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自从Stephan和Erker两位科学家提出“位阻型(Frustrated)Lewis酸碱对”概念以来,Lewis酸碱对的催化化学得到极大的关注。近年来,人们也发现Lewis酸碱对在催化极性乙烯基单体和内酯单体聚合中有着重要的应用。Lewis酸碱对催化极性乙烯基单体聚合可形成具有高分子量和窄分子量分布的聚合物,而催化活性与所使用的Lewis酸碱对关系密切,最有效的Lewis酸是Al(C6F5)3和B(C6F5)3,Lewis碱是有机磷、氮杂环卡宾和氮杂环卡宾烯和膦腈超强碱,可聚合的单体包括甲基丙烯酸甲酯、γ-甲基-α-亚甲基-γ-丁内酯、α-亚甲基-γ-丁内酯、丙烯酸正丁酯、N,N-二甲基丙烯酰胺、N,N-二苯基丙烯酰胺、乙烯基磷酸二乙酯、2-乙烯基吡啶、2-异丙烯基-2-氧唑林以及非对称的极性二乙烯基单体。聚合过程包括:链引发、链增长和链终止。链引发过程是通过Lewis酸、Lewis碱和单体相互作用形成两性离子,链增长是通过双金属活化单体加成方式进行,链终止通过两种途径:1)增长聚合物链中活化的酯氧负离子对相邻酯中羰基碳原子的亲核进攻形成δ-戊内酯;2)增长聚合物链中活化的烯酯碳负离子对倒数第三个酯中羰基碳原子的亲核进攻形成β-酮酸酯。Lewis酸碱对催化内酯单体聚合可形成线形和环状聚合物,所使用的Lewis酸为Zn(C6F5)3、有机铝、氯化铟,Lewis碱为有机胺。
Since Stephan and Erker two scientists proposed the concept of “Frustrated Lewis acid-base pairs,” the catalysis chemistry of Lewis acid-base pairs has received a great deal of attention. In recent years, it has also been found that Lewis acid-base has an important application in the polymerization of catalyzed polar vinyl monomers and lactone monomers. Lewis acid-base polymerization of the catalytic polar vinyl monomer can form a polymer with high molecular weight and narrow molecular weight distribution, and the catalytic activity is closely related to the Lewis acid and alkali used. The most effective Lewis acid is Al (C6F5) 3 And B (C6F5) 3, Lewis bases are organic phosphorus, azacyclo carbene and azacyclo carbene and phosphazene super alkali, the polymerizable monomers include methyl methacrylate, γ-methyl-α- Γ-butyrolactone, n-butyl acrylate, N, N-dimethylacrylamide, N, N-diphenylacrylamide, Ethyl ester, 2-vinylpyridine, 2-isopropenyl-2-oxathiazole, and asymmetric polar divinyl monomers. The polymerization process includes: chain initiation, chain growth and chain termination. Chain initiation is the formation of zwitterions through the interaction of Lewis acids, Lewis bases and monomers. Chain growth proceeds through the addition of bimetallic activating monomers and the chain terminates in two ways: 1) increasing the amount of activated esters in the polymer chain Oxy anions nucleophilic attack on the carbonyl carbon atoms in the adjacent ester to form δ-valerolactone; 2) increasing the nucleophilic attack of the carbonyl carbon atoms in the penultimate ester resulting from the activation of the enolic ester carbanion in the polymer chain to form β Keto acid ester. Lewis acids and bases can form linear and cyclic polymers for the polymerization of catalytic lactone monomers. The Lewis acids used are Zn (C6F5) 3, organoaluminum, indium chloride and Lewis base are organic amines.