Research On The Chirality Of Polysilane Aggregates

In the world, there are lots of chiral structures which are considered to beclosely related to the origin of life on the Earth. The existence of natural chiral polymerssuch as cellulose, starch, protein, RNA and DNA, makes life possible. Now, muchresearch on the origin of homochirality, chirality transfer and amplification, chiralrecognition, as well as chiral memory has been carried out. With the development inpolymer science, people gradually realized that the special asymmetrical structure is notonly of great significance in the life sciences, but also has a wide range of applications indaily life, such as pharmaceutical and display fields. Therefore, the study of chiraltransfer using different methods is not only to build bridges between synthetic polymersand biological macromolecules, but also to provide a theoretical reference for exploringthe origin of life. Because the chiral molecules are usually expensive, it is meaningful toprepare chiral polymers by macroscopic vortex stirring. Moreover, chiral transferbetween polymers is firstly reported.Firstly, a series of achiral polysilanes, polyisobutylnonylsilane (PSi1) andpoly(2-ethyl)butyldecylsilane (PSi2), were designed and synthesized. The monomerswere characterized using nuclear magnetic resonance (NMR), and the molecular weightand molecular weight distribution of polymers were characterized using gel permeationchromatography (GPC). The achiral polysilane aggregates were studied under vortexflow using ultraviolet-visible (UV) spectrophotometer and circular dichroism (CD). Inaddition, the chiral transfer behavior between chiral and achiral polysilanes was studied.It was found that exciton coupling CD signals appeared in both the vortex system and thebinary polysilane aggregate one. For the polysilanes shown here, both the odd-eveneffect and the moleculer weight have no significant influence on chirality transfer.Secondly, poly[4,4’-(S)-(2-methylbutoxy)biphenyloxy]phosphazene (PP-C) bearinga chiral side group was designed and synthesized. They were characterized using Fouriertransform infrared spectroscopy (FT-IR),1H-and31P-NMR, GPC spectroscopy, wideangle X-ray diffraction (WA-XRD) and differential scanning calorimetry (DSC). The results indicated that PP-C had a Mwof2.18×105and PDI of1.96. PP-C has acrystallizing point of-2.0oC and a melting point of28oC. The conformational chiralityof PP-C was studied using CD. It was found that the biphenyl groups of PP-C twistedrandomly in tetrahydrpfuran. However, for the PP-C aggregates, the biphenyl groupstended to twist in single-handedness which was believed to be controlled by the adjacentchiral alkoxygroups.Finnaly, poly[4-(4’-cyanophenylethynyl)phenoxy]phosphazene (PP-F) and4-(4’-cyanophenylethynyl)phenol (F) was synthesized and characterized using FT-IR,NMR, GPC, WA-XRD, thermogravimetric analysis and DSC. The results indicated thatPP-F had a Mwof1.55×105and PDI of2.35and a crystallizing point of0.35oC, as well asa melting point of28.88oC. The emission behaviour of PP-F and F was studied in a seriesof co-solvents with different proportions of good solvent and poor one. It was found thatthe fluorescence intensity of F decreased rapidly with the increasing of water/THF ratio.For PP-F, the fluorescence intensity increased slightly with the increasing ofmethanol/THF ratio. The results indicated that F possesses Aggregation-Caused Quenching(ACQ) behaviour, and PP-F possesses the Aggregation-induced emission behaviour. WhenF was linked to the polyphosphazene backbone, the ACQ phenomenon didn’t occur.