摘要:

AbstractAdvanced solid‐state NMR techniques exploiting1H spin diffusion are described, which rely on selecting1H magnetization of one of the components on the basis of1H chemical shift or mobility differences under multiple‐pulse irradiation. To monitor the progression of1H spin diffusion, the higher resolution of13C CP MAS spectra is exploited for NMR detection. For evaluation of the data, full quasi‐analytical solutions of the diffusion equation as well as initial‐rate approximations are derived, applied and discussed. In order to obtain quantitative results, the1H spin‐diffusion constant has to be determined. To this end, the domain sizes in poly(styrene)‐poly(methyl methacrylate) systems including symmetrical diblock copolymers have been measured. The comparison of the NMR results with SAXS and TEM data yields the spin‐diffusion coefficient for PS and PMMA. The resulting value ofD=0.8 nm2/ms is expected to be typical for rigid organic systems. The domain sizes investigated range from approximately 1 nm

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440101

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dielectric constant and dielectric loss values have been determined in the 103‐106Hz frequency range for amorphous random copolymers of poly(ethylene terephthalate) (PET) and poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN). The dielectric behaviour has been interpreted in terms of the Havriliak‐Negami formulation. On this basis the variation of the dielectric properties with temperature has been qualitatively related mainly to two processes: The α process which is associated to the glass transition of the polymer and depends on the molar ratio of PET and PEN. The β process which is assigned to a local motion of the ‐COO groups attached to the aromatic rings. The existence of a β*process in between the α and the β processes has been observed in PEN at low frequencies. The relaxation time spectrum has been discussed in terms of molecular structure alterations. Finally, the temperature variation of the relaxation time is analyzed in the light of vario

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440102

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe cold crystallization of pure and filled poly(ethylene terephthalate) (PETP) after quenching from the melt has been investigated by dielectric measurements in two different modes: The first one using constant heating‐rate (in the temperature range from 320 to 480 K) and the second one under isothermal conditions (at 378 K). The complex dielectric constant (ϵ′, tan δ) is influenced by crystallization. Two α‐relaxation regions are identified: The αa‐relaxation region from the pure amorphous phase and the α′‐relaxation region from the spherulitic phase. The investigations on the filled systems (PETP + 10% aramid puple, PETP + 30% short glass fibres) prove that an influence of the fillers on the time delay and rate of crystallization and on the geometry of the growing sp

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440103

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractA method is suggested which allows the determination of a complex of relaxation characteristics describing the process of glass transition of amorphous polymers from the results of calorimetric measurements in one single experiment.

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440104

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rotational dynamic behaviour of a polymer of the hairy rod type has been investigated in the solid state. Octa‐(alkoxy)‐phthalocyaninatopolysiloxanes have been synthesized selectively deuterated at the aromatic core positions for this study. They form a hexagonal columnar structure without any phase change in the temperature range from 170 to 470 K. Thermally activated uniaxial rotation involving the phthalocyanato moiety around the long axis of the polymer is detected by solid‐echo2H‐NMR spectroscopy. Two‐dimensional NMR spectroscopy shows that the motional process involves 90° jumps with considerable broadening of the reorientation potential, reflecting the four‐fold symmetry of the repeat unit. This indicates that the siliconphthalocyanine moieties can rotate around their covalent Si‐O bond within a single macromolecule, rather than the molecules as a whole around their

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440105

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractMany polymeric glasses must be orientationally ordered for the materials to exhibit useful characteristics. The objective of this work was to understand the dynamics of the orientation and relaxation processes and to relate these behaviours to the structural characteristics of the polymeric material. In this study we considered materials suitable for nonlinear optical applications. In particular, thin polymer films, either doped with nonlinear optical chromophores or films with the chromophores covalently bonded to side groups were studied. Orientation of these chromophores was achieved by the application of an external electric field. Ellipsometry was used to measure the birefringence resulting from chromophore orientation and the steady state and transient behaviours were studied. Materials characteristics studied included method of chromophore incorporation, chromophore concentration, spacer length, and molecular weight. Our results showed that the polymer structure, specifically the tacticity, was the dominant factor determining the steady state and transient behaviours. The relationship between monomer and polymer structure and the resulting effect on the orientation dynamics is discussed. Qualitative agreement with theoretical predictions was obtained for the simpler guest/host system, but the model was shown to be inadequate to explain the behaviours of the more complex systems studied. The results reported here have provided valuable insight into the molecular processes that occur during the chromophore orientation and relaxation, and the effects of structural characteristics of the polymers on these mechanisms.

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440106

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe synthesis of a Diels‐Alder ladder polymer with imino and ether bridges is described. The structure proof is based upon a comparison of its high resolution13C‐NMR spectrum with those of model compounds. The molecular weights can reach values as high as M̄n= 52000 which are the highest ones observed so far for a double stranded polymer. The X‐ray structure of model compound8is also pre

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440107

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440108

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY

ISSN:0323-7648    

DOI:10.1002/actp.1993.010440110

出版商:Akademie Verlag GmbH    

年代:1993

数据来源: WILEY