Cationic Polymerizability of Vinyl Acetate: Alternating Copolymerization with 1,3-Dioxolan-4-ones and Branched Copolymer Formation with Cyclic Acetals
Cationic Polymerizability of Vinyl Acetate: Alternating Copolymerization with 1,3-Dioxolan-4-ones and Branched Copolymer Formation with Cyclic Acetals
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乙酸乙烯酯的阳离子聚合性：与 1,3-二氧戊环-4-酮交替共聚以及与环状缩醛形成支化共聚物
DOI：
10.1021/acs.macromol.2c00979
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发表时间：
2022
期刊：
影响因子：
5.5
通讯作者：
S.
中科院分区：
文献类型：
--
作者：
Azuma;J.; Kanazawa;A.; Aoshima;S.
醋酸乙烯酯（VAc）由于与乙烯基相邻的氧原子通过共振提供电子而潜在地表现出阳离子聚合性。在这项研究中，VAc 和几乎没有或没有均聚性的共聚单体的阳离子共聚显示出非常频繁的交叉反应。当 1,3-二氧戊环-4-酮通过开环产生与氧相邻的碳正离子且不具有均聚性时，将其用作共聚单体，在 GaCl3 催化下与 VAc 进行共聚时，可产生交替共聚物。 VAc与2,5-二甲基-1,3-二氧戊环-4-酮共聚得到Mn为6.4×103的交替共聚物。此外，VAc与具有适当结构的环状缩醛共聚时生成了含有部分分子量超过105的支化共聚物。具体来说，从主链中的半缩醛酯部分中抽出VAc衍生的乙酰氧基很可能导致碳正离子的生成以及随后与单体的反应以形成支化结构。当用α-当归内酯代替VAc时，由于其刚性环状结构，半缩醛酯部分不太可能发生反应，与1,3-二恶烷共聚时得到Mn为10.4×103的交替共聚物。基于核磁共振波谱对聚合产物的详细分析，讨论了产生此类共聚物结构的共聚机理。
Vinyl acetate (VAc) potentially exhibits cationic polymerizability due to electron donation from the oxygen atom adjacent to the vinyl group through resonance. In this study, cationic copolymerizations of VAc and comonomers with little or no homopolymerizability were shown to proceed with very frequent crossover reactions. Alternating copolymers were produced when 1,3-dioxolan-4-ones, which generate a carbocation adjacent to oxygen via ring opening and exhibit no homopolymerizability, were used as comonomers in copolymerizations with VAc catalyzed by GaCl3. An alternating copolymer with anMnof 6.4 × 103was obtained in the copolymerization of VAc and 2,5-dimethyl-1,3-dioxolan-4-one. Moreover, branched copolymers containing a portion with molecular weights over 105were generated in copolymerizations of VAc with cyclic acetals exhibiting appropriate structures. Specifically, abstraction of the VAc-derived acetoxy group from the hemiacetal ester moiety in the main chain most likely resulted in carbocation generation and subsequent reaction with a monomer to form branched structures. The reaction of a hemiacetal ester moiety did not occur likely due to the rigid cyclic structure whenα-angelicalactone was used instead of VAc, resulting in an alternating copolymer with anMnof 10.4 × 103in the copolymerization with 1,3-dioxane. The copolymerization mechanisms generating such copolymer structures were discussed based on detailed analyses of the polymerization products by NMR spectroscopy.
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