Kinetics and Mechanism of Polymerization

Initiation The mechanism of initiation of anionic polymerization of vinyl monomers with alkyllithium compounds and other organometallic compounds is complicated by association and cross-association phenomena in hydrocarbon solvents and by the presence of a variety of ionic species in polar media [3, 4, 45, 48, 55, 56]. The kinetics of initiation is complicated by competing propagation and the occurrence of cross-association of the alkyllithium initiator with the propagating organolithium [55]. Thus, only the initial rates provide reliable kinetic data. 

Typical kinetics of the initiation reaction of n-butyllithium with styrene in benzene exhibits a first-order dependence on styrene concentration and approximately a one-sixth order dependence on n-butyllithium concentration as shown in Equation 7.14. 

The kinetic order for. yec-butyllithium-initiated polymerization of styrene is close to 0.25 in benzene solution this result is also consistent with initiation by unassociated. yec-butyllithium, since yec-butyllithium is associated predominantly into tetramers in benzene solution [44]. The experimentally observed energy of activation (18 kcal/mol) for n-BuLi/styrene initiation [56] appears to be too low to include the enthalpy of complete dissociation of the aggregates, estimated to be 108 kcal/mol [82]. An alternative mechanism is the incomplete or stepwise dissociation of the aggregate [3]. 

The observed inverse correlation between reaction order dependence for alkyllithium and degree of alkyllithium aggregation is not observed in aliphatic solvents. The use of aliphatic solvents leads to decreased rates of initiation and pronounced induction periods. In fact, a different reaction mechanism involving the direct addition of monomer with aggregated organolithium species has been proposed for aliphatic solvents [3, 56], 

Propagation The anionic propagation kinetics for styrene (S) polymerization with lithium as counterion is relatively unambiguous. The reaction in monomer concentration is first order, as it is for polymerization of all styrene and diene monomers in heptane, cyclohexane, benzene, and toluene [3, 55, 56], The reaction order dependence on total chain-end concentration, [PSLi]o, is one-half as shown in Equation 7.15. The observed one-half kinetic order dependence on chain-end concentration is consistent with the fact that poly(styryl)lithium is predominantly associated into dimers in hydrocarbon solution [85, 86], If the unassociated poly(styryl)lithium is the reactive entity for 

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Kinetics and mechanism of polymerization of vinyl monomers initiated by ylides. 

Allen, P.E.M. Patrick, C.R. Kinetics and Mechanisms of Polymerization Reactions Ellis Horwood Chichester, 1974. 

Secondly, new techniques have been developed which allow a more detailed characterization of both polymer microstructures and the kinetics and mechanism of polymerizations. This has allowed mechanism-structure-property relationships to be more rigorously established. 

P. E. Allen and C. R. Patrick, Kinetics and Mechanism of Polymerization Reactions , Ellis Horwood, Chichester, 1974. 

Allen, P. E. M Patrick, C. R., "Kinetics and Mechanisms of Polymerization Reactions", John Wiley Sons, (1974)... 

Wei Y, Chan CC, Tian J, Jang GW, Hsueh KF (1991) Electrochemical polymerization of thiophenes in the presence of bithiophene or terthiophene kinetics and mechanisms of polymerization. Chem Mater 3 888-897... 

Two frequently asked questions are (1) How do the metal-metal bonded species affect the kinetics and mechanisms of polymerization compared to... 

The kinetics and mechanism of polymerization of IV-carboxy-a-amino acid anhydrides as well as the biological properties of poly-a-amino acids have been studied and reviewed extensively (70,79,80). The critical chain length for helix formation varies from one amino acid to another (81,82). The critical chain length in L-methionine oligopeptides is the heptamer (83). 

M. F. Dmmm and J. R. LeBlanc, in Kinetics and Mechanisms of Polymerization Step Growth Polymerizations (Ed. D. H. Solomon), Marcel Dekker, New York, 1972. 

Goodman, M. Pegglon, E., Pure and Appl. Chem. 1981, 53, 699. Shalltin, Y., in "Kinetics and Mechanisms of Polymerization,... 

Relmschuessel, H.K., In "Kinetics and Mechanisms of Polymerization, Volume 2, Ring Opening Polymerization" Frisch, K.C. Reegen, S.L., Eds. Marcel Dekker New York, 1969 Chapter 7. 

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