ISSN:0959-8103    

DOI:10.1002/pi.4990300202

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAmphipathic triblock copolymers of polyisobutylene‐block‐polyoxy‐ethylene‐block‐polyisobutylene were synthesized by a coupling technique. Seven triblock copolymers were prepared by varying their hydrophobic and hydrophilic chain lengths. The stabilizing effectiveness of these polymeric surfactants was studied as a function of structural variations of the block copolymers in aqueous polymerizations of styrene, methyl methacrylate, and viny

ISSN:0959-8103    

DOI:10.1002/pi.4990300203

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractConversion curves have been determined at 60°C for the polymerization of acrylamide in percolating inverse microemulsions. Ammonium peroxo‐disulphate (APS) and dibenzoyl peroxide (DBP) were used as initiators of free‐radical polymerization in the presence or absence of potassium nitrosodisulphonate (Fremy's salt, FS). The percolation decreases the rate of polymerization of acrylamide initiated by APS. The polymerization is inhibited by FS. After an inhibition period, retardation of acrylamide polymerization is more pronounced in non‐percolating microemulsions. No inhibition periods were observed for DBP‐initiated polymerization of acrylamide. The percolation shortens the time interval of the ‘slow’ polymerization of acrylamide, but the rates of rapid acrylamide polymerization above 10% conversion are the same for percolating and for non‐percolating inverse microemulsions. The polymer particle diameter is a function of acrylamide/water weight ratio and of [water]/[AOT](AOT: bis(2‐ethylhexyl)‐sulphosuccinate sodium salt) molar ratio. No effect of the initiator's nature either in the presence or in the absence of FS was found. The results are interpreted on the basis of initiator and/or nitroxide radical partitioning between oil and water phases of the inverse microemulsion, and are discussed with respect to the mechanism of acrylamide polymerization and polymer particle formation proposed for non‐percolating in

ISSN:0959-8103    

DOI:10.1002/pi.4990300204

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe method for preparation of monodisperse polymer particles by activated swelling was first presented 12 years ago. Since then the principle of activated swelling has resulted in procedures for the production of a number of monodisperse systems with particle sizes and compositions that were unattainable by previous methods. It has also formed the basis for several new applications of polymer particles. A short review of the basic theoretical principles which have been used in the development of the new processes is given. Methods for preparation of monosized polymer particles are described, and the most important biochemical and biomedical applications of various types of particles, including magnetic particles, are given.

ISSN:0959-8103    

DOI:10.1002/pi.4990300205

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe desorption of emulsifier from the particle surface of latices prepared by emulsion polymerisation has been followed by spectroscopic techniques: transmission IR, X‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) ‐fast atom bombardment mass spectrometry (FAB‐MS).In IR spectra, the extra band at 1710 cm−1due to carboxylic groups originating from the emulsifier is fortunately visible because it is located within a window of the polystyrene peaks.XPS is a valuable surface method of analysis (contrary to IR). Nevertheless, for the latices considered here, it is impossible to extract from the very intense carbon peak information concerning variation in the carboxyl groups, which amount to less than 1%.Another important method for surface analysis is static‐SIMS, which allows detection of elements and molecular species present in the first few layers with a detection limit which is less than 10−4%. FAB‐MS permits the detection of the parent ion of the emulsifier employed. Freeze‐dried powders of latices extensively purified with mixed‐bed ion‐exchange resins were studied for us using FAB‐MS at UMIST in Manchester (UK).A comparison is made of the results obtained with these three spe

ISSN:0959-8103    

DOI:10.1002/pi.4990300206

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractNetwork formation in free‐radical polymerization is investigated both from experimental and theoretical points of view. In a bulk free‐radical crosslinking copolymerization, the radical concentration increases significantly due to a decrease in the bimolecular termination rate. Some fraction of radicals is trapped during the course of network formation, and the reactivity of the radicals in liquid state is completely different from that in solid state (trapped radicals) in terms of both propagation and termination.In emulsion crosslinking polymerization, the crosslinking density tends to be fairly high even from the start of the polymerization. The crosslinking density development is substantially different from that in bulk and solution polymerizations, in which the crosslinking density increases with time, at least in the earlier stages of polymerization. Due to the elastic contribution of free energy change, the monomer concentration in the polymer particles is lower than for linear emulsion polymerizations as long as the monomer droplets exist, resulting in an enhanced tendency toward crosslinking reacti

ISSN:0959-8103    

DOI:10.1002/pi.4990300207

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA thermodynamic analysis and a mathematical model were developed to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Two experimental composite latex systems were used to verify and establish limitations of the model. The two latex systems were based on polystyrene/poly(methyl methacrylate), one prepared by conventional seeded emulsion polymerization and the second system by direct emulsification of a solution of a blend of the two polymers. The influence of several experimental parameters on latex particle morphology was investigated. These included monomer/polymer ratio, surfactant type, and initiator type in the seeded emulsion polymerization system. The influence of local viscosity, shear effects, and molecular weights of polymers were investigated in the artificial latex system.

ISSN:0959-8103    

DOI:10.1002/pi.4990300208

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA kinetic model for network structure development during crosslinking copolymerization of vinyl and divinyl monomer is proposed. The model calculations suggest that polymer networks synthesized by free‐radical copolymerization are, in general, inhomogeneous at least on a microscopic scale. By application of the same kinetic parameters as those for bulk polymerizations, it was found that the crosslinking density of the polymers formed in the earlier stages of polymerization is very high in emulsion polymerizations and polymer networks tend to be highly heterogeneous. Homogeneous networks cannot be formed even under Flory's simplifying assumptions for vinyl/divinyl copolymerization in emulsion polymerizations. The present kinetic model can be used to find semi‐batch policies to control the network structure, and semi‐batch policies were used to illustrate the synthesis of homogeneous polymer net

ISSN:0959-8103    

DOI:10.1002/pi.4990300209

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe application of a continuous Couette‐Taylor vortex reactor to continuous emulsion polymerization was studied. First, the mixing characteristics of the reactor were examined by the stimulus‐response method. It was found that the reactor performance was similar to that of a continuous flow reactor consisting of more than 60 well‐stirred tanks in series if the reactor was properly designed and operated near the critical Taylor number. It was also demonstrated by a comparison of the particle size distributions of the latexes produced in a batch reactor and in the continuous Couette‐Taylor vortex reactor that the continuous reactor could produce latex particles with fairly narrow size distribution. Furthermore, since no stirrer is involved, this continuous reactor is suited for the purpose of avoiding coagulation of latex particles that are very sensitive to mechanica

ISSN:0959-8103    

DOI:10.1002/pi.4990300210

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAn improved version of a novel method first employed by Nagy&Keller for the preparation of monodisperse ellipsoidal polystyrene latex particles is described. The method involves embedding monodisperse spherical polystyrene latex particles as starting material in a deformable polymer matrix such as poly(vinyl alcohol) and deforming these mechanically to various predetermined macroscopic draw ratios to give ellipsoids of various axial ratios. Ellipsoids with lengths ranging from about 350 to 12250nm were prepared. Stable aqueous dispersions of these were recovered and characterised with respect to particle size and axial ratio distributions and surface morphology using electron microscopy. Axial ratios ranging from 2.0 to 5.65 were obtained for the resulting ellipsoids. Various factors influencing the monodispersity of the resulting ellipsoids in the preparation method are discussed.

ISSN:0959-8103    

DOI:10.1002/pi.4990300211

出版商:John Wiley&Sons, Ltd    

年代:1993

数据来源: WILEY