Synthesis And Supramolecular Construction Of Branched Polymers And Study On Its Macromolecular Self-assembly Behavior

Branched polymers possess the unique chemical and physical properties. Theconstruction of them consist of covalent bonding and non-covalent interaction.Therefore, branched polymers may not only possess some interesting characters in theresearch of the relationship between properties and structures, but also gain someimportant applications in various fields, such as molecular inclusion, supramolecularself-assembly and nano materials. In this study, one miktoarm star polymers, twoH-shaped polymers, one cyclodextrin-based dumbbell-shaped polymers and twosupramolecular branched polymers were designed and synthesized. The self-assemblybehaviors of the polymers were investigated. The influences of the incorporation ofCDs into the polymers resulting in their properties change were also exhibited. Themain contents and results are summarized as follows:(1) A ABC miktoarm star terpolymer MPEG-PTHF(-PDMA) was synthesized by thecombination of click chemistry， atom transfer radical polymerization (ATRP) andcationic ring opening polymerization (CROP). A block copolymer of poly(ethyleneglycol)(PEG) and poly(N,N-dimethylaminoethyl methacrylate)(PDMA), which bearsan azido at diblock junction (MPEG-N3(-PDMA)) was first prepared by atomtransfer radical polymerization. Then, an alkynyl-terminated narrow distributedpolytetrahydrofuran (PTHF-Alk) was synthesized as another building block viacationic ring opening polymerization. The well-defined ABC miktoarm star shapedterpolymer was afforded by clicking MPEG-N3(-PDMA) onto the chain end ofPTHF-Alk. The structure of the star terpolymer was characterized by the FT-IR, NMRand SEC/MALLS. The self-assembly behavior of the polymer was investigated bydynamic light scattering (DLS) and transmission electron microscopy (TEM). Thisstar shaped terpolymer consists of a hydrophobic PTHF chain, a hydrophiphilic PEGchain and another stimuli-responsive PDMA chain. It can self-assemble into micelleswith different sizes and morphologies at various pH values, such as5.0,7.4and9.5.The micellar size also exhibits temperature-dependence at pH7.4and9.5. Thevariation of size and morphology of the micelles with the solution pH and temperaturewas ascribed to the pH-and thermo-responsive properties of the PDMA block.(2) We devoted our efforts on the synthesis and self-assembly of a well-defined H-shaped terpolymer. The well-defined H-shaped terpolymer was afforded by clickingPEG-N3(-PDMA) onto both chain-ends of PTHF-Alk. We use the ultrasonic vibration,evaporation, and dialysis methods for the preparation of amphiphilic H-shapedterpolymers micelles. They can produce different micellar morphologies in water,including large complex micelles, dot-like micelles, and worm-like micelles. Theformation of large complex micelles depends on the hydrophobic-hydrophilic ratios ofthe different blocks in the H-shaped terpolymers. Furthermore, the large complexmicelles discovered were the result of the cooperative effects of ultrasonic vibration,proper hydrophobic-hydrophilic block ratio, and H-shaped branched architecture.Therefore, these results will further broaden the exploration of complex micelles asrobust building blocks for the formation of self-assembly nanostructures withunprecedented functional features.(3) We synthesized another well-defined H-shaped terpolymer. A triblock copolymerof poly(ethylene glycol)(PEG) and poly(N-isopropylacrylamide)(PNIPAM), whichbears two azido at diblock junction (PEG-2N3(-2PNIPAM)) prepared by atomtransfer radical polymerization. Then, an alkynyl-terminated narrow distributedpolytetrahydrofuran (PTHF-Alk) was synthesized as another building block viacationic ring opening polymerization. The well-defined H-shaped terpolymer wasafforded by clicking PTHF-Alk onto PEG-2N3(-2PNIPAM). This H-shapedterpolymer can self-assemble into complex micelles. The micellar size also exhibitstemperature-dependence. The variation of size and morphology of the micelles withthe solution temperature is ascribed to the thermo-responsive properties of thePNIPAM block. Moreover, it was found that the thermo-induced dehydration ofPEG-2PTHF(-2PNIPAM) was a gradual and continuous process throughout the wholetemperature increasing course.(4) The thermally-responsive dumbbell-shaped polymer PEG-2[CD-(PNIPAMr)x]was synthesized using a combination of click reaction and ATRP polymerization. Thepolymer consists of a PEG central segment and two β-CD as bridge units, with whichabout4-5PNIPAM arms were linked. Above the LCST of PNIPAM segment, thepolymer can self-assemble into flower-like nano-assemblies, in which PNIPAMsegments act as a core part and PEG segments serve as a corona part. The polymershows the evident molecular inclusion ability using Ada-COONa and pyrene as guest molecules. The addition of Ada-COONa into polymer solution can effectively adjustthe size of nano-assemblies.(5) Two AB2type amphiphilic β-CD dimmer, Ibu-CD2and Ada-CD2simultaneouslypossessing two kinds of supramolecular driving forces were synthesized. For Ibu-CD2,branched SPs can be formed in pure water through the host-guest complexationinteraction of β-CD and ibuprofen moieties in Ibu-CD2molecule structure, whereasspherical or irregular nano-micelles were found in water/organic mixtures based onthe hydrophilic-hydrophobic interaction of two hydrophilic β-CD units and onehydrophobic Ibu moiety. The size of SPs increased with the increase of Ibu-CD2concentration, whereas the size of micelles decreased with increasing the volume ratioof water in mixtures. For Ada-CD2, SHPs can be formed in DMF/H2O mixed solventsbased on an AB2type amphiphilic β-CD monomer. The formed SHPs can be thentransferred into spherical nano-micelles with the addition of Ada-Na. Therefore,combining two supramolecular driving forces into one functional small moleculeopens up a convenient and effective way to control the morphology and size ofsupramolecular aggregates in solutions.