摘要:

AbstractSince the first reports on the combination of liquid crystalline polymers in block (1985) and graft (1986) copolymers with amorphous and semi‐crystalline polymers, the scientific interest has been focused on understanding how the size and type of the mesophase displayed by the liquid crystalline part(s) affects the LC → isotropic transition and the order in the LC domains themselves with respect to the morphology displayed. An overview of the work that has been done so far will be given, as well as a closer discussion of the interaction between morphology and LC phase behavior as evaluated on a large number of very well defined LC side group block copolymers. Furthermore, applications and results of mechanical and optical investigations are discus

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471001

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractDynamic mechanical,2H NMR and dielectric spectroscopy techniques were used to identify the nature of the local motions involved in the secondary relaxations of a thermotropic aromatic terpolyester prepared frompara‐hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted β, γ, and δ, were detected. A β relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude π‐flip processes observed by2H NMR. Correlated motions of thepara‐substituted rings and adjacent carbonyl groups may also participate in the β process. Then, at lower temperatures, a γ process is detected by both dielectric and dynamic mechanical experiments. It is assigned to small amplitude oscillations of the isophthalic acid units of the HBA33 polymer. At high temperatures, a heavy overlap of broad rate distributions for the β and γ processes observed in the measurements precludes a more detailed analysis. A dielectric relaxation, denoted δ relaxation, is observed at very low temperatures. It likely comes from motions of a very small number of water molecules trapped in the structure of t

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471002

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractWe report detailed measurements on the thermal conversion of the tetrahydrothiophene prepolymer to poly(p‐phenylene vinylene) (PPV) and show the influence of the elimination conditions on the properties of PPV and on light emitting devices (LEDs) prepared in the configuration ITO/PPV/Al. Electroluminescence correlates with a diode behavior in the current—voltage characteristic and can be observed for PPV heated at a minimum temperature of 130°C. Increase of the elimination temperature results in a red‐shift of both the photoluminescence and electroluminescence spectra by ≈10 nm, which enables us to control the color of our LEDs in a small range. We have observed that refered to the brightness of the devices the optimum elimination temperature is 160°C, and we show that a further increase of temperature does not improve the properties of

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471003

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe kinetics of the emulsion polymerization of butyl acrylate at 20°C in Smith‐Ewart interval III were investigated using a redox initiator system peroxodisulfate–bisulfite–copper. The aim of this work was to obtain more basic knowledge about the kinetic behavior of the butyl acrylate system. Monomer conversion into polymer was based on gravimetrically calibrated online densitometry. The experimentally obtained conversion versus time curves for these seeded reactions were fitted by a linear regression procedure (slope and intercept) as well as by a nonlinear regression procedure based upon zero‐one kinetics. The conclussion is that the emulsion polymerization of butyl acrylate may reflect zero‐one kinetics up to a particle size of approximately 130 nm. The rate coefficients for entry and exit can be obtained fairly accurately with the slope and intercept procedure and with the nonlinear regression method if the propagation rate coefficient is accurately known. However, this is not the case. Therefore the development of universal procedures for obtaining the propagation rate coefficients is essential, since this parameter is of paramount importance in all further model calculations concerning emulsion poly

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471004

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractPolyisoprene and polybutadiene samples, prepared from the respective monomers using lanthanide‐based catalysts, have been analyzed in terms of microstructure, glass transition temperatures and stabilities to thermo‐oxidative degradation. Quantitative determination of 1,4‐cis/trans, 1,2‐ and 3,4‐contents have been made from the IR spectra of the polymers. Attempts to use1H and13C NMR and Raman spectroscopy to analyze the microstructure of the materials has at best proved only partially successful. TGA and IR spectroscopy have been used to study the influence of catalyst residue on the thermo‐oxidative degradation of t

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471005

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe synthesis of dendronized acrylate and styrene monomers with Fréchet‐type as well as urethane‐based dendrons of the first and second generation and their radically initiated polymerization to the high molecular weight dendrimers6(G‐1,2) and8a(G‐2) is reported. The latter polymer carries four THP‐protected hydroxy functions per repeat unit whose quantitative deprotection is also

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471006

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe dielectric and conductivity behavior of some selected solid polyelectrolyte‐surfactant complexes (PE‐surf) is characterized by broadband dielectric spectroscopy in the frequency range 10−2–107Hz. Depending on phase‐morphology and volume fraction of alkyl‐tails, electrical conductivities at room temperature of up to 10−4S/cm are found. In addition, the behavior at low temperatures is characterized by two distinct β‐relaxations which show an Arrhenius‐like activation, and their relaxation strength depends on temperature, in contrast to the standard behavior of dielectric media. The relaxations are assigned to surfactant movements, the number or strength of which increase with temperature, which are obviously important already well below the glass transition temperature of the ionic layers. Doping of a selected complex showing a rather high basic conductivity with LiClO4results in a decrease of the conductivity, which is explained by an increase in the glass transition temperature

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471007

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe barrier properties of thin fluorocarbon films toward toluene are studied. Mixtures of trifluoromethane and ethylene are used as monomers in an electron cyclotron resonance plasma discharge. The measured permeation fluxes of toluene through polyethylene show that thin fluorocarbon layers strongly reduce the permeation, e. g. by a factor of about 3000 when an appropriate tapered layer is deposited on polyethylene foils. Different tapering of the barrier layers was investigated with respect to low permeation and good adhesion of the films. The amount of permeated toluene through the untreated and treated polyethylene foils are measured as a function of time using a gas chromatograph with a flame ionization detector.

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471008

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

ISSN:0323-7648    

DOI:10.1002/actp.1996.010471009

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY