Isobutyl vinyl ether concentration

The only studies on olefin polymerisations in methylene dichloride in which kp was deduced directly from the rate of reaction were carried out by Ledwith and his collaborators [9, 13] with extremely low concentrations of monomer and catalyst. They polymerised isobutyl vinyl ether and N-vinyl carbazole in a Biddulph-Plesch calorimeter with trityl or tropylium salts and obtained the first-order rate constants k1 from the conversion curves. Since different catalysts gave the same ratio of kx c they concluded that for each of them Xxr = c0 and hence identified with kp which must in fact be k p, as explained above. It seems unlikely that if several initiators give the same value of kp, they do so because they are all equally inefficient, and the inference that they do so because they are all 100% efficient, i.e., that for all of them x = c0, seems plausible - but it would be useful to have a direct check of this. 

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... 

Apart from some experiments with methyl and /i-chloroethyl vinyl ethers the initiator concentrations employed were such that the initiating cations, and presumably the propagating species, were essentially dissociated from the corresponding counterion. Once again therefore this data is a measure of the reactivity of the free polymeric cations derived from the various monomers. Isobutyl vinyl ether is the monomer most widely studied, and as would be anticipated for free cationic reactivities, the data varies little with the counterion employed (SbClg or BF4), or indeed with the carbocation used as initiator (C7H7 or Ph3C+) under similar experimental conditions. 

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. 

Ueno et al. (35) have reported similar behavior for styrene. In their work, at 30°C. and a dose rate of 2.42 X 1014 e.v. cc. 1 sec. 1, there was an approximate inverse linear relationship between the rate of polymerization of styrene and the concentration of triethylamine, between 10 6 and 10 4M amine. Ammonia and amines have also been observed to inhibit the polymerization of isobutyl vinyl ether (6) and a-methvl-styrene (17). 

Figure 25 The total concentration of living end ([P ]/[HI]0 P active + dormant species) as a function of time in the polymerization of isobutyl vinyl ether with the HI/I2 initiating system in toluene (A) and CH2CI2 (B) at temperatures 0 to -40° C [M]0 = 0.38 M [HI]0 = 10 mM [I2]o = 5.0 mM (in toluene) or 0.20 mM (in CH2CI2). [P ] is determined by quenching the reaction with the sodium salt of ethyl malonate followed by H NMR end group analysis of the product. The vertical arrows indicate the time for 100% conversion at each temperature. (From Ref. 85.)...

Figure 27 H NMR spectra (270 MHz) of the HCI-adduct of isobutyl vinyl ether (A) and its mixtures (B-D) with SnCU in CDzCU/rt-hexane (9 1 v/v) at -78° C at varying SnCU concentrations [adduct]0 = 100 mM. [SnCl4]0 0 (A), 20 (B) 50 (C) 150 (D) tnAf. (From Ref. 105.)...

The only studies on olefin polymerisations in methylene dichloride in which kp was deduced directly from the rate of reaction were carried out by Ledwith and his collaborators (9, 13) with extremely low concentrations of monomer and catalyst. They polymerised isobutyl vinyl ether and N-vinyl carbazole in a Biddulph-Plesch calorimeter with trityl or tropylium salts and obtained the first-order rate constants kt from the conversion curves. Since different catalysts gave the same... 

Kennedy has prepared poly(styrene-b-isobutylene)52,53)bythis technique employing 2-bromo-6-chloro-2,6-dimethyl heptane as the initiator. Similarly, Stannett has prepared poly(vinyl carbazole-b-isobutyl vinyl ether) by addition of the vinyl ether to poly(vinyl carbazole) initiated with Ph3CSbCl6(54). To successfully prepare block copol3rmers it is necessary to maintain a low solvent/monomer ratio (to surpress chain transfer), and a high initiator concentration. 

Previously Funt and co-workers had used a similar electrode to study stable radical-cations (from polynuclear compounds) electrogenerated at the disc (anode) and collected at the ring (cathode). In the presence of either isobutyl vinyl ether or styrene, the concentration of the carbocations reaching the ring decreased. From studies of the collection efficiency, values of the first-order rate constants showed a similar trend to those obtained by other methods. Mengoli and Vidotto were the first to use such radical-cations in electropolymerization and in a recent paper they extend their work on the reaction of radical-cations... 

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