The Self-assembly Of TSOST Pentablock Terpolymers And Their Hydrolyzed Derivatives

The self-assembly of block copolymers is one of the most important parts in nanotechnology fields.The microphase separation caused by incompatibility between blocks in bulk and the self-assembly derived from amphiphilic properties in solutions are two most popular branches.The nanoparticles formed by block copolymers have great potential for application in several advanced high-tech fields,such as energy and batteries,electronics and information technology as well as biomaterials and pharmacy because of their unique nanostructures,controllability as well as physical and chemical properties.In last few decades,the self-assembly of traditional AB-type block copolymers in bulk and solutions have been comprehensively studied,and solid foundation has been established experimentally and theoretically.In order to enlarge the possible morphologies of nanostructures,more kinds of monomers and more complex topologies are introduced.Among then,the linear ABCBA-type pentablock terpolymer is considered to be the simplest model of multiblock copolymers.The systematical investigations of multiblock copolymers might offer alluring opportunities to gain further understanding of biomacromolecules,such as DNA,RNA and proteins with a variety of sequence combinations and design new materials with tailored phase structures and functionalities.In this thesis,ABCBA-type pentablock terpolymer poly（tert-butyl acrylate-b-styrene-b-ethylene oxide-b-styrene-b-tert-butyl acrylate）（Pt BA-b-PS-b-PEO-b-PS-b-Pt BA）and their hydrolyzed derivatives were prepared and the impact of block lengths and compositions on the self-assembly of these pentablock terpolymers in bulk and solutions were explored.Firstly,three symmetric linear pentablock terpolymers Pt BA-b-PS-b-PEO-b-PS-b-Pt BA（T_zS_yO_xS_yT_z）with similar lengths of PS（S）and Pt BA（T）blocks on the two sides but various lengths of PEO（O）blocks in the middle,namely T₉₅S₆₂O₄₆S₆₂T₉₅,T₁₀₅S₆₀O₉₀S₆₀T₁₀₅ and T₁₀₇S₆₅O₁₃₆S₆₅T₁₀₇ were synthesized from a two-step atom transfer radical polymerization（ATRP）.The crystallinity of middle PEO block increases with the increase of molecular weight,but is greatly hindered by the blocks on the two sides.Therefore,the three T_zS_yO_xS_yT_z pentablock terpolymers were totally amorphous.The length of PEO block was found to significantly affect the phase structure of the obtained pentablock terpolymers.The phase structures of T₉₅S₆₂O₄₆S₆₂T₉₅,T₁₀₅S₆₀O₉₀S₆₀T₁₀₅ and T₁₀₇S₆₅O₁₃₆S₆₅T₁₀₇ pentablock terpolymers were three-domain lamellae（LAM₃）,core-shell double gyroid(Q²³⁰)and three-phase hexagonal perforated lamellae（HPL₃）,respectively.Particularly,the Q²³⁰ network structure formed by T₁₀₅S₆₀O₉₀S₆₀T₁₀₅ was experimentally observed for the first time in a symmetric linear ABCBA-type pentablock terpolymer.In addition,T₁₀₅S₆₀O₉₀S₆₀T₁₀₅were compared with its homologous triblock terpolymer O₄₅S₅₆T₁₁₀,which formed hexagonal cylinders（HEX）in bulk.It is revealed that the strong restrict of middle blocks lead to some changes of microphase behavior.Moreover,the HPL₃ structure was also observed in unsheared T₁₀₇S₆₅O₁₃₆S₆₅T₁₀₇.Temperature-variable SAXS showed that T₉₅S₆₂O₄₆S₆₂T₉₅ maintained an ordered lamellar phase structure in the temperature range of 25 to 210 and an order-to-disorder transition occurred for T₁₀₅S₆₀O₉₀S₆₀T₁₀₅at around 170 ^oC.The HPL₃ phase of T₁₀₇S₆₅O₁₃₆S₆₅T₁₀₇ still partially remained with decreased ordering at temperature up to 210,which revealed that the T_ODT is not only related to the molecular weight of pentablock terpolymers,but also the relative contents of each block and the thermo-stability of certain microphases.Then,linear symmetrical T_xS₁₃₀O₉₀S₁₃₀T_x（x=40,75,100,165 and 200）with constant length of PS and PEO blocks but different length x of Pt BA block were synthesized from their parent triblock copolymers S₁₃₀O₉₀S₁₃₀ by ATRP.T_xS₁₃₀O₉₀S₁₃₀T_x formed various vesicular nanostructures in dilute aqueous solutions as revealed by transition electron microscopy（TEM）,cryogenic transmission electron microscopy（Cryo-TEM）and scanning electron microscopy（SEM）.Genus vesicles with nanometer sizes and various genus value（g）,including the vesicles with large g values（g>3）,double-rings vesicles（g=2）,single ring-shaped vesicles（g=1）and individual spherical vesicles（g=0）were obtained from ABCBA pentablocks in aqueous solution for the first time.The genus value（g）of vesicles formed by T_xS₁₃₀O₉₀S₁₃₀T_x decreased with increasing the length x of Pt BA block.Meanwhile,the increasing strength of microphase separation between PS and Pt BA blocks result the difference of density distribution and chain arrangement in hydrophobic domains.In addition,the formation mechanism of genus vesicles was preliminarily discussed by the combination of membrane bending energy,the area-difference-elasticity and the edge effect.Especially,the vesicles with g of 0,1,2 and 3 were clearly observed for T₁₀₀S₁₃₀O₉₀S₁₃₀T₁₀₀.The coexistence of vesicles with various genus confirmed that the minimization of free energy of vesicle has multiple solutions.Moreover,a series of ABCBA-type pentablock terpolymer with alternated hydrophilicity poly（acrylic acid-b-styrene-b-ethylene oxide-b-styrene-b-acrylic acid）(PAA-b-PS-b-PEO-b-PS-b-PAA,A_xS₄₈O₄₆S₄₈A_x)with various lengths x of the PAA block were prepared via the completely hydrolysis of their precursor T_xS₄₈O₄₆S₄₈T_x（x=15,40,60 and 90）.The A_xS₄₈O₄₆S₄₈A_x pentablock terpolymers formed micelles in dilute aqueous solution,of which the morphologies were dependent on the length x of the PAA block.The morphology of A_xS₄₈O₄₆S₄₈A_x micelles changed from spherical vesicles with ordered porous membranes to long double nanotubes,then to long nanotubes with inner modulated nanotubes or short nanotubes,and finally,to spherical micelles or large compound vesicles with spherical micelles inside when x increased from 15 to 90.Dynamic light scattering（DLS）,and zeta potential measurement were employed to investigate the chain structures,size,and size distribution of the obtained micelles.The hydrophobic PS blocks formed the walls of vesicles and nanotubes as well as the core of spherical micelles.The hydrophilic PEO and partially ionized the PAA block chains located on the surfaces of vesicle membranes,nanotubes,and spherical micelles,leading to the negative zeta potential of the A_xS₄₈O₄₆S₄₈A_x micelles and stabilizing the micelles in dilute aqueous solutions.Finally,a series of（A_mT_n）S₄₈O₄₆S₄₈（A_mT_n）pentablock tetrapolymers with different degree of hydrolysis（0%,16%,30%,61%,70%,100%）of Pt BA block were prepared,and they formed disorder state（DIS）,gyroid（GYR）,hexagonal perforated layer（HPL）,hexagonal cylinder（HEX）and lamellae（LAM）phase in bulk,respectively.The effective Flory-Huggins parameterχbetween each pair were calculated,which revealed that the pentablock copolymers transformed from a non-frustrated system to a frustrated system with the increase of hydrolysis degree.The hydrogen-bonding formed between PEO and PAA blocks have remarkable impact on the microphase behavior,and their quantity and strength depend on the chain lengths of PEO and PAA blocks as well as the shielding effect of PS on PEO blocks.