Design, Synthesis And Self-assembly Of Optically Active Helical Substituted Polyacetylenes

Recently, optically active helical polymers have attractedever-increasing attentions owing to their unique structures and propertiessuch as chiral recognition, chiral separation, chiral memory, asymmetriccatalysis, and so on. Various kinds of helical polymers have beensynthesized in the past several decades and widely applied in the fields ofoptical coatings, liquid-crystal materials, photoelectric sensors,biomedical chemistry, etc. In this dissertation, hydrophobic substitutedpolyacetylens with stable helical conformations were prepared in aqueousmedium instead of toxic and volatile organic solvents; furthermore,optically active amphiphilic polymer brushes based on helicalpolyacetylenes were prepared via atom transfer radical polymerizationand then self-assembled into core/shell nanoparticles, whichsimultaneously possessed optical activity and thermosensitivity.The major contents are as follows:1. A series of hydrophobic substituted acetylene monomers (M111)were examined as to their abilities to form inclusion complexes with both HP-β-CD and HP-γ-CD. The inclusion model of the monomer andcyclodextrin was also quantitatively investigated. Afterward, theinclusion complex underwent catalytic polymerization in aqueousmedium in the presence of water-soluble rhodium catalyst to providesubstituted polyacetylenes. UV-vis and CD analyses demonstrated thatthe as-prepared polymers also adopted helical conformations, just liketheir counterparts prepared in organic solvents. By comparing the twodifferent polymerization methods (polymerization in aqueous media byusing monomer inclusion complex vs. polymerization in organic solventby directly using monomer), we further found that the polymersseparately obtained via the two different routes exhibited no pronounceddifference in terms of polymers' yield, composition, and the ability toform helical conformations. The reusability of cyclodextrins in thepolymerization was also investigated quantitatively. We found that mostof the cyclodextrin used in this polymerization system remained in theaqueous solution and can be reused for several times.2. A novel N-propargylamide monomer (M12) was synthesized andthen copolymerized with chiral monomer (M11) to produce the helicalpolymers bearing α-bromoisobutyryl pendent groups. Optical rotations,UV-vis and CD spectra demonstrated that both poly(116-co-12₁) andpoly(1110-co-12₁) can form helical conformations and furthermore showconsiderable optical activitities. Polymer brushes based on the helical polyacetylenes were further prepared by using poly(116-co-12₁) andpoly(1110-co-12₁) as macroinitiators via a "grafting from" method. Theas-prepared polymer brushes also possessed remarkable optical activities,which origined from the preferential one-handed screw sense of thepolymer backbone. Moreover, the polymer brushes can self-assemble inthe mixture of THF and water into core/shell nanoparticles, whichsimultaneously showed optical activities and thermosensitivities. TEM,UV-vis and CD analyses further indicated that the core/shell nanoparticleswere composed of optically active poly(N-propargylamide)s core andthermosensitive PDMAEMA shells.3. Optically active, thermosensitive, and amphiphilic polymer brushes,which consist of helical poly(N-propargylamide)s main chains andthermosensitive PNIPAm side chains, were prepared via a novelmethodology combining catalytic polymerization, ATRP, and clickchemistry. Helical poly(N-propargylamide)s bearing α-bromoisobutyrylpendent groups (poly(11-co-12)) was synthesized via catalyticpolymerization, followed by substituting the–Br moieties with azidogroups. Then, alkynyl terminated PNIPAm formed via ATRP wassuccessfully grafted onto the azido functionalized poly(11-co-12) viaclick chemistry, providing the expected polymer brushes(poly(11-co-12)-g-PNIPAm). GPC, FT-IR, and1H-NMR measurementsindicated the successful synthesis of the novel amphiphilic polymer brushes. UV-vis and CD spectra evidently demonstrated the helicalstructures of the polymer backbones and the considerable optical activityof the final brushes. The polymer brushes self-assembled in aqueoussolution forming core/shell structured nanoparticles, which werecomprised of optically active cores (helical polyacetylenes) andthermosensitive shells (PNIPAm).4. Rod-coil amphiphilic copolymer brush(PNIPAm-b-poly(13)-g-poly(11)) consisting of optically active helicalsubstituted polyacetylene as hydrophobic rod-like side chains andpolyacrylamide as hydrophilic coil main chain was synthesized by athree-step process:(1) synthesis of amphiphilic diblock copolymerbearing polymerizable C≡C bonds via consecutive ATRP, followed by (2)self-assembly of the diblock copolymer to provide polymer micelles; and(3) catalytic emulsion polymerization of substituted acetylene monomerconducted by using the polymer micelles as nanoreactors to produce thecore/shell nanoparticles. Both the core/shell nanoparticles and therod-coil copolymer exhibited remarkable optical activities, arising fromthe optically active helical substituted polyacetylene constructing the rodblock. UV-vis and CD spectra demonstrated the helical structures of thepolyacetylenes and the considerable optical activity of both the core/shellnanoparticle and rod-coil copolymer, and further indicated thatPNIPAm-b-poly(13)-g-poly(11) was comprised of optically active helical polyacetylenes side chains and thermosensitive PNIPAm main chain.