NMR and ESR studies of the solid‐state polymerization of vinyl monomers. II. Acrylic acid
作者:
A. Forchioni,
C. Chachaty,
期刊:
Journal of Polymer Science Part A‐1: Polymer Chemistry
(WILEY Available online 1972)
卷期:
Volume 10,
issue 7
页码: 1923-1943
ISSN:0449-296X
年代: 1972
DOI:10.1002/pol.1972.150100704
出版商: John Wiley&Sons, Inc.
数据来源: WILEY
摘要:
AbstractThe post‐polymerization of acrylic acid, γ‐irradiated at 77°K, has been studied by broad‐line NMR and ESR between 240°K and 286°K (mp). The changes in the structure of NMR spectra during the polymerization has been related to the conversion yield checked by gravimetry of the polymer formed. The very fast reaction occurring above ⋍270°K has been followed simultaneously by NMR and thermal analysis. This last method indicates an activation energy of chain propagation of 18.6 ± 2 kcal/mole in satisfactory agreement with the value given by the initial slope of the conversion—time curves. ESR experiments show that, while the average radical concentration decays by a factor of about ten between 77°K and 240°K, the local concentration of radicals persisting after prolonged annealing atT>240°K, remains the same as at 77°K, i.e., 1.4 × 1019spins/g. A kinetic scheme, assuming an exponential decay of propagation and termination rate constants with chain length, has been proposed to explain the shape of conversion—time curves as well as the almost constancy of the local concentration of
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