Odian Book Chapter 3-15, 5-3

Living Polymerization

Living Polymerization Neutral and Highly Reactive or

Living Polymerizations Living polymerizations are chain growth polymerizations which proceed in the absence of irreversible chain transfer and termination steps.* Diagnostic Characteristic of Living Polymerizations The reaction proceeds until all monomer is consumed. If more monomer is introduced then the polymerization will continue The number average molecular weight, Mn, is a linear function of conversion. The number of propagating chains (active centers) is constant and independent of conversion. Mn can be controlled by the reaction stoichiometry. Sequential monomer addition results in the preparation of block copolymers. Resulting polymers will exhibit a narrow molecular weight distribution and the polymer must exhibit a Poisson distribution in molecular weight.** * Szwarc, M., Nature, 1956, 178, 1168. ** Flory, P. J., J. Am. Chem. Soc., 1940, 62, 1561.

Living Polymerization No termination or chain-transfer side reaction during polymerization Control of molecular weight Mn= Narrow molecular weight distribution Synthesis of block copolymers by sequential monomer addition Control of polymer chain microstructure End-group functionalization grams of monomer Moles of initiator

Initiation Nucleophilic Initiation of Vinyl Monomers

Anionic Polymerization of Styrene

Anionic Polymerization of Styrene

Anionic Polymerization of Styrene

Anionic Polymerization of Styrene

Initiators: Organolithiums Soluble in hydrocarbons Direct nucleophilic attack No electron transfer (RLi)N N= 6,4,2 MW= g of monomer moles of initiator

The Poisson Distribution in Molecular Weight The constraints imposed on a living polymer require that the polymer exhibit a Poisson distribution in molecular weight.*

Scale of “Livingness” Conversion should be linear with time in semi-logrithmic coordinates Deceleration indicates termination or deactivation of catalyst. When chain termination cannot be completely suppressed (kt > 0): deviation from living behavior becomes more pronounced with time The degree to which a reaction deviates at time, t, is proportional to the ratio of the rate of propagation to termination.

End Group Functionalization Carboxylic acid terminated: Primary alcohol terminated:

End Group Functionalization

Monomers Generally olefin w/ EWG or delocalizing groups Methyl acrylate (MA) Methyl methacrylate (MMA) t-Butyl methacrylate (tBuMA)

Ion Pair Aggregation Need to stabilize propagating anions

Ion Pair Aggregation Need to stabilize propagating anions