural defects. Light-emitting diodes fabricated from the four polymers with the configuration of ITO/PEDOT:PSS (50 nm)/polymer (80 nm)/LiF (0.4 nm)/Ca (20 nm)/Ag emitted a saturated green light and demonstrated maximum current efficiencies of 5.1, 4.5, 4.7, and 1.4 cd/A for polymers 1-4, respectively. The much higher current efficiencies of polymers 1-3 than polymer 4 are ascribed to more balanced charge transport in the polymer layers of the three polymers, which has been confirmed by time of flight (TOF) charge mobility measurement. The hole mobilities of the polymers at the applied electric field of 2.0×10⁵ V/cm are 4.70×10⁻⁶, 3.83×10⁻⁶, 7.21×10⁻⁶, and 1.76×10⁻⁵ cm²/Vs for polymers 1-4. This research indicated that fine tuning the substitution pattern of the polymer side chains is an effective way to optimize the LED device performance by controlling the structural defects as well as balancing the charge mobility of the polymers.     

Random vs. alternating donor-acceptor copolymers: A comparative study of absorption and field effect mobility

The influence of the arrangement of donor and acceptor units in a conjugated copolymer chain on the absorption and field effect mobilities was studied. We synthesized a target random copolymer and compared it with two structurally relevant alternating copolymers, all consisting of 2,1,3-Benzothiadiazole (BT) as acceptor and 3-Hexylthiophene (Th) as donor units. Especially, bifunctional AB-type monomers were developed to obtain the desired randomly linked copolymer r-BT-2Th. We chose AA/BB-type monomers as well to obtain relevant alternating copolymers a-BT-2Th and a-BT-1Th. The systematic structural variation enables us to compare the copolymers in a precise manner. In dilute solutions r-BT-2Th and a-BT-2Th resemble closely in absorption spectra and have similar oxidation potentials regardless of random or alternating arrangement of donor and acceptor. In thin films, a-BT-2Th shows the lowest optical gap and depicts the highest field effect hole mobility of 1.5 × 10⁻³ cm² V⁻¹ s⁻¹.     

Synthesis, characterization and third-order non-linear optical properties of novel fluorene monomers and their cross-conjugated polymers

We designed and synthesized two novel fluorene monomers of D-A-D (donor-acceptor-donor) type (M1 and M2), and their two corresponding polymers (PM1 and PM2) and a copolymer (CPM). These high molecular weight, film-forming polymers were obtained from metal-free, superacid-catalyzed reactions of the monomers with N-phenylisatin. The cubic NLO response (χ⁽³⁾) for these new compounds, in solid thin films, was measured through the use of third-harmonic generation (THG) Maker-Fringes technique at IR wavelengths given values of the order of 10⁻¹² esu from which, the corresponding second hyperpolarizabilities (γ) were estimated to be of the order of 10⁻³³ esu for monomers and 10⁻³¹ esu for polymers. Second hyperpolarizabilities have also been estimated theoretically at B3LYP/6-31G(d) level of theory in gas phase and related with the electronic structure of the synthesized molecules.     

A new low band gap electrochromic polymer containing 2,5-bis-dithienyl-1H-pyrrole and 2,1,3-benzoselenadiazole moiety with high contrast ratio

A new low band gap electrochromic polymer containing of 3-(2,5-di-2-thienyl-1H-pyrrol-1-yl)-9-ethyl-9H-carbazole (SNSC) and 2,1,3-benzoselenadiazole (BSe) moiety has been reported. Structural identification of initial compounds and product were carried out by using FT-IR and ¹H NMR spectroscopy results. The resulting polymer, poly(SNSC-BSe), was completely soluble in various common organic solvents and its weight-average molecular weight (M_w) were 9420 (PDI: 1.22). According to AFM results, the RMS (root mean surface) roughness of poly-(SNSC-BSe) was found to be 48.6 nm. Besides, the thermogravimetric analysis presented that the poly(SNSC-BSe) is moderately stable against to thermal effect with the initial degradation temperature at 182 °C. The lowest energy transition band maxima of poly(SNSC-BSe) was 498 nm in thin film and the optical band gap calculated from the onset wavelength of the optical absorption was 1.77 eV. On the other hand, the electrochemical band gap calculated from oxidation and reduction onset values was 1.60 eV, respectively. Finally, the electrochromic performance of the polymer film represents a high contrast ratio in the NIR region (51%), fast response time of about 1 s, high coloration efficiency (274 cm² C⁻¹) and retained its performance by 94.6% even after 1000 cycles.     

Anionic polymerization of 2-haloethyl methacrylates

The anionic polymerizations of 2-chloroethyl methacrylate (1), 2-bromoethyl methacrylate (2), and 2-iodoethyl methacrylate (3) were carried out in THF at −78 °C with 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The polymerizations proceeded in a controlled manner to quantitatively afford polymers with predictable molecular weights and narrow molecular weight distributions. Under similar conditions, the anionic block copolymerizations by the sequential addition of methyl methacrylate (MMA) followed by 1, 2, and 3 generated the corresponding diblock copolymers with well-defined structures. On the other hand, in the block copolymerization by the reverse addition of monomer, a well-defined diblock copolymer, poly(1)-block-PMMA, could be synthesized only by the sequential addition of 1 followed by MMA, whereas the block copolymerizations using 2 and 3 were not successful because of instabilities of the propagating chain-end anions derived from 2 and 3. The side reactions which occurred during the polymerization were discussed.     

Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

The synthesis and electrochemical characterisation of the following oxotitanium tetra-substituted phthalocyanines are reported: 1,(4)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (5a); 1,(4)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (5b); 2,(3)-(tetrabenzyloxyphthalocyaninato)titanium(IV) oxide (6a) and 2,(3)-{tetrakis[4-(benzyloxy)phenoxy]phthalocyaninato}titanium(IV) oxide (6b). The electrochemical characterisation of complexes octa-substituted with 4-(benzyloxy)phenoxy (9b), phenoxy (9c) and tert-butylphenoxy (9d) groups is also reported. The cyclic voltammograms of the complexes exhibit reversible couples I-III and couple IV is quasi-reversible for complexes 5a, 5b, 6a and 6b. The first two reductions are metal-based processes, confirmed by spectroelectrochemistry to be due to Ti^IVPc²⁻/Ti^IIIPc²⁻ and Ti^IIIPc²⁻/Ti^IIPc²⁻ redox processes and the last two reductions are ring-based processes due to Ti^IIPc²⁻/Ti^IIPc³⁻ and Ti^IIPc³⁻/Ti^IIPc⁴⁻. Chronocoulometry confirmed a one-electron transfer at each reduction step. The electrochemistry of the above complexes is also compared to the previously reported 5c, 5d, 6c and 6d.     

Polymeric molecular shuttles: Polypseudorotaxanes & polyrotaxanes based on viologen (paraquat) urethane backbones & bis(p-phenylene)-34-crown-10

Reaction of di(p-isocyanatophenyl)methane (MDI, 4) with N,N′-di(2-hydroxyethyl)- (1b) or N,N′-di[2-(2′-hydroxyethoxy)ethyl]-4,4′-bipyridinium di(hexafluorophosphate) (1e) and other diols [oligo(ethylene glycol)s and poly(tetramethylene oxide)s] in the presence of bis(p-phenylene)-34-crown-10 (2) afforded polyurethane (pseudo)rotaxanes as statistical (7P or 7R) and segmented analogs 10P (P = pseudorotaxane, R = rotaxane). In 7R a bulky alcohol was incorporated at the chain ends and in 13R a bulky diol as in-chain units to form polyrotaxanes and preclude the possibility of dethreading. The crown ether 2 in 10P and 13R was shown by ¹H NMR spectroscopy to be shuttling between the viologen (paraquat) and urethane sites; in DMSO the crown ether prefers the urethane site, probably because of H-bonding with the N–H moieties and complexation of the pyridinium site by the dipolar solvent, while in acetone at low temperatures the viologen site is preferred by the crown ether, with ΔH = −6.91 kcal/mol and ΔS = −22.9 eu for 13R.     

Structure-property relationships for a series of polyimide copolymers with sulfonated pendant groups

A series of high molecular weight, sulfonated polyimide copolymers (8a-f) with controlled acid contents have been obtained using 2,2′-bis(4-sulfobenzyloxy)benzidine (14) prepared via a flexible synthetic route. This series of novel sulfonated polyimide membranes were found to possess higher hydrolytic stability than polyimides in which the sulfonic acid groups are bound directly to the polymer main chain. An in-depth analysis of conductivity data was also performed for 8 and compared to the results for Nafion^® (1), sulfonated poly(ether ether ketone) (2) and a main-chain sulfonated polyimide (3). In order to remove the influence of acid strength, the proton mobility value for 8 at infinite dilution was calculated and found to be 1.2(±0.6) × 10⁻³ cm² s⁻¹ V⁻¹. A catalyst-coated membrane (CCM)-MEA based on a polyimide incorporating 60% sulfonated monomer (8d) was found to exhibit comparable beginning-of-life fuel cell performance as a Nafion^®-based CCM MEA at 50 °C.     

Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

Novel fluorene-based light-emitting copolymers containing cyanophenyl pendants and carbazole-triphenylamines: Synthesis, characterization and their PLED application

A series of novel blue light-emitting copolymers PCC-1, PCC-2, and PCC-3, composed of different ratios of electron-withdrawing segments (spirobifluorene substituted with cyanophenyl groups) and electron-donating segments (carbazole-triphenylamines), has been synthesized and characterized. In order to investigate the effect of hole/electron charge transporting segments, two reference polymers PSF and PCF, containing only one charge transporting moiety in the polymer backbone, were also synthesized. Incorporation of the rigid spirobifluorene units substituted with cyanophenyl groups into the polymer backbone improved not only the thermal stabilities but also the photoluminescence efficiencies. The polymers except PSF possess similar hole injection barriers but different hole transporting abilities. With the device configuration of ITO/PEDOT:PSS/polymers:PBD/CsF/Ca/Al, PCC-2 showed the best performance with the lowest turn-on voltage of 3.1 V, the highest luminance of 6369 cd/m², the highest current efficiency of 1.97 cd/A, and the best power efficiency of 1.40 lm/w.     

Synthesis and photovoltaic properties of donor–acceptor polymers incorporating a structurally-novel pyrrole-based imide-functionalized electron acceptor moiety

A structurally-novel pyrrole-based imide-functionalized electron accepting monomer unit, 4,6-dibromo-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD), was prepared. The new DPPD unit was copolymerized with pyrrole-based electron rich monomers, such as thiophene-(N-alkyl)pyrrole-thiophene (TPT) and fused thiophene-(N-alkyl)pyrrole-thiophene (DTP) derivatives, to afford two new polymers, namely P(TPT-DPPD) and P(DTP-DPPD), respectively. The two polymers showed a strong absorption band at 300–600 nm and 300–650 nm, respectively, and their calculated optical band gaps were 2.09 eV and 1.89 eV, respectively. The electrochemical analysis reveals that the highest occupied molecular orbital (HOMO) energy levels of P(TPT-DPPD) and P(DTP-DPPD) were positioned at −5.55 eV and −5.24 eV, respectively, whereas their lowest unoccupied molecular orbital (LUMO) energy levels were positioned at −3.46 eV and −3.35 eV, respectively. The preliminary photovoltaic properties of the polymers, P(TPT-DPPD) and P(DTP-DPPD), were examined by fabricating polymer solar cells (PSCs) with each polymer as an electron donor and PC₇₁BM as an electron acceptor. The PSCs fabricated with the configuration of ITO/PEDOT:PSS/P(TPT-DPPD) or P(DTP-DPPD):PC₇₁BM/LiF/Al showed maximum power conversion efficiency (PCE) of 0.73% and 1.64%, respectively.     

Photovoltaic performance of solid-state DSSCs sensitized with organic isophorone dyes: Effect of dye-loaded amount and dipole moment

Two isophorone sensitizers (S4 and D-3) were utilized in solid-state dye-sensitized solar cells (DSSCs) using spiro-OMeTAD as hole-transporting material. The dye-loaded amount of D-3 was almost 1.5 times as that of S4 which lead to higher light harvesting efficiency than S4. Moreover, the larger dipole moment along the direction for D-3 could cause more negative charges located close to the TiO₂ surface than that of S4, resulting in a larger conduction band (CB) upshift of TiO₂ for D-3 which was beneficial to an increase of V_oc. Promising results sensitized by D-3 in solid-state DSSCs were achieved with a short-circuit photocurrent density (J_sc) of 3.4 mA cm⁻², an open-circuit photovoltage (V_oc) of 760 mV, a fill factor (FF) of 0.71, and an overall efficiency (η) of 1.92% while ruthenium dye N3 produced a η of 2.55% under the same conditions (AM 1.5, 100 mW cm⁻²).     

Low bandgap polymers with benzo [1,2-b:4,5-b′] dithiophene and bisthiophene-dioxopyrrolothiophene units for photovoltaic applications

New donor/acceptor polymers PBDTTPT1 and PBDTTPT2 with alternating benzodithiophene (BDT) and bisthiophene-dioxopyrrolothiophene (TPT) units were synthesized by Stille coupling reaction. The polymers had optical bandgaps of 1.78 and 1.82 eV, and HOMO energy levels of −5.30 and −5.35 eV for PBDTTPT1 and PBDTTPT2, respectively. Polymeric solar cell devices based on these copolymers as donors and PC₇₁BM as acceptor showed the highest open circuit voltage of 0.95 V and power conversion efficiency of 2.68% under the illumination of AM 1.5, 100 mW/cm².