摘要:

AbstractA review of recent developments is given, with a focus on those which promise the greatest future advancements of the science and technology of polymer colloids. Only those which involve Radical Copolymers are discussed. The topics are (1) Particle Formation, (2) Phase‐separated Latex Particles, (3) New Techniques of Characterization and Analysis, and (4) Surface Chemistr

ISSN:1022-1360    

DOI:10.1002/masy.19950920103

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA simple means is deduced for determining conditions for secondary particle formation in emulsion polymerization systems in systems where the amount of added surfactant is below the cmc. A new radical formed from initiator in the aqueous phase will undergo some polymerization with aqueous‐phase monomer, but must have three possible eventual fates: aqueous‐phase termination, entry into a preexisting particle, or creation of a new particle. The means for determining the onset and extent of secondary nucleation is to modify HUFT theory to take into account a successful model for entry [Macromolecules, 24, 1629 (1991)] which states that entry occurs if and only if the aqueous‐phase radical has achieved a critical degree of polymerization z. Particle formation below the cmc is by homogeneous/coagulative nucleation which (if coagulation is ignored) gives an upper bound to the rate of formation of precursor particles; these are of a degree of polymerizationJcrit>z. The resulting equations are readily solved, and require only a knowledge of the aqueous‐phase propagation and termination rate coefficients (the latter is very high:ca.109dm3mol−1s−1for termination between the very small radicals), z andjcrit. Easily applied means are given for estimating all these quantities. The treatment gives good accord with experimentally observed conditions for the onset of secondary nucleation in low‐surfactant systems (including takingin situmicellization

ISSN:1022-1360    

DOI:10.1002/masy.19950920104

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractPulsed laser polymerizations of styrene were performed in microemulsion droplets and in latex particles. From the molecular weight distribution of the resultant polymer either the propagation rate coefficient in the droplets or the monomer concentration in the particles could be determined. Furthermore for microemulsion droplets with a low initiator concentration the rate coefficient for transfer to monomer could be determined. Because in very small particles the termination rate can be very high, instantaneous termination may occur, leading to a shift of the low molecular weight inflection point as the best measure of the propagation rate coefficient to the maximum in the molecular weight distribution.forming pulsed laser polymerization experiments directly in emulsion systems gives specific information on the special features associated with doing polymerizations in heterogeneous and compartmentalized systems.

ISSN:1022-1360    

DOI:10.1002/masy.19950920105

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIndependent, quantitative models for free energy associated with crosslinked seed latices, and monomer and surfactant at the polymer/water interface have been integrated into a predictive model for latex particle morphology. It has been found that very low levels of crosslinking are predicted to influence the particle morphology in a dramatic fashion. Free energy calculation also highlight the often critical role played by surfactant. Highly active surfactants tend to equalize the two polymer/water interfacial tensions and allow the polymer/water interfacial energy to significantly influence the particle morphology.

ISSN:1022-1360    

DOI:10.1002/masy.19950920106

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis review focusses on processes in which emulsion polymerizations are carried out in stages so that previously formed particles are either overcoated in subsequent polymerization stages or engulf the second and later stage polymers. These products are often called “core‐shell” particles. Basically, the most stable state of the final system is the one with the lowest net interfacial energy. In the case of a two‐stage emulsion polymerization there can be three interfacial tensions to consider. Several mutually consistent, effective thermodynamic treatments have been published. At present, they serve primarily to predict when the morphology of multi‐stage polymerization products may not be a simple reflection of the synthesis sequences. It is possible, and frequently desirable, however to produce particle structures that appear at first glance to be thermodynamically forbidden. This is achieved either by changing the surface characteristics of a polymer from those of the bulk material or by employing kinetic factors to anchor energetically unprofitable morphologies. This paper summarizes methods of both types that have been reported to control the texture of structured latex particles in order to produce designed mor

ISSN:1022-1360    

DOI:10.1002/masy.19950920107

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThe rationale for rubber‐toughening of brittle plastics is presented together with a discussion of the advantages of using pre‐formed toughening particles prepared by emulsion polymerisation. Rubber‐toughened acrylic and epoxy resin materials are used to illustrate the preparation and use of pre‐formed emulsion polymer particles for toughening. For both types of material, tensile properties are controlled by the volume fraction of rubbery polymer, essentially independent of the size and morphology of the toughening particles. However, under the additional constraint ahead of propagating cracks, toughening particle size and morphology are shown to be important, and to have different effects in the two types of material due to inherent differences in the mechanism of yielding of the matrix

ISSN:1022-1360    

DOI:10.1002/masy.19950920108

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThree kinds of micron‐sized monodispersed polystyrene (PS)/ poly(styrene ‐ divinylbenzene) composite particles were produced by two kinds of seeded copolymerizations of styrene (S) and divinylbenzene (DVB) (PS seed/ (S+DVB)=2/1, wt. ratio; S/DVB=1/1, molar ratio) in the presence of about 2 μm‐sized monodispersed PS particles, and their morphologies were examined. One was produced by a seeded dispersion copolymerization where almost monomers and initiators exist in an ethanol/water (12.6/4.0, w/w) medium. The others two were produced by seeded copolymerizations with the dynamic swelling method where almost monomers exist in the monomer‐swollen particles using 2, 2'‐azobisisobutyronitrile in monomer‐swollen PS seed particles or using 4, 4'‐azobis (4‐cyanopentanoic acid) in an ethanol/water (7/43, w/w) medium. In the former polymerization, the produced composite particles had a high dense crosslinked shell, whereas in the latter two polymerizations, they did the comparatively homogeneous crossl

ISSN:1022-1360    

DOI:10.1002/masy.19950920109

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA description is given of the application of small angle neutron scattering to examine structural aspects of copolymer particles. Analysis of recent data obtained using a “single shot” polymerisation to prepare polystyrene‐poly (methyl methacrylate) particles shows that these have a core‐shell mor

ISSN:1022-1360    

DOI:10.1002/masy.19950920110

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractCore‐shell latexes based on poly (butyl acrylate) and poly(methyl methacrylate) were synthesized with varying shell content at high and low temperature. Electron microscopy combined with advanced solid‐state NMR techniques have been used to investigate the entire structure and the interphase morphology in these core‐shell particles depending on the reaction conditions. Distinct differences of the interphase morphology were found for particles synthesized at high and low temper

ISSN:1022-1360    

DOI:10.1002/masy.19950920111

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper is a brief survey showing the versatility and unicity of NMR spectroscopy for characterizing the macromolecular architecture in copolymers originated from an emulsion process. Three cases are more particularly described using various NMR techniques i) to carry out high resolution13C NMR in order to investigate the microstructure (mainly the monomer sequence distribution as a function of process variables, ii) to perform direct analysis of latex particles by13C NMR so as to get insight on the surface morphology of functional particles, iii) to deal with solid‐state NMR on as‐dried particles (or films) in order to obtain quantitative information on the internal morphology of composite late

ISSN:1022-1360    

DOI:10.1002/masy.19950920112

出版商:Hüthig&Wepf Verlag    

年代:1995

数据来源: WILEY