Seeded RAFT Polymerization And In-situ Synthesis Of Triblock Terpolymer Nano-objects

Over the past decade, block copolymer nano-objects have aroused great interest because of their potential use in many fields. Among them, triblock terpolymer nano-objects is more favoured to enable complex morphologies as flowerlike nanoparticle, vesicles and multicompartment nanoparticles. However, the traditional synthesis of nano-objects by self-assembly of triblock terpolymer suffers from the drawback of diluted colloidal dispersion and poor stability, and the mechanism of the formation of triblock terpolymer nano-objects is still not clear. Seeded polymerization is a convenient method to synthesize polymeric nanoparticles. By employing the RAFT technology in the seeded polymerization, block copolymer nano-objects with high polymer concentration have been successfully prepared. Inspired by this strategy, in this study, a new stragety named seeded RAFT polymerization under "quasi" heterogeneous condition is proposed. Concentrated seeded nano-objects including spherical nanoparticles and vesicles of diblock copolymer is employed as macro-RAFT agent to mediate well-controlled seeded RAFT polymerization. Well-difined flowerlike and multicompartment nanoparticles of triblock terpolymer are prepared and the dissambly of diblock copolymer vesicles into triblock terpolymer nanoparticles is also investigated. Therefore, the content of this dissertation is described in three aspects:1. Seeded dispersion RAFT polymerization and synthesis of well-defined ABA triblock terpolymer flowerlike nanoparticlesIn this section, a new kind of heterogeneous RAFT polymerization named seeded dispersion RAFT polymerization is proposed to prepare well-defined triblock terpolymer flowerlike nanoparticles. Concentrated seed-nanoparticles of the amphiphilic PS-b-PDMA-TTC diblock copolymer including the Z-group RAFT terminal are prepared by sequential solution RAFT polymerization and the micellization of PS-b-PDMA-TTC diblock copolymer in the styrene/ethanol/water ternary solvent mixture. Well-controlled seeded dispersion RAFT polymerization subsequently is achieved, and the polymerization runs much faster than a soluble macro-RAFT agent mediated dispersion polymerization since very short or no induction-time is observed. The PS-b-PDMA-b-PS triblock terpolymers synthesized at different polymerization time have well-controlled molecular weight with narrow molecular weight distribution. The seeded dispersion RAFT polymerization affords in-situ synthesis of well-defined flowerlike nanoparticles of the PS-b-PDMA-b-PS triblock terpolymer, and the size of the flowerlike nanoparticles decreasing with the central PDMA block while increasing with the outer PS block is concluded.2. Seeded solution RAFT polymerization and synthesis of multicompartment nanoparticles of linear BAC triblock terpolymerMulticompartment nanopaticles are designed as elaborate structure with discrete domains of two solvophobic fragments that are mutually incompatible, which are generally prepared by self-assembly strategy of block copolymers. In this section, a new strategy of in-situ synthesis of multicompartment nanoparticles of the linear BAC triblock terpolymer of PS-b-PDMA-b-P4VP is proposed as so-called "seeded solution RAFT polymerization". This strategy includes the initial seeded RAFT polymerization of 4-vinylpyridine in the presence of PS-b-PDMA-TTC seed-nanoparticles in ethanol/water solvent mixture, and the subsequent transfer of the in-situ synthesized core-corona nanoparticles of PS-b-PDMA-b-P4VP into water by N2 bubbling to deposit the newly-formed P4VP block onto the PS core to form discrete P4VP nodules and to form multicompartment nanoparticles. The size of the P4VP domain on the PS core of the multicompartment nanoparticles increases with the increasing polymerization degree of the P4VP block. Two reasons of (1) the P4VP block being immiscible with the PS block and (2) the special seeded RAFT polymerization avoiding the P4VP block being entrapped into the PS core are ascribed to the successful preparation of the linear BAC triblock terpolymer multicompartment nanoparticles.3. AB diblock copolymer vesicle mediated seeded solution RAFT polymerization and the disassembly of block copolymer vesiclesIn this section, an AB diblock copolymer vesicle mediated seeded solution RAFT polymerization of N,N-dimethylacrylamide was performed in ethanol/water solvent mixture, in which concentrated vesicle dispersion of PVEA-b-PS was synthesized by general dispersion RAFT polymerization with a soluble macro-RAFT agent. The polymerization undergoes with a pseudo-first-order kinetics and the synthesized PVEA-b-PS-b-PDMA triblock terpolymers have increasing molecular weight with increasing polymerization time and low morecular weight distribution. The disassembly of block copolymer vesicles during the RAFT polymerization was investigated. It is found that the PVEA-b-PS diblock copolymer vesicles were gradually disassembled with the increasing polymerization degree of the PDMA block. The vesicles were firstly flattened to form tubules, then tubules were broken to form the jellyfish-like morphology, and lastly jellyfish converted into worms and worms minced into PVEA-b-PS-b-PDMA nanospheres. It is believed that the present vesicle mediated RAFT polymerization affords a real-time observation of vesicle disassembly, which is helpful to clarify the assembly of block copolymer vesicles.