The Synthesis And Application Of Initiators With Chiral Oxazoline Groups In Helix-sense-selective Polymerization

Study and synthesis of chiral polymer is an important subject in the field of asymmetric synthesis, but it usually originated from expensive chiral monomer. Therefore, using the achiral monomer to prepare helical polymers has very important significance. Due to competing effects between the solvent and ligand ligand, anionic polymerization of achiral monomer in the presence of optically active alkyl lithium and chiral ligands is easily influenced by the solvent property. However, this disadvantage can be eliminated with chiral organic lithium as initiator in the polymerization. At present, very limited optically active initiators with chiral centre were exploited, especially carbon anionic chiral initiators were rarely reported. In order to expand the type of chiral anionic initiator and extend chiral polymer preparation method, carbon anionic initiators containing chiral oxazoline group were well designed and synthesized and its applications in the asymmetric polymerization were investigated. The effects of initiator structure in anionic polymerization were also studied.The research work contains three parts:1) Design and synthesis of chiral carbon anionic initiatorFluorenyl lithium is an achiral carbon anionic initiator, which is also used in anionic asymmetric polymerization with chiral ligand to prepare the helical polymer. Therefore, two chiral compounds,(S)-1-(9H-fluorene-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-1-FIDD) and(S)-2-(9H-fluorene-2-yl)-4-isopropyl-4,5-dihydrooxazole((S)-2-FIDD), were exquisitely designed and synthesized based on fluorene moiety. Active methylene on fluorene ring of these compounds can react easily with alkyl lithium to produce fluorenyl lithium derivative, and introducing chiral oxazoline group on fluorene ring will afford chiral source of the initiators.2) Asymmetric anionic polymerization of achiral isocyanatesPolyisocyanates are well known as typical semiflexible polymers with a rigid rodlike main chain consisting of amide bonds, and the steric effect between the carbonyl on main chain and side chain is the main reason for isocyanate monomer polymerization to form a helical polymer. Thus, anionic asymmetric polymerization of five kind of achiral isocyanates(n-Butyl isocyanate(n-BI), tert-Butyl isocyanate(t-BI), Cyclohexyl isocyanate(CI), m-Methylphenyl isocyanate(m-MPI) and m-Methyloxyphenyl isocyanate(m-MOPI)) with chiral anionic initiators such as(S)-1-FIDH-Li and(S)-2-FIDH-Li were carried out. All the obtained polyisocyanates exhibited optical activity which should be originated from asymmetric induction effect of chiral initiators. We also found that the molar ratio of monomer and initiator, the polymerization solvent, the substituents types of isocyanate monomer and the substituent position of chiral initiator have a great influence of the chiroptical properties of polyisocyanates.3) Asymmetric anionic polymerization of achiral N-VinylcarbazoleThe effects of the molar ratios of monomer and initiator, the polymerization solvent, the substituent position of chiral initiator and the polymerization temperature were studied in the anionic asymmetric polymerization of N-Vinylcarbazole. The monomer initiated by chiral anionic initiator n-BuLi-(-)-Sp and FlLi-(-)-Sp were aslo investigated. The results show that in the process of NVC anionic asymmetric polymerization, ligand control was not more effective than chiral initiators control. There may be two reasons:(1) the serious side reaction in the anionic polymerization of NVC using RLi as an initiator and(2) the effect was small between ligand control and initiator control due to short polymer chain.