+ Ionic polymerization Cme/mse 404G polymeric materials ionic polymerization

+ outline Characteristics Cationic polymerization Propagation reaction Termination reaction Kinetic chain length ionic polymerization 2

+ characteristics used for making stereoregular polymers with high tacticity selectivity is high, and is due to stabilization of the reactive chain site Table 4.13 gives some typical commercial polymers initiation of the ion pair has a low activation energy, and the rate is not sensitive to temperature ion pairs do not reaction with each other: there are few or no termination reactions solvents should be very pure ionic polymerization 3

+ Cationic polymerization Table 4.14 shows the polarity range over which some catalysts, solvents and monomers are used. We will review and extend Example Problem 4.9. Cationic Polymerization of Styrene ionic polymerization 4

+ Polymer/copolymerMajor uses Cationic polyisobutylene, polybuteneAdhesives, sealants, insulating oils, moisture barriers isobutylene-cyclopentadiene copolymerInner tubes, engine mounts, chemical tank linings, protective clothing, ozone-resistant rubber isobutylene-cyclopentadiene copolymer hydrocarbon and polyterpene resinsInks, varnishes, paints Coumarone-indene resinsFlooring, coatings, adhesives poly(vinyl ether)sPolymer modifiers, adhesives Anionic cis-1,4-polybutadieneTires; replacement for natural rubber Styrene-butadiene rubberTire treads, belting, hose, flooring SB block, star copolymersArtificial leather, wire and cable insulation ABA block copolymers thermoplastic elastomers Polycyanoacrylateadhesives ionic polymerization 5

+ initiation where the term on the far right hand side is the reacting chain site. If this reaction goes far to the right, almost all of the sulfuric acid will start chains when monomer is present. ionic polymerization 6

+ propagation The reaction center continues to add monomer ionic polymerization 7

+ termination In this case, the reacting center can terminate via a monomolecular reaction ionic polymerization 8

+ In-class problem. QUESTION Can the quasi-steady state assumption apply to this problem? [are the reactive site production and loss rates in equilibrium?] ionic polymerization 9

+ In-class problem. ANSWER Since the reaction of the acid with monomer is instantaneous and irreversible, the qssa does not apply we can integrate the termination reaction from the initial condition to the reactive site concentration at time t. ionic polymerization 10 This equation can be substituted into the propagation equation to get the concentration of monomer as a function of time.

+ Kinetic chain length We can estimate the kinetic chain length by taking the ratio of the propagation to the termination step. This is the ratio of the rate of monomer addition to the chain, divided by the ratio of chain loss. ionic polymerization 11

+ In-class problem. QUESTION How can we keep the polymer chain length constant during an ionic polymerization ionic polymerization 12