摘要:

AbstractExperimental equipment was constructed for simultaneous measurements of wide angle X‐ray scattering (WAXS), small angle X‐ray scattering (SAXS) and differential scanning calorimetry (DSC) using synchrotron radiation as a strong source of X‐rays. The crystallization occurring during heating of an initially amorphous sample with constant heating rate was investigated. Poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN), poly(ethylene terephthalate) (PET) and the copolymer PEN‐co‐PHB (90:10), where PHB stands for poly(p‐hydroxybenzoic acid), were used as materials. By comparing the change of the degree of crystallinity as measured by WAXS and DSC with the change of the SAXS powerQ, it was shown that the primary crystallization, during which morphological units like spherulites axe growing, is followed by a secondary crystallization during which the degree of crystallinity with the lamellar stacks in the spherulites is increased. Assuming a two‐phase system for the semicrystalline structure, consisting of crystals and amorphous regions, three different processes were shown to be responsible for this increase: The formation of new crystal lamellae within the already existing lamellar stacks, the thickening of already existing crystals at the expense of the amorphous regions, and the complete melting of crystals followed by formation of new,

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440601

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe structures of the series of oligothienyls (T4‐T5‐T6) have been determined and refined from X‐ray powder diffraction data using the Rietveld full‐profile analysis. Unlike polythiophene, all the molecules in the isomorphous series display no internal symmetry, being only approximately planar within 12°. Packing is always achieved through a common molecular disposition, which is usually defined as aherringbonearrangement, with an angle between mean planes of adjacent molecules which spans from 60

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440602

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe microfibrils and the microfibrillar network in poly(p‐phenylene terephthalamide) (PPTA) fibers formed during the coagulation from a monodomain lyotropic fiber are stabilized by critical point drying and characterized by electron microscopy and small angle X‐ray scattering. The diameter of the microfibrils varies from 20 to 49 nm depending on the PPTA concentration in the lyotropic solution used for the spinning. A formation mechanism for the microfibrils and the microfibrillar network is suggested. During the coagulation, the spinodal decomposition (phase separation) is assumed to occur before the crystallization (phase transition), resulting in the formation of the microfibrils. The formation of the microfibrillar network is considered to be related to the misorientation of macromolecules and the density fluctuation in the cross‐section of the filament during spinodal decompos

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440603

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo new solid‐state NMR methods for measuring orientation distributions in partially ordered solids are applied to high tensile‐strength fibre polymers. Both methods use the anisotropy of the carbon‐13 chemical shift tensor as a probe for local molecular directions, but they differ in the manner in which the information is extracted and complement one other. The spectral resolution is higher in the ORDER (ORientation Distributions with Enhanced Resolution) experiment, which employs rotor‐synchronized three‐dimensional magic angle spinning (MAS) NMR, while the angular precision with which the orientation distribution can be determined is higher in the DECODER (Direction Exchange with Correlation of Orientation Distribution Evaluation and Reconstruction) experiment. The utility of the two techniques is demonstrated by their application to the study of industrially produced poly(p‐phenyleneterephthalamide) fibres. Both give the same result for the width (χ= 13°) and the order parameters (=0.85,=0.57,=0.34,=0.14) of the orientation

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440604

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractA simple mathematical model for the continuous emulsion polymerization of vinyl chloride based on nonlinear ordinary differential equations for the variation of particle concentration, total particle volume, and water‐soluble oligomeric products was developed and used to investigate which reactions influence whether or not sustained oscillations of latex properties occur at high conversion steady state. Results of the calculations are in good qualitative agreement with experimental data. Specifically, numerical analysis showed that the occurrence of sustained oscillations depends on particle coalescence as well as on the conversion dependence of both particle volume growth rate and particle coalescence rate. The model makes it possible to calculate the dynamic behavior of continuous emulsion polymerization reactors with regard to latex properties such as particle concentration, mean particle size, latex surface tension, solid content, and degree of coverage of latex surface with emulsifier from the start‐up into a high conversion steady st

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440605

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractPolyphenylenes were prepared by using biphenyl‐AlCl3‐CuCl2according to cationic oxidative polymerization. The chlorobenzene soluble fraction was doped with 10% (w/v) solution of FeCl3in acetonitrile. The alternating electrical conductivity, X‐ray diffractograms and the FTIR‐spectra of both undoped and doped polyphenylenes were measured. The proportion of the components used for the preparation of polyphenylenes strongly influences their structure as well as their conductive properties. The undoped polyphenylenes were found to be insulators, but most of them became semiconductors after doping. The increase of the alternating electrical conductivity σ' (resulting from the real part of the admittance‐vector) of the doped polyphenylenes has been explained considering the factors that influence the polyphenylenes structure: the high ratio of para/meta, the presence of both amorphous and crystalline regions, and the presence of polynuclear structures. On the other hand, the presence of aliphatic structures interrupts the conjugation system, leading to lower

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440606

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractAbsorption measurements in the wavelength range from 300 to 700 nm are used to study the orientation of nonlinear optical side groups in an acrylic polymer oriented by corona poling inside a spectrophotometer. The poling and relaxation behavior of these films are measured. The in‐situ poling process produces efficient orientational order in acrylic side‐chain polymers, which can be described by an order parame

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440607

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe miscibility behavior of ternary poly(vinyl chloride)/poly(n‐propyl methacrylate)/poly(n‐amyl methacrylate) (PVC/PPMA/PAMA) and poly(vinyl chloride)/poly(n‐butyl methacrylate)/poly(n‐amyl methacrylate) (PVC/PBMA/PAMA) blends was investigated by differential scanning calorimetry. In both systems, a binary mixture of the two polymethacrylates is totally immiscible (PPMA with PAMA, and PBMA with PAMA). For PVC/PPMA/PAMA blends containing less than 70% PVC, the immiscible phase consists of two coexisting binary PVC/PPMA and PVC/PAMA phases. For an equal amount of the two polymethacrylates in the ternary blend, the PVC/PPMA phase contains 65% of the total weight of PVC and the whole quantity of PPMA; the total amount of PAMA mixes with the remaining 35% PVC to form the PVC/PAMA phase. In contrast, the miscibility zone is predominant in the ternary PVC/PBMA/PAMA system, since blends containing 30% or more of PVC exhibit a single glass transition temperature. In the immiscibe zone, the PVC is distributed equally between PBMA and PAMA, which is in contrast to the 65%‐35% distribution found in the previous system. These results are consistent with the differences of miscibility observed in the binary PVC/polymethacrylate blends

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440608

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe β relaxation of PET is studied as a function of its crystallinity. The variation of the magnitude of tan Φ is explained taking into account the mechanical coupling of crystalline and amorphous phases by means of a series‐parallel model which is intermediate between the purely parallel and series ones. The adjustable parameter which is considered in such a model is related to the amorphous volume fraction which ensures the mechanical coupling and which appears to be proportional to the reciprocal long period. The morphology analysis shows that the variation of the crystalline fraction (between 0.32 and 0.53) during treatments carried out for one hour between 120°C and 230°C affects mainly the crystalline lamellae thickness while the long period evolves much less. Therefore, the coupling fraction remains almost unchanged. Moreover, an important feature of this work is that the β relaxation in semicrystalline polymers does not linearly evolves with the crystallinity while β relaxation does not exist in the crystalli

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440609

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440612

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY