POLYMER MOLECULAR WEIGHT DISTRIBUTIONS

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Abstract
The problem of the calculation of the molecular weight distribution for a polymer is an important one for the chemical engineer, since any rational attempt to tailor the properties of a polymer must eventually depend on how the various polymers are distributed in the mixture. It follows, therefore, that the rational design of a polymerization reactor requires a detailed knowledge of the rates of the almost infinite number of reactions which take place. One says almost infinite because the number may be so large that infinite mathematical processes may be utilized. There are certainly not an infinite number of species, since all species in the reaction mixture will have a finite molecular weight. In principle, if one knew the rates of all the chemical reactions taking place in the polymerization process, then for a particular reactor geometry one could predict exactly the molecular weight distribution in a batch reactor or in the effluent of a continuous reactor. One says in principle, for it may happen that the reactor geometry is such or the fluid mechanical properties of the system are such that the mathematical computations required may be so long and tedious that their being carried out is unlikely. For simple batch reactors or for simple continuous reactors the task can be carried out and has been, but for more complicated flow reactors the task is formidable.