Chiral Polymer-based Micro/Nano Functional Materials:Design,Preparation And Applications

Chirality and helical structures are basic characters of nature and are closely related to human lives.The importance of chirality has been widely recognized and chirality has attracted worldwide attention from different disciplines.In recent decades,chirality has constituted a unique research area and remarkable progress has been made.To have a better understanding and further make use of chirality,a series of artificial chiral helical polymers have been synthesized.Among the chiral helical polymers,chiral helical polyacetylenes are extremely interesting due to their conjugated main-chains and the well-known "chiral amplification effect",which benefit them to be applied to chiral enantioselective release,chiral resolution,asymmetric catalysis and circularly polarized luminescence(CPL)for practical applications.Chiral helical polymers can be prepared by directly polymerizing chiral monomers,but the high cost and limited variety of chiral monomers have severely impeded their further development.To overcome this challenge,we established helix-sense-selective polymerization(HSSP)of achiral acetylenics induced by chiral solvent,and prepared a series of helical polyacetylenes with predominant one-handed helical structures.Moreover,we also prepared chiral helical polyacetylene copolymers-based CPL-active materials with good glum by introducing achiral fluorescent acetylenics to the above mentioned HSSP system.Moreover,to enrich the types of chiral helical polymeric materials and realize accurate control of their morphologies,we further applied chiral helical polyacetylenes for the preparation of Janus particles,and a series of polyacetylene Janus particles were fabricated.As a kind of chiral small molecules,chiral solvent is hard to be eliminated thoroughly,which is undesirable for applications and recycling use of chiral sources;accordingly,we used chiral biomacromolecules(cellulose nanocrystals)as chiral source,and prepared ternary chiral porous hybrid particles,which demonstrated enantioselectivity toward chiral drugs.Research details are stated as follows.(1)Two achiral monomers,M1 and M2,respectively bearing three or two phenyl groups were synthesized.CHCl3,chiral ?-pinene and isobutanol were employed to constitute a ter-solvent system,in which M1 underwent helix-sense-selective precipitation polymerization to provide optically active polymer nanomaterials.Chiral ?-pinene transferred its chirality to the resulting polymers in the course of polymerization through non-covalent interactions with phenyl groups.Chiral nano-materials with different morphologies,e.g.,nanofibers,nanorods and nanospheres were obtained by simply changing solvent composition.Repalcing isobutanol by other alkanols,effects of polarity and amount of alkanol on chiral transfer and products'morphology were systematically investigated.(2)Based on the HSSP system established above,we further prepared a series of chiral helical copolymers by introducing another achiral acetylenic with tetraphenylethylene(TPE)pendant group(defined as M3)to the HSSP system.With PMMA as supporting material and CHCl3 as solvent,chiral helical copolymers/PMMA films with CPL character were obtained,taking advantage of the aggregation-induced-emission(AIE)effect of M3.CD and CPL signals are strengthened intensely with increasing ratio of M1,accompanied by the decrease of fluorescence intensity.Moreover,solvent composition had great impact on the intensity of CD and CPL signals.Chiral helical copolymer films with CPL character can be easily prepared by using another achiral fluorescent monomer M4,demonstrating the wide applicability of the established approach to prepare CPL-active materials starting from achiral monomers.(3)Five acetylenics,including two achiral monomers(M5 and M6)and three chiral monomers(M7,D-M8 and L-M8)were employed to prepare polymeric Janus particles(PJPs)through emulsion polymerization combined with solvent evaporation-induced phase separation.With PMMA as template,SDS and PVA as co-stabilizers,CHCl3 as solvent,a series of optically active PJPs were prepared.Concentration of SDS,mass ratio of PMMA and monomers,and affinity of polyacetylenes to aqueous phase all had effects on the formation and morphologies of PJPs.Mushroom-and bowl-like PJPs can be acquired by simply changing the feeding ratio of M7 to PMMA.A possible formation mechanism of PJPs was proposed,which laied a solid foundation for the further development of PJPs.(4)Making use of the natural chirality of cellulose nanocrystals(CNCs),ternary chiral porous hybrid particles(TCPHPs)constructed by CNCs,helical substituted polyacetylenes and inorganic silica were fabricated starting from achiral acetylenic M9.Alkynylated-CNCs served as stabilizers,chiral sources and co-monomers simultaneously,and transferred their chirality to the resulting polymers by copolymerizing with achiral monomers M9.Helical polyacetylenes formed chiral helical structures and thus endowed TCPHPs with intriguing optical activity.Inorganic material formed rigid framework and covalently bonded with organic species with the help of M10.Phase separation process rendered particles with abundant pores.The as-prepared TCPHPs demonstrated chiral enantioselectivity toward chiral naproxen,and preferentially released R-naproxen;the equilibrium enantiomeric excess(e.e.)value was determined to be 65%.The covalent bonds between CNCs and helical substituted polyacetylenes played crucial role in achieving chiral discrimination toward chiral drugs.