Polymerization Reactions and Processes

The objective of this chapter is to demonstrate how the molecular structure of a polymer is governed by the polymer synthesis reaction mechanism and how this, in turn, depends on polymerization conditions. This information is essential for establishing relationships between molecular structure and rheological properties. It is only from knowing the reaction process that we can have any a priori knowledge of the molecular structure. 

This chapter begins with a description of two schemes used to classify a polymer on the basis of either its structure or the type of reaction used to produce it and proceeds to a list of the various features that define molecular structure. This is followed by a description of the processes used to prepare samples with uniform and well-defined structures for research purposes. Finally, we discuss the processes used to make commercial polymers and the types of molecular structure that result. An important modern development that comes close to bridging the gap between laboratory samples and commercial products was the discovery of metallocene or single-site catalysts. The polymers produced using these catalysts have structures that are much more homogeneous and well-defined than earlier commercial polymers. 

Because the development of polymerization catalysts and the processes for the commercial use are intimately associated with certain individuals, it will be of interest to mention these ingenious people in this chapter. More detailed accounts of the history of polymer science can be found in several interesting books [2-4]. 

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Juba, M. R., A Review of Mechanistic Considerations and Process Design Parameters for Precipitation Polymerization, in Polymerization Reactions and Processes, ACS Symposium Series No. 104, Washington D.C., 1979, pp. 267-279. 

Off-line analysis, controller design, and optimization are now performed in the area of dynamics. The largest dynamic simulation has been about 100,000 differential algebraic equations (DAEs) for analysis of control systems. Simulations formulated with process models having over 10,000 DAEs are considered frequently. Also, detailed training simulators have models with over 10,000 DAEs. On-line model predictive control (MPC) and nonlinear MPC using first-principle models are seeing a number of industrial applications, particularly in polymeric reactions and processes. At this point, systems with over 100 DAEs have been implemented for on-line dynamic optimization and control. 

Table 10.8 Polymerization Reactions and Processes and Some Polymer Products... 

Polychloroprene elastomers are produced by free radical emulsion polymerization of 2-chloro-l,3-butadiene monomer. The emulsion polymerization of chloroprene involves the dispersing of monomer droplets in an aqueous phase by means of suitable surface active agents, generally at a pH of 10-12. Polymerization is initiated by addition of free radical catalyst at 20-50° C. To obtain a bigb conversion in the polymerization reaction and processable polymer, the addition of sulfur, thiuram disulfide, or mercaptans is necessary (Whitehouse 1986). 

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