电子亲和势法判断负离子聚合单体的活性

ELECTRON AFFINITY METHOD FOR DETERMINING THE ACTIVITY OF MONOMERS IN ANIONIC POLYMERIZATION

提出了利用不同取代基烯类单体的电子亲和势来判断其负离子聚合反应活性的方法.采用密度泛函理论的B3LYP/6-31G(d)方法优化了不同取代基烯类单体几何构型,在B3LYP/6-311++G(3df,2p)水平上计算了其电子亲和势.通过电子亲和势计算值与文献报道实验数据比较,表明本文采用的计算方法是比较可靠的.结合不同取代基烯类单体的电子亲和势的计算结果,通过与Q-e关系及取代基常数σ数据进行比较表明,电子亲和势可以用来判断不同单体负离子聚合反应的活性高低.

The electron affinities（EA） of the vinyl monomers with different substituents were used to determine the anionic polymerization activities of the vinyl monomers. To obtain the theoretical EA data of the vinyl monomers, the Gaussian 03 program based on density functional theory was employed. The geometry of the monomers with different substituents was first optimized by a B3LYP method with 6-31G（d） basis sets, then the electron affinities were calculated at the level of B3LYP/6-311 ＋＋ G（3df,2p）. It is suggested that the method used to calculate the molecular electron affinity is reliable according to the comparison between the predicted and the experimental EA values. The Mulliken charges of C=C double bonds in different monomers is helpful to determine the reactive sites of the anionic polymerization. The monomers with EA values less than - 20 kJ·mol^-1 are mainly conjugated alkenes without polarity, which only react with strong nucleophilic initiators. The EA vaules of the monomers with a relatively strong electron-withdrawing substituent are generally in the ranges of - 20 - 60 kJ·mol^-1, which can be polymerized with the weak nucleophilic. While the EA values of the monomers with two strong electron-withdrawing substituents are generally more than 60 kJ·mol^-1, and the corresponding monomers can react with very mild nucleophiles. Therefore, the EA values of the monomers with different substituents could be used to determine the anionic polymerization activities of the monomers. This conclusion was further validated according to the comparison with the Q-e and σ values.