A New Conformation of Methacrylic Acid Radicals in Solid-State Polymerization

Bamford, C. H.; Eastmond, G. C.; Sakai, Y.

doi:10.1038/2001284a0

Cited by 25 publications

(1 citation statement)

References 4 publications

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“…It was found that the signal produced by the initial radicals of structure I in acrylic acid [20] , acrylamide [17] and barium methacrylate [22] changed in shape when the crystal was rotated in the magnetic field. This anisotropy of the signal demonstrates that the radicals are oriented in the crystal, the CH 3 -C bonds lying parallel to the double bonds of the monomer [20] .…”

Section: ) Orientation Of Initial Radicalsmentioning

confidence: 99%

Initiation and Propagation Steps in the Solid State Polymerization of Vinyl Monomers

Chapiro

1972

Israel Journal of Chemistry

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Several problems raised by initiation and propagation steps in solid-state polymerizations are reviewed on the basis of data taken from the literature as well as from unpublished work. The nature of the initial active centers is briefly considered; their addition to double bonds within the crystal is discussed. Examination of initiation yields in radiation-induced polymerizations shows that the efficiency of chain initiation rises with temperature. In most vinyl monomers, the propagation process, which is severely hindered in the crystal, presumably starts at lattice imperfections and thereafter proceeds on behalf of the additional imperfections introduced by the accumulated polymer. In a few specific cases the orientation of the double bonds in the crystal or their localization in certain regions of the crystal favours chain propagation and may result in a stereocontrolled reaction. The role of crystallite boundaries is emphasized particularly in the case of copolymerizations which take place in eutectic mixtures of two monomers.The polymerization of numerous monomers in the crystalline state has led to a large number of investigations in the past decade and a vast amount of experimental data is now available most of which are summarized and discussed in several review articles [1,2,3] . However, the detailed mechanisms of the individual reaction steps are still scarcely understood. It is the purpose of the present paper to consider some problems raised by the reaction steps in solid-state polymerization with the aim of providing a picture of possible mechanisms. It is clear that a complete analysis of this broad field cannot be covered in this discussion, which will be confined to a few aspects of initiation and propagation in crystalline vinyl monomers.

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Section: ) Orientation Of Initial Radicalsmentioning

confidence: 99%

Initiation and Propagation Steps in the Solid State Polymerization of Vinyl Monomers

Chapiro

1972

Israel Journal of Chemistry

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Decay of the ESR signal in ultraviolet‐irradiated poly(methyl methacrylate)

Michel

Chapman

Mao

1967

J. Polym. Sci. A‐1 Polym. Chem.

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ESR spectra of poly(methacrylic acid) and poly(methyl methacrylate): Reinterpretation of the 9‐line spectrum

Iwasaki

Sakai

1969

J. Polym. Sci. A‐1 Polym. Chem.

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The temperature dependence of the ESR spectra of poly(methacrylic acid) and poly‐(methyl methacrylate) γ‐irradiated at room temperature was studied between −196°C and +25°C. The conventional 9‐line spectrum was observed throughout this range with no significant spectral change, in contrast to the propagating radical ··· CH2°C(CH3)COOR found in methacrylic acid monomer or barium methacrylate dihydrate irradiated at −196°C. In addition, the irradiation of methacrylic acid monomer with a low dose at 0°C gave the same 13‐line spectrum as that of the propagating radical obtained by the irradiation at −196°C, while prolonged irradiation at 0°C gave the same conventional 9‐line spectrum as that of poly(methacrylic acid) or poly(methyl methacrylate). The conventional 9‐line spectrum has a much weaker 4‐line component than that of the propagating radical. The difference comes from the surrounding matrix, and the conventional 9‐line spectrum is well interpreted by introducing the concept of the distribution of the conformational angle in the irregular polymer matrix. From simulation of the ESR spectrum, it was found that the intensity of the 4‐line component is very sensitive to the distribution, and that the observed 9‐line spectrum is well reproduced assuming a Gaussian distribution (half‐height width of 5–6°) around the most probable conformation which is nearly the same as that of the propagating radical, where the conformational angles of the two CHβ bonds to the half‐filled p‐orbital are 55° and 65°.

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A New Conformation of Methacrylic Acid Radicals in Solid-State Polymerization

Cited by 25 publications

References 4 publications

Initiation and Propagation Steps in the Solid State Polymerization of Vinyl Monomers

Initiation and Propagation Steps in the Solid State Polymerization of Vinyl Monomers

Decay of the ESR signal in ultraviolet‐irradiated poly(methyl methacrylate)

ESR spectra of poly(methacrylic acid) and poly(methyl methacrylate): Reinterpretation of the 9‐line spectrum

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