Emulsion polymerization reaction engineering

Polymerization Reaction Engineering Continuous Emulsion Polymerization... 

This chapter is focused on the challenge of achieving the efficient, safe, and consistent production of emulsion polymers of the desired microstructure. First, the main features of emulsion polymerization are discussed in Sections 6.2 and 6.3. Sections 6.4-6.7 are devoted to the understanding of the kinetics of the process. Finally, the emulsion polymer reaction engineering is addressed in Sections 6.8-6.11. 

Thus it is rapidly becoming possible to continuously monitor the critical states of an emulsion polymerization. The challenge, then, for the polymerization reaction engineer is to make full use of this data in designing reactor trains and open and closed-loop control policies to tailor polymer properties and end-use needs. 

The reaction engineering aspects of these polymerizations are similar. Excellent heat transfer makes them suitable for vinyl addition polymerizations. Free radical catalysis is mostly used, but cationic catalysis is used for non-aqueous dispersion polymerization (e.g., of isobutene). High conversions are generally possible, and the resulting polymer, either as a latex or as beads, is directly suitable for some applications (e.g., paints, gel-permeation chromatography beads, expanded polystyrene). Most of these polymerizations are run in the batch mode, but continuous emulsion polymerization is common. 

The rational design of a reaction system to produce a desired polymer is more feasible today by virtue of mathematical tools which permit one to predict product distribution as affected by reactor type and conditions. New analytical tools such as gel permeation chromatography are beginning to be used to check technical predictions and to aid in defining molecular parameters as they affect product properties. The vast majority of work concerns bulk or solution polymerization in isothermal batch or continuous stirred tank reactors. There is a clear need to develop techniques to permit fuller application of reaction engineering to realistic nonisothermal systems, emulsion systems, and systems at high conversion found industrially. A mathematical framework is also needed which will start with carefully planned experimental data and efficiently indicate a polymerization mechanism and statistical estimates of kinetic constants rather than vice-versa. 

Description of suspension polymerizations fits most appropriately in Chapter 10, where polymer reaction engineering is the topic. This chapter focuses on dispersion and emulsion polymerizations. 

Many operations in chemical engineering require the contact of two liquid phases between which mass and heat transfer with reaction occurs. Examples are hydrometallurgical solvent extraction, nitrations and halogenations of hydrocarbons, hydrodesulfurization of crude stocks, emulsion polymerizations, hydrocarbon fermentations for single-cell proteins, glycerolysis of fats, and phase-transfer catalytic reactions. A most common method of bringing about the contact of the two phases is to disperse droplets of one within the other by mechanical agitation. 

K. -H. Reichert and W. Geiseler, Polymer Reaction Engineering Emulsion Polymerization, High... 

Beckman, E.). (2005) Inverse emulsion polymerization in carbon dioxide, In Supercritical Carbon Dioxide, (eds M.F. Kemmere and T. Meyer) Polymer Reaction Engineering, Wiley-VCH Verlag GmbH, Weinheim, Germany, pp 139-156. 

TSE s have been used to prepare new families of engineering materials of high performance, polymers and their blends. Polycondensation, free radical, anionic and cationic polymerizations were conducted to obtain, e.g., PA, PEST, POM, styrenic or acrylic resins. When the reaction is conducted in a low molecular weight liquid (e.g., solution or emulsion polymerization), usually devolatilization and compounding are carried out in a cascade second extruder. Functionalization and chemical modifications have been performed in TSE on virtually all polymers. 

The next section describes measurements of interfacial tension and surfactant adsorption. The sections on w/c and o/c microemulsions discuss phase behavior, spectroscopic and scattering studies of polarity, pH, aggregation, droplet size, and protein solubilization. The formation of w/c microemulsions, which has been achieved only recently [19, 20], offers new opportunities in protein and polymer chemistry, separation science, reaction engineering, environmental science for waste minimization and treatment, and materials science. Recently, kinetically stable w/c emulsions have been formed for water volume percentages from 10 to 75, as described below. Stabilization and flocculation of w/c and o/c emulsions are characterized as a function of the surfactant adsorption and the solvation of the C02-philic group of the surfactant. The last two sections describe phase transfer reactions between lipophiles and hydrophiles in w/c microemulsions and emulsions and in situ mechanistic studies of dispersion polymerization. 

Poehlein GW. Reaction engineering for emulsion polymerization. In Asua JM, editor. Polymeric Dispersions Principles and Applications. The Netherlands Kluwer Academic Publishers 1997. p 305. 

The production of polyolefins by means of coordination polymerization, which is the highest tonnage polymerization process, is discussed first. The following chapters present the production of polymers by free-radical polymerization in homogeneous, heterogeneous and dispersed (suspension and emulsion) media. Afterwards, the reaction engineering of step-growth polymerization is discussed. The last chapter is devoted to the control of polymerization reactors. 

This Report will be concerned primarily with recent developments in the understanding of the mechanistic aspects of emulsion polymerization, rather than with such matters as the chemical engineering aspects or the applications of the polymer colloids produced by the reaction. The Report wilt commence by briefly reviewing some of the more important of the problems concerned with the reaction which have received recent attention. This review will provide a framework within which to order some at least of the new contributions to which attention will be drawn in the remainder of the Report. 

Barandiaran MJ, de la Cal JC, Asua JM. Emulsion polymerization. In Asua JM, editor. Polymer Reaction Engineering. Oxford Blackwell Publishing 2007. p 248-254. 

PoeMein, G.W. (1997) Reaction engineering for emulsion polymerization. In J.M. Asua (ed), Polymeric Dispersions Principles and Applications. Kluwer Academic Publishers, Dordrecht, p. 305. Popovici, S.T. (2004) Towards Small and Fast Size-Exdusion Chromatography. Ph.D. thesis. University of Amsterdam, Amsterdam. 

Emulsions, suspensions, and dispersions are examples of colloidal systems. It is important to mention that these terms are not always used consistently in the literature and that this situation may be confusing for students and nonpolymer scientists [24]. From the point of view of polymer science and engineering, these terms refer to heterogeneous polymerizations, particularly polymerizations in aqueous/alcoholic dispersed media. Thus, the aforementioned terms have connotations that have to do with the initiator, monomer, and polymer solubility in each phase as well as with particle size and the main locus of polymerization. These aspects are treated in detail later for the moment, let us assume that there are no chemical reactions and that such terms are used in the context of colloid science. 

Emulsion graft polymerization processes can be used to obtain coreshell modifiers, in which the core consists of crosslinked poly B (Tg = -6 to -85) or NBR (Tg -45). The latex particle size is very crucial for effective toughening of the diverse matrices styrenic polymers require larger particles (d > 0.2 pm) than engineering polymers id < 0.2 pm), due to their different toughening mechanisms. The ABS composition and properties are affected by the following polymerization variables (1) monomer amount (2) initiator type and amount (3) emulsifier concentration (4) reaction temperature and time (5) chain transfer agents. 

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