Conventional Polymerization Kinetics and Processes

Dj - thermodynamic diffusion coefficient (also equal to the intrinsic diffusion coefficient (Eq. 1.2.29) 

Jo - zeroth-order Bessel function of the first kind 

J - first-order Bessel functions of the first kind 

Moo - weight of penetrant uptake at equilibrium (infinite time), kg 

Re - Reynolds number for pipe flow, dimensionless Re - Reynolds number for tank mixing, dimensionless Tg - glass transition temperature, K 

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In this chapter, we restrict discussion to approaches based on conventional radical polymerization. Living polymerization processes offer greater scope for controlling polymerization kinetics and the composition and architecture of the resultant polymer. These processes are discussed in Chapter 9. 

In summary, there has been a tremendous effort devoted to the fundamental aspects of emulsion polymerization mechanisms, kinetics and processes since the early twentieth century. Representative review or journal articles concerning the conventional emulsion polymerization can be found in literature [20-25, 48-60]. The research areas related to both miniemulsion [42,61-64] and microemulsion [44-47, 65] polymerizations have received increasing interest recently. 

Although the early literature described the application of a tubular reactor for the production of SBR latexes(1), the standard continuous emulsion polymerization processes for SBR polymerization still consist of continuous stirred tank reactors(CSTR s) and all of the recipe ingredients are normally fed into the first reactor and a latex is removed from the last one, as shown in Figure 1. However, it is doubtful whether this conventional reactor combination and operation method is the most efficient in continuous emulsion polymerization. As is well known, the kinetic behavior of continuous emulsion polymerization differs very much according to the kind of monomers. In this paper, therefore, the discussion about the present subject will be advanced using the... 

On the other hand copolymer with a trioxane unit at the cationic chain end (Pi+) may be converted intp P2+ by cleavage of several formaldehyde units. These side reactions change the nature of the active chain ends without participation of the actual monomers trioxane and dioxo-lane. Such reactions are not provided for in the kinetic scheme of Mayo and Lewis. In their conventional scheme, conversion of Pi+ to P2+ is assumed to take place exclusively by addition of monomer M2. Polymerization of trioxane with dioxolane actually is a ternary copolymerization after the induction period one of the three monomers—formaldehyde— is present in its equilibrium concentration. Being the most reactive monomer it still exerts a strong influence on the course of copolymerization (9). This makes it impossible to apply the conventional copolymerization equation and complicates the process considerably. 

Compared to conventional heterogeneous Ziegler-Natta systems in which a variety of active centers with different structures and activities usually coexist, homogeneous metallocene-based catalysts give very uniform catalyt-ically active sites which possess controlled, well-defined ligand environments [37]. Consequently, the polymerization processes in homogeneous systems are often more simple, and kinetic and mechanistic analyses for these systems are greatly simplified [38]. 

Among other subjects the influence of the conditions, in which the polymerization process is conducted, on the supramolecular structure of the polymer formed is discussed in studies40-42. Using these data the researchers analyzed the impact of polymerization kinetics on the polymers supramolecular structure and formulated the basic principles for controlling the structure of the polymer in the course of its synthesis. They also proposed a new thermodynamic approach for controlling supramolecular structures. The possible uses of this method are demonstrated in the polymerization of trioxane and triethylamine in different solvents and at different monomer concentrations. The purpose of this approach and the manner in which it differs from the conventional kinetic approach are roughly illustrated by the scheme in Fig. 5. 

The present review will mainly focus on inverse emulsion polymerization, the most commonly employed water-in-oil synthesis method and on inverse microemulsion polymerization which is more recent and offers some new prospects. The formulation components and their actions, the various structures of the colloidal dispersions prior to polymerization and some latex properties will be discussed. The kinetics and the mechanisms occurring in these water-in-oil systems will also be analysed and compared to the more conventional emulsion polymerization process. 

Reimschuessel reviewed the water-initiated, ring-opening polymerization of caprolactam in detail [27]. In an attempt to analyze the process from its kinetic and mechanistic aspects, the equilibrium reactions 2.11, 2.12, and 2.13 are conventionally presented as follows ... 

Within the radical polymer field, two broad areas of application for ab initio kinetic modeling are model development and process optimization. The RAFT case study presented in this chapter is an example of the former type of application we are currently using the same ab initio approach to conventional radical polymerization to develop better models for predicting copolymer composition and microstructure, structural defect formation as a result of side reactions, and the effect of solvent and additives on the stereochemistry of the resulting polymer. 

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