Study On Self-assembly And Application Of Fluorine-containing Block Copolymers

Block copolymers are composed of two or more chemically distinct, and frequentlyimmiscible, polymer blocks covalently bound together. The block copolymers, with variouscomplex structures, could e self-assemble to diverse ordered nanostructured materials. Withthe improvement of living polymerization technology, a large number of novel well-definedblock copolymers with controlled molecular weights and narrow molecular weightsdistributions were prepared. By tailoring of the structure, and hence the properties, of both theindividual blocks and the ensemble, combining "top-down" and "bottom-up" methods, thelength scales of the ordered periods could be range from nanometers to micrometers. Due tothe special structures of the block copolymers, as well as the introducing of functionalsegments, nano and micro materials from block copolymers found a lot of potentialapplication in many fields, such as, nano synthesis, biomedical materials, photonic crystal,drug control-release system, separation technology, micro-electronics, catalyst, and so on. Sothe self-assembly of block copolymers has also focused much attention from both applied andtheoretical viewpoints. By the incorporation of fluorine-containing segments, their uniqueproperties such as chemical inertness, low refractive index and coefficient of friction, and lowsurface energy could not only maintain in the block copolymers, but also facilitate theself-assembly of block copolymers. And the fluorine-containing block copolymers, withspecial solvophobic and incompatibility with other polymers, would self-assemble to somenovel structures. In this dissertation, poly(tert-butylacrylate)-b-poly(2-[(perfluorononenyl)oxy] ethyl methacrylate)(PtBA-b-PFNEMA) without hydrophilic segment and poly(ethyleneoxide)-b-poly(2-[(perfluorononenyl) oxy] ethyl methacrylate)(PEO-b-PFNEMAs) with hydrophilic segment were synthesized by Atom transfer radicalpolymerization (ATRP). And the self-assembly of these two kinds of fluorine-containingblock copolymers in diverse solvent systems, the surface and internal structures of theself-assembled nano-and micro-polymeric particles, the transitions between diverse phasestructures, and the poterntial applications were investigated systemically.For the series of PtBA-b-PFNEMAs, three aspects were involved:a) Polymeric particles with diverse surface and internal hierarchical nanostructures wereprepared by the dynamic self-organized precipitation (D-SORP) ofPtBA-b-PFNEMAs in THF/water mixtures. The surface patterns and internalstructures both originated from the microphase separation of PtBA-b-PFNEMAs andcould be tuned by the preparation conditions, including polymer concentration, watercontent and preparation temperature. Almost parallel cylindrical domains, twistedinterconnected cylindrical domains, or spherical domains were obtained on thesurface of the particles. Meanwhile, the internal structures of the particles transformedfrom inner stacked lamella with outer onion-like structures, inner disordered withouter onion-like structures, to bicontinuous structures as the chain mobility andincompatibility of the two blocks could be controlled by the preparation condition.Besides the morphology of the particles provides the interface limitation andgeometric confinement for the microphase separation, hierarchical structures withdiverse cylindrical structures on the surface and bicontinuous or onion-like structureswithin the particles were achieved. The coexisting of diverse microphase structures inthe same particles has great means no matter for the theoretical research about thephase separation under confinement or for the potential application of themuiltcomponent system.b) The two-tier hierarchical assembly of PtBA-b-PFNEMA was performed to obtain superstructured microspheres. The as-formed PtBA-b-PFNEMA onion-like polymerparticles was further assembled to microspheres through an evaporation assistantprocess. The sizes of the nanospheres could be tuned by the water addition rates, andthe inside onion-like structures consist of several polygon were obtained by thecrystallization of the fluorocarbon side chains. The utilizing of the PtBA-b-PFNEMAonion-like polymer particles as the building block for the secondary assembly isfundamentally different from usual self-assembly studies, as the finallysuperstructured microspheres were hierarchical assembly of diblock copolymer andmeaningful for the structure control at different length scales.c) The as-formed fluorinated diblock copolymer micelles in chloroform were not onlyutilized to stabilize the templated water droplets in bulk, but also introduced as thewater droplets stabilizer in four other commercial polymers, including polystyrene(PS), polycarbonate (PC), polylactic acid (PLA), and polymethylmethacrylate(PMMA) via breath figures method. The micropore sizes of PtBA-b-PFNEMAs couldbe tuned by the casting volumn, polymer concentration, and the utilizing of differentPtBA-b-PFNEMAs. By the investigation of PS honeycomb microporous films withdifferent PtBA-b-PFNEMA compositions, the water droplets were stablized by thePtBA-b-PFNEMA micelles as "polymer-bag". And the micropore sizes of PShoneycomb microporous films could also be tuned by changing the composition ofPtBA-b-PFNEMA and the concentration of PS.For the series of PEO-b-PFNEMAs, the self-assembly of PEO-b-PFNEMAs in THF/watersystem was investigated. And the resulted micelles were utilized for the synthesis of goldparticles. PEO-b-PFNEMAs with different lengthes of fluorine-containing segment couldform uniform spherical aggregations with different sizes. And these aggregations could beutilized to preparation of gold nanospheres and plates. The size and morphology of the goldparticles could be tuned by the temperature and polymer concentration. And the introduction of fluorine-containing segment greatly changed the amphipathy of the block copolymer, andmade a better selective absorption of the polymer on diverse crystallographic planes of thegold nanocrystals. The gold nanoplates were obtained at relatively low temperature. Weinvestigated the co-assembly of PtBA-b-PFNEMA and PEO-b-PFNEMAs. The introducing offluorophilic interaction into D-SORP method prevented the microdomain separation of thetwo block copolymers and sustained the delicate control of the phase stuctures in polymericparticles. The location of PEO-b-PFNEMAs between PtBA phases and PFNEMA phase wasdirected by the fluorophilic interaction, thus could be tuned by the composition ofPEO-b-PFNEMAs, water content, and temperature. Order-order transitions from onion-likelamellar structures to stacked lamellar structures and cylindrical structures were observed.