Polyimides from 3,3 '-dioxo-[1,1 ']-spirodiphthalan-5,5 ',6,6 '-tetracarboxylic dianhydride

A novel dianhydride, 3,3'-dioxo-[1,1']-spirodiphthalan-5,5',6,6'-tetracarboxlic dianhydride, was synthesized and used as a monomer to prepare polyimides with several diamines via a conventional two-stage procedure. The intermediate poly(amic-acid)s had inherent viscosities of 0.84-1.71 dL/g and could be thermally converted into lightly yellow, transparent, flexible and tough films. Films cast from chemically imidized polyimides were transparent and colorless. The glass transition temperatures (Tg) were > 400 degrees C, and the 5% weight-loss temperatures were > 420 degrees C in N-2 and in air. The solubilities of these polyimides in various solvents were evaluated. The mechanical properties of some polyimides were also tested. (C) 1999 Elsevier Science Ltd. All rights reserved.

Syndiotactic polystyrene/thermoplastic polyurethane blends using poly(styrene-b-4-vinylpyridine) diblock copolymer as a compatibilizer

The effect of adding diblock copolymer poly(styrene-b-4-vinylpyridine) (P(S-b-4VPy), to immiscible blends of syndiotactic polystyrene (sPS)/thermoplastic polyurethane (TPU) on the morphology, thermal transition, crystalline structure, and rheological and mechanical properties of the blends has been investigated. The diblock copolymer was synthesized by sequential anionic copolymerization and was melt-blended with sPS and TPU. Scanning electron microscopy (SEM) showed that the added block copolymer reduced the domain size of the dispersed phase in the blends. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the extent of compatibility between sPS and TPU affected the crystallization of the sPS in the blends. Tensile strength and elongation at break increased, while the dynamic modulus and complex viscosity decreased with the amount of P(S-b-4VPy) in the blend. The compatibilizing effect of the diblock copolymer is the result of its location at the interface between the sPS and the TPU phases and penetration of the blocks into the: corresponding phases, i.e. the polystyrene block enters the noncrystalline regions of the sPS, and the poly(4-vinylpyridine) block interacts with TPU through intermolecular hydrogen bonding. (C) 1999 Elsevier Science Ltd. All rights reserved.

Preparation of polymer-supported zirconocene catalysts and olefin polymerization

A novel polymer-supported metallocene catalyst with crosslinked poly(styrene-co-acrylamide) (PSAm) as the support has been prepared and characterized. The probability of long sequences of acrylamide (Am) in PSAm is still low even at an Am amount of 32.8 mol %, implying the relatively homogeneous distribution of Am. The infrared spectra of PSAm and the supported catalyst substantiate that an amide group in PSAm coordinates with methylaluminoxane through both oxygen and nitrogen atoms. Ethylene/alpha-octene copolymerization showed that the catalytic activity is not markedly affected by adding alpha-octene. C-13 NMR analysis of the ethylene/alpha-octene copolymer indicated that the composition distribution of the copolymer is uniform. (C) 1999 John Wiley & Sons, Inc.

Potential-dependent adsorption/desorption of organic adsorbate at HOPG electrode and accompanying delamination of graphite surface

In situ electrochemical scanning tunneling microscopy, alternating current voltammetry, and electrochemical quartz crystal microbalance have been employed to follow the potential-dependent adsorption/desorption processes of nucleic acid bases on highly oriented pyrolytic graphite (HOPG) electrode. The results show that (i) potential-dependent adsorption/desorption of nucleic acid bases on HOPG electrode was accompanied by delamination of the HOPG surface, and the delamination initiates from steps or kinks on the electrode surface, which provide highly active sites for adsorption; (ii) the delamination usually occurred when the electrode potential was changed or when the electrode was at potentials where the phase transition of adsorbate occurred. These results suggest that the surface stress resulting from the interaction between the substrate and adsorbate, as well as the interaction due to potential-induced surface charge distribution and the hysteresis of charge equilibrium are the main factors resulting in HOPG delamination. (C) 1999 The Electrochemical Society. S0013-4651(97)12-013-4. All rights reserved.

Effect and mechanism in compatibilization of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer in poly(2,6-dimethyl-1,4-phenylene oxide) poly(ethylene-ran-acrylic acid) blends

The compatibilization effect of poly(styrene-b-2-ethyl-2-oxazoline) diblock copolymer, P(S-b-EOx), on immiscible blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and poly(ethylene-co-acrylic acid) (EAA) is examined in terms of phase structure and thermal, rheological and mechanical properties, and its compatibilizing mechanism is investigated by Fourier-transform infrared spectroscopy. The block copolymer, synthesized by a mechanism transformation copolymerization, is used in solution blending of PPO/EAA. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion on addition of a small amount of P(S-b-EOx). Thermal analysis indicates that the grass transition of PPO and the lower endothermic peal; of EAA components become closer on adding P(S-b-EOx), and the added diblock copolymer is mainly located at the interface between the PPO and EAA phases. The interfacial tension estimated by theological measurement is significantly reduced on addition of a small amount of P(S-b-EOx). The tensile strength and elongation at break increase with the addition of the diblock copolymer for PPO-rich blends, whereas the tensile strength increases but the elongation at break decreases for EAA-rich blends. This effect is interpreted in terms of interfacial activity and the reinforcing effect of the diblock copolymer, and it is concluded that the diblock copolymer plays a role as an effective compatibilizer for PPO/EAA blends. The specific interaction between EAA and polar parts of P(S-b-EOx) is mainly hydrogen bonding. (C) 1998 Elsevier Science Ltd. All rights reserved.

Preliminary investigations on polymerization catalysts composed of lanthanocene and methylaluminoxane

The polymerization of butadiene(Bd), isoprene(Ip) and styrene(St) has been examined using the six catalyst systems composed of lanthanocene, (C5H9Cp)(2)NdCl(I), (C5H9Cp)(2)SmCl(II), (MeCp)(2)SmOAr'(III), (Ind)(2)NdCl(IV), Me2Si(Ind)(2)NdCl(V) and (Flu)(2)NdCl(VI), and methylaluminoxane(MAO) respectively. All of them can be used to form the polyisoprene with molecular weights of 1 to 10 thousand and cis-1,4-unit contents of 41 to 47%. (I), (II) and (III) of them can be also used to form the polybutadiene with molecular weights of 10 to 20 thousand and cis-1,4-unit contents of 62 to 78%. In addition, the catalysts from (II) to (V) are still active for St polymerization and (II) of them gives a syndio -rich random polystyrene. It is noteworthy that (II) and (III) are active for homopolymerization of Bd, Ip and St in the same polymerization condition.

Blue-light emitting diodes and flat display based on poly(p-phenylenevinylene) copolymers

Copolymers containing alternating flexible aliphatic blocks and rigid poly(p-phenylenevinylene) (PPV) blocks were synthesized and characterized. It was found that the fluorescent intensity increases with increasing length of the flexible blocks. Bright blue-light emitting diodes were fabricated using PPV copolymers as electroluminescent layers. The devices show 190 cd/m(2) light-emitting brightness at 460 nm and 15 V rum-on voltage. The effects of oxadiazole derivative PBD and tris(8-hydroxyquinoline) aluminum Alq(3) electron-transporting layers on the luminance and stability of the devices are discussed.

A novel rare earth coordination catalyst for polymerization of biodegradable aliphatic lactones and lactides

A novel rare earth coordination system composed of lanthanide trifluoroacetates Ln(CF3COO)(3) (Ln = Y, Yb, Nd, Tm, Ho, La, Pr) and triisobutylaluminium Al(i-Bu)(3) was used as catalyst for the polymerization of epsilon-caprolactone (CL), D,L-lactide (DLLA) and their copolymerization. The influence of temperature, time and catalyst concentration on polymerization yields and molecular weights of the polyesters have been studied. It was shown that the ring-opening polymerization of cyclic esters catalysed by Ln(CF3COO)(3)/Al(i-Bu)(3) has some living character and the molecular weight of the polyester could be controlled by adjusting the molar ratio of monomer to catalyst. The DLLA/CL copolymer was synthesized by sequential addition of monomers and the structure of the copolyester was characterized by GPC, NMR and DSC. (C) 1998 SCI.

The synthesis and thermotropic liquid crystalline behaviour of novel main chain poly(aryl ether ketone)s containing a lateral phenyl group

Novel main chain poly(aryl ether ketone)s containing a lateral phenyl group were synthesized by nucleophilic substitution reactions of 4,4'-biphenol and phenylhydroquinone with either 4,4'-difluorobenzophenone or 1,4-bis(4-fluorobenzoyl)benzene and their thermotropic liquid crystalline properties were characterized by a variety of experimental techniques. Thermotropic liquid crystalline behaviour was observed in the copolymers containing 50 and 70mol% biphenol. Melting (T-m) and isotropization (T-i) transitions both appeared on the DSC thermograms. A banded texture was formed after shearing the sample in the liquid crystalline nematic state. As expected, each of the copolymers had a relatively lower melting transition than the biphenol-based homopoly(aryl ether ketone)s because of the copolymerization effect of the crystal-disrupting monomer phenylhydroquinone.

Barrier properties of vinylidene chloride methyl acrylate copolymer

A series of vinylidene dichloride (VDC) copolymers with methyl acrylate (MA) as comonomer (3-12wt%), was prepared by free-radical suspension copolymerization. The permeability coefficients of the copolymers to oxygen and carbon dioxide were measured at 1.0 MPa and at 30 degrees C, and those to water vapor were measured at 30 degrees C and 100% relative humidity. All the VDC/MA copolymers studied are semicrystalline. As the MA content increases, the permeability coefficients of the copolymers to oxygen, carbon dioxide, and water vapor are progressively increased, caused by decrease in crystalline fraction and increase in free volume of VDC/MA copolymers.

Polymerization of ethylene by zirconocene-B(C6F5)(3) catalysts with aluminum compounds

Ethylene polymerization by zirconocene-B(C6F5)(3) catalysts with various aluminum compounds has been investigated. It is found that the catalytic activity depended on zirconocenes used, and especially on the type of aluminum compounds. For Et(H(4)Ind)(2)ZrCl2 (H(4)Ind : tetrahydroindenyl), the activity decreases in the following order: Me3Al > i-Bu3Al > Et3Al much greater than Et2AlCl. While for Cp2ZrCl2(Cp : cyclopentadienyl), it varies as follows: i-Bu3Al > Me3Al much greater than Et3Al. Furthermore, the activity is significantly affected by the addition mode of the catalytic components, which may imply that the formation of active centers is associated with an existing concentration of catalytic components. Results of thermal behavior of polyethylene (PE) studied by differential scanning calorimetry(DSC) show that crystallinity of the polymer prepared with Et3Al is higher than that with Me3Al or i-Bu3Al. It is also found that the number-average molecular weight ((M) over bar) of the polymers prepared with Me3Al or i-Bu3Al is much higher than that with Et3Al. H-1-NMR studies substantiate that i-Bu3Al is a more efficient alkylation agent of Cp2ZrCl2 in comparison with Me3Al. (C) 1997 John Wiley & Sons, Inc.

Effect of crystal-disrupting chlorohydroquinone on the first-order transitions of poly(aryl ether ketone)s containing biphenyl units

The novel poly(aryl ether ketone)s were synthesized by nucleophilic substitution reactions of 4,4'-difluorobenzophenone with 4,4'-biphenyldiol and chlorohydroquinone. As expected, the copolymers have lower melting transitions than the biphenyldiol-based homopoly(aryl ether ketone) because of the copolymerization effect of the crystal-disrupting monomer chlorohydroquinone. Copolymers containing 50 and 70% biphenyldiol show two first-order transitions which are associated with the crystal-to-liquid crystal transition and the liquid crystal-to-isotropic transition.

Crystallization and intriguing morphologies of compatible mixtures of tetrahydrofuran-methyl methacrylate diblock copolymer with poly(tetrahydrofuran)

The crystallization and unusual crystalline morphologies of compatible mixtures of tetrahydrofuran-methyl methacrylate diblock copolymer with tetrahydrofuran homopolymer were studied. It is shown that the PTHF [poly(tetrahydrofuran)] block of the copolymer cocrystalizes with the PTHF homopolymer in the PTHF microphase of the blend. However, the degree of crystallinity of the PTHF block is always lower than that of the PTHF homopolymer in the PTHF microphase. The crystallizability of the PTHF microphase increases appreciably with increasing PTHF microphase size and PTHF homopolymer weight fraction in the microphase. The morphology study of the blends shows that the crystalline morphology is strongly dependent on blend composition, copolymer composition and PTHF block length, as well as crystallization temperature. When alternating PTHF and PMMA [poly(methyl methacrylate)] lamellae are formed, the macroscopic crystalline morphology could be only observed when the thickness of the PTHF lamellae is large enough (similar to 20 nm). In the blend where PMMA spherical or cylindrical microphases are formed, the crystalline morphology changes dramatically with the change in the PTHF microdomain size and PMMA interdomain distance. Many unusual crystalline morphologies have been observed. A study of the solution-crystallized morphology of the blends at different temperatures shows that the morphology is also strongly dependent on the isothermal crystallization temperature, suggesting that the PMMA microdomains may have different effects on the morphology formation when the blend is crystallized at different rates.

Charge transport of indigo-carmine doped polypyrrole

Charge transport in polypyrrole doped with indigo-carmine was investigated by the method of electrochemical alternating current impedance. By the nonlinear least square fitting, the equivalent circuit and parameter of each component are obtained. The apparent diffusion coefficients and heterogeneous electron transfer constants are given. It is found that, along with the increasing of film thickness, D-app and k(0) increase also.

Synthesis of lanthanide-alkylaluminium bimetallic complexes and studies on their catalytic activities for polymerization of some polar monomers

Three new lanthanide (Ln)-alkylaluminium (Al) bimetallic complexes with the formula [(mu-CF3CO2)(2)Ln(mu-CF3CHO2)AIR(2) . 2THF](2) (Ln = Nd, Y, R=i-C4H9 (i-Bu); Ln=Eu, R=C2H5(Et); THF=tetrahydrofuran) were synthesized by the reaction of Ln(CF,CO,), (Ln=Nd, Y) with HAI (i-Bu)(2) and of Eu(CF3CO2)(3) with AlEt(3), respectively. Their crystal structures were determined by X-ray diffraction at 233 K. [(mu-CF3CO2)(2)Nd (mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Nd-Al) and [(mu-CF3CO2)(2)Y(mu-CF3CHO2)Al(i-Bu)(2) . 2THF](2) (Y-Al) are isomorphous and crystallize in space group with a=12.441(3) Angstrom [12.347(5) Angstrom for Y-Al], b=12.832(3) Angstrom [12.832(4) Angstrom], c=11.334(3) Angstrom [11.292(8) Angstrom], alpha=104.93 (2)degrees [104.45(4)degrees], beta=98.47(2)degrees [98.81(4)degrees], gamma=64.60(2)degrees [64.30(3)degrees], R=0.519 [0.113], R(w)=0.0532 [0.110], Z=1 and [(mu-CF3CO2)(2)Eu(CF3CHO2)AlEt(2) . 2THF](2)(Eu-Al) in space group P2(1)/n with a=11.913(6) Angstrom, b=14.051(9) Angstrom, c=17.920(9) Angstrom, alpha=101.88(11)degrees, beta=gamma=90 degrees, R=0.0509, R(w)=0.0471 and Z=2. The six CF3CO2- (including CF3CHO2-) of each complex, among which pairs are equivalent, coordinated to Ln and Al in three patterns: (A) the two oxygen atoms in one of the three CF3CO2- type coordinated to two different Ln; (B) the two oxygen atoms in the second of CF3CO2- type coordinated to Ln and Al, respectively; (C) one of the two oxygen atoms in the third CF3CO2- type bidentately coordinated to two Ln and another oxygen coordinated to Al and one of the two Ln, respectively. Unlike types A and B, in type C the carboxyl carbon with a hydrogen atom bonded to it was found to appear as an sp(3)-hybridized configuration rather than an sp(2)-one. 1D and 2D NMR results further confirmed the existence of such a disproportionated CF3CHO2- ligand. Methyl methacrylate (MMA) and epichlorohydrin (ECH) could be polymerized by Y-Al or Eu-Al as a single-component catalyst and highly syndiotactic poly(MMA) was obtained. THF could also be polymerized by Y-Al in the presence of a small amount of ECH.