Selective Formation of Solute Radicals in the Radiolysis of Neopentane-Cyclopentane Mixtures at 4 and 77 K as Studied by Capillary Gas Chromatography and ESR Spectroscopy

Tilquin, Bernard; Gourdinserveniere, C.; Miyazaki, Tsuyoshi; Fueki, Kenji

doi:10.1246/bcsj.57.2029

Cited by 5 publications

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Reactivity and Crystal Structure

Ohashi¹

1994

Reactivity in Molecular Crystals

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Investigation of solid-state polymerization of crystalline monomers has attracted increasing attention over the past three decades.') Development of this subject relied on the use of ultraviolet(UV) light and ionizing radiation. The high penetration of y rays enables homogeneous initiation of the polymerization in whole crystals. It is also easy to determine the polymer yields per absorbed energy and t o compare inherent reactivities of monomer crystals. O n the other hand, the homogeneous initiation of the polymeri7ation with UV light is difficult unless extinction coefficients of monomers at irradiation wavelengths are sufficiently low. Reflection and scattering of U V light make it impossible to determine quantum yields of polymers. The advantage of U V light is selective excitation by choice of irradiating wavelengths.This chapter gives a comparison of the inherent reactivities of a series of crystalline diethynylbenzene derivatives in solid-state polymerization, which is initiated by radicals generated upon irradiation with y rays. Effects of the molecular packing in the crystals on the reactivities are described. The structures of the monomers are shown in Fig. 6. I , whereNumerous studies have been published on the solid-state polymerization of acetylenic compounds. Most of them examine diacetylenes having a wide variety of substituents.2' The polymeri7ation of the diacetylenes has been interpreted by a typical lattice-controlled mechanism. Crystalline 1,4-diethynylnaphthalene and its analogs including 1,4diethynylbenzene (1) are also known to polymerize when irradiated with UV light.') One of the ethynyl groups participates in the polymeriiation resulting in conjugated polyene backbones having ethynyl groups as pendants. 1,4-Diethynylbeni-ene is regarded as the simplest acetylenic compound that is crystalline at room temperature. Various crystalline diethynylbenzene derivatives, which are dimethyl-, dimethoxy-, or methylmethoxysubstituted bis(3-acetoxy-1 -propynyl)benienes (2-8), were synthesi~ed by procedures in the l i t e r a t~r e .~) The monomer crystals were sealed in Pyrex tubes under vacuum and irradiated with y rays from a h°Co source at room temperature. The product formation in the solid-state polymerization was correlated to the molecular packing in the crystals. When 0.5 M benzene solutions of the monomers were irradiated, there was no difference in the yields and the molecular weight distributions of the products among the monomers. R = CH20COCH1.

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