ISSN:
0449-296X
Schlagwort(e):
Physics
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
To elucidate the propagation mechanism in the cationic polymerization of vinyl ethers and β-substituted vinyl ethers, the electron distribution in these monomers was computed by the extended Hückel method. Propylene and styrene derivatives were also studied in comparison with the vinyl ether derivatives. Attempts were made to explain the experimental results by various calculated reactivity indices. With the unsaturated hydrocarbons, the reactivity indices on the β-carbon parallel with the relative reactivity in the cationic polymerization or oligomerization. This agreement suggests that the transition state for the rate-determining step of the propagation reaction is represented by a model in which the carbonium ion interacts with the β-carbon of a monomer. On the other hand, the effect of β-alkyl or alkoxyl groups on the reactivity of vinyl ethers could not be explained by the model in which the carbonium ion interacts with an olefinic carbon or an ether oxygen, or both with two atoms. The following model was proposed on the basis of the electronic stabilization energy due to the de- localization from the occupied orbital of a monomer to the vacant orbital of a carbonium ion. This model can explain reasonably the relative reactivity of vinyl ethers and β-substituted vinyl ethers observed in the cationic copolymerization catalyzed by BF3·O(C2H5)2.
Zusätzliches Material:
6 Tab.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1969.150071109
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