Polymer reaction engineering aspects

Polymer reaction engineering aspects 3.4.1 Heat removal and temperature programming... 

This chapter will deal with ionic chain growth polymerization for monomers which are of some industrial importance. It will deal mainly with those polymer reaction engineering aspects which are relevant for designing processes and products. As it cannot cover the entire subject, the systems dealt with are chosen as examples of the most important features of ionic polymerization. 

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. 

Reactive extrusion is a new tool in polymer reaction engineering. From an environmental viewpoint, the need for only small quantities of volatile solvents, and consequent reduced cost, are positive aspects. From an economical point of view, the expensive extrusion equipment is compensated by there being no need to separate the polymer from the solvent The process is largely complicated by the occurrence of various nonlinear effects that may introduce instabilities into the process, these being of thermal, hydrodynamic, and chemical origin. 

We regard the essential aspects of chemical reaction engineering to include multiple reactions, energy management, and catalytic processes so we regard the first seven chapters as the core material in a course. Then the final five chapters consider topics such as environmental, polymer, sohds, biological, and combustion reactions and reactors, subjects that may be considered optional in an introductory course. We recommend that an instmctor attempt to complete the first seven chapters within perhaps 3/4 of a term to allow time to select from these topics and chapters. The final chapter on multiphase reactors is of course very important, but our intent is only to introduce some of the ideas that are important in its design. 

Many aspects of homopolymerisation reaction engineering have been studied in recent years (1-4). Much attention has been given the nature of the dependence of the polymer molecular weight (MW) and molecular weight distribution (MWD) on the operating conditions of the polymerisation reactor. 

The various properties of water in different aspects (being important for the reactivity, reaction kinetics or mechanisms, reaction engineering, or other concerns) are discussed elsewhere. The procedures for tailoring the water-solubility of the catalysts are many-sided and may be generalized much more easily than the corresponding methods for SHOP (cf. Section 7.1), fluorous phase (Section 7.2), supercritical solvents (Section 7.4), water-soluble polymer-bound catalysts (Section 7.6), or NAIL utilization (Section 7.3) no wonder that all other biphasic applications remain singular or are still just proposals. Both the scientific and industrial com-... 

One of the most important areas for application of concepts discussed in the previous section is the selection of polymerization reactors. The properties of polymers depend on their molecular weight distribution (M WD) and so the design should ultimately use this as its basis. The subject is a vast one, and so only the basic concepts will be briefly discussed. Several excellent reviews now exist, covering various aspects of the area from a chemical reaction engineering viewpoint see Shinnar and Katz, Keane, and Gerrens, [18, 19, 20]. The latter presents a masterful survey of the effects of the choice of reactor type. 

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. 

In the past decades, nuclear magnetic resonance (NMR) spectroscopy has been used extensively to study various aspects of polymer chemistry and engineering. Fig. 1 shows the relationship among polymerization conditions, polymer structure, and the material s physical structure and end uses. Solution, solid state, and imaging NMR techniques contribute to imderstanding the physical and chemical aspects of the route from raw materials to final product. Solution NMR provides information about all aspects of the polymerization reactions and the final structure of the synthesized polymer. This information can be correlated with the material s final properties and provide feedback to control the initial polymerization process so that the fraction of structures responsible for desirable properties can be controlled in a systematic way. 

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