Preparation And Properties Of Chiral Nano-and Micro-materials From Helical Substituted Polyacetylenes

Chirality is a universal characteristic of nature,which plays an indispensable role in the generation and evolution of life.Thereinto,chiral helical polymers have attracted much interest due to their intriguing helical structures and chiral amplification effect.Chiral materials,especially chiral solid materials with regular morphology,have become the research hotspot,such as chiral polymer particles with specific morphology,macro-continuous chiral nanofibers,and chiral porous materials.These chiral materials have important application potentials in the fields of chiral sensing,asymmetric catalysis,chiral drug delivery,chiral separation membrane,and chiral recognition/separation.Therefore,the research and design of chiral nano-and micro-materials have important theoretical research and practical application value.In this thesis,three tapes of optically active nano-and micro-scaled materials were derived from chiral helical polyacetylenes.First,a series of non-spherical chiral polymer particles with adjustable morphology were prepared by electrospraying technology,and the related forming mechanism was investigated.Second,macroscopic and continuously chiral electrospun nanofibers were prepared by electrospinning technology,and the optical activity of the nanofibers was explored in detail.Lastly,an unprecedented,one-step strategy was prepared for judiciously combining chiral helical polymer with graphene to construct chiral hybrid foams.The strategy established in this study provides an effective method for preparing more advanced chiral materials.The major contents are as follows:1.This thesis prepared chiral polyacetylene particles with uniform size distribution by using electrospraying technology,through controlling the concentration of polymer electrospraying solution and adjusting the relevant electrospraying parameters.Achiral/chiral helical substituted polyacetylenes(PPA/PFA)were selected as the representative helical polymers.In order to further enrich the types of chiral particles,the copolymers of two monomers(FA/PA)and the blends of their polymers(PFA/PPA)were further used in electrospraying.A variety of chiral polymer particles with adjustable morphology,structure and chirality were prepared by adjusting the composition ratios of the copolymers and blends.The particles were characterized by SEM,CD,Raman and GPC techniques.According to the results,we summarized the regulation rules of the morphology of various electrospraying particles and proposed the corresponding forming mechanism.2.By using electrospinning technology,continuous chiral nanofibers were prepared via controlling the content of chiral helical substituted polyacetylene(PFA)in spinning solution and adjusting relevant electrospinning parameters.In order to further improve the properties of chiral nanofibers,conventional electrospun polymers(PAN and TPU)were used as substrates to prepare composite nanofibers with excellent mechanical properties by blending with chiral polymer.In order to better explore the chirality of electrospun nanofibers,circular dichroism(CD)and UV-vis absorption spectra were characterized in three different ways:solution method,solid KBr tablet method,and solvent infiltration method.In addition,we also found that chiral helical polyacetylenes can play a role of toughening or reinforcing filler in composite nanofibers,which is expected to open up a new research direction for chiral helical polyacetylene as a functional modifier of common high polymers.3.A simple and feasible method was developed to combine chiral helical polymer with graphene to construct chiral hybrid foam.Graphene oxide(GO),ascorbic acid(L-AA),Rh catalyst,and an achiral acetylenic monomer bearing phenylboronic acid group were mixed in an aqueous dispersion.Under mild conditions,the monomer underwent polymerization;meanwhile GO transformed into reduced graphene oxide(RGO)which in situ self-assembled to construct a 3D porous structure.Herein L-AA simultaneously played double roles:(1)working as a chiral source for the monomer to undergo helix-sense-selective polymerization or transferring its chirality to the polymer chains via forming borate structure;and(2)working as a reducing agent for reducing GO.The eventually obtained chiral hybrid foams demonstrate advantages of porous structure,chirality,and reversible borate functional groups.