Radiation-induced cationic polymerization of vinyl ethers in solution: 4. Polymerization of isopropyl vinyl ether in bulk and in various solvents

Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers

“…Last, almost no polymerization was observed in nitromethane, an outcome that agrees with the reported low propagation rates of cationic polymerization of vinyl ethers in this solvent. 21 Initial One-Electron Oxidation, a Critical Step for Activation. The elucidation of the electron transfers among species in solution is key to understanding the activation of the cationic process (step I).…”

“…Last, almost no polymerization was observed in nitromethane, an outcome that agrees with the reported low propagation rates of cationic polymerization of vinyl ethers in this solvent. 21 …”

Absolute propagation constants in vinyl polymerization

“…Propagation constants for isopropylvinylether 37 were higher at 6 ϫ 10 5 in benzene, 3.5 ϫ 10 5 in ether, and 1.5 ϫ 10 4 M Ϫ1 s Ϫ1 in methylene chloride. The differences between the two monomers are linked to a halving of the activation energy in the latter case.…”

Kinetics of methyl, ethyl, and isopropyl vinyl ether polymerizations initiated by trityl salts

“…Radiation polymerization in bulk led to a kp value about 60 times higher and to a less negative £*". A first explanation for this higher rate could be the dielectric constant effect as radiation experiments performed by Stannett et al13 in media of increasing polarity (from bulk, D = 3, to monomer-nitromethane mixture, D -19.5 at 30 °C) follow roughly the Laidler-Eyring linear relation between In kp and D™1 (see Table II in ref 13). Values of AS*p observed in CH2C12 solution for IPVE (-25 cal mol™1 K™1, radiation; -29 cal mol™1 K™1, chemical) show that in both cases the main contribution results from immobilization of monomer on an unsolvated end and that the equilibrium between bare and intrasolvated cations is shifted toward the former.…”

“…The situation is less coherent for EVE, as the kinetic parameters observed for polymerizations chemically initiated in CH2C12 differ by a factor of ~8 from those obtained by radiation in CH2C12 solution and are in fact comparable to those obtained from radiation in bulk. Radiation polymerizations of EVE were also performed in media of increasing polarity by Stannett et al (see again Table II in ref 13). The plot of In kp versus D~l deviates from the Laidler-Eyring relationship, but the average slope of the curve is noticeably smaller than that observed in the case of IPVE.…”