ISSN:0323-7648    

DOI:10.1002/actp.1996.010470401

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractCombined LC‐polymers possess the structural properties of both LC main chain and LC side chain polymers. Beneath this structural speciality, their broad LC‐phases and their polymorphism (different smectic phases and one nematic phase as a function of temperature) make them interesting. Crucial to an understanding of them is the fact that main chain and side chain mesogens orient parallel to each other and interact cooperatively to form the LC‐phase. Due to this synergism the temperature range of the LC‐phase is much broader than that of the corresponding LC main chain and LC side chain polymers. This interplay of main chain and side chain mesogens allows structures to be designed with preferably nematic or smectic phases. Whenever both types of mesogens can arrange in the same height, preferably smectic phases are formed. If this is not possible, the nematic phase dominates.The incorporation of chiral groups allows cholesteric and chiral smectic C* phases to be prepared. For the latter, ferroelectric modes have been observed dielectrically. By crosslinking of combined LC‐polymers, combined LC‐elastomers can be prepared, in which the LC‐phases are nearly unchanged. These elastomers allow a mechanical orientation of the LC‐phases and, in particular, an untwisting of the helical superstructure of cholesteric and chiral smectic C* phases. In the latter case ferroelectric monodomains are obtained. The piezoeffect — to be expected — for LC‐elastomers with chiral smectic C* phases was first demonstrated for t

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470402

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractRelaxation in glass‐forming liquids as measured by dielectric, by light‐ and by neutron‐scattering experiments can be described with the aid of the conformon model. Conformons behave like bosons which display a photon statistics. Conformons are excited and can also be annihilated. They show a universal reduced energy density distribution, revealing their thermodynamic roots. Each relaxation mode is assumed to be directly connected with a distinct conformon. The coupling is described by an empirical power law. The actual relaxation time distribution is then obtained by scaling each relaxation mode with the same kinetic factor. The relaxation behavior of liquids is therefore self‐similar, characterized by individual factors such as the relaxation power, the coupling parameter and the temperature of pressure dependence of the kinetic factor (“shift

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470403

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe structure of EPDM grafted onto polyamide 66 has been analyzed with high resolution solid state13C NMR and IR spectroscopy. Details about the EPDM rubber include the amount of rubber incorporated in this blend, the sequence analysis of the EPDM rubber and an estimate of the type and amount of termonomer used (in this case onlytrans1.4‐hexadiene). The sample contains 20% EPDM rubber, 6% polyamide 66 grafted onto EPDM rubber and 74% neat polyamide 66. Some evidence has been obtained via IR spectroscopy for the presence of cyclic imide groups, derived from grafted maleic anhydride groupings. No evidence for the use of a coupling agent could be obtained from either the13C SPE‐MAS spectra of the interphase enhanced polyamide 66 or from the isolated rubber ph

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470404

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe interfacial reaction of immiscible polymeric systems containing oxazoline and carboxylic acid groups, respectively, has been studied by FTIR spectroscopy and FTIR microscopy. A poly(butadiene‐co‐acrylonitrile) rubber, where the nitrile groups are partially converted to oxazoline groups, is thermally annealed in a two‐layer specimen with poly(ethene‐co‐methacrylic acid). The formation of the esteramide in the interface is measured quantitatively by FTIR difference spectroscopy. Evaluating the formation of the amide I band leads to reaction rate constants ranging from 0.0125 to 0.022 s−1in the temperature range from 170 to 230°C. It can be shown by FTIR microscopy that this system is immiscible because there is no interdiffusion across the interface. Also the formation of an esteramide in the interfacial reaction of the system poly(ethene‐co‐methacrylic acid)/bis(1,3‐oxazoline‐2‐yl)‐terminated poly(dimethylsiloxane) is monitored qualitativ

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470405

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractDespite the fact that graft copolymerization is a favored reaction for cellulose xanthate, a significant part of the cellulose and lignin component is subject to undesired degradation reaction. Exposure of thermomechanical pulp to ozone followed by grafting by the xanthation method further degrades the cellulose and decreases graft yield. Graft yield can be improved by introducing chemical crosslinks to the cellulose backbone before or after ozone exposure. It is suggested that crosslinking with formaldeyde recombines some of the degraded chains of hydroxylated cellulose after ozone exposure and also helps to prevent degradation of cellulose chain during grafting of cellulose xanthate. Sizing of pulp with dispersed and saponified rosin—Al complexes slows down the grafting reaction and decreases the polymer add‐on percentage significantly. An exposure to ozone before or after the sizing process improves grafting efficiency and graft yield and the copolymer formation is the preferred reaction. The surface morphology of sized pulp has practically no influence on the grafting parameters. Unlike the sizing mechanism, the chemical nature of the sizing agent influences the grafting process. Sizing of pulp with an alkyl ketene dimer significantly decreased the copolymer formation by preventing reactive cellulose hydroxyl group from react

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470406

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractAn experimental investigation on the streaming potential and sorption ofN‐cetylpyridinium chloride on Leacril fibers has been carried out. The results reveal that the uptake ofN‐cetylpyridinium chloride on Leacril fibers takes place by means of electrostatic attraction between the cation of the surface‐active agent used and both the sulphonate and the sulfate end‐groups of the Leacril.Given the hydrophobic character of Leacril and the amphiphilic nature of theN‐cetylpyridinium chloride molecules, hydrophobic attractions between the fiber and the hydrophobic part of the surfactant might account for the interaction, explaining the sorption ofN‐cetylpyridinium chloride even when it is hindered by electrostatic repulsion.The electrical characterization of Leacril fibers has been carried out and the methods employed for the determination of zeta potentials of Leacril fibers are discussed, on the basis of streaming potential technique. In our case for this hydrophobic fiber, the linear model of Goring and Mason of a bundle of capillaries gives the most precise values of zeta potential. Also discussed is the behavior of the surface conductance of the system in the above process

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470407

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY

摘要:

AbstractThe physical behavior ofpolyamides of type N 6 with different contents ofN‐trialkylsilylcaprolactam (SL) has been investigated by mechanical spectrometry, differential scanning calorimetry and wide‐angle X‐ray scattering. The copolymers have been obtained by an anionic polymerization in bulk under isothermal conditions. The presence of a bulky substituent at the nitrogen atom of the amide group plays an essential role for the number of the hydrogen bonds as well as for the formation of physical and chemical bonds. This bonds results in significant changes of the physical behavior of the modified polyamides. These changes have been st

ISSN:0323-7648    

DOI:10.1002/actp.1996.010470408

出版商:Akademie Verlag GmbH    

年代:1996

数据来源: WILEY