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Polymerization Reaction Kinetics

The free radical reaction takes place in three major steps, Initiation, Propagation, and Termination. The initiation is the first step that forms the free radical from the monomer, or existing polymer chains, that grow even larger. The initiation step basically forms free radicals that react with other neighboring molecules that have the propensity to form radicals too. The radicals are formed and the propagation step begins. Here, the radicals continue to collide and form other radicals, and hence initialize a chain reaction of radical formation. The rate of propagation is determined by the concentration of free radicals in the reactor. As radicals collide with one another, the radicals form longer chain molecules. This is essentially what chain termination involves. Below are a series of reaction mechanisms that characterize the free-radical polymerization process.

The rate laws are then used to derive the mass and energy balances that describe the dynamics of the reaction process. The mass balances shown are derived for the ethylene monomer, acetylene and the initiator.

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