Kanae Hayashi

Radiation-induced polymerization by free ions. Part 3.—Rate constants for cationic polymerization

The general kinetics of radiation-induced ionic polymerization are discussed and the effects resulting from impurity termination are analyzed quantitatively. A method is described for the calculation of the propagation rate constants kp by combining measurements of polymerization rates with conductivity determinations of the ionic lifetime in the stationary state. The rate constant for cationic propagation by free ions is ca. 4 × 106 M–1 sec–1 for both styrene and α-methylstyrene in the bulk monomer. This large value suggests that the lower results obtained previously for styrene by the use of chemical cationic catalysts refer mainly to ion pairs of varying reactivity.

Radiation-induced polymerization by free ions. Part 2.—Electrical conductivity measurements

The radiation-induced specific electrical conductivities σ of rigorously dried cyclohexane, styrene, α-methylstyrene, and isobutyl vinyl ether have been measured as a function of dose rate I. A dependence of σ∝In is observed with n between 0.50 and 0.59, depending upon the system. It is confirmed that the absolute measurements of σ for cyclohexane are consistent with G(free ions)≃ 0.1, on the basis of reasonable values for the ionic mobilities. The mean lifetime τ(sec) of the ions in the stationary state is obtained directly from σ(ohm–1 cm–1) by means of the relation 1/τ= 3.6 × 1012πσ/Iµ, where Iµ is the dielectric constant; τ is about 50 msec at I= 1015 eV cm–3 sec–1 for the monomer systems. At the same dose rate, the σ values for styrene and α-methylstyrene are lower than for cyclohexane by a factor of about 2. These results suggest that some charge carriers in the monomers have mobilities comparable to those in cyclohexane. The radiation-induced conductivities of the hydrocarbon monomers are not appreciably affected by the addition of ethanol and ammonia, but are reduced by water. Some possible reasons for this behaviour are examined.

Recent Progress of Photo- and Radiation-Induced Ionic Polymerizations

Abstract Photoinduced ionic polymerizations of the monomers α-methylstyrene, cyclohexeneoxide, nitroethylene, and acrylonitrile were carried out in the presence of electron acceptor or donor molecules. These polymerizations are proved to be initiated by ions formed through the dissociation of the photoexcited electron donor-acceptor complex and to proceed by ionic mechanism. The molecular weight distribution of the polymer and the light intensity dependency on the rate of polymerization indicate that free ionic and ion-pair propagations coexist in the cationic polymerization of α-methylstyrene. Anionic polymerizations were observed for the nitroethylenetetrahydrofuran and acrylonitrile-dimethylformamide systems. Radiation-induced cationic polymerizations of styrene and α-methylstyrene were found to proceed by free cationic propagation. The effect of added electron acceptors in these polymerizations was investigated.

ION RADICALS OF STYRENE IN IRRADIATED ORGANIC GLASSES STUDIED BY ELECTRON SPIN RESONANCE.

Abstract In order to study the correlation between active species formed from styrene by radiation and its radiation-induced polymerization, irradiated organic glasses containing styrene were examined by the electron spin resonance (ESR) method at 77°K. In 2-methyltetrahydrofuran glass, anion radicals of styrene were formed by the transfer of electrons ejected by radiation from the glass matrix molecules to styrene. In n-butylchloride glass, cation radicals of styrene were formed by the transfer of positive charges. The ESR spectrum of the anion radicals is a broad singlet with a width between the maximum slope points of 15 Gs and is not bleached readily by visible light, whereas that of the cation radicals has a width of 23 Gs and is not bleached. The radiation-induced polymerization proceeded in the glass where the cation radicals were present. Otherwise, no polymerization was found. This suggests that the radiation-induced polymerization of styrene, especially in the glassy state, proceeds by a cationic mechanism.