Research On Micellization Of Doubly Thermo-responsive Block Copolymer And Preparation Of Multicompartiment Block Copolymer Nanoparticles

In recent years, doubly thermo-responsive block copolymers have drawn much attention due to their complex and interesting self-assembly behavior and potential applications. In this paper, two doubly thermo-responsive block copolymers of poly[N-(4-vinylbenzyl)-N,N-diethylamine]-block-poly[N-isopropylacrylamide]-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PVEA-b-PNIAPM-b-PVEA) that has two LCSTs (lower critical solution temperature) and poly(tert-butyl methacrylate)-block-poly[N-(4-vinylbenzyl)-N,N-diethylamine] (PtBMA-b-PVEA) that has LCST and UCST (upper critical solution temperature) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, then their temperature-induced micellization were investigated. Based on the solubility of PVEA and PtBMA in ethanol/water mixture, a novel method of preparing multicompartment block copolymer nanoparticles (MCBNs) by RAFT dispersion polymerization of styrene using simultaneously them as macro-RAFT agents was proposed. The content of this dissertation involves the following three aspects:1. Research on micellization of doubly thermo-responsive ABA triblock copolymer of PVEA-b-PNIPAM-b-PVEAIn this section, a doubly thermo-responsive triblock copolymer of PVEA-b-PNIAPM-b-PVEA triblock copolymers were synthesized by RAFT polymerization and its thermo-responsive micellization in the different proportion methanol/water mixture was studied. In the methanol-rich mixture, PVEA blocks showed LCST-type phase transition and PNIPAM blocks soluted, while in the water-rich mixture, PNIPAM blocks showed the LCST-type phase transition and PVEA blocks disoluted, so this triblock copolymer exhibited solvent-tunable doubly thermo-responsive behavior. Specifically, in the methanol-rich mixture, the triblock copolymer self-assemblied from soluble molecular chains to flower-like micelles constructed with a PVEA core and PNIPAM corona; in the water-rich mixture, the triblock copolymer self-assemblied from flower-like micelles to micelles aggregates; in the middle proportion methanol/water mixture, the triblock copolymer kept flower-like micelles and no LCST was detected. Besides, the effect of block chain length on the two LCSTs was investigated.2. Synthesis of doubly thermoresponsive’schizophrenic’PtBMA-b-PVEA diblock copolymers and its temperature-sensitive flip-flop micellizationIn this section, a doubly thermo-responsive diblock copolymer of PtBMA-b-PVEA was prepared via RAFT polymerization and its temperature-induced’schizophrenic’ micellization was investigated. In methanol, PtBMA blocks could show UCST-type phase transition while PVEA blocks could show LCST-type phase transition. So with the environment temperature increased, PtBMA-b-PVEA diblock copolymer could undergo two phase transitions. That is, at temperature below the UCST of PtBMA block, PtBMA-b-PVEA formed PtBMA@PVEA micelles constructed with PtBMA-core and PVEA-corona, at temperature above the UCST of PtBMA block and below the LCST of PVEA block, PtBMA-b-PVEA kept soluble molecular chains, at temperature above the LCST of PVEA block, PtBMA-b-PVEA formed inverse PVEA@PtBMA micelles constructed with PVEA-core and PtBMA-corona. The transformation from core-corona micelles, to soluble polymer chains, lastly to inverse core-corona micelles in methanol confirmed the ’schizophrenic’ behavior of PtBMA-b-PVEA. Besides, the effect of the block chain length on the LCST and UCST was studied.3. Preparation of multicompartment block copolymer nanoparticlesIn this section, by simultaneously employing two macro-RAFT agents of PVEA and PtBMA in dispersion RAFT polymerization of styrene, one-pot synthesis multicompartment block copolymer nanoparticles (MCBNs) with high solid content constructed with two diblock copolymers of PtBMA-b-PS/PVEA-b-PS was achieved. These MCBNs contain a PS core and discrete PVEA and PtBMA sub-domains on the PS core. Then the influence of the ratio of two macro-RAFT agents of PVEA and PtBMA and PS chains length on the morphology of the MCBNs was investigated.