ISSN:
0360-6376
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The effects of three types of free radical initiators (HO·, H2N·, and H3C·) from redox systems, have been studied for four types of methallyl monomers, by use of ESR with a flow system. The structure, the relative concentrations, and the steric conformations of the monomer radical intermediates have been derived from the ESR spectra. In the case of H2N · and HO · addition to methallyl alcohol (MAA), methallyl amine (MAAm), and sodium methallyl sulfonate (SMAS), the ESR spectra of the reacting species are interpreted as monomer head radicals only (H2N · and HO · are added to the monomer tail). Methallyl acetate (MAAc) with HO ·, is an exception, giving hydrogen abstraction to form an allyl type radical. This reaction may influence the polymerization behavior of MAAc. The methallyl monomers behave differently from the allyl monomers, where appreciable amounts of monomer tail radicals were found in addition to the head radicals which were the main species. For methallyl monomers, this may be due to steric hindrance caused by the two substituents on the α carbon. The CH3 radicals add only to positively polarized reactive double bonds, i.e., in SMAS in this study, and allyl alcohol in a previous study. The coupling constants of β CH2 protons vary considerably with the substituents. For β1 protons, the coupling constants decrease in the order OH 〉 CH3 〉 NH2. For β2 protons (allyl hydrogen), the coupling constants decrease in the order CH2OH 〉 CH2NH2 〉 CH2OCOCH3Na, i.e., the constants decrease in the order of increased bulkiness of the groups. Some exceptions are interpreted as due to complex formation with Ti4+. The effects of pH of the reaction medium are largely those expected.
Zusätzliches Material:
10 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1973.170110812
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