Theory And Application Of Polymerization Induced Self-assembly And Reorganization To Fabricate Polymeric Nanomaterials

Polymeric nanomaterials have attracted great attention because of their application in biomedicine, catalysis, micro-electronics and environmental fields, etc. It has been illustrated that the performance of the polymeric nanomaterials is strongly affected by their morphology, and polymeric nanomaterials with various morphologies have been fabricated with the self-assembly of block copolymer in the past20years. However, there are limitations with the traditional self-assembly method, such as it usually needs multistep and conducted in low concentration (1mg/mL). Polymerization induced self-assembly and reorganization (PISR), which developed recently, can well circumvent these problems and it allows fabricating polymeric nanomaterials in much high concentration in one-pot, but the research of PISR is still in its infancy, so it becomes much valuable to conduct more systematic studies of PISR. Therefore, this dissertation focus on the following projects, study on the factors which influence the morphology and morphology transition in PISR, fabrication of polymeric nanomaterials with more morphologies and investigation of the formation mechanism of them in PISR, carry out the application research of the polymeric nanomaterials benefit for the advantages of efficient preparation of polymeric nanomaterials with PISR. The primary results are listed as follows:1) Polymerization induced self-assembly and reorganization (PISR) is conducted via RAFT dispersion polymerization of styrene in ethanol using PDMAEMA-CPDB as macro RAFT agent. Various nanoparticles, such as sphere micelles, nanowires, lamellas, vesicles, large compound vesicles and inverted hexagonally packed hollow hoops (HHHs) are fabricated by carefully adjusting the polymerization times, the content of ethanol and the initial ratio of St/PDMAEMA-CPDB. The detailed phase diagrams are elucidated to predict the conditions of fabrication various morphology. Lamellas are formed during the transformation of nanowires-to-vesicles, which is consistent with the report in the aqueous RAFT dispersion polymerization, and it is the first time to discover this phenomenon in the alcoholic RAFT dispersion polymerization. To the best of our knowledge, the HHHs are fabricated via PISR for the first time.2) We successfully fabricate the spaced concentric vesicles (SCVs) via RAFT dispersion polymerization, and continuous propagation of the residual polymer chains inside the large vesicles induces self-assembling to form SCVs. Concentration of the residual polymer chains in the solution of the nascent-formed vesicles is the determining factor for formation of SCVs, and continuous propagation of less or too more residual polymer chains will not form SCVs but form other morphologies. After formation of the single-wall vesicles in the RAFT dispersion polymerization, the polymerization behaviors inside the vesicles, in the outer wall, and in the solution outside the vesicles are different:the Rp inside the vesicles is faster than the Rp in the outer wall, but both Rps are in the same order, whereas the Rp outside the vesicles is too low to be detected by GPC and NMR. The Rmw inside the vesicles is much larger than that in outer wall. The concentrations of residual polymer chains in solution at the phase separation and morphology transition are generally very small; however, their amount can be adjusted through variation of recipe and use of appropriate macro-RAFT agents. The polymerization in larger vesicles forms inner vesicles and produces copolymers with very high molecular weight (above1x106g/mol), but smaller vesicles are difficult to transform into SCVs. Appropriately increasing the amount of residual copolymer chains in solution will promote formation of the SCVs and can increase the possibility of smaller vesicles to form SCVs.3) In the RAFT dispersion polymerization of St using P4VP-TC as the macro-RAFT agent in ethanol, sea cucumber-like micelles (SC) with lots of tentacles are fabricated. The chain length ratio of the hydrophobic to the hydrophilic block (R) is the determining factor for the final morphology, and the morphology transformed from vesicles to large compound vesicles and then to the SC with the R increasing. The content of the residual polymer chains have important influence on the morphology, too more residual polymer chains in the solution after formation of the large compound vesicles is not benefit to fabricate SC. The precise conditions of fabricating SC are researched by adjusting the content of ethanol, polymerization time and the initial molar ratio of the St/P4VP-TC, and the detailed phase diagrams are designed according to the research results.4) Silica nanotubes with tunable lengths, interior diameters and wall thicknesses have been fabricated by the template-directing method and the PDMAEMA-PS block copolymer nanowires are used as sacrificial templates. The nanowires are fabricated by RAFT dispersion polymerization of St in methanol using PDMAEMA as macro-RAFT agents, and their diameters and lengths are controlled by adjusting the chain length of the hydrophilic PDMAEMA. The silica nanotubes are successfully prepared through hydrolysis and condensation reactions of TEOS in the presence of polymer nanowires and subsequent calcinations, and dimensions of the resultant nanotubes are completely controlled by the dimensions of their templates. Their interior diameters and wall-thicknesses are regulated respectively by chain lengths of the core PS and the shell PDMAEMA. Moreover, this strategy allows fabrication of polymeric nanowires at high concentration via PISR. Thus, we supply a facile method to fabricate sacrificial1D templates of high quality and large quantity under mild conditions.5) The polymeric nanowires with photochromic spiropyran (SP) species have been successfully prepared through RAFT dispersion polymerization using P(4VP-SPMA) as a RAFT agent. The nanowires display reversible photochromism, and the fluorescence of the nanowires can be switched on and off owing to the reversible interconversion between the SP and the ME forms of SP under alternative irradiation with UV and visible light. The dispersion of nanowires in methanol exhibits stronger fluorescence and higher photo stability in comparison with the corresponding block copolymer solution in DMF. Polymeric fibers have been successfully fabricated by electro spinning a mixture of a solution of the nanowires and the poly(N-vinylpyrrolidone)(4:1, w/w), and all the nanowires are aligned with the axis direction of the fibers. The SP groups in the electrospun fibers also display reversible photochomism, and relatively strong red fluorescence is achieved after UV irradiation. Red fibers can be clearly seen at an excitation wavelength of510-550nm. This red fluorescence can be switched off by visible-light irradiation, and the fluorescence is restored by UV irradiation. Thus, the fibers have the function of a fluorescence switch.