ISSN:0323-7648    

DOI:10.1002/actp.1995.010460101

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of molecular structure on the glass transition temperature of end‐linked networks has been studied by examining a series of stoichiometrically imbalanced poly(propylene glycol)‐Desmodur RF (PPG‐DRF) and poly(isoprene)tristar‐hexamethylene diisocyanate (PIP‐HDI) networks. A range of different molecular weights of each prepolymer was used. The PPG‐DRF system shows a strong influence of the copolymer contribution onTg. The modified copolymer approach (MCA) gives good theoretical correspondence with the experiments. This approach successfully predicts theTgbehavior of other cross‐linked systems with relatively high cross‐link densities. Other existing universal theories have been shown not to describe theTgwell for the PPG‐DRF system. Correction of the MCA is possible to account for a small plasticizing effect observed for highly stoichiometrically imbalanced samples. The PIB‐HDI system shows no strong contribution of the copolymer effect by virtue of its structure. The difference in cross‐link density can explain the changes inTg. The MCA also yields reasonable results. For both systems it is necessary to consider all cross‐linkers for the purpose of determining

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460102

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractRedoxactive liquid crystalline (LC) side group polymers were prepared by copolymerization of liquid crystalline acrylates and ferrocene‐containing acrylates. The corresponding liquid crystalline ionomers were synthesized by a reversible redox reaction. The incorporation of tetra‐alkylated ferrocene derivatives leads to LC polymers with reduced redox potential. These polymers can be oxidized under mild conditions to the corresponding ionomers, which are much more stable in solution than LC ionomers containing monoalkylated ferrocenium ions. Dynamic mechanical measurements and small angle X‐ray scattering (SAXS) perfomed on LC ionomers prove the existence of ionic superstructures (clusters) which are typical for ionomers and a gelation of the LC ionomers.In biphasic polymer blends consisting of liquid crystalline and amorphous ionomers (partially sulfonated polystyrene) we investigated the influence of the concentration of ionic groups in the LC component on the size of phase separated regions. It was found that blends without ionic interactions are macroscopically phase separated. In blends consisting of two ionic components, microphase separated regions of approximately 100 nm were found. The size of phase separated regions decreases continuously with increasing concentration of ionic groups in the LC component and can therefore be adjusted by a reversible redox reaction.The incorporation of ionic groups in LC polymers leads on a macroscopic scale to a combination of the liquid crystalline properties of the LC component with the elastic behavior of the amorphous ionomer. Therefore microphase separated ionomer blends show homogeneous liquid crystalline textures and behave mechanically like reversible crosslinked ion

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460103

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractMicrogels with cross‐link densities close to the critical value of gel transition are synthesized via polymerization in microemulsion stabilized with a polymeric surfactant. The resulting structures are characterized by static and dynamic light scattering, viscometry, small angle neutron scattering and dynamic‐mechanical shear experiments.The proximity of the gel point influences the different properties in a different way. Global properties such as particle shape are closely connected with the gel point whereas the local structure and relaxation show critical behavior even quite far from the gel po

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460104

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractEthynylphenyl‐methyldichlorosilane (EPDMS) has been prepared as a new monomer for the synthesis of polysilylenes with triple bonds attached to the catenated Si chain. A series of copolymers with methylphenyldichlorosilane (MPDS) as well as the homopolymer, PEPMS, have been synthesized. The content of ethynylphenyl substituents was quantitatively analyzed by FTIR spectroscopy. The optical properties of the new polymers were studied with respect to potential π−σ interaction. No significant bathochromic shift of the UV‐absorption maximum could be detected. Unexpectedly, increasing content of incorporated EPMS units led to a decrease of the (σ−σ*) absorption. The ethynylphenyl‐substituted polysilylenes exhibited strong, temperature‐dependent fluorescence in solution as w

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460105

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractAcrylic acid (AA)/glycidyl methacrylate (GMA) mixtures were bulk polymerized in the presence of cellulose in order to prepare cellulose/GMA/AA cation exchange composites using sodium persulfate as an oxidant, alone or in conjunction with sodium sulfite, sodium thiosulfate, sodium metabisulfite or glucose as a reductant. The presence of the reductant has the effect of shortening the polymerization time, expressed as the solidification time (ST), with little improvement in the polymerization extent, expressed as percentage total conversion (%TC), as well as the percentage yield and the carboxyl content of the crude and the purified composites. Sodium sulfite was selected as the the reductant that can achieve best polymerization. The effect of the concentrations of “sodium persulfate/sodium sulfite, redox system, acrylic acid and glycidyl methacrylate” and temperature on the formation of the composite were investigated. Four cation exchange composites were prepared and characterized by investigating their potentiometric titration, water solubility and swellability as well as durabil

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460106

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractElectrical current noise and electrical resistivity as well as viscosity were measured in aqueous solutions of gelatin containing KCl during the sol—gel transition. While the viscosity rises toward infinity at the transition, the current noise power and the resistivity are continuous functions of the time and are therefore potentially useful probes for characterizing polymers undergoing gelatio

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460107

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractX‐ray diffraction measurements on thin films of poly(hexyl‐pentylsilane) cast on silicon substrates are presented. The polymer chains pack in a hexagonal lattice which is oriented such that the chains lie parallel to the surface. In addition, a remarkable degree of orientational order was found with the planes containing the neighbor molecules lying in the surface plane. Parallel to the film surface, the average crystallite size is 600 Å, while perpendicular to the surface, there is nearly perfect interchain stacking of the polymers throughout the thickness of the

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460108

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractPermittivity ϵ′ and dielectric loss ϵ″ of novolac have been determined in the temperature interval from —150 to 150°C and in the frequency interval from 102.5to 106Hz. Novolac exhibits a main and a secondary relaxation process. For the main relaxation a master curve of ϵ″ was calculated, the shape of which was described by the Havriliak—Negami function (HN). The parameters of the HN fit were interpreted by a model that relates the values to the polymer structure. Furthermore, the temperature dependence of the dielectric relaxation times was analyzed by a WLF approach for the main relaxation and an Arrhenius approach for the secondary relaxation. The dielectric relaxation times of the main relaxation were correlated with the electrical conductivity and the m

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460109

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA novel class of liquid rubber comprises bis(4‐hydroxybenzoate)‐terminated poly(tetrahydrofuran), which reacts with bisphenol A diglycidyl ether to form segmented liquid rubbers with poly(tetrahydrofuran) and poly(hydroxyether) segments. In anhydride‐cured epoxy resins such segmented liquid rubbers afford improved toughness. Diol‐ and bis(hydroxybenzoate)‐terminated poly(tetrahydrofuran)‐based liquid rubbers are compared. It is possible to control the polymer morphology by the variation of the molecular architecture of segmented poly(tetrahydrofuran)‐based liquid rubbers. The average size of the dispersed rubber phases depends on the molecular weight of the segmented liquid rubbers and correlates with impact strength

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460110

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY