Kinetics emulsion polymerisation

Process monitoring using Raman spectroscopy (mainly in its NIR Fourier transform variant) is proposed for QA/QC purposes, on-line polymer analysis, in situ cure kinetics, emulsion polymerisation, non-invasive analysis of physical parameters (in situ crystallinity determination, etc.) and reactor compositions, real-time measurements, molecular interactions, and components in aqueous solutions. 

Emulsion Polymerization. Emulsion SBR was commercialised and produced in quantity while the theory of the mechanism was being debated. Harkins was among the earliest researchers to describe the mechanism (16) others were Mark (17) and Elory (18). The theory of emulsion polymerisation kinetics by Smith and Ewart is still vaUd, for the most part, within the framework of monomers of limited solubiUty (19). There is general agreement in the modem theory of emulsion polymerisation that the process proceeds in three distinct phases, as elucidated by Harkins (20) nucleation (initiation), growth (propagation), and completion (termination). 

Equation (4) clearly shows that the number average degree of polymerisation Xn is inversely proportional to the reaction rate Rp, meaning that, in radical chain polymerisation high reaction rates are linked to low molecular masses and vice versa. One way to avoid this dilemma is to use emulsion polymerisation where the lifetime of a radical (i.e., the "kinetic" chain length) is independent of... 

Emulsion polymerisation is a special case of heterogeneous addition polymerisation in which the reaction kinetics are modified because the A are compartmentalised in small polymer particles [48, 49]. These particles are usually dispersed in water and reaction (78) occurs in the aqueous phase. Initiating radicals diffuse to the particles which are stabilised by surfactant material. Chain termination becomes retarded physically and a relatively high polymerisation rate is obtained. If chain transfer is not prominent, a high molecular weight polymer is produced. The polymerisation rate is given by the expression... 

Tauer, K. (2003) The role of emulsifiers in the kinetics andmechanism of emulsion polymerisation. In D.R. Karsa (ed.), Surfactants in Polymers, Coatings, Inks and Adhesives. Blackwell Publishing, CRC Press, Boca Raton, FL. 

The reason for this behaviour is obscure it is not apparently due to the presence of peroxides in the surfactant. However, it is perhaps significant that an emulsion polymerisation reaction in which the rate of polymerisation is first-order with respect to surfactant level is consistent with Smlth-Ewart "Case 2" kinetics for a system in which the surfactant functions as an initiator as well as a micelle generator. 

According to the theory of Smith and Ewart [4] of the kinetics of emulsion polymerisation, the rate of propagation Rp is related to the number of particles N formed in a reaction by the equation. 

The kinetics of a polymerisation refers to the rate at which the polymerisation occurs (397). In emulsion polymerisation, the fundamental polymerisation kinetics theory is that of Smith and Ewart (377, a. 13). They proposed a theoretical framework in which monomer-swollen polymer particles are entered by radicals at a constant rate (radical flux). The radicals may desorb from the particle, terminate with one another, or initiate polymerisation within the particles. Through mathematical analysis, the average number... 

Gaseous vinyl chloride monomer is polymerised under high pressure conditions. Since polyvinyl chloride polymer is insoluble in its own monomer, the reaction kinetics do not follow the classical emulsion polymerisation kinetics. During polymerisation, chain transfer to monomer is extensive, and molecular weight development depends upon the reaction temperature rather than the initiator concentration. Consequently, lower reaction temperatures are needed to reach higher molecular weights. A typical formulation for the suspension polymerisation of polyvinyl chloride is given in Table 5. 

PS/PU hybrid latex particles were synthesised using water soluble or dispersible PU resins as emulsifiers. Two kinds of PU resins were prepared from isophorone diisocyanate, poly(l,2-propylene glycol)s and 2,2-bis(hydroxymethyl)-propionic acid. Emulsion polymerisation of styrene with the PU resins showed similar kinetic dependence on stabiliser and initiator concentration as with conventional... 

Details are given of the preparation of SAN latexes by micro-emulsion polymerisation using sodium dodecyl sulphate as an anionic surfactant. Kinetics of copolymerisation was studied at different temperatures using different concentrations of potassium persulphate and hydrogen peroxide/ascorbic acid. The latexes were characterised for particle size and number of particles by dynamic light scattering and TEM. Products were examined using NMR and thermal analysis. 20 refs. INDIA... 

The polymerisation of styrene and acrylic acid by seeded batch emulsion polymerisation was investigated. The effects of acrylic acid content and pH on the polymerisation rate and the amount of carboxyhc acid groups in the final latex product was studied. Aqueous conductometric titration and nonaqueous potentiometric titration were used to determine the distribution of the functional groups over the aqueous phase, the latex particle surface and the interior of the latex particle. The carboxylic acid group distribution along with kinetic results provided information about the process of incorporation of acrylic acid into the latex product. In order to increase the surface incorporation efficiency a two-step process in which a shot of acrylic acid was performed in the last stage of the reaction of investigated. 23 refs. 

The kinetics of polymerisation of styrene-in-water microemulsions is investigated using dilatometry. From plots of percentage conversion versus time, the rate of polymerization, Rp, is determined. From log-log plots of Rp versus styrene and initiator (2,2 -azobis(isobutyronitrile), AIBN) concentrations a relationship is estabhshed. The exponents are similar to those predicted by the theory of emulsion polymerisation. The results also show a rapid conversion in the initial period (interval 1) followed by a slower rate at longer times (interval 2). It is suggested that in interval 1, the main process in nncleation of the microemnlsion droplets, whereas in interval 2 propagation is the more dominant factor. The rapid polymerisation of microemnlsions is consistent with their strncture, whereby very small droplets with flexible interfaces are prodnced. 4 refs. 

The relationship between the surface characteristics of colloidal copper particles and the kinetic parameters of heterogeneous catalytic initiation in aqueous polymerisation was investigated. The dependence of the rate of emulsion polymerisation initiated by the colloidal copper on the nature of the monomer used (styrene, methyl methacrylate, vinyl acetate and N-vinyl pyrrolidone) and method of manufacture of the copper powder was examined. The characteristics of styrene emulsion polymerisation initiated by modified and unmodified colloidal copper particles are reported and the ability of... 

A review is presented of topics discussed at the 2nd International Symposium on Free Radical Polymerisation, held in Santa Margherita Figure, Italy, on 26th-31st May 1996. These included methods for the control of molecular weight and molecular structure, control of particle size and particle size distribution in emulsion polymerisation processes, and results of experimental and theoretical studies of polymerisation mechanisms and kinetics. 

Emulsion polymerisations of styrene and butyl acrylate were conducted using varying amounts of Triton X-405, octyl phenoxy polyethoxy ethanol, as emulsifier. Polymerisation mechanisms and kinetics are discussed. Particle size distributions were examined. 17 refs. 

Clearly, an objective of commercial production is to obtain a stable latex which has as high a solids content as remains consistent with producing the required balance of pol3naer properties after drying. The colloidal stability of latices is enhanced by the addition of surfactants. Latices prepared by emulsion pol3mierisation techniques usually have solids content of 40-45%. The kinetics and mechanism of emulsion polymerisation of VCM have been extensively reviewed by Ugelstad et al (9). 

Othman N, Santos A, Fevotte G, McKenna TF. Monitoring of emulsion polymerisations a study of reaction kinetics in the presence of secondary nucleation. Can J Chem Eng 2002 80 88-104. 

This book is aimed at MSc students, Ph.D. students and reasonably experienced chemists in university, government or industrial laboratories, but not necessarily experts in emulsion polymerisation or the properties and applications of emulsion polymers. For this audience, which is often struggling with the theory of emulsion polymerisation kinetics, this book will explain how theory came about from well-designed experiments, making equations plausible and intuitive. Another issue experienced, especially in the industry, is that coupling theory and everyday practice in latex production is really hard. This is another aim of the book showing how theory works out in real life. 

In academia, these developments were closely paralleled by increasing understanding of the mechanistic and, subsequently, kinetic theories. Among these, the Harkins and Smith-Ewart theories are the most prominent and important. The Harkins theory has already been mentioned in the citation from Hohenstein and Mark (1946). It appeared in a series of publications between 1945 and 1950 (Harkins, 1945, 1946, 1947,1950 Harkins et al, 1945). Harkins interest was chiefly the role of surface-active substances in emulsion polymerisation. The Harkins theory is therefore a qualitative theory, but it is often looked upon as the starting point of all modern theories of emulsion polymerisation (Figure 1.1). The essential features of the theory are as follows (Blackley, 1975) ... 

Stockmayer also presented solutions for the case that takes into account desorption of radicals. This solution, however, is wrong for the most important range in desorption rates. But Sto ckmayer s solution(s) lead the way for the possibility of exact mathematical solution of emulsion polymerisation kinetics at a time when digital computers were not yet very important in chemical computations. The general solution when desorption is taken into account was presented by O Toole (1965). He applied a modified form of the Smith-Ewart recursion equation that gave the solution... 

Emulsion polymerisation kinetics have important differences from solution and bulk polymerisations. These differences can lead to many advantages for example, an increase in molar mass can be achieved without reducing the rate of polymerisation. Emulsion polymerisation is known for its relatively high rates of polymerisation and high molar masses as compared to other polymerisation techniques. A disadvantage of emulsion polymerisation is the presence of surfactant and other additives, which may result in deleterious properties under some circumstances. 

It is important to realise that the same basic free-radical polymerisation mechanisms operate in solution, bulk and emulsion polymerisations. The kinetic relations in Chapter 2 are therefore valid in an emulsion polymerisation. The differences commence with the actual concentrations of the various species at the locus of polymerisation. Instead of using the overall concentration of the monomer and radicals in the reactor, based on the volume... 

In free-radical polymerisations, rates are controlled by the processes of initiation, propagation, transfer and combination. Although these same processes operate in an emulsion polymerisation, the kinetics in an emulsion polymerisation particle are in general different... 

Under any of these circumstances, a pseudo-bulk emulsion polymerisation follows the same kinetics as the equivalent bulk system ... 

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