Morphological study of the organization behavior of rod-coil copolymers and their blends in thin solid films

A detailed study of the self-assembly ability of triblock coil-rod-coil copolymers containing a rigid di(styryl)-anthracene segment covalently linked to oxadiazole-based blocks and their binary blends with oxadiazole-based homopolymers is presented here. The self-organized microdomains seem to pack into a fascinating ordered hexagonal structure obtained at a critical concentration without any significant influence of the sample preparation method, based on evidence obtained by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy studies. The compatibilization efficiency of these coil-rod-coil copolymers in polymer blends composed of an electron-accepting polyoxadiazole and a luminescent polyanthracene-based pair was studied by atomic force microscopy (AFM). The common feature of all observed morphologies is the compatibilizing function of the rod-coil molecule, which intercalates between the incompatible domains to prevent the formation of well-defined phase separated nanostructured surfaces.     

Synthesis and optical properties of green‐light‐emitting copolymers containing side‐chain oxadiazole units

Atom transfer radical polymerization was used to prepare well‐defined vinyl polyoxadiazole homomacromonomers with a properly modified α‐dicarboxylic acid methyl ester as the initiator. Macromonomers of various molecular weights with narrow polydispersities in some cases were obtained, as proved by gel permeation chromatography (GPC). The structures of the obtained macromonomers were then identified with ¹H NMR spectroscopy. These macromonomers were subsequently copolymerized with a dihydroxy anthracene based monomer by a polycondensation technique, and this resulted in polymacromonomers. Coil–rod–coil copolymers containing side‐chain anthracene and oxadiazole units were also synthesized by atom transfer radical polymerization. The resulting copolymers combined an anthracene derivative as the rigid block with a random copolymer of the desired anthracene‐ and/or oxadiazole‐based monomers as the flexible block. These copolymers were primarily characterized with GPC and ¹H NMR techniques. Additionally, the optical properties of all these copolymers were investigated in detail, and they suggested energy transfer from the oxadiazole to the anthracene chromophores, which became much more efficient in the solid state. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1049–1061, 2005     

Poly(sodium styrene sulfonate)-b-poly(methyl methacrylate) diblock copolymers through direct atom transfer radical polymerization: Influence of hydrophilic–hydrophobic balance on self-organization in aqueous solution

A series of poly(sodium styrene sulfonate)-b-poly(methyl methacrylate), PSSNa-b-PMMA, amphiphilic diblock copolymers have been synthesized through atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in N,N-dimethylformamide/water mixtures, starting from a PSSNa macroinitiator. The kinetics of the polymerization was followed by ¹H NMR, while the chemical composition of the copolymers was verified by a variety of techniques, such as ¹H NMR, FTIR and TGA. The MMA content of the copolymers ranges from 0 up to 60 mol%, while the number–average molecular weight of the PSSNa macroinitiator was 9000 g/mol. The self-association of the diblock copolymers in aqueous solution was compared to the respective behavior of similar random P(SSNa-co-MMA) copolymers through optical density measurements, pyrene fluorescence probing, dynamic light scattering and surface tension measurements. It is shown that the diblock copolymers form micellar structures in water, characterized by an increasing hydrophobic character and a decreasing size as the length of the PMMA block increases. These micelle-like structures turn from surface inactive to surface active as the length of the PMMA block increases. Moreover, contrary to the MMA-rich random copolymers, the respective diblock copolymers form water insoluble polymer/surfactant complexes with cationic surfactants such as hexadecyltrimethyl ammonium bromide (HTAB), leading to materials with antimicrobial activity.     

Blends of Aromatic Polyethers Bearing Polar Pyridine Units and Their Evaluation as High Temperature Polymer Electrolytes

Aromatic polyethers containing polar pyridine units in the main chain have been synthesized using different difluoride monomers. Copolymers of 2,5-(4′,4″dihydroxy biphenyl)-pyridine and 3,3′,5,5′-tetramethyl-[1,1′-biphenyl]-4,4′-diol with bis(4-fluorophenyl) sulfone or phenyl phosphine oxide difluoride or decafluorobiphenyl (PTMPySF, PTMPyPO, PTMPyDF) were synthesized. These polymeric structures despite their common structural characteristics, showed totally different behavior in terms of solubility and acid doping ability. Blends of these copolymers have been prepared in order to be evaluated in terms of fuel cell relevant parameters like acid doping ability and conductivity. In most cases flexible membranes were obtained by solution casting. The acid doping ability was controlled based on the blend constituents and composition. The doped membranes exhibited high conductivity values, in the range of 10⁻³ S/cm at room temperature which is increased at 2.5 × 10⁻² S/cm at temperatures up to 180 °C.     

The interaction of water vapors with H3PO4 imbibed electrolyte based on PBI/polysulfone copolymer blends

The interaction of steam with phosphoric acid imbibed electrolyte composed of PBI/PPy(50)coPSF 50/50 polymer blend and its effect on fuel cell performance was studied regarding its permeability through and its chemical interaction with the membrane. It was found that steam is the only gas that permeates the membrane with a permeability coefficient 1.1 × 10⁻¹⁴ mol cm cm⁻² s⁻¹ Pa⁻¹ at 150 °C. This is attributed either to the high solubility of water in phosphoric acid or to the chemical interaction with pyrophosphoric acid_. The latter was demonstrated by carrying out TGA experiments under various water vapor partial pressures. Water reacts with pyrophosphoric acid in order to maintain the equilibrium concentration of phosphoric acid at high level, thus improving proton conductivity and fuel cell performance. In addition it is shown that excess water dissolves in the membrane thus maintaining the “membrane/acid” system at high hydration level. This depends both on temperature and steam partial pressure. Although in the present study it is shown that steam plays a significant role in the performance of the high temperature Polymer electrolyte membrane (PEM) fuel cell, nevertheless its feed with humidified gases is not necessary, due to the back transport of the water produced at the cathode.     

Rod-coil block copolymers incorporating terfluorene segments for stable blue light emission

Spectroscopic studies on a series of rod-coil block copolymers with terfluorene as the rigid segment demonstrate that the main cause of color instability in fluorene oligomers and polymers is aggregate and/or excimer formation and not the presence alone of keto defects (fluorenone formation) along the molecular chain. Keto defects, when present, contribute to the appearance of the undesirable "green" emission band but are not the leading cause of color instability. Thus, the synthesis of materials where aggregation and/or interchain, intersegment interactions are inhibited is the key approach for the production of stable polymeric light-emitting devices (PLED's). The potential of this method is verified by the synthesis of photooxidative stable fluorene/styrene diblock copolymer blue emitters.     

Synthesis and characterization of soluble aromatic polyesters derived from substituted terphenyl and quinquephenyl diols

Rigid aromatic polyesters containing alkoxy or phenyl-substituted oligophenyls were prepared. Soluble polymers were obtained also in cases where phenyl-substituted quinquephenyl diols were combined with asymmetric phenyl-substituted terephthalic acid. The synthesized polyesters were characterized by viscosimetry, gel permeation chromatography, thermal analysis, and dynamic mechanical analysis. The temperature dependence of the intrinsic viscosity was sensitive to the type of side groups. Thermogravimetry has shown that polyesters with aromatic substituents were stable up to 380–400°C. The glass transition temperatures of the polyesters with aromatic side groups were in the 220–260°C range as determined by DSC. Polyesters with hexyloxy side chains show crystallinity. Dynamic mechanical analysis showed that in the cases where aromatic substituents were used to increase solubility, the obtained polymers have very useful mechanical properties at high temperatures. The polymer having the quinquephenyl unit in the main chain has an almost constant modulus up to 340°C. © 1996 John Wiley & Sons, Inc.     

Comparative study of electrostatic binding vs. complexation of Cu2+ ions with water‐soluble polymers containing styrene sulphonic acid and/or maleic acid units or their sodium salt forms

The interaction of Cu²⁺ ions with the homopolymer poly(styrene sulfonic acid) (PSSH), as well as with the copolymers of maleic acid (MAc) with styrene sulfonic acid (SSH) or vinyl acetate (VAc), was investigated in dilute aqueous solution through turbidimetry, potentiometry, viscometry, and spectrophotometry in the visible region. Cu²⁺ ions were introduced either through neutralization with Cu(OH)₂ of the acid form of the (co)polymers (PSSH, P(SSH‐co‐MAc) and P(VAc‐co‐MAc)) or through mixing of the sodium salt form of the (co)polymers (PSSNa, P(SSNa‐co‐MANa) and P(VAc‐co‐MANa)) with CuSO₄. Turbidimetry, potentiometry, and spectrophotometry revealed that the first carboxylic group of MAc or both carboxylate groups of MANa are involved in the complexation with Cu²⁺ ions when neutralization with Cu(OH)₂ or mixing with CuSO₄ are applied, respectively. The increased values of the reduced viscosity observed mainly at the first stages of neutralization of P(VAc‐co‐MAc) with Cu(OH)₂ indicate that interchain polymer‐Cu²⁺ complexation takes possibly place. Finally, the spectrophotometric behavior observed upon neutralization of P(SSH‐co‐MAc) with Cu(OH)₂ or mixing of P(SSNa‐co‐MANa) with CuSO₄ revealed that the strength of counterion binding by the sulfonate groups is, in fact, comparable with the complexation of Cu²⁺ ions with the carboxylate groups of MAc. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1149–1158, 2008     

Synthesis of alternating polystyrene/poly(ethyleneoxide) branched polymacromonomers

Newly designed PS/PEO alternating branched polymacromonomers have been obtained by polycondensation of alpha-dicarboxy-functionalized polystyrene and alpha-dihydroxy-functionalized polyethyleneoxide. 4-[3,5-Bis(methoxycarbonyl)phenoxymethyl]benzyl bromide was used as atom-transfer radical polymerization (ATRP) initiator for the synthesis of alpha-dicarboxy functionalized polystyrenes. These macromonomers possess low polydispersities and molecular weights in the range of 7000 to 100,000, as proved by gel permeation chromatography (GPC) and 1H NMR. Alpha-dihydroxy functionalized polyethyleneoxide (PEO) was synthesized by treatment of monofunctionalized PEO with 3,5-bis(benzyloxy)benzoyl chloride. Polycondensation of the alpha-dicarboxy PS with the alpha-dihydroxy PEO in solution or in bulk resulted in alternating PS/PEO polymacromonomers, which were effectively purified from the unreacted macromonomers and characterized by using 1H NMR, GPC, thermal analysis, and optical microscopy. Light-scattering measurements in organic solvents like THF or dioxane have shown that these polymacromonomers form stable micelles.