摘要:

AbstractThe commercial applications of anionic polymerization have become wide‐spread with regard to the preparation of linear and star shaped homopolymers and block copolymers (Diene‐35TM, KratonTM, VectorTM, SolpreneTM, K ResinTMand ShellVisTM). Furthermore, randomized styrene/butadiene linear copolymers (SolpreneTM) and low molecular weight, 10K or less, polybutadienes (LithenesTM) of various microstructures are commercially available. Recently Liquid KratonsTMwith OH functional units in place on one or both chain ends have become items of commerce. The lithium based systems yield materials of uniform composition and molecular weights with virtually monodisperse molecular weight distributions. Both molecular weightandcomposition are tunable via the simple expedient of manipulating the monomer/initiator ratio. Although the synthetic aspects of these anionic systems have been well‐mastered and exploited over the years the mechanistic features have remained controversial; issues which revolve around active center aggregation behaviorandthe reactivity (or its absence) of these self‐assembled anionic lipophobic head‐groups. Thus a study of these systems was undertaken using modern scattering techniques and data analysis procedures.Small angle neutron scattering (SANS) in combination with dynamic and static light scattering,DLSandSLS, has been used to evaluate the association behavior of the styryl‐ and dienyllithium head‐groups in benzene and cyclohexane solutions. Both types of lipophobic active centers were found to aggregate as dimers which in turn can self‐assemble to yield large‐scale wormlike micelles (prolate ellipsoids). These systems thus emulate the behavior of diblock copolymers and surfactants in their capacity to form flexible cylindrical micelles. It was also found for all head‐groups that the combination of long chain lengths and high polymer concentrations favored the presence of the dimer structure. This commonality of aggregation state is in consonance with re

ISSN:1022-1360    

DOI:10.1002/masy.19971210103

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThis paper describes research activities towards the development of polymer materials and devices for optoelectronics. Electroluminescent devices, lasers and photovoltaic devices from polymers or oligomers are discussed.

ISSN:1022-1360    

DOI:10.1002/masy.19971210104

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA new class of segmented non‐conjugated dopable polymers, built up from short conjugated blocks connected with flexible chains (spacers), has been proposed. After the redox reaction of doping these polymers exhibit properties similar to those of the fully conjugated polymers and increase considerably their electrical conductivity. A solid state polymer effect has been observed. It has been found that the conjugated building units (biphenyl, diphenyl ether and 1,3,4‐oxadiazole) do not interact with the dopant when included in a low molecular weight substance. When these units are incorporated in a polymer chain they change their reactivity and the polymer can be doped. The doping process takes place only when the polymer is in the solid state and the nature of this phase is of considerable importance. The phenomenon observed, i.e. doping of non‐conjugated polymers with segmented structure could be explained with a favourable arrangement of the conjugated blocks in the solid phase, leading to enhanced π‐π ‐ interaction (equivalent to extended conjugation). By the collective interaction of several conjugated blocks with the dopant the polymer is partially oxidized and charge carriers are formed. The result is enhanced electrical c

ISSN:1022-1360    

DOI:10.1002/masy.19971210105

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractRecent developments of new synthetic methods are stimulating the design of new polymers. Modern generations of highly active and selective transition metal catalysts give excellent control on molecular weight, regio‐ and stereoregularities, long‐ and short‐chain‐branching, polymer crystallization, and morphology of olefin, diene, cyclolefin, and styrene polymers. Ethene is copolymerized with polar comonomers such as carbon monoxide and acrylates in new low pressure processes. Catalytic coupling reactions of aromatic halogen compounds and bisphenols afford rigid polyarylenes. „Living” radical polymerization (“TEMPO” and “ATRP”) produce a wide range of telechelics, block copolymers and cascade macromolecules. In reactive processing oxazoline‐mediated coupling reactions are the key to melt diversification of well‐known polymers. Supramolecular concepts are being applied to tailor hybrid polymers and nanocomposites. Precision in polymer synthesis is the key to new materials with

ISSN:1022-1360    

DOI:10.1002/masy.19971210106

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractAmphiphilic block copolymers made by a variety of techniques form in selective solvents micelles of well defined size and shape. We report on the underlying principles of micelle formation, as revealed by light scattering experiments.In addition, we will delineate some applications of these block‐copolymer micelles where we focus on two technological relevant cases, namely the stabilization of polymer particles in low cohesion energy environments as well as the stabilization of metal and semiconductor colloids inside specially functionalized block copolymer micelles. In the latter case, stable hybride materials are obtained where the properties both of the polymer and the inorganic are added in a synergistic way. First data on special catalytic properties, the generation of superparamagnetic materials, and special colloids with optical functionality are presente

ISSN:1022-1360    

DOI:10.1002/masy.19971210107

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractRegular star polymers with functionality f = 64 and f = 128 have such high segment density that they resemble “hard sphere” objects in dilute solution. In semi‐dilute solution they form a macrocrystalline ordered phase with spacings of the order of 100 to 500Å. They are physical gels. Their melt properties are characterized by a long term relaxation process not found in stars with fewe

ISSN:1022-1360    

DOI:10.1002/masy.19971210108

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractRecently a few papers have been devoted to the scattering by polymer solutions and blends(1,2)assuming that the systems under investigation are compressible, contrarily to what is usually done. This is motivated by the fact that if one uses the theory of incompressible mixtures in scattering experiments, one obtains values of the Flory(3)χ parameter which are inconsistent with the values obtained by other techniques. In this paper we would like to show that, contrarily to what has been said, the effect of compressibility can be easily evaluated; it is very small and already corrected in the classical treatment of the data used in light or neutron scattering experiments

ISSN:1022-1360    

DOI:10.1002/masy.19971210109

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractMonte Carlo calculations have been performed for different types of chain molecules whose units interact through Lennard‐Jones potentials. From the averaged Mayer function, we have evaluated the intermolecular two‐body cluster integral, obtaining results for second virial coefficients. We have investigated the following points: a) the site modelization of alkanes by comparison of our results with gas phase data of different linear and branched alkanes and their mixtures. b) the prediction of interpenetration factors for flexible linear and star polymer chains in a good solvent (or excluded volume conditions). c) the determination of the theta point for a model of flexible polymer chains and the comparison of data for finite chains with theoretical predicti

ISSN:1022-1360    

DOI:10.1002/masy.19971210110

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractWe present results on the glass transition in polymer melts using Monte Carlo simulations of the bond fluctuation lattice model. There are two questions we address in this work. What is the temperature dependence of the entropy density in such a model polymer melt and how well is it described by theories like the Gibbs‐DiMarzio theory of the glass transition? And to what degree is one able to map the Hamiltonian of such an abstract lattice model onto a specific polymer material and use it to model the large scale and long time properties of a realistic polymer mel

ISSN:1022-1360    

DOI:10.1002/masy.19971210111

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractMonodisperse block copolymer systems in the homogeneous melt exhibit small angle X‐ray scattering peaks at finite nonzero angle due to characteristic correlation hole concentration fluctuations. Here we will address these fluctuations for comblike copolymer systems obtained by strong association between polymers and end‐functionalized oligomers. Experimentally, the dominant fluctuations have been found by us to vary between conventional long wave length fluctuations (for weak hydrogen bonding) as for simple mixtures, and finite wave length fluctuations (strong hydrogen bonding), characteristic for block copolymer systems. Monte Carlo computer simulations show that both regimes will occur in one and the same system depending on the temperature. The transition between both regimes is directly related to the fraction of free oligomers, which depends on the temperature and the interactions. The structure factors are analysed in terms of the Random Phase Approximation applied to a mixture of free oligomers and comb copolymers, using a uniform distribution of teeth along the polymer chains and a binomial distribution in the number of polymers with a given number of teeth, confirmed numerically, as input. The agreement is excellent both at high and low temperatu

ISSN:1022-1360    

DOI:10.1002/masy.19971210112

出版商:Hüthig&Wepf Verlag    

年代:1997

数据来源: WILEY