摘要:

AbstractEmulsion polymerization systems are so complex that different workers often believe contradictory mechanisms for ostensibly the same system. A number of case studies are examined wherein data have been obtained that are able torefutemechanistic postulates (as distinct from supporting a mechanism by showing that a mathematical model incorporating it is able to reproduce a limited range of data). These examples are: (1) particle nucleation (refutation of micellar entry); (2) free radical desorption (refuting its unimportance for systems with insoluble monomers, and showing that the transfer/diffusion mechanism for this process is suspect); (3) entry (refutation of 100% initiator efficiency); (4) propagation (refutation of the assumption that the propagation rate coefficient (kp) drops to zero at the glass transition); and (5) termination (refutation of the assumption that dependence on lengths of each chain can always be ignored).

ISSN:0258-0322    

DOI:10.1002/masy.19900310103

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe problem of the locus of initiation in conventional emulsion polymerization is discussed on the basis of the literature survey (copolymer composition in the early stages of emulsion polymerization, particle size distribution). The idea of homogeneous nucleation of polymer particles even for non‐polar monomers is supported by recent studies of emulsion polymerization in the presence of oil‐soluble inhibitor. The method of the oil‐soluble inhibitor was also used for inverse emulsion polymerization systems. The studies have brought new experimental evidence for the locus of initiation in classical as well as in inverse emulsion polymerization systems. It seems now reasonable to accept the idea that in conventional emulsion polymerization systems the locus of initiation is the water phase. In inverse emulsion polymerization systems the results point to the phase boundary between the continuous phase and (oil‐soluble part of) inverse micelles as the main locus of initiation for the systems with oil‐soluble

ISSN:0258-0322    

DOI:10.1002/masy.19900310104

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAccurate investigations of batch homopolymerization and copolymerization allow to derive mechanisms for emulsion polymerization; if they are not actually general, they are assumed to be valid for a given co‐monomer system, at least. A lot of approaches have been devoted to the mathematical modelling of emulsion polymerization, with the objective to take into account all of the experimental parameters or only some of them. Many of these approaches are quite complex and assume that a huge number of parameters are know

ISSN:0258-0322    

DOI:10.1002/masy.19900310105

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA kinetic study of the photoinitiated polymerization of acrylamide in oil/AOT/H2O reverse micelles has been investigated. Determinations of the dependence of the rates of polymerization and the molecular weights of the polymers on initiator and monomer concentrations, as well as the relative light intensity and the identity of the oil employed were performed. Rates of polymerization were measured by dilatometry, and polymer molecular weights were determined by viscometry. The polymerization was shown to be first order in monomer concentration, and the order of the termination step of the polymerization depended strongly upon the oil employed. When the oil was benzene, termination occurred by a biradical process. When benzene was replaced by toluene, a monoradical termination was shown to occur, suggesting that a degradative chain transfer to toluene is occurring in this case. The similarities and differences of polymerization in conventional emulsions and in micelles are discussed on the basis of these results.

ISSN:0258-0322    

DOI:10.1002/masy.19900310106

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA comprehensive investigation of the photopolymerization in microheterogeneous structure is carried out with a view to elucidate the role played by the excited states in the initiation process.The radical initiation of methyl methacrylate in either anionic or cationic micelles or of acrylamide in reverse microemulsion is thus examined by UV spectroscopy, steady state photolysis and time resolved laser spectroscopy. The question of the localization of the initiator is dealt with special attention. Moreover, the influence of several parameters is also considered (concentration of reactants, incident light intensity, temperature or presence of external magnetic field).This contribution demonstrates the importance of a general approach involving a thorough knowledge of the elementary steps of initiation in the understanding of any polymerization conducted in a microheterogeneous medium.

ISSN:0258-0322    

DOI:10.1002/masy.19900310107

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractMiniemulsion polymerization involves initiation of polymerization in preformed stable monomer emulsion droplets with average droplet diameter of 50–500 nm. At the end of the polymerization, only a fraction of the initial number of monomer droplets become polymer particles. The emulsifier system used for the preparation of such emulsions comprises a mixture of ionic surfactant and a fatty alcohol or long chain alkane (termed cosurfactant). The cosurfactant is essential for the formation of stable emulsion droplets and in addition it plays an important role in the interparticle monomer transport.Kinetic results are presented on conventional emulsion and miniemulsion copolymerization of different pairs of monomers, showing the main differences for both processes. These differences were related to the particle formation mechanism and the influence of the cosurfactant in the miniemulsion process.A theoretical model was developed, based on mass balances and equilibrium thermodynamics, which was found to describe accurately the experimentally generated data on comonomer distribution during the course of the copolymerization process and the interdroplet mass transport proces

ISSN:0258-0322    

DOI:10.1002/masy.19900310108

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSemi‐continuous emulsion polymerization of acrylic monomers was investigated from the point of view of the particle growth. In the process no seed latex was used and the monomers were fed in an emulsion form. Oscillations of surface tension and particle number indicated a periodical generation and flocculation of particles during the polymerization. Investigation of particle size and molecular weight changes in the first tens of seconds of polymerization has shown that the coagulation process proceeds even in the earliest stage of the polymerization. Initial emulsifier concentration in the reactor strongly affects the particle growth and the final particle numbe

ISSN:0258-0322    

DOI:10.1002/masy.19900310109

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA survey is given of recent developments in emulsion polymerization regarding improved auxiliary materials, e.g. vinyl tensides and surface active initiators. Results of the emulsion polymerization of styrene are presented with 3‐(alkyloxycarbonyl‐acryloyloxy)propanesulfonates (2) as polymerizable emulsifiers and with surface active azo initiators. The results show, that the content of water soluble surface active compounds in the latexes can be reduced. Investigations of the molecular weight of the polymers show the great importance of the initiator‐emulsifier system. Azo initiators leading to higher molecular weights than persulfate. Under the same conditions the highest molecular weights were obtained with a surface active azo init

ISSN:0258-0322    

DOI:10.1002/masy.19900310110

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractPolymeric dispersions with a concentric core‐shell structure of the latex particles were obtained by a two‐stage emulsion polymerization technique. Conditions for the formation of shells on polymeric seeds are discussed. SANS and SAXS investigations were carried out in order to verify the core‐shell structure of the particles. DSC and IR measurements indicate the existence of an interfacial layer between core and shell polymers. The results are transferred to emulsion polymers containing inorganic filler part

ISSN:0258-0322    

DOI:10.1002/masy.19900310111

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe decomposition rate of potassium persulphate in various aqueous solutions was measured by isotachophoresis using pure water, sodium dodecyl sulphate (SDS) solution, emulsifier‐free polystyrene emulsion, SDS solution containing acrylamide monomer or an SDS‐containing emulsion polymerization system for styrene. “Free” SDS molecules in the monomolecular dispersed state were found to increase markedly the decomposition rate, whereas those which formed micelles and became adsorbed onto polystyrene particles did not increase it. The acceleration phenomenon in the former case disappeared in the presence of a small amount of

ISSN:0258-0322    

DOI:10.1002/masy.19900310112

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY