Post on 19-Oct-2014
description
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