Copolymerizability Evaluation in Cationic Vinyl-Addition and Ring-Opening Copolymerization of Vinyl Ethers and Oxiranes: Effects of Bulkiness and the Number of Substituents Introduced into Oxiranes
2021
Kawamura, Yui | Hotta, Daisuke | Kanazawa, Arihiro | Aoshima, Sadahito
The kinds of alkyl substituents and the number of substituents were demonstrated to affect the reactivity of oxiranes in the cationic copolymerization with alkyl vinyl ethers. A series of di-, tri-, or tetrasubstituted oxiranes with two alkyl groups at the 2-position, which generate a tertiary carbocation by ring opening, were designed and synthesized. When 2,2-dialkyl-substituted oxiranes with a methyl group and a propyl, isopropyl, or neopentyl group at the 2-position were copolymerized with isopropyl vinyl ether, the incorporated amounts of oxiranes into copolymer chains decreased in this order, which indicates that oxiranes with bulkier substituents exhibit a lower reactivity. The order of the reactivities of these oxiranes in copolymerization was also consistent with the reactivity in methanolysis by an acid catalyst. In addition, the bulkiness of the substituent at the 3-position of trisubstituted oxiranes with two methyl groups at the 2-position affected the reactivity in copolymerization in a manner similar to that of the disubstituted oxiranes. Tetrasubstituted oxiranes were also examined; however, insoluble products were obtained or oxiranes were not incorporated into polymer chains. Oxiranes with six- or five-membered fused ring structures, such as limonene oxide, exhibited relatively high reactivities. The results obtained in this study can lead to a systematic understanding of the polymerizability of oxiranes.
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