Dependence of Propagation Rate Constant on Monomer Structure

3 Dependence of Propagation Rate Constant on Monomer Structure 

Recent data for kp arc summarized in Tabic 4.11. Monomers have been 

---

Dependence of propagation rate constant on monomer structure... 

The overall polymerization rates and the apparent rate constants of propagation (/c/pp = RP/[M][I]0) for the same initiating system are, however, very different for each class of monomers. For example, the same initiating system, that will polymerize a-methylstyrene (aMeSt) in 1 h, will complete polymerization of vinyl ether within less than 1 min but would require a few days to polymerize styrene and isobutene under otherwise identical conditions. This trend is due to the equilibria between dormant and active species. In this case the apparent rate constant of propagation is the product of the rate constant of propagation (weakly depending on monomer structure) and the ionization constant (kpapp = kp + -Kf). This equilibrium constant is much higher for more stable cations derived from vinyl ethers than from aMeSt, than styrene or isobutene. 

---