Vinyl Ether Oligomers with Conjugated-Polyene and Acetal Terminals: A New Chain-Transfer Mechanism for Cationic Polymerization of Vinyl Ethers
Vinyl Ether Oligomers with Conjugated-Polyene and Acetal Terminals: A New Chain-Transfer Mechanism for Cationic Polymerization of Vinyl Ethers
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具有共轭多烯和缩醛末端的乙烯基醚低聚物：乙烯基醚阳离子聚合的新链转移机制
DOI：
10.1295/polymj.16.249
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发表时间：
1984
期刊：
影响因子：
2.8
通讯作者：
T. Higashimura
中科院分区：
文献类型：
--
作者：
S. Aoshima;T. Higashimura
在70°C苯中，以BF_3OEt_2、I_2、CF_3SO_3H、CH_3SO_3H和CH_3COClO_4为引发剂，进行了异丁基乙烯基醚（IBVE）和2-氯乙基乙烯基醚（CEVE）的阳离子齐聚反应，并对产物的结构和分子量分布进行了研究。所获得的低聚物由具有共轭多烯（I）或缩醛（II）末端的低聚（乙烯基醚）构成。为了解释I和II的形成，已经提出了一种新的链转移机制，该机制涉及从生长链连续脱醇以得到多烯I和释放的醇与生长的乙烯基醚阳离子反应以产生缩醛封端的低聚物II。含氧酸引发剂（CH_3SO_3 H、CF_3SO_3 H和CH_3COClO_4）比BF_3 OEt_2或碘更能诱导脱醇反应，得到更高的I产率。研究还表明，多烯和缩醛末端不仅在高温下的低聚反应中形成，而且在0°C左右的聚合反应中也形成。因此，乙烯基醚聚合反应中反应混合物的着色现在已被解释为多烯I的形成。
Cationic oligomerizations of isobutyl vinyl ether (IBVE) and 2-chloroethyl vinyl ether (CEVE) were carried out with various initiators (BF3OEt2, I2, CF3SO3H, CH3SO3H, and CH3COClO4) in benzene at 70°C, and the structure and molecular weight distribution of the products were investigated. The oligomers obtained were constituted of oligo(vinyl ether)s with a conjugated polyene (I) or an acetal (II) terminal. To account for the formation of I and II, a new chain-transfer mechanism has been proposed, which involves successive dealcoholation from the growing chain to give polyene I and a reaction of the released alcohol with the growing vinyl ether cation to yield acetal-capped oligomers II. Oxo acid initiators (CH3SO3H, CF3SO3H, and CH3COClO4) induced the dealcoholation more than BF3OEt2 or iodine, giving higher yields of I. It was also demonstrated that the polyene and acetal terminal are formed not only in the oligomerization at high temperatures but also in the polymerization at around 0°C. Thus the coloration of reaction mixtures in vinyl ether polymerization has now been interpreted by the formation of polyenes I.