在离子液体介质中对甲基苯乙烯阳离子聚合的研究

Cationic Polymerization of p-Methylstyrene in Ionic Lquids Media

以离子液体为介质,通过密度泛函理论计算和实验分析,研究了离子液体对甲基苯乙烯(p-MeSt)的阳离子聚合的影响;考察了不同引发体系和不同离子液体对聚合的影响.通过核磁共振氢谱(1H-NMR)和傅里叶红外变换光谱(FTIR)对产物结构进行表征,凝胶渗透色谱(GPC)测定产物分子量与分布,温度记录仪跟踪测定体系温度与聚合时间的关系.结果表明,在离子液体中枯基醇(CumOH)/BF3·OEt2引发体系具有较好的引发效果;与传统分子溶剂相比,在1-丁基-3-甲基咪唑双(三氟甲烷磺酰)亚胺(缩写[Bmim][NTf2])离子液体中得到的聚合产物分子量和产率均较高(达99%),且分子量分布较窄(Mw/Mn～2.0);离子液体在阳离子聚合中仅是惰性溶剂,未直接参与反应,虽然离子液体的离子环境并不能完全抑制链转移反应,但具有稳定活性种和分散正电荷的作用,且使聚合反应更温和;离子液体回收利用实验结果表明,离子液体可多次循环利用,对产物影响不大;最终推导了离子液体中由CumOH/BF3·OEt2引发的p-MeSt阳离子聚合的基元反应机理.

In this study,cationic polymerization of p-methylstyrene(p-MeSt)was studied in ionic liquid(IL)reaction media.The effects of ILs on p-MeSt cationic polymerization were analyzed through density functional theory(DFT)and experimental method.The influences of various initiating systems on p-MeSt cationic polymerization were investigated,and the efficiencies of various ILs as reaction solvents were discussed.The structure of the polymerization product was characterized through 1 H-NMR and FTIR characterization analyses;number-average molecular weight(Mn)and molecular weight distribution were measured through gel permeation chromatography(GPC);a temperature recorder tracked the relationship between polymerization system temperature variation and reaction time.The results showed that a CumOH(2-phenyl-2-propanol)/BF3·OEt2 initiating system is relatively effective in IL media over those frequently used in cationic polymerization reactions.The products polymerized in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide([Bmim][NTf2])IL media have higher molecular weight and yield(up to 99%)and narrower molecular weight distribution(Mw/Mn is^2.0)than those in traditional molecular solvents(such as CH2 Cl2).An analysis of the effects of ILs on polymerization indicated that ILs act as inert solvents in p-MeSt cationic polymerization and do not directly participate in the polymerization reaction.The ionic environment of IL cannot inhibit a chain transfer reaction completely,but can stabilize active species and disperse positive charges.Thus,the polymerization reaction is milder in IL media than that in traditional molecular solvents.The results of IL recovery and reuse showed that these solvents can be used as reaction medium over a number of cycles without remarkable influence on the products.Finally,the corresponding elementary reaction mechanism of the cationic polymerization of p-MeSt initiated by the CumOH/BF3·OEt2 system in[Bmim][NTf2]IL media was proposed in this study.As is known,ILs are recyclable and environmentally friendly green solvents.This study expands the reaction solvent of cationic polymerization and promotes the development of green chemistry.