Electron spin resonance styrene polymerization

The formation of ion radicals from monomers by charge transfer from the matrices is clearly evidenced by the observed spectra nitroethylene anion radicals in 2-methyltetrahydrofuran, n-butylvinylether cation radicals in 3-methylpentane and styrene anion radicals and cation radicals in 2-methyltetrahydrofuran and n-butylchloride, respectively. Such a nature of monomers agrees well with their behavior in radiation-induced ionic polymerization, anionic or cationic. These observations suggest that the ion radicals of monomers play an important role in the initiation process of radiation-induced ionic polymerization, being precursors of the propagating carbanion or carbonium ion. On the basis of the above electron spin resonance studies, the initiation process is discussed briefly. 

Finally, various attempts have been reported to interpret the kinetics of radiation grafting. The study by Mock, and Vanderkooi (123) concerned the mutual radiation grafting of styrene from the vapor phase to ethyl cellulose film at 50° C. The radical flux was determined separately using electron spin resonance. The kinetic scheme rigorously took account of the diffusion controlled nature of the reaction and the appropriate diffusion constants were separately determined (124). The value for the ratio of for the graft polymerization was determined as... 

Despite of this inherent limitation, several spectacular results have been obtained. It should be noted that the initiation mechanism of the cationic polymerization of styrene described above was also deduced from the results of pulse radiolysis experiments. The pulse radiolysis combined with other techniques, such as the matrix isolation technique, the electron spin resonance technique and usual polymerization techniques, definitely provides a powerful means for investigating fundamentals of polymerization. 

ESR (electron spin resonance) experiments of disappearance of OH-TEMPO in reactions of polymerization in which pure styrene or stjrene with small amounts of MA (1-2% wt.) are heated at 80 °C in the presence of a small amount of OH-TEMPO (4.5 X 10 M), are shown in Figure ID. These indicate that the nitroxide disappears faster when the concentration of MA increases. The disappearance of the nitroxide would be probably due to the formation of the corresponding alkoxya-mine. The possibility of reaction with a free... 

Grassi, A. Pellecchia, C. Oliva, L. Laschi, F. A combined NMR and electron spin resonance investigation of the (C5(CH3)5)Ti(CH2C6H5)3/B(C6F5)3 catalyst system active in the syndiospecific styrene polymerization. Macromol. Chem. Phys. 1995,196, 1093-1100. 

MacLeod RP, Veregin N, Odell PG, Georges MK. Electron spin resonance studies of the stable free-radical polymerization of styrene. Macromolecules 1998 31 530-531. 

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... 

The electron spin resonance (ESR) spectra of the toluene mixtures of the different titanium compounds, MAO, and TIBA are the same (Rg. 2.5). The active site of the syndiospecific styrene polymerization is the same after the reaction of the titanium compounds with TIBA. 

The catalyst for the styrene polymerization is prepared by the mixing of a compound with MAO. The catalytic activity of Cp Ti(OMe)3 is increased by the mixing time under room temperature, and the intensity of the electron spin resonance (ESR) spectrum (g=1.998) also showed an increase of the trivalent titanium species (Fig. 4.6). The polymerization activity of a titanium catalyst increases with an increase in the molar ratio of MAO to Ti. 

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