Vinyl isobutyl ether radical polymerization

Radical polymerization of AN is monotonously retarded by the addition of isobutyl vinyl ether (IBVE) when initiated by azobisiso-butyronitrile in the dark. The rate of initiation would be kept constant at varying concentrations of IBVE and the change of rate of polymerization must be caused by a reduced rate of propagation or an enhanced... 

Use of triphenylmethyl and cycloheptatrienyl cations as initiators for cationic polymerization provides a convenient method for estimating the absolute reactivity of free ions and ion pairs as propagating intermediates. Mechanisms for the polymerization of vinyl alkyl ethers, N-vinylcarbazole, and tetrahydrofuran, initiated by these reagents, are discussed in detail. Free ions are shown to be much more reactive than ion pairs in most cases, but for hydride abstraction from THF, triphenylmethyl cation is less reactive than its ion pair with hexachlorantimonate ion. Propagation rate coefficients (kP/) for free ion polymerization of isobutyl vinyl ether and N-vinylcarbazole have been determined in CH2Cl2, and for the latter monomer the value of kp is 10s times greater than that for the corresponding free radical polymerization. 

Application of these arguments to those data which are unequivocally free ion values does seem to work, however. For example the radiation induced polymerizations produce pre-exponential factors of 10 —10 1 mole sec , slightly larger than the accepted range for the free radical polymerization of styrene. Similarly the work on iV-vfnylcarbazole [29] produces Ap — 10 1 mole" sec", somewhat larger than the free radical value [106], and presumably affected by solvation contributions. The data for isobutyl vinyl ether [31] indicate a value for Ap of 10 —10 , consistent with the idea that free cations are the main contributors. 

Combination of a living ionic polymerization and a metal-catalyzed radical polymerization also leads to comb polymers, where both the molecular weights of the arm and main-chain polymers are well controlled. PMMA with poly(vinyl ether) arm polymers of controlled molecular weights (C-l) were prepared by the copper-catalyzed radical polymerization of methacrylate-capped macromonomers carrying a poly-(isobutyl vinyl ether), which were obtained by living cationic polymerization with a methacryloxy-capped end-functionalized initiator.428 Comb polymers with... 

In addition to free radical polymerizations, however, cationic and anionic polymerizations may, depending on solvent used, also be observed. The anodic discharge of acetate ions into the homogeneous phase, for example, produces a free radical polymerization of styrene or acrylonitrile. The anodic discharge of perchlorate or boron tetrafluoride ions, on the other hand, leads to the cationic polymerization of styrene, iV-vinyl carbazole, and isobutyl vinyl ether. In contrast, the cathodic decomposition of tertaalkyl ammonium salts induce acrylonitrile to polymerize anionically. 

The evidence in the case of styrene, where both modes of radiation-induced polymerization can be conveniently studied, is quite convincing that reduction of the concentration of water changes the predominating mode of propagation from purely free radical to essentially ionic. Evidence for an ionic propagation initiated by radiation has also been obtained in pure a-methylstyrene (3, 24), isobutylene (12, 32), cyclopenta-diene (5), / -pinene (2), 1,2-cyclohexene oxide (II), isobutyl vinyl ether (6), and nitroethylene (38), although the radical process in these monomers is extremely difficult, if not impossible, to study. 

There seems little doubt that in radiation induced polymerizations the reactive entity is a free cation (vinyl ethers are not susceptible to free radical or anionic polymerization). The dielectric constant of bulk isobutyl vinyl ether is low (<4) and very little solvation of cations is likely. Under these circumstances, therefore, the charge density of the active centre is likely to be a maximum and hence, also, the bimolecular rate coefficient for reaction with monomer. These data can, therefore, be regarded as a measure of the reactivity of a non-solvated or naked free ion and bear out the high reactivity predicted some years ago [110, 111]. The experimental results from initiation by stable carbonium ion salts are approximately one order of magnitude lower than those from 7-ray studies, but nevertheless still represent extremely high reactivity. In the latter work the dielectric constant of the solvent is much higher (CHjClj, e 10, 0°C) and considerable solvation of the active centre must be anticipated. As a result the charge density of the free cation will be reduced, and hence the lower value of fep represents the reactivity of a solvated free ion rather than a naked one. Confirmation of the apparent free ion nature of these polymerizations is afforded by the data on the ion pair dissociation constant,, of the salts used for initiation, and, more importantly, the invariance, within experimental error, of ftp with the counter-ion used (SbCl or BF4). Overall effects of solvent polarity will be considered shortly in more detail. 

M.U. Kahveci, M.A. Tasdelen, and Y. Yagci, Photochemically initiated free radical promoted living cationic polymerization of isobutyl vinyl ether. Polymer 2007, 48(8), 2199-2202. 

Solutions of maleic anhydride in ether will initiate cationic polymerizations of isobutyl vinyl ether or Af-vinyl carbazole, if subjected to attacks by free radicals. The same is true if the solutions are irradiated with ultraviolet light or gamma rays. Also, active species are generated from reactions of aldehydes or ketones with maleic anhydride when attacked by free radicals or irradiated by UV light, or gamma rays from These active species are presumed to be formed through... 

If a supporting electrolyte is first oxidized to a radical, indirect cationic polymerization can result. The radical in a subsequent step oxidizes the monomer to a first initiating entity, the cation radical. Such an indirect initiation was also suggested for electropolymerization of isobutyl vinyl ether in the presence of BF4 supporting electrolyte ... 

Three different types of radicals were identified by electron spin resonance (ESR) spectroscopy. In the first case, isolated poly(maleic anhydride) contained one radical identifiable as the MA propagating radical. This same radical was shown to be capable of polymerizing styrene and copolymerizing styrene-methyl methacrylate mixtures. It was also shown that the two other radicals were transformed into active species capable of the cationic polymerization of isobutyl vinyl ether or vinyl ethers in the presence of monomeric... 

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