Melt Crystallization and Morphology of Poly(p‐phenylene sulfide) under High Pressure

The high‐pressure melt‐crystallization behaviors of poly(p‐phenylene sulfide) (PPS) were investigated using WAXD, DSC, TEM and SEM. PPS extended‐chain crystals with c‐axis thickness exceeding 4.5 µm were formed at high pressure. The DSC results showed that the melting temperature and melting enthalpy of high‐pressure crystallized PPS samples were up to 327.53 °C and 94.96 J · g^?1, respectively, which were higher than the values of ideal PPS perfect crystals used by some researchers, and the melting enthalpy of the samples fluctuated regularly during the thickening growth of the PPS crystals. Other characteristic morphologies obtained at high pressure, i.e. spherulites and rod‐like crystals, were also presented with the SEM measurements.

     

Thermally Cross‐Linkable Poly(p‐xylylene)s for Advanced Low‐Dielectric Applications

A novel series of poly(p‐xylylene) homopolymer and copolymers containing thermally cross‐linkable cyclohexenyl moiety are prepared via base‐catalyzed Gilch route to yield high‐molecular‐weight polymers. The resulting polymers are highly soluble in a wide range of organic solvents and could be solution cast into flexible and transparent films. The polymers are thermally stable up to 350 °C and the glass transition temperature (T_g) is in the range of 136 ? 250 °C. They undergo thermal cross‐linking via the cyclohexenyl moiety. The cross‐linked polymer exhibits a high T_g of 294 °C, a low coefficient of thermal expansion (CTE) of 45 ppm K^?1. A low dielectric constant of 2.5 and a very low dielectric loss tan δ of 0.0004 at 1 GHz are obtained, which are superior to conventional interconnect polymers.     

Poly(p‐phenylene sulfide) Isothermal Cold Crystallization Investigated by Usual and Unusual Methods

In this paper we want to report the results obtained in our study of the cold‐crystallization kinetics of PPS samples quenched from the melt state and analyzed in the crystallization temperature range 90–112°C. Such a wide range was explored by employing three different experimental techniques: the first one was the usual Differential Scanning Calorimetry (DSC), for the highest temperature range, the second and third ones were the less conventional FT‐IR spectroscopy and energy dispersive X‐ray diffraction (EDXD), able to explore the lowest temperature range. The experimental data obtained by the three above mentioned methods have been all together analyzed by means of the Avrami equation. FT‐IR and EDXD have also allowed us to study the secondary crystallization process of PPS, which otherwise could not be observed just with the DSC technique. The overall crystallization process of such a polymer has been interpreted in the light of the model proposed by Ravindranath and Jog to explain the crystallization of the polymer from the melt state.     

Soluble and Processable Poly(p‐phenylene) with Pendant Imide Groups

We have investigated a soluble and processable poly(p‐phenylene) (PPP) having two pendant imide groups. A novel π‐conjugated PPP was prepared by dehalogenation polycondensation of a dibromo aromatic compound with a zerovalent nickel (Ni(0)) complex. The monomer and polymer were characterized by ¹H NMR, FT‐IR, elemental analysis, TGA, and DSC. The resulting polymer showed a good solubility in polar aprotic solvents such as DMAc, DMSO, and NMP. This polymer was also easily cast on a glass plate to give an orange‐yellow film. The polymer showed a high glass transition temperature of 295°C. The present polymer exhibited photoluminescence with a maximum band at 553 nm in DMAc solution.     

Blue Emission of a Soluble Poly(p‐phenylene) with a Cross‐Conjugated Bisimidazole‐Based Chromophore

A novel poly(p‐phenylene) ( 6 ) has been synthesized by a cruciform combination of a polyphenylene backbone with 2,2′‐(p‐phenylene)‐bis(4,5‐diphenylimidazole) ( 5 ) as an additional, orthogonal chromophore. Polymer 6 showed in solution and in the solid state, a blue‐green emission, which is obviously arising from the second bisimidazole‐based chromophore. UV‐Vis spectroscopy, and cyclic voltammetry revealed that the optical and electronic properties of 6 were fully determined by the incorporated 2,2′‐(1,4‐phenylene)bisimidazole structure. The bisimidazole unit led to high solubility and, despite the steric demand of the substituents, at the same time to the blue‐green emission of the poly(p‐phenylene) ( 6 ). In addition, the oxidation of 6 with potassium ferricyanide yielded a low bandgap polymer with a quinoid‐type structure and a bandgap of 1.6 eV.

     

Dielectric Relaxation of Poly(ester‐block‐amide) Multiblock Copolymers

A series of poly(ester‐block‐amide)s, composed of crystallized sequences of poly(butylene terephthalate) (PBT) and an amorphous, aliphatic oligoamide (PA 36.6) obtained by the reaction of diamines and dimerized fatty acids, has been synthesized by polycondensation in the melt. The dielectric properties of these multiblock copolymers have been investigated as a function of temperature and PBT/PA ratio in the frequency range from 5·10² to 10⁶ Hz. The melting and glass transition temperatures as well as the degree of crystallinity were characterized by means of DSC. The dielectric properties vary with temperature due to two relaxation processes: a) the β‐relaxation process, associated with the local motion of polar groups attached to the soft and hard segments of the copolymer chain, and b) the α‐relaxation process, associated with long‐range molecular motions near the glass‐transition temperature. This behaviour is discussed by means of the Havriliak‐Negami analysis.     

Synthesis and Characterization of Soluble Poly(p‐phenylene) Derivatives for PLED Applications

PPP derivatives with high molecular weights were synthesized and characterized by FT‐IR, ¹H, ¹³C NMR and GPC. The decomposition temperatures of 2a–2c were above 300–400 °C. DSC analysis indicated their nature to be crystalline as all of them exhibited a melt temperature on controlled heating. Optical and electrochemical band gaps was determined using UV/Vis spectroscopy and CV. Single‐layer PLEDs fabricated with 2a–2c displayed high threshold voltages due to high potential barrier for holes. Their EL spectra reveal a small shift in blue peak and the emission form higher wavelength shoulder peak is enhanced.

     

Molecular Packing and Orientation Transition of Crystalline Poly(2,5‐dihexyloxy‐p‐phenylene)

The effect of thermal treatment on the transition of molecular packing and orientation of the semiconducting poly(2,5‐dihexyloxy‐p‐phenylene) (PPP) film is probed by the combination of in situ 2D grazing incidence X‐ray diffraction (2D GIXD) and selected area electron diffraction (SAED). The structure analysis indicates that PPP crystallizes in an orthorhombic unit cell with a = 21.20 Å, b = 3.78 Å, and c = 4.24 Å. A variation of the annealing temperature from 80 °C to 100 °C demonstrates that the worm‐like morphology in the pristine film melts and develops into nanowires. Furthermore, the molecular orientation transforms from face‐on to edge‐on via thermal annealing. Remarkably, a previously unknown metastable state of “slope” edge‐on with a tilt angle of 51.1° is observed. This orientation change arises from the heterogeneous nucleation and growth of edge‐on PPP crystal during crystallization from the melt.

     

Connector Effect in Electroluminescent Properties of Poly(p‐phenylene vinylene) Derivatives Containing Triazole Chromophores

Summary: We report the thermal, optical, electrochemical and electroluminescent properties of four polymers P1 – P4 consisting of hole‐transporting [1,4‐bis(hexyloxy)‐2,5‐distyrylbenzene;DSB] and electron‐transporting [4‐(4‐(hexyloxy)phenyl)‐3,5‐diphenyl‐4H‐1,2,4‐triazole; TAZ] fluorophores linked by four kinds of connectors: (1) ether spacers, (2) single bonds, (3) 1,4‐phenylenes, and (4) 1,4‐divinylbenzenes. These polymers are soluble in common organic solvents such as chloroform, N‐methylpyrrolidone (NMP) and CH₂Cl₂CH₂Cl₂ and exhibit good thermal stability with decomposition temperatures higher than 340 °C. Compounds M1 – M3 containing a TAZ or DSB core were employed as a model to study the optical properties of the polymers. The photoluminescence (PL) spectral maxima of P1 – P4 in CHCl₃ were spread over a wide range, from 453 nm to 501 nm, depending upon the chemical structures of the connectors. In the film state, the PL maxima shifted bathochromically from 464nm to 538 nm, which can be attributed to the formation of excimers. From the optimized semiempirical modified neglect of diatomic overlap (MNDO) calculations, the adjacent benzene rings between DSB and TAZ chromophores in P2 and P3 twist about 81–89° which is significantly different from P4 (circa 0°). The effect of the twisted connector architectures on optical and electrochemical properties for P1 – P4 is discussed. The electroluminescences of P1 – P4 and corresponding Commission Internationale de l'Eclairage (C.I.E.) coordinates are also depicted to indicate that incorporating different connectors to these polymers changed their color from blue, to green, to the yellow region.

The C.I.E. 1931 diagram of lights emitted from the PLED devices (ITO/PEDOT:PSS/ P1 – P4 /Al).     

Dielectric Relaxation Behavior of a Poly(ethylene carbonate)‐Lithium Bis‐(trifluoromethanesulfonyl) Imide Electrolyte

A new class of polymer electrolytes, consisting of poly(ethylene carbonate) (PEC) and metal salts, is expected to find application in all‐solid‐state batteries because of its excellent performance as an electrolyte. To study the ion‐conductive mechanism in PEC‐based electrolytes, broadband dielectric spectroscopy is used to analyze the correlation between dielectric relaxation and ionic conduction in PEC‐lithium bis‐(trifluoromethanesulfonyl) imide electrolytes over a broad range of salt concentration (0–150 mol%) at 40 °C. The PEC system has two relaxation modes, α and β, associated respectively with the segmental motion and the local motion of PEC chains. The conductivity increases exponentially with increasing salt concentration, while the α relaxation frequency (f_α) decreases with increasing strength (Δε_α) at low salt concentrations, whereas in contrast f_α increases with Δε_α being saturated at high salt concentrations above 10 mol%. It is believed that the mobility of PEC segment at high concentration is enhanced by two factors. The first is that intermolecular interactions decrease, given the existence of many ion pairs and aggregated ions around saturated PEC domains where the dissociated ions are highly concentrated. The second is that intramolecular interactions between C?O and CH₂ are lowered by the ion–dipole interaction.

     

Study of new modifications of poly(p‐phenylene) synthesis via oxidative polycondensation

The results of recent studies of polyphenylene synthesis are summarized. The experimental results about the role of the AlCl₃ quality, new catalysts, and solvents to obtain high‐molecular polymer film by electrochemical oxidation under extremely high working potentials are described. A mechanism of polyphenylene formation is suggested. An idea concerning the influence of the doping and of the solubility of the growing chain on the maximum polyphenylene molecular weight during the oxidative polycondensation process is presented.     

Relaxation Processes of Poly(tert‐butyl acrylate) Chemically Confined via Hydrogen Bonds

In this work, tailored copolymers of tert‐butyl acrylate and acrylic acid (AA) with an ABA type structure were systematically analyzed via dynamic‐mechanical analysis with regard to their relaxations, in which the main focus was put on a chemical confinement (cc) mode caused by hydrogen bonds. Four different relaxation modes were detected, whereupon two modes seem to depend on the length of the inner B‐block and one on the length of the outer A‐blocks. One mode below room temperature could be identified as a secondary relaxation which belongs to the B‐block and is most likely induced by a cc. A softening of the polymer corresponding to the glass transition is found near to room temperature and surprisingly shifts to lower temperatures with increasing chain length of the B‐block. A second softening of the ABA type copolymers is caused by the AA containing A‐blocks and was found at higher temperatures.

     

Tensile Behavior of a Substituted Poly(m‐,p‐phenylene) versus Its Parent Counterpart and Synthesis of Related Polyarylenes

In a recent report, a poly(m ,p‐phenylene) with acid‐cleavable trialkylsilyl side chains is synthesized by Suzuki polycondensation in a molecular weight of M _w = 300 kDa determined by gel permeation chromatography (GPC). Such a high value suggests this polymer as a potentially attractive material for strong films and fibers both in the presence and absence of the side chains. After confirming these molecular weights by static light scattering, the polymer is processed into thin films for tensile stress measurements. Above the glass transition, thus >180 °C, the material shows an extended plasticity, which is used to obtain elongated samples of draw ratios ranging from 1.5 to 6. The elongated samples show a Young's modulus of up to 5 GPa and a yield strength of 140 MPa. Upon removal of the solubilizing side chains, these values further increase to a Young's modulus of 7.5 GPa in the direction of drawing and a maximum strength of 300 MPa. Motivated by these findings, the scope of this polymer class is broadened by synthesizing two new high molecular weight poly(m ,p‐phenylene)s. The structural variation allows to tune the glass transition temperatures between 125 and 240 °C depending on the amount of the meta connected phenylene units.

     

Selective Fluorescence Quenching by Group 8 Metal Ions of a Water‐Soluble Poly(p‐phenylene vinylene) Derivative Bearing Oligo(oxyethylene) Pendants

A new fluorescing, water‐soluble derivative of poly(p‐phenylene vinylene), poly[2,5‐bis(oligooxyethylene)‐1,4‐phenylene vinylene], P(OE‐PV), is synthesized via a multistep route. The UV‐vis absorption and photoluminescence properties of the polymer are studied in aqueous solutions in the presence of 25 different metal ions. Among the ions studied, Fe(III), Os(III) and Ru(III) are found to effectively quench the fluorescence of P(OE‐PV). The Ru(III) is the most efficient in the fluorescence quenching. This observation implies that the polymer is a sensitive and selective chemosensor for these ions. It is suggested that the photoinduced electron transfer from the excited state of P(OE‐PV) to the metal ions may be the quenching mechanism application to the present systems.

     

Poly(p‐phenylene vinylene) Derivatives with Different Contents of cis‐Olefins and their Effect on the Optical Properties

Soluble poly[(2,5‐dihexyloxy‐1,4‐phenylene vinylene)‐alt‐(2,5‐diphenyl‐1,4‐phenylene vinylene)] (DPO‐PPV) with a majority of cis‐vinylenes (>87%) has been synthesized by the Wittig reaction. A series of DPO‐PPV derivatives with different contents of cis‐olefins from approximately 0.05% to 87% was successfully prepared using the photoisomerization technique. On the basis of ¹H NMR, Fourier transform IR (FTIR), ultraviolet (UV), and photoluminescence (PL) spectroscopy, as well as fluorescence quantum efficiency measurements, the effect of cis‐olefins on the optical properties of the polymer in solution and in film was systemically studied. The results indicate that with a cis‐configuration above 75%, the luminescence of DPO‐PPV is decayed due to cis‐trans isomerization with rotational motions of the double bonds; however, the luminescence is dramatically improved on increasing of the trans‐configuration.

     

p‐Doping Poly(3‐hexylthiophene) in Solvent Mixtures

One method to improve the conductivity of conjugated polymers, like poly(3‐hexylthiophene) (P3HT), is to “chemically dope” them analogous to inorganic materials. One electron acceptor that has been used in tandem to p‐doped P3HT is 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ), and recently there has been much interest in the nature of the interactions between F4TCNQ and P3HT in the solution phase. To date, however, there are few reports that investigate the behavior of F4TCNQ‐doped P3HT in binary solvent mixtures. The study reported herein is an investigation of F4TCNQ‐doped P3HT in mixtures of chloroform (CF) with dichloromethane (DCM) or acetonitrile (AcN), wherein variations in the doping efficiency in these mixtures are observed using UV–vis absorption, Raman, and electron paramagnetic resonance spectroscopic techniques. The contrasting solubility and charge transfer behavior of F4TCNQ‐doped P3HT in CF:DCM and CF:AcN show that judicious selection of solvent mixtures may be exploited to improve the doping efficiency and solution processability of p‐doped P3HT dispersions.     

New Polymers Based on Fluorenylidene‐Linked Conjugated Oligo(p‐phenylene)s

New thermally stable, fluorescent copolymers consisting of fluorenylidene‐linked conjugated oligo(p‐phenylene) segments are presented. The copolymers have been prepared by the palladium‐catalyzed Suzuki polycondensation method. The copolymers obtained are found to be soluble and easily processable from conventional organic solvents such as chloroform, toluene or tetrahydrofuran, and have been characterized by ¹H and ¹³C NMR spectroscopy, FT‐IR spectroscopy and elemental analysis. The degree of polymerization has been estimated by gel permeation chromatography (GPC). The thermal properties of the copolymers were characterized by differential scanning calorimetry (DSC). The optical properties of the polymers have been investigated in solution by UV/VIS spectroscopy.     

Synthesis and optical properties of novel poly(p‐phenylene ethynylene)s

In order to explore the influence of chemical modifications on the photophysical properties of poly(p‐phenylene ethynylene)s (PPEs), a series of PPE‐copolymers was synthesized employing Heck‐type cross‐coupling reactions. UV/Vis absorption and photoluminescence experiments clearly demonstrate that the design of PPE‐copolymers which comprise conjugated segments of well‐defined length and (aliphatic) spacers in a strictly alternating fashion allows to tune the bandgap to higher energies, and thus the absorption and emission maxima to shorter wavelengths. The derivatization of the PPE backbone with electron‐withdrawing substituents, by contrast, is found to be significantly less effective and only leads to comparably small shifts in the absorption and emission spectra.     

Thermally Induced Crosslinking of Poly(N‐Propargyl Glycine)

As polypeptoids become increasingly popular, they present a more soluble and processable alternative to natural and synthetic polypeptides; the breadth of their potential functionality slowly comes into focus. This report analyzes the ability of an alkyne‐functionalized polypeptoid, poly(N‐propargyl glycine), to crosslink upon heating. The crosslinking process is analyzed by thermal analysis (differential scanning calorimetry and thermogravimetric analysis), Fourier‐transform infrared, electron paramagnetic resonance, and solid‐state NMR spectroscopy. While a precise mechanism cannot be confidently assigned, it is clear that the reaction proceeds by a radical mechanism that exclusively involves the alkyne functionality, which, upon crosslinking, yields alkene and aromatic products.

     

Specific Interactions in Miscible Poly(p‐vinylphenol)/Poly(N‐methyl‐3‐piperidinemethyl methacrylate) Blends

Poly(p‐vinylphenol) (PVPh) is miscible with poly(N‐methyl‐3‐piperidinemethyl methacrylate) (PM3PMA). The glass transition temperatures of the blends are higher than those calculated from a linear additivity rule. Fourier transform infrared spectroscopy shows the existence of hydrogen‐bonding interactions between the hydroxyl groups of PVPh and the carbonyl groups of PM3PMA. In addition, X‐ray photoelectron spectroscopy shows that the piperidine nitrogen atoms of PM3PMA also interact with the hydroxyl groups of PVPh as shown by the development of a high‐binding‐energy N 1s peak in each blend. In contrast, we have earlier reported that the piperidine nitrogen atoms of poly(N‐methyl‐4‐piperidyl methacrylate) are not involved in hydrogen‐bonding interactions with PVPh. To better understand the interactions in various blends, ab initio calculations were performed on hydrogen‐bonded dimers of saturated monomers.