摘要:

AbstractA new Monte Carlo approach for the kinetics of emulsion polymerization is discussed. The diameters of polymer particles produced in emulsion polymerizations are in the submicrometer range; therefore, it is straightforward to simulate the formation processes of all polymer molecules in each polymer particle by application of the Monte Carlo method with a well‐designed algorithm. In the Monte Carlo technique, virtually any kinetic event, such as the desorption of oligomeric radicals, chain‐length‐dependent reaction kinetics, branching and crosslinking reactions, can be accounted for. In principle, neither idealizations nor approximations, which are usually required in the analytical approaches, are not necessary. As a consequence one can observe the structure of each polymer molecule directly; therefore, very detailed information can be obtained easily, including the full distributions of the dead and live polymer molecular weights, and the spatial distribution of the branched and crosslinked polymer chains in the case of nonlinear polymerizations. Monte Carlo simulations promise to provide greater insight into the complex molecular processes which occur during emulsion polymeriza

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460301

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractSurfaces have a profound effect on the structure and related properties of multiphase polymeric materials, such as polymer mixtures and block copolymer mesophases. In particular, phase transitions in the bulk (unmixing, microphase separation, etc.) may be complemented by surface‐induced transitions (formation of wetting layers, surface‐directed spinodal decomposition, surface‐induced ordering). This review gives a brief introduction to the phenomenological theories of such phenomena, emphasizing the simplest approach based on Flory—Huggins—de Gennes free energy functionals and associated Monte Carlo simulations. More sophisticated theories and recent experiments are mentione

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460302

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractNon‐aqueous dispersions of colloidal PMMA microparticles with average sizes ranging from 70 to 330 nm were prepared by living polymerization of methylmethacrylate (MMA) and methylmethacrylate/ethyleneglycoldimethacrylate (EDMA) inn‐heptane diluent using 2‐methyl‐1‐methoxy‐1‐trimethylsilyloxy‐prop‐1‐ene (MTS) as initiator in the presence of tetrabutylammonium fluoride (TBAF) or tetrabutylammonium cyanide (TBAC) as catalyst, and polystyrene‐block‐poly‐(ethene‐alt‐propene) (SEP) as dispersing agent. The influence of process parameters such as concentrations of MMA, EDMA crosslinking agent, TBAF, and SEP on conversion, molecular weight, particle size, and molecular weight and particle size distributions has been investigated. In contrast to GTP in solution, group transfer dispersion polymerization (GTDP) was markedly slower and accompanied by agglomeration and drastic broadening of both molecular weight and particle size distributions with increasing MMA conversion. In a new GTDP process colloidal PMMA microparticles, obtained by free radical dispersion polymerization, were added as seeds, thus affording much narrower particle size distrib

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460303

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of comb‐like ionenes with aliphatic side chains of different length and organic main chain spacer groups of different size have been synthesized by the step‐growth polymerization of long aliphatic chain‐substituted diamines with α,ω‐dibromoalkanes. Highly ordered films of layered structure have been obtained by solution casting. The long side chains crystallize with an interdigitating hexagonal packing perpendicular to the film plane. The perfection of the side chain packing is related to the size of the spacer group in the main chain as well as to the valence of the counterions, but also depends on the thermal history of the samples. It is in all cases comparable to the quality of aliphatic chain packing in LB multilayers of surfactants. The comb‐like ionenes exhibit liquid‐crystalline textures above their side chain melti

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460304

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractChemical as well as structural modifications of highly branched polycyanurates can be achieved by using the reaction of dicyanates with monofunctional phenols. The key products of this reaction are iminocarbonic esters formed by addition of cyanato and phenolic groups. Two mechanisms are discussed for the second reaction step: an addition of two cyanato groups and an iminocarbonic ester (Route A) and a stepwise addition of iminocarbonic esters (Route B). The crucial difference between the two reactions is the number of abstracted phenolic groups per formation of one triazine ring: one for Route A and three for Route B. The effects of these reaction mechanisms on the gelation behavior and network buildup are studied theoretically with the help of cascade theory as well as experimentally by the reaction of dicyanate of bisphenol A with five different monophenols. The results clearly show that only with a model which is based on Route B can both the critical conversions at the gelation threshold and the gel fractions be modeled quantitatively. Furthermore, phenols with low pKavalues were found to have an increased tendency of incorporation into the network.

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460305

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractPoly(vinylbenzyltrialkylammonium) salts with alkyl groups having 1 to 8 carbon atoms on the ammonium nitrogen atom were synthesized. The polymers are soluble in water but have different solubility when low molecular salts such as sodium chloride are added. The reduced solution viscosity in water showed typical polyelectrolyte behavior. Larger alkyl groups make the polymers much less soluble and even insoluble in water. The polymers are still soluble in methanol. To study the counterion‐polyion interactions in semidilute and dilute solution the electrical conductivity and counterion activity were investigated in a range of low polyelectrolyte concentration (10−6

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460306

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractThermal field‐flow fractionation (TFFF) coupled with multi‐angle laser light scattering (MALLS) is a promising quantitative method for determining the molecular‐weight distribution (MWD) of complex polymers and their aggregates. This paper describes the application of TFFF‐MALLS to linear polystyrene as well as highly cross‐linked microgel and sulfonated polystyrene samples. In addition, the chromatographic characterization of block copolymer micelles with different core chemistry is performed. The dependence of retention volume on the mass diffusion coefficientDand the thermal diffusion coefficientDTwas confirmed. It is shown thatDT, as predicted by theory, depends only on the solvent, being independent of both molecular weight and

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460307

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractX‐ray methods have been used to investigate the structure of fibers of aromatic copolyimides prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA),o‐tolidine (OTOL) andp‐phenylene diamine (PPD). We have shown previously that the non‐periodic layer lines in the X‐ray fiber diagrams of these copolymers are indicative of a random comonomer sequence. In the present paper, we analyze the shifts in the layer line positions that occur with increasing draw ratio. These changes are to be understood primarily in terms of increases in the correlation lengths for the stiff chain conformation. At high draw ratios there is also evidence for the development of a more extended chain conformation, probably due to torsional variation changes in the torsion angles. It is shown that the data are sufficiently sensitive to allow quantitative analysis of these separate effects, and their dependence on

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460308

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY

摘要:

AbstractBiaxial extensional flow behavior of monodisperse polystyrene melts has been investigated by using a lubricated squeezing flow method at constant strain rates. Master curves for the biaxial stress growth coefficient η B+are obtained by applying the time‐temperature superposition principle. The coefficient η B+deviates from a linear viscoelastic curve at very small strain such as 0.1, and then approaches a quasi steady state. The quasi‐steady‐state viscosity ηB,qsdecreases with the strain rate ηB. At very small strain rates, the coefficient η B+increases again after the quasi steady state and becomes much larger than the linear viscoelastic curve. The strain rate dependence curves of ηB,qsobtained for different molecular weight samples can be superposed to give a super master curve using the weight‐average relaxation time η0as a reducing parameter. It is found that the biaxial viscosity ηB,qsbegins to decrease at much smaller reduced strain rate (ϵBτ0=0.01) compared with the shear viscosity, which begins to decrease at reduced s

ISSN:0323-7648    

DOI:10.1002/actp.1995.010460309

出版商:Akademie Verlag GmbH    

年代:1995

数据来源: WILEY