Addition or Drip Feed Process

Monomer and any reaction modifiers are premixed and fed at a predetermined rate into the reaction vessel containing solvent maintained at reaction temperature. Initiation is fed to the reaction vessel at a rate contiguous with the premixed monomer addition. 

Reaction conditions in commercial polymerisations are selected to favour rapid controllable conversion of the monomer and this, together with a timed, uniform feed rate, restricts the build-up of unreacted monomer. 

The graph shows an addition over a time period to to ti. 

Ideally, conversion will keep pace with the feed rate and at tj there will be complete conversion of monomer to polymer. In practice, the conversion will lag a little behind the addition rate, the reaction not being complete until time t2. 

It is usual, when conducting commercial polymerisations, to monitor the reaction profile against a predetermined norm. Because the reactants are being continually renewed at a rate close to the rate of consumption, the copolymer composition tends to be more uniform. Since the ratio of initiator to monomer remains more constant than that which is experienced with an all-in process, a much narrower molecular weight distribution results. 

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If the initiator concentration does not vary much during polymerisation (as for example when using a continuous addition or drip feed process) and the initiator frequency f is independent of the monomer concentration (as is the case when f approaches 1) then... 

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