Preparation of brush-like crystals of poly[2,6-(1,4-phenylene)-benzobisimidazole]

Poly[2,6-(1,4-phenylene)-benzobisimidazole] (PPBI) crystals were prepared by using reaction-induced crystallization of oligomers during solution polymerization of 1,2,4,5-tetraaminobenzene and diphenyl terephthalate. Polymerizations were carried out at a monomer concentration of 4.3 × 10⁻² mol L⁻¹ at 350 °C for 6 h. Brush-like PPBI crystals were obtained in a mixture of structural isomers of dibenzyltoluene, in which many needle-like crystals came out vertically from the surface of the ribbon-like crystals. Average width and thickness of the ribbon-like crystals were 0.75 μm and 0.11 μm, respectively. And average length and diameter of the needle-like crystals were 0.36 μm and 50 nm, respectively. The brush-like crystals possessed high crystallinity and exhibited good thermal resistance. The ribbon-like crystals were formed by the crystallization of imidazole oligomers at an initial stage of polymerization, and then the needle-like crystals grew from the surface of the ribbon-like crystals. Polymerization occurred on the crystals when the oligomers were crystallized, leading to the high molecular weight PPBI crystals.     

Preparation of needle-like poly(azomethine) crystals by means of reaction-induced crystallization of oligomers

Needle-like poly(azomethine) crystals were successfully prepared by the polycondensation of 1,4-phenylenediamine and 1,4-terephthalaldehyde in liquid paraffin at 180 °C. The favorable polymerization concentration for the preparation of the well-defined needle-like crystals was 2.0×10⁻² mol l⁻¹. The average length and width of the needle-like crystals were 7.7 and 0.6 μm, respectively. These crystals possessed high crystallinity and good thermal stability. The extended polymer chains were aligned along the long axis of the needle-like crystal. The morphological observations indicated that the needle-like crystals were formed through the spiral growth of the oligomer lamellae caused by the screw dislocation.     

Preparation and reversible photo-crosslinking/photo-cleavage behavior of 4-methylcoumarin functionalized hyperbranched polyester

A novel hyperbranched polymer endcapped with 4-methylcoumarin group (MCTH40) was prepared via thiol-ene addition reaction of thiol-modified hyperbranched polyester (fully thioglycolic acetate of Boltorn™ H40, TAH40) with a vinyl monomer (7-(4-vinyl-benzyloxyl)-4-methylcoumarin, VBMC), and characterized with ¹H NMR and FT-IR spectroscopies. Its reversible photo-crosslinking/photo-cleavage behavior was evaluated based on the UV-vis spectroscopic analysis, and compared with the linear polymer, poly(7-(4-vinyl-benzyloxyl)-4-methylcoumarin (PVBMC)). The absorbance at 319 nm in the UV-vis spectrum gradually decreased under UVA irradiation (λ_max = 365 nm), and then rapidly recovered under UVC irradiation (λ_max = 254 nm). The fluorescence intensity of MCTH40 (λ_max = 469 nm) recovered to 85.2% of original level after photo-cleavage under UVC irradiation, higher than 83.5% of PVBMC (λ_max = 472 nm). The UV-vis analysis results indicated that MCTH40 performs more rapid photo-response than linear PVBMC under the same conditions. Furthermore, the average doses of UVA irradiation for the maximum degree of photo-crosslinking were 22.08 J cm⁻² for MCTH40 and 28.29 J cm⁻² for PVBMC. The average UVC doses of complete photo-cleavage were 9.44 J cm⁻² for MCTH40 and 9.58 J cm⁻² for PVBMC. The GPC analysis indicated that the average molecular weight and its PDI of MCTH40 showed a slight increase after three reversible cycles.     

High glass transition and thermal stability of new pyridine-containing polyimides: Effect of protonation on fluorescence

A new diamine monomer containing heterocyclic pyridine and triphenylamine groups, 4-(4,4′-diaminotriphenylamine)-2,6-bis(4-methylphenyl)pyridine (4), was synthesized by Chichibabin and nucleophilic fluoro-displacement reactions. The diamine was used to prepare a series of novel polyimides via polycondensation with various aromatic tetracarboxylic dianhydrides in N-methyl-2-pyrrolidinone. The polyimide 4a derived from the diamine 4 with 4,4′-hexafluoroisopropylidenediphthalic anhydride and having high T_g (313 °C), mechanical, and thermal properties was soluble in various organic solvents, such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, N,N-dimethylformamide, pyridine, chloroform, tetrahydrofuran, at room temperature. The polyimide (4a) could be cast into a self-standing film from DMAc solution and was thermally converted into tough and flexible film. The film had high tensile modulus of 2.2 GPa and exhibited excellent thermal stability in both nitrogen and air (T_d¹⁰ > 550 °C). The pristine polymer exhibited the UV-vis absorption bands in the region 240-400 nm and protonated polymer exhibited absorption in the region 390-500 nm. The protonated polymer possessed strong orange fluorescence (around 600 nm) in THF solution after protonation with acids as excited at 438 nm. The fluorescent intensity was influenced by the acid concentrations and the chemical structure of conjugated bases. The fluorescent intensity at 600 nm increased as acid concentration from a lower to a moderate concentration and decreased at higher concentrations.     

Reversible addition-fragmentation chain transfer polymerization of 7-(4-(acryloyloxy)butoxy)coumarin

The light sensitive vinyl monomer with coumarin unit, 7-(4-(acryloyloxy)butoxy)coumarin (7AC), was synthesized. The reversible addition-fragmentation chain transfer (RAFT) polymerization of 7AC, initiated by 2,2′-azobisisobutyronitrile (AIBN), was carried out using 2-cyanoprop-2-yl dithiobenzoate (CPDB) as a RAFT agent in N,N-dimethylformamide (DMF) solution. The kinetics exhibited first-order relationship with respect to the monomer concentration. The molecular weight of the polymer increased linearly with the monomer conversion. The chain extension of poly(7-(4-(acryloyloxy)butoxy)coumarin) (P7AC) using styrene (St) as the second monomer demonstrated that the obtained polymers were almost “living”. The fluorescence intensity of P7AC increased with the molecular weight of P7AC and was stronger than that of the monomer. The obtained polymer had strong ultraviolet (UV) absorption at 322 nm. The molecular weights of the polymer had no effect on its ultraviolet absorption intensity. The coumarin structure existing in P7AC underwent [2 + 2] cycloaddition reaction (photodimerization) under UV irradiation in tetrahydrofuran (THF) solution, which can be further used to prepare small particles from the single polymer.     

Nanostructural features of a spider dragline silk as revealed by electron and X-ray diffraction studies

Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to examine the nanostructure of a natural polymer—a spider dragline silk—that has potential applications as an engineering material. The silk studied was collected from the cob-web weaving spider Latrodectus hesperus. Single crystal and polycrystalline electron diffraction patterns indicate the presence of crystals with a bimodal size distribution, in the range of 2 nm and 40-120 nm. The chain axis of the smaller crystals is more strictly aligned with the fiber axis than that of the larger crystals. Lattice parameters for the orthogonal unit cell are: a=9.4 Å (interchain), b=7.0 Å (dipeptide, fiber axis) and c=10.8 Å (intersheet). A fine structure in single crystal electron diffraction patterns indicates possible composition-dependent lattice strains. Results of tensile tests of the spider dragline silk are reported, and a simple model is presented linking the observed nanostructural features to the force-elongation response of this material.     

Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties

Cubic Pt nanoparticles were prepared from a solution of K₂PtCl₄ containing sodium polyacrylate as a capping reagent. The effects of the Pt/polymer molar ratio, the average molecular weight (M_w) of the polymer, and reaction temperature on the shape and size were investigated. When the polymer of M_w = 5100 was added at a molar ratio of Pt/polymer = 1/12, cubic platinum nanoparticles of an average size of 10.3 nm were predominantly formed (ca. 50% in number) at 25 °C. The electron diffraction pattern of the cubic nanoparticles revealed that they are single crystals with Pt {1 0 0} faces on the surface.The cubic nanoparticles were electrochemically active, and showed strong features of Pt {1 0 0} faces on cyclic voltammogram under argon atmosphere. After repeated potential cycling in the range 0.05-1.4 V, the features of Pt {1 0 0} were gradually lost, and changed to those of polycrystalline Pt. Rotating ring disk electrode measurements in O₂-saturated H₂SO₄ solution revealed that the cubic nanoparticles had a high catalytic activity for oxygen reduction reaction (ORR). After polycrystallization by repeated potential cycling, the activity for ORR and hydrogen peroxide formation decreased slightly, which were attributed to the surface structural change from Pt {1 0 0} to polycrystalline.     

Simple synthesis of surface-modified hierarchical copper oxide spheres with needle-like morphology as anode for lithium ion batteries

Hierarchical, nanostructured copper oxide spheres were synthesized in a stirred solution of cupric acetate and ammonium hydroxide. Cetyltrimethylammonium bromide (CTAB) was used as a surfactant to modify the surface morphology of CuO spheres. Ordered nano-needle arrays can be formed on the surface of the CuO spheres (instead of disordered nano-leaves) in the presence of CTAB. Each CuO sphere is about 2 μm in diameter and possesses a large number of nano-needles that are about 20-40 nm in width and more than 300 nm in length. The needle-like hierarchical structure can greatly increase the contact area between CuO and electrolyte, which provides more sites for Li⁺ accommodation, shortens the diffusion length of Li⁺ and enhances the reactivity of electrode reaction, especially at high rates. After 50 cycles, the reversible capacity of the prepared needle-like CuO can sustain 62.4% and 56.4% of the 2nd cycle at a rate of 0.1C and 1C, respectively.     

Facile electrosynthesis of nitro-group-substituted oligopyrene with bicolored emission

Nitro-group-substituted oligopyrene (ONP) film with fairly high electrical conductivity (1.25 × 10⁻¹ S cm⁻¹) and good thermal stability was electrochemically synthesized by direct anodic oxidation of its monomer 1-nitropyrene (NP) in boron trifluoride diethyl etherate (BFEE). The oxidation potential of NP in this medium was determined to be 1.12 V vs. SCE, which was lower than that in acetonitrile +0.1 mol L⁻¹ Bu₄NBF₄ (1.27 V vs. SCE). ONP films obtained from this medium showed good redox activity and structural stability in both BFEE and concentrated sulfuric acid. Fourier transform infrared spectra and theoretical calculations showed that the electropolymerization of the NP monomer mainly occurred at the C(3), C(6) and C(8) positions. The fluorescence spectra suggested that soluble ONP emits strong blue or green fluorescence when excited at 402 nm or 504 nm, respectively. Scanning electron microscopy showed that highly crystalline nitro-group-substituted oligopyrene was formed on the electrode surface. All these results indicate that as-prepared ONP film has many potential applications in various fields.     

Molecular shape recognition-structure correlation in a phenylalanine-based polymer-silica composite by surface-initiated atom transfer radical polymerization

A polymerizable l-phenylalanine-derived monomer (N′-octadecyl-N^α[4-(acryloyloxy)-butanoyl]-l-phenylalanineamide (3)) has been newly synthesized and characterized. We reported an advanced approach to molecular shape recognitive hybrid materials that involves immobilization of radical initiator on mesoporous silica particles (average diameter, pore size and surface area are 4 μm, 12 nm, and 300 m² g⁻¹, respectively) and surface-initiated atom transfer radical polymerization of monomer 3 from initiator-grafted particles. All samples were characterized by elemental analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, solid state NMR measurements (¹³C CP/MAS NMR and ²⁹Si CP/MAS NMR), differential scanning calorimetry and scanning electron microscopy. The obtained polymer-silica hybrid material was used as a stationary phase for reversed-phase high performance liquid chromatography (RP-HPLC) to investigate its molecular shape recognition ability towards polycyclic aromatic hydrocarbons (PAHs). The new composite material showed better planarity selectivity than octadecylsilane stationary phase as a conventional RP-HPLC packing material and also enhanced linearity selectivity compared with the recently reported poly(N′-octadecyl-N^α-(4-vinyl)-benzoyl-l-phenylalanineamide)-grafted silica. Such selectivity enhancement can be attributed to the combination of hydrophobic effect due to octadecyl chains and multiply carbonyl π-benzene π interaction between the amide groups of the stationary phase and delocalized electrons of PAHs.     

Polymorphism and β-form structure of poly(octamethylene 2,6-naphthalate)

It was revealed that poly(octamethylene 2,6-naphthalate) (PON) existed in two different crystal structures, α- and β-form, depending on crystallization process: The α-form crystal was dominantly developed from the cold-crystallization, whereas the β-form was from the melt-crystallization. The apparent melting temperatures of α- and β-form crystals were characterized to be 175 and 183 °C, respectively. On the basis of X-ray diffraction and molecular modeling studies, the crystal structure of β-form, developed dominantly from the melt-crystallization, was identified to be triclinic with dimensions of a = 0.601 nm, b = 1.069 nm, c = 2.068 nm, α = 155.68°, β = 123.25°, γ = 52.85°, and with the space group of . The calculated crystal density was 1.243 g/cm³, supporting that one repeating unit of PON exists in a unit cell. The octamethylene units in the PON backbone take largely all-trans conformation in the β-form unit cell.     

Atomic force microscopy studies of surface and dimensional changes in LixCoO2 crystals during lithium de-intercalation

An in situ electrochemical atomic force microscopy (EC-AFM) cell was developed to study surface and dimensional changes of individual Li_xCoO₂ crystals during lithium de-intercalation. Discrete Li₂CO₃ particles having 50-250 nm in diameter and 5-15 nm in height were observed on the surface of stoichiometric LiCoO₂ crystals and they were shown to gradually dissolve into the LiPF₆-containing electrolyte. The dimensional change of individual Li_xCoO₂ crystals along the c_hex. axis was monitored in situ during lithium de-intercalation. Evidence of surface instability or structural instability was not found in Li_xCoO₂ single crystals upon de-intercalation to 4.2 V versus Li.     

The effect of polystyrene-block-poly(4-vinylpyridine) prepared by a RAFT method in the dispersion polymerization of MMA

The dispersion polymerization of methyl methacrylate (MMA) has been carried out using polystyrene-block-poly(4-vinylpyridine) copolymer [P(S-b-4VP)], which was prepared by a reversible addition-fragmentation chain transfer (RAFT) method, as a steric stabilizer in an alcohol media. The stable polymer particles were obtained when the block copolymer concentrations increased from 1 to 10 wt% relative to the monomer and the average particle sizes decreased from 5.3 to 3.4 μm with the increasing concentration of the block copolymer. In particular, the incorporation of 2 wt% polystyrene-block-poly(4-vinylpyridine) produced 4.3 μm of monodisperse PMMA particles with 2.14% of C_v. Thus, the P(S-b-4VP) block copolymer prepared by the RAFT method is working not only as a steric stabilizer, but also in providing monodisperse micron-sized PMMA particles.     

In situ UV-vis spectroelectrochemistry of poly(o-phenylenediamine-co-m-toluidine)

Results of in situ UV-vis spectroelectrochemical studies of the electropolymerization of o-phenylenediamine (OPD), m-toluidine (MT) and the copolymerization of OPD with MT are reported. Electropolymerization was performed in aqueous acidic medium at a constant potential of E_SCE = 1.0 V at an indium doped tin oxide (ITO) coated glass electrode. The course of homopolymerization was followed for MT and OPD solutions with various monomer concentrations. The spectral characteristics of the mixed solutions were studied at a constant concentration of MT and various concentrations of OPD in the comonomer feed. An absorption band at λ = 497 nm was assigned to the head-to-tail mixed dimer/oligomer resulting from the cross reaction between OPD and MT cation radicals. UV-vis spectra recorded during copolymerization show dependence of the growth of the band at λ = 497 nm on OPD concentration in the feed. At lower OPD feed concentration it appears as the major band in the corresponding spectra. The UV-vis spectra recorded for the copolymer films suggest the incorporation of both monomer units in the copolymer. The FT-IR spectra of the copolymers show the presence of phenazine type structures in the copolymer backbone.     

Soluble polyimides from unsymmetrical diamine containing benzimidazole ring and trifluoromethyl pendent group

New unsymmetrical diamine monomer containing both the benzimidazole ring and trifluoromethyl group, 6,4′-diamino-2′-trifluoromethyl-2-phenylbenzimidazole, was prepared from 2-bromo-5-nitrobenzotrifluoride and 4-nitro-1,2-phenylenediamine. The monomer was polymerized with ODPA, BTDA and 6FDA by using one-pot synthetic method to obtain corresponding polyimides. All the prepared polyimides were soluble in aprotic polar solvents. Incorporation of trifluoromethyl groups unsymmetrically in the rigid polyimides improves their solubility without decreasing their physical properties. The polymers showed high glass transition temperature (T_g = 289-352 °C), high thermal stability (T_d10 > 500 °C), and relatively low coefficient of thermal expansion (CTE = 26.1-46.4 ppm/°C) because of their rigid-rod like structure. Also, they showed low refractive indexes (n = 1.46-1.68) and low birefringence (Δ ≈ 0.02) due to the trifluoromethyl pendent groups that interrupt chain packing and increase free volume.     

Synthesis and characterization of perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer

Perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer containing hydrophilic poly(ethylene glycol) segment was synthesized by atom transfer radical polymerization (ATRP). Perfluorocyclobutyl-containing methacrylate-based monomer, 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate, was prepared firstly, which can be polymerized by ATRP in a controlled way to obtain well-defined homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30). The molecular weights increased linearly with the conversions of monomer and the apparent polymerization rate exhibited first-order relation with respect to the concentration of monomer. ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based macroinitiators with different molecular weights to obtain amphiphilic diblock copolymers with narrow molecular weight distributions (M_w/M_n < 1.35) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylate monomer. The critical micelle concentrations of these amphiphilic diblock copolymers in water and brine were determined by fluorescence probe technique. The morphologies of the micelles were found to be spheres by TEM.     

Color lightness and highly organosoluble fluorinated polyamides, polyimides and poly(amide-imide)s based on noncoplanar 2,2′-dimethyl-4,4′-biphenylene units

A new diamine monomer containing noncoplanar methyl substitution, 2,2′-dimethyl-4,4′-bis(2-trifluoromethyl-4-aminophenoxy)biphenyl (DBTFAPB) was successfully synthesized and used in the preparation of a series of polyamides and polyimides by direct polycondensation with various aromatic dicarboxylic acids and tertacarboxylic dianhydrides. A new noncoplanar dicarboxylic acid monomer containing noncoplanar methyl substitution, 2,2′-dimethyl-4,4′-bis(2-trifluoromethyl-4-trimellitimidophenoxy)biphenyl (DBTFTPB) was also successfully synthesized by refluxing the diamine, DBTFAPB, with trimellitic anhydride in glacial acetic acid. A series of new poly(amide-imide)s were prepared directly from DBTFTPB with various diamines in N-methyl-2-pyrrolidinone (NMP). All the polymers exhibited excellent solubility in solvents, such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, tetrahydrofuran (THF), cyclohexanone and γ-butyrolactone at room temperature or upon heating at 70 °C. Inherent viscosities of the polymers were found to range between 0.60 and 1.34 dL g⁻¹. Gel permeation chromatography (GPC) of the polymers showed number-average and weight-average molecular weight up to 7.3×10⁴ and 17.9×10⁴, respectively. These polymers showed that the glass transition temperatures were between 230 and 265 °C, and the 10% mass loss temperatures were higher than 460 °C in nitrogen atmosphere. All the polymers could be cast into flexible and tough films from DMAc solutions. They had a tensile strength in the range of 82-124 MPa and a tensile modulus in the range of 1.9-2.9 GPa. These polymers exhibited low dielectric constants ranging from 2.87 to 4.03, low moisture absorption in the range of 0.29-3.20%, and high transparency with an ultraviolet-visible absorption cut-off wavelength in the 347-414 nm range.     

A soluble conducting polymer: 1-Phenyl-2,5-di(2-thienyl)-1H-pyrrole and its electrochromic application

A thiophene-functionalized monomer 1-phenyl-2,5-di(2-thienyl)-1H-pyrrole (PTP) was synthesized. The chemical polymerization of PTP (CPTP) was realized by using FeCl₃ as the oxidant. The structures of both the monomer and the soluble polymer (CPTP) were investigated by Nuclear Magnetic Resonance (¹H and ¹³C NMR) and Fourier Transform Infrared (FTIR). The average molecular weight of the chemically synthesized polymer was determined by gel permeation chromatography (GPC) as Mn = 7.2 × 10³. The electrochemical oxidative polymerization of PTP was carried out via constant-potential electrolysis. Characterizations of the resulting polymer were done by cyclic voltammetry (CV), FTIR, Scanning Electron Microscopy (SEM) and UV-vis Spectroscopy. The conductivity of sample was measured by four-probe technique. Moreover, the spectroelectrochemical and electrochromic properties of the polymer film were investigated. Spectroelectrochemical analysis of P(PTP) revealed electronic transitions at 413, 577 and 884 nm corresponding to π-π^* transition, polaron, and bipolaron band formations, respectively. Kinetic studies evaluated the switching ability of the P(PTP); the percent transmittance T% was found as 27%. The homopolymer of PTP was used to construct dual-type polymer electrochromic devices (ECDs) against poly(3,4-ethylenedioxythiophene) (PEDOT). Spectroelectrochemistry, electrochromic switching and open circuit stability of the devices were investigated.     

A novel quinoxaline bearing electroactive monomer: Pyrrole as the donor moiety

A novel electroactive monomer 5,8-di(1H-pyrrol-2-yl)-2,3-di(thiophen-2-yl)quinoxaline (PTQ) was successfully synthesized and its electrochromic properties were reported. Nuclear magnetic resonance (¹H NMR-¹³C NMR) and mass spectroscopy were used to characterize the monomer. The monomer was electrochemically polymerized in the presence of tetrabutylammonium perchlorate (TBAP) as supporting electrolyte in dichloromethane. Monomer reveals relatively low oxidation potential at +0.70 V. Spectroelectrochemical behaviors and switching ability of homopolymer were investigated by UV-vis spectroscopy and cyclic voltammetry. Two π-π* transitions were observed at 400 and 815 nm with a low band gap, 1.0 eV. Polymer possesses 66% optical contrast in the Near IR region, which may be promising in NIR electrochromic device applications.     

N-(2-biphenylenyl)-4-[2′-phenylethynyl]phthalimide—new monomer synthesis, cure and thermal properties of resulting high temperature polymer

A synthetic route is described to a new monomer, N-(2-biphenylenyl)-4-[2′-phenylethynyl]phthalimide (BPP), which contains both phenylethynyl and biphenylene reactive functional groups. The monomer can be made either from N-(2-biphenylene)acetamide or 2-aminobiphenylene, by reaction with the phenylethynyl-containing anhydride. The monomer was characterised fully and the thermal cure of the material was studied by infrared (IR) spectroscopy and differential scanning calorimetry (DSC). The IR spectra showed that the phenylethynyl group reacted completely within 1 h at 370 °C. DSC showed the polymerisation exotherm of BPP centred at 379 °C, lower than two NASA-developed phenylethynyl-terminated imide (PETI) resins. In comparison with the PETI systems, the T_g of cured BPP was ca. 100 °C higher, making it a candidate for possible high temperature applications.