Preparation And Characterization Of Chiral Polysilanes

“Chiral transfer and amplification” exists everywhere in nature, which has a strong relationship with the origin of life. This phenomenon has been already found not only in asymmetric catalysis, but also in helical polymers. Herein, this phenomenon was studied using optically active copolymers and blends in aggregate states. Optically active-domination phenomenon was firstly observed, which was also preliminary studied in this these. Moreover, it was also found that the optically inactive polydialkylsilanes could be driven to exhibit optical activity by centrifugation. The optical activity was proposed to originate from vortex flow.On the first hand, chiral phenomena of optically active copolydialkylsilanes and polydialkylsilane blends were studied in aggregate states. A series of polydialkylsilanes with same chiral side chains and different achiral side chains were synthesized. Due to the existence of the same chiral side chains, all of them adopted a same preferential screw sense with an enantiomeric excess of right-handed screw sence in solution. It was found that poly[ethyl-(S)-2-methylbutylsilane] could control the optical activity of the co-aggregates constructed by two polydialkylsilanes. Transmission electron microscopy(TEM) images and wide angle X-ray diffraction(WAXRD) patterns indicated that microphase separation existed in the co-aggregates. This microphase separation was driven by the nucleation of poly[ethyl-(S)-2-methylbutylsilane] within the aggregates. This nucleation also destroyed the ordered organization of the other polydialkylsilane. Therefore,optical activity-domination phenomenon was occurred. For the optically active copolydialkylsilanes, poly[ethyl-(S)-2-methylbutylsilane] segments controlled the optical activity of the aggregates. Microphase separation was also identified in the aggregates using TEM and WAXRD. This optical activity-domination phenomenon was also driven by the microphase separation.On the second hand, the effect of centrifugation on the conformation of the optically inactive polydialkylsilanes was studied. It was found that optically inactivepolydialkylsilanes with achiral β-branched alkyl chains could be driven by centrifugation to exhibit optical activity in tetrahydrofuran solutions. Vortex flow was proposed to be driven by the cooperation of gravity and centrifugal forces. Then, the polymer main chains were induced to adopt a preferential screw sense with an enantiomeric excess of single-handed screw sense. This work not only laid a theoretical foundation for the preparation of optically active polymers, but also provided the experimental data for the origin of homochirality on the earth.