Self-assembly of amphiphilic ABC star triblock copolymers and their blends with AB diblock copolymers in solution: self-consistent field theory simulations

The self-assembled morphologies of amphiphilic ABC star triblock copolymers consisting of hydrophilic A blocks and hydrophobic B and C blocks and the blends with their counterpart linear AB diblock copolymers in solution are investigated by 2D real-space implementation of self-consistent field theory (SCFT) simulation. The star triblock copolymers self-assemble in solution to form various micellar structures from hamburger, to segmented wormlike, to toroidal segmented micelles, and finally to vesicles with simultaneously increasing hydrophobic lengths of blocks B and C. When the length of hydrophobic blocks B and C is asymmetric, specific bead-on-string worm micelles are found. Particularly, when the star ABC triblock copolymer is in a strong segregation regime and both B and C blocks are strongly hydrophobic, quite long segmented wormlike micelles are obtained, which had not been found in previously investigated diblock and linear ABC triblock copolymers solution. Additionally, raspberry micelles with beads dispersed on the core also occur in the strong segregation regime of bulk star ABC triblock copolymers. Furthermore, the aggregate morphology of ABC star triblock copolymers is strongly influenced by the addition of linear AB diblock copolymers. The most significant feature is that the long segmented worms will become shorter, to form hamburger micelles with the addition of AB diblock copolymers. These simulations are in good agreement with the experimental findings by Lodge's group.     

嵌段序列对聚合物囊泡形成过程影响的Monte Carlo模拟

采用Monte Carlo模拟方法研究了具有相同链长和组分比的不同嵌段序列的AB两嵌段共聚物与ABA三嵌段共聚物在选择性溶剂中形成囊泡的动力学过程. 模拟结果表明, AB两嵌段共聚物囊泡的形成与ABA三嵌段共聚物囊泡的形成的动力学过程不同. 在慢速退火条件下, ABA三嵌段共聚物囊泡是通过亲水链段向胶束的表面和中心扩散而形成的, 而AB两嵌段共聚物囊泡则由片层弯曲闭合而形成. 相对而言, 退火速度对AB两嵌段共聚物囊泡形成的动力学过程没有显著影响, 其改变仅影响亲水链段与疏水链段发生相分离的难易程度. 当退火速度较快时, 亲水链段和疏水链段发生相分离的速度较快且相分离发生在囊泡形成之前; 而当退火速度较慢时亲水链段和疏水链段之间的相分离在囊泡形成之后仍在进行.     

基于非共价键作用的二嵌段共聚物/均聚物超分子体系的自组装行为

采用实空间求解的自洽场理论,研究了两亲性二嵌段共聚物(AB)/均聚物(C)超分子体系在溶液中的自组装行为,其中B疏水嵌段的自由末端与C均聚物的一个末端形成可逆的非共价键.在稀溶液中,AB/C超分子聚合物体系通过自组装形成了一系列不同形貌的胶束,如核-壳-冠的三层胶束和蠕虫状胶束等.研究发现,胶束形貌受到非共价键强度和初...     

Aggregation Behavior of Polyether Block Copolymers with Dendritic Structure in Aqueous Solutions

Two dendritic block copolymers with the same contents of PPO and PEO but different branches and blocks were synthesized by anion polymerization. Their aggregation behavior and aggregation morphology were investigated by steady-state fluorescence and transmission electron microscopy. For SD64 copolymer with PPO-PEO diblock branch, it can be proved that only intermolecular aggregates are formed, the aggregation number and aggregation diameter are increased with concentration. Whereas for SD343 dendritic copolymer with PPO-PEO-PPO triblock branch, hydrophobic PPO chains located on the edge of SD343 copolymers can associate within the same polymer chain and also between different polymer chains, so the aggregates were inclined to change from intramolecular micelles to intermolecular clusters with concentration increasing.     

Micellar shape change and internal segregation induced by chemical modification of a tryptych block copolymer surfactant

We report the detailed characterization of micelles formed by two nonionic, amphiphilic ABC triblock copolymers. Poly(ethylene oxide)-b-poly(styrene)-b-1,2-poly(butadiene) (PEO-b-PS-b-PB) triblock copolymer "OSB" forms core-corona spherical micelles in aqueous solution, and the two hydrophobic blocks S and B are mixed homogeneously within the micelle core. PEO-b-PS-b-PB:C6F13I triblock copolymer "OSF" was prepared by selective fluorination of the B block in OSB with n-perfluorohexyl iodide. Fluorination of the B block induces internal segregation into an inner F core and an intermediate S shell. Furthermore, the strong incompatibility that results from fluorination drives a shape change into an oblate ellipsoid. These micellar morphologies are confirmed by combined light, neutron, and X-ray scattering measurements, as well as TEM imaging.     

Depletion-induced surface alignment of asymmetric diblock copolymer in selective solvents

Phase separation of asymmetric diblock copolymer near surfaces in selective solvents is theoretically investigated by using the real-space version of self-consistent field theory (SCFT). Several morphologies are predicted and the phase diagram is constructed by varying the distance between two parallel hard surfaces (or the film thickness) W and the block copolymer concentration f(P). Morphologies of the diblock copolymer in dilute solution are found to change significantly with different film thicknesses. In confined systems, stable morphologies found in the bulk solution become unstable due to the loss of polymer conformation entropy. The vesicle phase region contracts when the repulsive interaction between the blocks is strong (strong segregation regime). The mixture of vesicles, rodlike and spherelike micelles and the mixture of vesicles and sphere-like micelles disappear in contrast to the weakly segregating regime. The walls strongly affect the phase separation of block copolymer in selective solvent, and the depletion layer near the surface contributes much to the micelle formation of the block copolymer. Interestingly, the self-assembled morphologies stay near the walls with the distance on the order of the radius of gyration of the block copolymer. The oscillation of the polymer distribution near the walls allows the surface phase separation to be observed due to the strong repulsion between the blocks A and B.     

嵌段结构对两亲嵌段共聚物水溶液行为的影响

在合成了二种具有相同组成不同嵌段结构排布的共聚物基础上对它们溶液的物理化学行为用荧光探针的方法进行了研究，结果表明：由于结构排布的不同其物理化学行为有着较大的差异，三嵌段结构的共聚物较二嵌段者更易于形成胶束体系，而二嵌段共聚物则易于发生凝胶化，对上述结果进行讨论和解释．     

Preparation of ABA triblock copolymer assemblies through “one-pot” RAFT PISA

Poly(N,N-dimethyl acrylamide)-block-poly(styrene)-block-poly(N,N-dimethyl acrylamide)(PDMAc-bPSt-b-PDMAc) amphiphilic triblock copolymer micro/nano-objects were synthesized through reversible addition-fragmentation chain transfer(RAFT) dispersion polymerization of St mediated with poly(N,Ndimethyl acrylamide) trithiocarbonate(PDMAc-TTC-PDMAc) bi-functional macromolecular RAFT agent.It is found that the morphology of the PDMAc-b-PSt-b-PDMAc copolymer micro/nano-objects like spheres,vesicles and vesicle with hexagonally packed hollow hoops(HHHs) wall can be tuned by changing the solvent composition.In addition,vesicles with two sizes(600 nm,264 nm) and vesicles with HHHs features were also synthesized in high solid content systems(30 wt% and 40 wt%,respectively).Besides,as compared with typical AB diblock copolymers(A is the solvophilic,stabilizer block,and B is the solvophobic block),ABA triblock copolymers tend to form higher order morphologies,such as vesicles,under similar conditions.The finding of this study provides a new and robust approach to prepare block copolymer vesicles and other higher order micelles with special structure via PISA.     

Simulation study of aggregate morphologies formed by ABC linear triblock copolymers in a selective solvent through the self‐consistent field theory

The effect of the hydrophobic properties of blocks B and C on the aggregate morphologies formed by ABC linear triblock copolymers in selective solvent was studied through the self‐consistent field theory. Five typical micelles, such as core‐shell‐corona, hamburger‐like, segmented‐wormlike, were obtained by changing the hydrophobic properties of blocks B and C. The simulation results indicate that the shape and size of micelle are basically controlled by the hydrophobic degree of the middle block B, whereas the type of micelle is mainly determined by the hydrophobic degree of the end block C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 484–492, 2009     

Evolution of multicompartment micelles to mixed corona micelles using solvent mixtures

Miktoarm star triblock copolymers mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] self-assemble in dilute aqueous solution to give multicompartment micelles with the cores consisting of discrete poly(ethylethylene) and poly(perfluoropropylene oxide) domains. Tetrahydrofuran is a selective solvent for both the poly(ethylethylene) and poly(ethylene oxide) blocks, and thus in tetrahydrofuran mixed corona micelles are favored with poly(perfluoropropylene oxide) cores. The introduction of tetrahydrofuran into water induces an evolution from multicompartment micelles to mixed corona [poly(ethylethylene) + poly(ethylene oxide)] micelles, as verified by dynamic light scattering and nuclear magnetic resonance spectroscopy. A mixed solvent containing 60 wt % tetrahydrofuran corresponds to the transition point, as verified by analysis of a poly(ethylethylene)-poly(ethylene oxide) diblock copolymer in the same solvent mixtures. Furthermore, cryogenic transmission electron microscopy suggests that, as the poly(ethylethylene) block transitions from the core to the corona, the micelle morphologies evolve from disks to oblate ellipsoid micelles (with some vesicles), with worms and spheres evident at intermediate compositions.     

Synthesis of pH-responsive amphiphilic diblock copolymers containing polyisobutylene via oxyanion-initiated polymerization and their multiple self-assembly morphologies

 Two pH-responsive amphiphilic diblock copolymers, namely polyisobutylene-block-poly[2-(N,N-dimethylamino)ethyl methacrylate] (PIB-b-PDMAEMA) and polyisobutylene-block-poly(metharylic acid) (PIB-b-PMAA), were synthesized via oxyanion-initiated polymerization, and their multiple self-assembly behaviors have been studied. An exo-olefin-terminated highly reactive polyisobutylene (HRPIB) was first changed to hydroxyl-terminated PIB (PIB-OH) via hydroboration-oxidation of C＝C double bond in the chain end, and then reacted with KH to yield a potassium alcoholate of PIB (PIB-O^-K⁺). PIB-O^-K⁺ was immediately used as a macroinitiator to polymerize DMAEMA monomer, resulting in a cationic diblock copolymer PIB-b-PDMAEMA. With the similar synthesis procedure, the anionic diblock copolymer PIB-b-PMAA could be prepared via a combination of oxyanion-initiated polymerization of tert-butyl methacrylate (tBMA) and subsequent hydrolysis of tert-butyl ester groups in PtBMA block. The functional PIB and block copolymers have been fully characterized by ¹H-NMR, FT-IR spectroscopy, and gel permeation chromatography (GPC). These samples allowed us to systematically investigate the effects of block composition on the pH responsivity and various self-assembled morphologies of the copolymers in THF/water mixed solvent. Transmission electron microscopy (TEM) images revealed that these diblock copolymers containing small amount of original PIB without exo-olefin-terminated group are able to self-assemble into micelles, vesicles with different particle sizes and cylindrical aggregates, depending on various factors including block copolymer composition, solvent polarity and pH value.     

三嵌段共聚物和两嵌段共聚物在水溶液中共混自组装成多室胶束结构的耗散粒子动力学模拟(英文)

利用耗散粒子动力学模拟研究了在水溶液中混合不同的线形三嵌段共聚物AxByCz和线形两嵌段共聚物AmBn对多室胶束的形貌多样性的影响.通过改变线形的三嵌段共聚物和两嵌段共聚物的链长来寻找多室胶束的形成条件.由线形三嵌段共聚物和线形两嵌段共聚物的不同混合形成的多室胶束结构是多种多样的,例如"蠕虫状"胶束、"汉堡包"胶束、"球上球"胶束、"核-壳-壳"胶束等等.多室胶束的整体形貌和内部结构的控制都可以从线形三嵌段共聚物和两嵌段共聚物的二元共混得到.为了表征获得的多室胶束结构,我们计算了密度图和成对分布函数图.在此工作中,可以获得和观察到复杂的多室胶束.结果表明,简单地混合线形的三嵌段共聚物和线形的两嵌段共聚物是一个控制多室胶束形貌和结构的有效方法,在工程实验中可以更简单更经济地形成多室胶束结构.因此,在设计新的多室胶束方面,聚合物共混仍然是未来值得更加关注的一个话题.     

Amphiphilic Seven-arm Star Triblock Copolymers with Diverse Morphologies in Aqueous Solution Induced by Crystallization and pH

Well-defined amphiphilic seven-arm star triblock copolymers containing hydrophobic crystalline poly(ε-caprolactone)(PCL) blocks, hydrophobic non-crystalline poly(tert-butyl acrylate)(PtBA) blocks and hydrophilic poly(ethylene glycol)(PEG) blocks were precisely synthesized by a combination of ring-opening polymerization(ROP), atom transfer radical polymerization(ATRP) and “click” reaction. Such star copolymers could self-assemble into “core-shell-corona” micelles and “multi-layer” vesicles depending on the fraction of each block. Meanwhile, the selective hydrolysis of middle PtBA blocks into the poly(acrylic acid)(PAA) blocks allowed the star block copolymers to further change their morphologies of aqueous aggregates in response to pH values.     

Aggregates in solution of binary mixtures of amphiphilic diblock copolymers with different chain length

The polydispersity effect of amphiphilic AB diblock copolymers on the self-assembled morphologies in solution has been investigated by the real-space implementation of self-consistent field theory (SCFT) in two dimensions (2D). The polydispersity is artificially obtained by mixing binary diblock copolymers where the hydrophilic or hydrophobic blocks are composed of two different lengths while the other block length is kept the same. The main advantage is that this simple polydispersity can easily distinguish the difference of aggregates in the density distribution of long and short block length intuitionally and quantitatively. The morphology transition from vesicles to micelles is observed with increasing polydispersity of copolymers due to the length segregation of copolymers. For polydisperse hydrophilic or hydrophobic blocks, the short blocks tend to distribute at the interfaces between hydrophilic and hydrophobic blocks while the long blocks stretch to the outer space. More specifically, by quantitatively taking the sum of all the concentration distribution of long and short chains over the inside and outside surface areas of the vesicle, it is found that long blocks prefer to locate on the outside surface of the vesicle while short ones prefer the inside. Such length segregation leads to large curvature of the aggregate, thus resulting in the decrease of the aggregate size.     

Computer simulation of architectural and molecular weight effects on the assembly of amphiphilic linear-dendritic block copolymers in solution

Langevin dynamics simulations are performed on linear-dendritic diblock copolymers containing bead-spring, freely jointed chains composed of hydrophobic linear monomers and hydrophilic dendritic monomers. The critical micelle concentration (CMC), micelle size distribution, and shape are examined as a function of dendron generation and architecture. For diblock copolymers with a linear block of fixed length, it is found that the CMC increases with increasing dendron generation. This trend qualitatively agrees with experiments on linear-dendritic diblock and triblock copolymers with hydrophilic dendritic blocks and hydrophobic linear blocks. The flexibility of the dendritic block is altered by varying the number of spacer monomers between branch points in the dendron. When comparing linear-dendritic diblock copolymers with similar molecular weights, it is shown that increasing the number of spacer monomers in the dendron lowers the CMC due to an increase in flexibility of the dendritic block. Analysis on the micellar structure shows that linear-dendritic diblock copolymers pack more densely than what would be expected for a linear-linear diblock copolymer of the same molecular weight.     

Synthesis and self‐assembly of highly incompatible polybutadiene–poly(hexafluoropropylene oxide) diblock copolymers

A versatile coupling reaction for the preparation of polybutadiene–poly‐(hexafluoropropylene oxide) (BF) diblock copolymers is described. Six diblock copolymers with different block lengths were characterized by nuclear magnetic resonance spectroscopy and size exclusion chromatography; all six had total molecular weights below 15,000. Microphase separation of the block copolymers in the bulk state was established by small‐angle X‐ray scattering (SAXS) and differential scanning calorimetry. SAXS data suggest that the diblocks are characterized by an unusually large Flory‐Huggins interaction parameter, χ, on the order of 10. However, extraction of χ from the order–disorder transition gave large (order 1) but significantly different values, thereby suggesting that these copolymers are too small and too strongly interacting to be described by block copolymer mean‐field theory. Dynamic light scattering was used to analyze dilute solutions of the title block copolymers in four selective organic solvents; the sizes of the micelles formed were solvent dependent. The micellar aggregates were large and nonspherical, and this is also attributed to the high degree of incompatibility between the two immiscible blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3685–3694, 2005     

Unique toroidal morphology from composition and sequence control of triblock copolymers

The mechanism by which the unique toroidal supramolecular assemblies were formed for triblock copolymers of acrylic acid (AA), methyl acrylate (MA), and styrene (S), PAA99-b-PMA73-b-PS66, was probed in this study by investigating the influences of the block copolymer compositions and sequences. Two triblock copolymers, PAA99-b-PMA73-b-PS66 and PAA99-b-PS76-b-PMA62, and two diblock copolymers, PAA99-b-PMA155 and PAA99-b-PS133, were studied under experimental solution-state conditions that involved a range of solvent/nonsolvent (tetrahydrofuran/water) compositions, each in the presence of 2,2'-(ethylenedioxy)bis(ethylamine). The resulting morphologies were determined by transmission electron microscopy. The failures to afford toroidal supramolecular assemblies from both diblock copolymers having comparable lengths of the total hydrophobic chain segment, either entirely PMA or entirely PS, and from the triblock copolymer having a reversed connection sequence for the hydrophobic (PMA and PS) segments demonstrate the unique self-assembly behaviors of triblock copolymers and the importance of the block copolymer sequence.     

Phase behavior and viscoelastic properties of entangled block copolymer gels

Triblock copolymers in midblock‐selective solvents can form physical gels. However, at low triblock contents (near the percolation threshold), the bridging of chains between micelles can lead to macrophase separation. Adding a styrene–isoprene diblock to a styrene–isoprene–styrene triblock copolymer in squalane can eliminate macrophase separation, yielding a wide range of stable, single‐phase gels with a disordered arrangement of micelles. The plateau modulus of these triblock gels scales with the 2.2 power of polymer content, indicating the importance of entanglements in dictating the modulus. Comparing gels made from the midblock‐saturated derivative of the same polymer [styrene‐(ethylene‐alt‐propylene)‐styrene] in squalane reveals that the modulus differences in the gels are a direct consequence of the difference in the entanglement molecular weight of the midblock homopolymer in bulk. Finally, the broad relaxation spectrum of these triblocks is well‐described by a recent theory for the dynamics of entangled star polymers, with the breadth of the relaxation spectrum dictated by the number of entanglements per midblock in the gel. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2183–2197, 2001     

Multicompartment micelles from silicone-based triphilic block copolymers

An amphiphilic linear ternary block copolymer was synthesised in three consecutive steps via reversible addition–fragmentation chain transfer polymerisation. Oligo(ethylene glycol) monomethyl ether acrylate was engaged as a hydrophilic building block, while benzyl acrylate and 3-tris(trimethylsiloxy)silyl propyl acrylate served as hydrophobic building blocks. The resulting “triphilic” copolymer consists thus of a hydrophilic (A) and two mutually incompatible “soft” hydrophobic blocks, namely, a lipophilic (B) and a silicone-based (C) block, with all blocks having glass transition temperatures well below 0 °C. The triphilic copolymer self-assembles into spherical multicompartment micellar aggregates in aqueous solution, where the two hydrophobic blocks undergo local phase separation into various ultrastructures as evidenced by cryogenic transmission electron microscopy. Thus, a silicone-based polymer block can replace the hitherto typically employed fluorocarbon-based hydrophobic blocks in triphilic block copolymers for inducing multicompartmentalisation.     

Characterization of amphiphilic hydrocarbon modified Poly(ethylene glycol) synthesized through ring-opening reaction of 2-(1-octadecenyl)succinic anhydride

Poly(ethylene glycol) (PEG) triblock and diblock amphiphilic block copolymers were synthesized from poly(ethylene glycol) and poly(ethylene glycol) monomethyl ether, respectively. The hydroxyl groups of PEG readily react with 2-(1-octadecenyl) succinic anhydride (OSA) at 140 °C through ring-opening reaction of the succinic anhydride. Both the PEG-OSA diblock and triblock copolymers are produced without use of any solvent or catalyst. The molecular structure of the copolymers was characterized by ¹H NMR and FTIR spectroscopy, and the thermal properties by DSC. The behavior of the copolymers in selective and nonselective solvents was studied by ¹H NMR spectroscopy in deuterium oxide and d-chloroform. The aggregation of the polymers in water was studied with a particle size analyzer and a transmission electron microscope (TEM) in bright field mode. The results show that the hydrophobic C₁₈ chain with intramolecular succinic anhydride linker can be attached to the hydrophilic PEG chain, an ester bond forming between the blocks. The copolymers exhibit flexible, liquid-like hydrophobic blocks even in water, which is a nonsolvent for OSA. PEG-OSA block copolymers self-organize in water, forming micellar polymer aggregates in nanoscale.