Polymer Reactor Design

By: M.Z.Iqbal

Lecture 2

Contents

• General introduction to Ionic polymerization• Cationic polymerization kinetics• Anionic Polymerization kinetics• Some controlling parameters and their effects• Chain transfer processes in ionic

polymerizations

Introduction• Both anions and cations can initiate the polymerization• Anions are relatively easy to discus because the cationic

initiators need some co-catalyst in the system.• Anionic pzn starts with the formation of carbanion which is

further capable of propagation.

• In cationic pzn, the initiation process consists of the interaction of cations with monomers to form carbonium ions.

• Sometimes, conventional acid (proton transfer specie) acts to initiate the pzn.

• The reaction with chloro acids is a bit different than floro acids due to certain reasons.

• The same concept lies that rate of propagation step is independent of chain length.

• Termination is a bit different from FRP reactions.

Kinetics of Cationic Polymerization• These kinetics are of special consideration because steady

state hypothesis doesn't seem to apply always.• A generalized behavior of cationic pzn is discussed here:

General behavior Curve

You need to solve the kineticExample given in your text

Kinetics of Anionic Polymerization• This approach resembles with cationic pzn in treatment and

in steady state treatment with FRPs.• From practical investigation, rate of pzn of styrene is

proportional to the square of monomer conc., half power of KNH2 conc.

• A mechanism was proposed meeting the above data. • Steady state conditions approach very rapidly as in case of

FRPs because there is nothing like co-catalyst that delays the process.

Treatment

Influence of Dielectric Constant• In the ionic pzn, the change in di-electric constant changes

the speed of reaction depending upon the mechanism of reaction.

• As D.C. increases, rate if initiation would increase.• Increase in D.E. can either increase or decrease the

termination process.• As a rule of thumb, increase in D.C. should decrease in D.P.

when rate of termination also increases with D.C.

Chain Transfer Processes in ionic Polymerization