摘要:

AbstractSome of the distinguishing features of emulsion polymerization kinetics at high conversion are discussed. The apparent anomaly that propagation rate coefficients deduced from bulk and emulsion systems at high conversion are greatly different actually arises because the initiator efficiency in the former is very low. At intermediate and at high conversions, termination kinetics must take account of the length of each terminating chain; data and a new theoretical model for this are found to be in accord. Modelling the reaction‐diffusion equations at high conversion (including new theory to account for polymer migration) shows that large (say,>200 nm radius) particles at high conversion will show strong spatial inhomogeneity (core‐shell structure) even in emulsion homopolymerizations, because of the slow diffusion of monomer and free radic

ISSN:0258-0322    

DOI:10.1002/masy.19900350103

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractKinetic and mechanistic features in the early stage of the emulsion copolymerization of styrene and methyl methacrylate were examined using sodium lauryl sulfate and potassium peroxidisulfate as emulsifier and initiator, respectively. Experimental results on copolymer composition, molecular weight distribution, the rate of copolymerization and the number of polymer particles found in the early stage of the reaction showed that: (1) The amount of copolymers produced in the water phase decreases with an increase in the concentration of emulsifier initially charged and can be practically neglected above the critical micelle concentration(CMC), and hence, (2) Polymer particles are regarded to be produced mainly from the emulsifier micelles sufficiently above the CMC. (3) Coagulation of polymer particles can be neglected in the process of particle nucleation.

ISSN:0258-0322    

DOI:10.1002/masy.19900350104

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAn approach for the estimation of kinetic parameters in emulsion copolymerization systems is presented. This approach is based on an algorithm for parameter estimation in differential equations and uses the time evolution of the conversions of the monomers in chemically initiated seeded emulsion copolymerizations. The approach is used to estimate the kinetic parameters of a mathematical model useful for predictive work. This mathematical model includes material balances for the monomers, population balances for particles containingiradicals and the free radical balance in the aqueous phase. Analysis of the variability of the parameters of the model during polymerization showed changes as large as 18% in the values of the parameters. These values were mainly due to changes in the particle size rather than to a shift in the composition of the reaction mixture. Combination of the present approach with methods for both parameter estimation in emulsion homopolymerization and estimation of reactivity ratios in emulsion copolymerization systems allows a reasonable good estimation of these varying kinetic parameters as constant parameters. Additionally, it was found that when the dependence of the parameters on the particle size was included in the estimation process, the parameters of the model were accurately estimated.

ISSN:0258-0322    

DOI:10.1002/masy.19900350105

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe multi‐component polymerization of the industrially important hydrophobic and hydrophilic monomers exhibits special features in comparison to the multi‐component emulsion polymerization of hydrophobic monomers. The main difference stems from the partial or total solubility of the hydrophilic monomer in the continuous water phase and in some instances also from the formation of water‐soluble polymer. The chemical and morphological structure of the polymer particles, beside the comonomer partitioning between water and oil phases, is governed also by the reactivity ratios of comonomer pair and by the extent of the mutual miscibility or phase separation of polymeric material of the particle. Compositional (chemical) heterogeneity of the polymer particles is also influenced by different affinity of the polymer (copolymer) to the water and oil phases. Structurally inhomogeneous polymer product results from the simultaneously proceeding polymerization in the water and oil phases. The polymer product represents a mixture of homopolymer (copolymer) formed in the water phase and of the copolymer (sometimes graft copolymer) formed on the surface of the polymer particles or in the interphase surrounding the polymer par

ISSN:0258-0322    

DOI:10.1002/masy.19900350106

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe mechanisms of mass transfer between miniemulsion droplets and polymer particles in the miniemulsion copolymerization of styrene‐methyl methacrylate were studied. A mathematical model was developed for the process. This model includes the mass transfer of highly water‐insoluble compounds from miniemulsion droplets to polymer particles by both molecular diffusion and collision between droplets and particles. According to previous results, the concentration of the monomers in the different phases were assumed to be under thermodynamic equilibrium. Both homogeneous nucleation and heterogeneous nucleation were accounted for. The mathematical model also includes the calculation of the average number of radicals per particle when a mixture of oil‐soluble initiator and water‐soluble initiator was used. This model was used to analyze a previously reported experimental result of seeded copolymerizations carried out in the presence of miniemulsion droplets containing a water‐insoluble inhibitor at different stirring speeds. The simulation results indicated that at 30 rpm, about 66% of the mass transfer of the highly water‐insoluble inhibitor occurred by diffusion and the rest by collision. On the other hand, at 120 rpm only about 20% of the inhibitor's mass transfer was by molecular diffusion, whereas 80% occurred b

ISSN:0258-0322    

DOI:10.1002/masy.19900350107

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent developments in dispersion copolymerization including particle formation in both polar and nonpolar media are discussed. The effects of stabilizer, reaction medium and initiation rate on particle size and distribution in homo‐ and copolymerization are described, and in particular, processes leading to the formation of monodisperse latices and the crosslinking of these microspheres will be examine

ISSN:0258-0322    

DOI:10.1002/masy.19900350108

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe structural and rheological properties of poly(acrylamide‐co‐sodium acrylate) latexes prepared in inverse nonionic microemulsions have been investigated. The formation of stable and optically transparent microlatexes is strongly related to the acrylate content in the feed due to a salting‐out effect of the ethoxylated surfactant. This salting‐out effect determines the optimum HLB value of the blend. The dimensions of the particles are rather low (d<100nm) with a narrow distribution. The inverse microlatexes which consist of water‐swollen copolymer particles dispersed in an isoparaffinic oil show a newtonian behavior up to high volume fractions (⋍ 50%) and a shear‐thinning behavior for volume fractions above 50%. The presence of charges in the copolymer leads to an apparent close‐packing volume fraction lower than that of 64% predicted for a random packing

ISSN:0258-0322    

DOI:10.1002/masy.19900350109

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIn suspension processes, polymerisation occurs in a monomer‐containing phase which is dispersed in a continuous liquid phase. Controlled agitation and the presence of drop stabilisers are necessary to maintain the suspension. Temperature control is usually better than that observed in corresponding bulk processes. Polymerisation kinetics are often similar to those which apply to bulk systems but high conversions increase the probability of gel effects. Drop sizes can depend on conditions of turbulence, viscosity and interfacial tension. Correlations for maximum drop sizes are discussed. Drop segregation can affect product quality and reactor design is important. Drop sizes can change with time and particle size distributions may become bimodal. Polymeric stabilisers may be present in both the continuous and dispersed phases. If polymer precipitates inside the drops, the stabiliser can influence the particle morphology. The stabilising action of particulate inorganic solids is not well‐understood. In copolymerisation, cross‐linking may occur. Precipitation of copolymer can be promoted by the use of diluents. Stabilisers can have a role in determining porosity of the final particles. Reactivity ratios may appear to differ from those expected in bulk processes when one or more of the comonomers is appreciably soluble in the continuous phase. Relevant literature is reviewed and topics requiring further work are ident

ISSN:0258-0322    

DOI:10.1002/masy.19900350110

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper is devoted to the synthesis and characterization of highly hydrophilic polymer gels based on acrylic monomers. These superabsorbant polymeric materials (SAPs) were prepared by polymerization of an aqueous solution of monomers dispersed in a continuous organic phase. This inverse suspension process (I.S) was carried out in cyclohexane, the aqueous dispersed mixture containing acrylic acid, partially neutralised, at a given crosslinker/monomer ratio. The dispersion is stabilized by the introduction of a surfactant like SPAN 80. Due to an almost complete lack of available scientific knowledge, it was necessary to perform a basic study covering the influence of the main parameters driving the behaviour of SAPs, especially maximum swelling and absorption kinetics. Further influence of crosslinking density, initial monomer concentration and process conditions have been studied on the base of a model recipe. These results led to optimisation of swelling and absorption behaviour, using various kinds of monomer species and different polymerization conditions.

ISSN:0258-0322    

DOI:10.1002/masy.19900350111

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractIn the suspension polymerization of VCM insoluble polymer particles are formed inside the vinyl chloride monomer droplets. The nucleation, growth and aggregation of these particles are responsible for the internal morphology and associated properties (i.e. surface area, pore size distribution) of the particulate PVC product. The objective of the present study is to develop a microscopic particle morphology model that can predict the dynamic behaviour of the primary particle size distribution in terms of the controlling process variables (i.e. temperature, initiator concentration, etc.) by formulating a population balance equation to follow the time variation of the primary particle density function from the point of nucleation of basic particles to the formation of particle aggregates. It is shown that model predictions of the primary size distribution are in very good agreement with experimental observations.

ISSN:0258-0322    

DOI:10.1002/masy.19900350112

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY