Dendritic Copolymers Systhesized By Anionic Polymerization And Their Self-Assembly Behavior

Dendritic block copolymers are a kind of multi-blocks hyperbranched copolymers bearing linear polymeric chains between branch points. Due to diversified functions brought by various blocks, these copolymers have wide applications in biological, medical and material areas. As a truly living polymerization method, anionic polymerization has advantages in synthesis of block copolymer with precise composition and well-defined architecture. Therefore, synthetic strategy based on anionic technique is a promising manner to prepare dendritic block copolymers. This thesis explored a continuous way to synthesize dendritic block terpolymers via anionic polymerization, and studied self-assembly properties of obtained copolymers. Amphiphilic dendritic block copolymers were also synthesized via transformation of terminal anionic centers of dendritic polymer into thiocarbonylthio moieties and following reversible addition-fragmentation chain transfer (RAFT) polymerization. Finally, dumbbell-shaped dendrigraft copolymers were prepared by iterative epoxidation reaction and anionic living species grafting step.Continuous synthesis of dendritic block terpolymers via anionic polymerization. Macroinimer was synthesized by quantitative monoaddition of polyisoprenyllithium (PILi) towards 1,3-bis(1-phenylvinyl)benzene (MDDPE) in THE Subsequent copolymerization of macroinimer with styrene after solvent-switch from THF to cyclohexane resulted in living dendritic diblock precursor with PI chain dangling on each branching point. After end-capping of living species with diphenylethylene and addition of lithium chloride,tert-butyl methacrylate (t-BMA) and dimethylaminoethyl methacrylate (DMAEMA) were in-situ initiated to form dendritic block terpolymers. Thiol-ene reaction on PI segment and hydrolysis of PtBMA part into poly(methacryalte acid) (PMAA) were conducted to modify the terpolymers.Self-assembly of dendritic block copolymers. Terpolymer bearing PtBMA segment could self-assemble into large hybrid micelles (LHMs) in the mixture of ethanol (a selective solvent for PtBMA) and THF (ethanol/THF=10/1, v/v). The obtained LHMs had vesicular shell and bicontinuous interior fabricated by interconnected worm-like micelles. It was argued that copolymer aggregated into large multimolecular micelles at low ethanol concentration and then experienced a morphological transformation from surface towards core to decrease interfacial area to form LHM with increase of ethanol amount. The existences of dendritic topology, PI segment and short PtBMA chain were confirmed as key factors to the formation of LHM. After further solvent switch into n-heptane, LHMs showed a programmable self-assembly into vesicle-like structure. Polymers with PDMAEMA chains aggregated into vesicles or micelles in water or acetone, respectively.Synthesis of amphiphilic dendritic block copolymers based on mechanism transformation. Anionic living dendritic polymer was prepared by copolymerization of inimer (synthesized from monoaddition of MDDPE with s-BuLi) and styrene in cyclohexane. The terminal living species were transformed into thiolcarbonylthio functionalities by sequential additions of DPE, CS2 and 1-phenylethyl bromide to give Macro-CTA. The resulting Macro-CTA was further used to mediate RAFT polymerization of N-isopropylacrylamide (NIPAM) to give amphiphilic block copolymer with PS core and PNIPAM shell. Such amphiphilic copolymers fromed aqueous solution with lower critical solution temperature (LCST) and showed emulsification effect to stabilize thermo-responsive emulsion in mixture of toluene and water.Synthesis of dumbbell-shaped dendrigraft copolymer. Linear terpolymer PI-b-PS-b-PI prepared via anionic polymerization was utilized as precursor. The PI segment in the precursor was subject to epoxidation reaction to introduce epoxy groups, which were subsequently attacked by PILi or PS-b-PILi to achieve grafting copolymer. Repeating the steps of epoxidation and anionic grafting reaction resulted in dumbbell-shaped dendrigraft copolymer with high generation. The molecular weights of copolymers increased dramatically with increase of generations, while the intrinsic viscosity of polymers decreased due to their increasing branching characteristics. Analysis of high generation copolymer including light scattering measurement and AFM observation confirmed its spherical structure.