Zhongwen Wu

Facile synthesis of phenyl-capped oligoanilines using pseudo-high dilution technique

Monodispersed phenyl-capped trianiline and tetraaniline were successfully synthesized by the reactions of diphenylamine with acetaldehyde-based Sckiffs bases of N-phenyl-1,4-phenylenediamine and 1,4-phenylenediamine, respectively, in the presence of ammonium persulfate and hydrochloric acid, subsequent deprotonation and reduction with phenylhydrazine. The reaction mechanism probably involves the slow hydrolysis of the Sckiffs bases and subsequent oxidative coupling reactions of the formed ammonium salts with diphenylamine at pseudo-high dilution condition of the salts.

Crystallization and melting behavior of poly(p-phenylene sulfide) in blends with poly(ether sulfone)

Crystallization and melting behaviors of poly(p-phenylene sulfide) (PPS) in blends with poly(ether sulfone) (PES) prepared by melt-mixing were investigated by differential scanning calorimetry (DSC). The blends showed two glass transition temperatures corresponding to PPS- and PES-rich phases, which increased with increasing PES content, indicating that PPS and PES have some compatibility. The cold crystallization temperature of the blended PPS was a little higher than that of pure PPS. Also, the heats of crystallization and melting of the blended PPS decreased with increasing PES content, indicating that the degree of crystallinity decreased with an increase of PES content. The isothermal crystallization studies revealed that the crystallization of PPS is accelerated by blending PPS with 10 wt % PES and further addition results in the retardation. The Avrami exponent n was about 4 independent on blend composition. The activation energy of crystallization increased by blending with PES. The equilibrium melting point decreased linearly with increasing PES content.

Effects of Pressure and Molecular Weight on the Miscibility of Polystyrene and Cyclohexane

With the aid of Sanchez-Lacombe lattice fluid theory (SLLFT), the phase diagrams were calculated for the system cyclohexane (CH)/polystyrene (PS) with different molecular weights at different pressures. The experimental data is in reasonable agreement with SLLFT calculations. The total Gibbs interaction energy, g*(12) for different molecular weights PS at different pressures was expressed, by means of a universal relationship, as g(12)* =f(12)* + (P - P-0) nu*(12) demixing curves were then calculated at fixed (near critical) compositions of CH and PS systems for different molecular weights. The pressures of optimum miscibility obtained from the Gibbs interaction energy are close to those measured by Wolf and coworkers. Furthermore, a reasonable explanation was given for the earlier observation of Saeki et al., i.e., the phase separation temperatures of the present system increase with the increase of pressure for the low molecular weight of the polymer whereas they decrease for the higher molecular weight polymers. The effects of molecular weight, pressure, temperature and composition on the Flory Huggins interaction parameter can be described by a general equation resulting from fitting the interaction parameters by means of Sanchez-Lacombe lattice fluid theory.

Synthesis, isolation, characterization, and properties of small-size aromatic macrocycles for poly(arylene ether ketone)s

A series of macrocyclic arylene ether ketone oligomers from 4,4′-difluorobenzophenone, 2,4′-difluorobenzophenone and 1,3-bis(4′-fluorobenzoyl)benzene were prepared via aromatic nucleophilic substitution according to the pseudo-high dilution principle. Small-size aromatic macrocycles were isolated by silica gel column chromatography with cyclohexane/ethyl acetate as eluent. The chemical structures of these small-size macrocycles were characterized by matrix-assisted laser desorption ionization–time-of-flight–mass spectrometry (MALDI–TOF–MS), IR, 19F-,1H-, and 13C-NMR, and GPC techniques. Molecular chain length and steric hindrance of monomers affected the product compositions. The NMR results show that there are different chemical shifts in the different ring-size macrocyclic poly arylene ether ketones in spite of having the same repeating unit. The crystallizability and thermal properties of small-size arylene ether ketone macrocycles were also investigated by DSC, WAXD, TGA, and the results suggest that the crystallization and thermal properties are related to their intrinsic chemical structures.

Crystallization behavior of poly(ether ether ketone ketone)

The melting behavior of semicrystalline poly(ether ether ketone ketone) (PEEKK) has been studied by differential scanning calorimetry (DSC). When PEEKK is annealed from the amorphous state, it usually shows two melting peaks. The upper melting peaks arise first, and the lower melting peaks are developed later. The upper melting peaks shown in the DSC thermogram are the combination (addition) of three parts: initial crystal formed before scanning; reorganization; and melting-recrystallization of lower melting peaks in the DSC scanning period. In the study of isothermal crystallization kinetics, the Avrami equation was used to analyze the primary process of the isothermal crystallization; the Avrami constant, n, is about 2 for PEEKK from the melt and 1.5 for PEEKK from the glass state. According to the Lauritzen-Hoffman equation, the kinetic parameter of PEEKK from the melt is 851.5 K; the crystallization kinetic parameter of PEEKK is higher than that of PEEK, and suggests the crystallizability of PEEKK is less than that of PEEK. The study of crystallization on PEEKK under nonisothermal conditions is also reported for cooling rates from 2.5 degrees C/min to 40 degrees C/min, and the nonisothermal condition was studied by Mandelkern analysis. The results show the nonisothermal crystallization is different from the isothermal crystallization

Synthesis and properties of poly(ether ether ketone ketone)–poly(ether sulfone) block copolymers

Poly(ether ether ketone ketone)-poly(ether sulfone) (PEEKK/PES) block copolymers were prepared from the corresponding oligomers via a nucleophilic aromatic substitution reaction, and the M n of the PEEKK segment was fixed at 12,000, while the M n s of the PES segment ranged from 250 to 12,680. The different properties of the copolymers were investigated by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The results showed that the relationship between T g and compositions of copolymers approximately followed the formula 1/T g = W 1 /T g1 + W 2 /Tg 2 . The PES content and the segment length of the copolymers had a significant influence on their melting points and crystallization behavior. The thermal properties and dynamic mechanical behavior of the copolymers were also studied. In the study of isothermal crystallization, the copolymers have the same nucleation mechanism and crystal growth as that of pure PEEKK. Owing to the introduction of the PES segment into the PEEKK main chain, it increases the free energy which forms the critical crystal nucleus and produces a resistant action to the whole crystallization process of the PEEKK segment.

Homoepitaxial crystallization in films of a thermotropic liquid crystalline chloro-poly(aryl ether ketone)

The homoepitaxial crystallization in the films of a thermotropic liquid crystalline chloro-ply(aryl ether ketone) is studied by transmission electron microscopy (TEM) and electron diffraction (ED). The homoepitaxy takes place in the temperature range 330-320 degreesC, in which a highly-ordered smectic crystalline phase of the copolymer with a single-crystal-like banded structure is formed during the cooling process from the isotropic melt. The homoepitaxial crystallizations with angles of 32 degrees and 122 degrees between the two b axes are the major populations observed, and possess epitaxial contact planes of (100)(I)-(210)(II) and (010)(I)-(210)(II); respectively.

A novel synthetic method to phenyl-capped penta- and hexaaniline

A new convenient method is reported for the synthesis of the phenyl-capped pentamer and hexamer of aniline. The method was accomplished by the reaction of the parent aniline tetramer in the pernigraniline oxidation state with diphenylamine and N-phenyl-1,4-phenylenediamine in the leucoemeraldine oxidation state, respectively. The mechanism probably involves the formation of cation radicals and their coupling.

Synthesis and properties of poly(aryl ether ketone) copolymers containing 1,5-naphthalene moieties

Poly(aryl ether ketone) copolymers possessing various compositions of 1,5-naphthalene and 1,4-phenylene moieties were prepared by the reaction of 4,4′-difluorobenzophenone with hydroquinone (HQ) and 1,5-dihydroxynaphthalene (DHN) in the presence of sodium carbonate and potassium carbonate in diphenyl sulfone. The synthesized copolymers were characterized by FT-IR spectra, differential scanning calorimetry, and thermogravimetric analysis. Thermal analyses of the copolymers showed that the glass transition temperature increased, while the melting temperature and 2.5% weight loss temperature decreased with increasing content of 1,5-naphthalene moieties. For the copolymers synthesized with the molar fraction of DHN in the dihydroxy monomers (DHN, HQ) being over 0.4, no cold crystallization temperature and melting temperature were detected, indicating that these copolymers are almost amorphous. The crystal structure of the copolymers with the molar fraction of DHN being not higher than 0.2 is rhombic, equal to poly(ether ether ketone). Poly(aryletherketon)-Copolymere mit unterschiedlichen Anteilen an 1,5-Naphthalin- und 1,4-Phenylen-Einheiten wurden durch Reaktion von 4,4′-Difluorbenzophenon mit Hydrochinon (HQ) und 1,5-Dihydroxynaphthalin (DHN) in Gegenwart von Natriumcarbonat und Kaliumcarbonat in Diphenylsulfon hergestellt. Die Copolymeren wurden mittels FT-IR-Spektren, Differential-Scanning-Kalorimetrie und thermogravimetrischer Analyse charakterisiert. Die thermische Analyse zeigte, das mit zunehmendem Anteil an 1,5-Naphthalineinheiten die Glasubergangstemperatur ansteigt, die Schmelztemperatur und die Temperatur bei 2,5% Gewichtsverlust jedoch abnehmen. Das Fehlen von Kaltkristallisations- und Schmelztemperatur bei den Copolymeren mit einem DHN-Anteil von mehr als 40 mol-% an den Dihydroxymonomeren deutet darauf hin, das diese vollstandig amorph sind. Die Kristallstruktur der Copolymeren mit DHN-Anteilen < 20 mol-% im Dihydroxymonomergemisch ist rhombisch wie bei Poly(etheretherketon).

The absorption behavior and crystallization of poly(aryl ether ketone) films

The absorption and subsequent desorption behaviors of amorphous polymer films of PEEK poly( ether ether ketone), PEEKK poly( ether ether ketone ketone), and PEKK poly( ether ketone ketone ) in solvent of 1,2-dichloroethane (C 2 H 4 Cl 2 ) are investigated and compared. The equilibrium absorption weight (M x ) of these polymers is related to their molecular ketone content or molecular chain rigidity and also to the experimental conditions. Especially, at a certain temperature, the molecular chains in the solvent can be polarized, which leads to producing greater M for polymer films; for example, at 60°C, M∞ = 46% for PEEK and M∞ = 65% for PEKK. The pseudodiffusion coefficients for PEEK, PEEKK, and PEKK all surpass the 6.0 x 10 -12 m 2 s -1 . The polymers molecular polarization has been proved in concentrated sulfur acid. Results also show that amorphous resins films become white and creeped in dichloroethane, which is more serious when metaphenyl links are introduced into PEEKK or PEKK molecular main chains. The residual solvent of 1% or so often exists in the films, even though a long desorption time ( over 100 h ) has been proceeded. Absorption has induced crystallization of amorphous polymer films, but this crystallization process is slightly different from that of the films crystallized from both the glassy state and the melting state in the solvent, which makes the amorphous interlayers grow progressively and more condensely; thus, the crystallized films will have higher T g s than these crystallized under annealing condition. The morphology results have shown that the solvent-crystallized films are less toughened than the amorphous ones because of the intermediate layer between the induced crystallized area and the amorphous area in the core.