Polymer Reactor Design 1

Polymer Reaction Engineering

By Muhammad Zafar Iqbal

Lecture 1

Contents

Chain Reactions in Liquid Phase

• These may be initiated by thermal, photochemical or any of radiation induction source

• In some respects, Liquid phase chain reaction resembles Gaseous phase chain reaction

• But in many respects, these two are different as the effect of non-ideality associated with solvents.

• The solvent also plays important role in chain length and structure of the final polymer.

• There is little difference in all types of chain reactions.

Free Radical Solution Polymerization• Rule of Thumb: If a single radical is involved in each step

reaction, then linear chain reaction will occur.• Of all the chain reactions, free radical reactions are the most

extensively studied.• From kinetic point of view, there is great similarity between

gas phase FRP and liquid phase FRP.• The initiation is very dependent on temp. and environment.• Temperature may change the nature and type of reacting

radicals.• Most important example: Benzoyl Peroxide

• Main drawback:

• Azo- compounds are free from such complications like side reactions:

• This is known to be free from side reactions but the complication lies again in the kinetics of cyano-isopropyl radical as ketene imino radical:

• The free radicals may be generated by some other modes but the actions series is same for all of them like:

Autoacceleration during solution polymerization

Degree of Polymerization and Chain Transfer• This definition is very sensitive to the reaction chemistry• In simple words, it is defined as the avg. no. of monomer units

per polymer chain.• For termination via disproportionation, This is equal to the

kinetic chain length.• For termination via chain combination, this is equal to the

twice the kinetic chain length.• Where kinetic chain length is defined as the avg. no. of

monomer units reacting with a given radical centre from its initiation to its termination.

Kinetics of Chain Transfer Processes• Chain transfer process is defined as the process whereby a

growing polymer radical transfers its activity to an adjacent monomer, initiator, solvent or any other polymer radical or terminated polymer molecule.

• The net effect of this termination process is that the original polymer radical loses its capacity for further growth and the second molecule called the transfer agent becomes the free radical capable of adding monomer units.

So the final equation becomes:

General relationship for chain transfer in radical chain reactions in solution

Transfer to monomer and Initiator

Transfer to the Solvent