Self-assembly via a complex phase transition in mixtures of polystyrene-block -polybutadiene block copolymer and poly(methyl vinyl ether)

The self-assembly of a binary mixture of polystyreneblock-polybutadiene (SB) and poly(methyl vinyl ether) (PVME) was studied by transmission electron microscopy and time-resolved light scattering. The self-assembly studied involved first microphase separation, in which a microdomain structure composed of polybutadiene block chains (PB) was formed in a matrix composed of polystyrene block chains (PS) and PVME homopolymers, and subsequently macrophase separation of the PVME from the microdomain phase of SB. The microphase separation was induced in a film preparation process using a solution cast method at room temperature. The macrophase separation was induced by rapidly heating the film specimens to above a critical temperature where PVME and PS undergo spinodal decomposition (SD). This complex phase transition, involving microphase separation followed by macrophase separation, was found to generate a superlattice structure (or a modulated structure) with two characteristic spacings: A_macro associated with the SD and A_micro associated with the microphase separation, both being generally time-dependent. The growth of the “macrodomains” was found to be pinned at A_macro ˜ 840 nm due to the elastic effect of the microdomain structure. The microdomain structure with A_micro ˜ 57 nm was found to undergo a morphological transition (a transition between two ordered phases of block copolymers) as a consequence of the local composition change of the two polymers induced by the SD.     

Interface stabilization and micelle formation in blends with a block copolymer

The phase separation behavior of ternary blends of two homopolymers, PMMA and PS, and a block copolymer of styrene and methylmethacrylate, P(S-b-MMA), was studied. The homopolymers were of equal chain length and were kept at equal amounts. Two copolymers were used with blocks of equal length, which exceeded or equaled that of the homopolymer chains. Varied was the copolymer contentf. Films were cast from toluene, which is a nonselective solvent. The morphologies of the cast films were compared with the structure of the critical fluctuations in solution, which were calculated in mean field approximation. The axis of blend compositionsf can be divided into parts of dominating macrophase and microphase separation. Above a transition concentrationf _o, all copolymer chains are found in phase interfaces. Belowf _o, part of them form micelles within the homopolymer phases.     

自洽平均场正则系综下计算嵌段共聚物/均聚物共混相图

在自洽平均场中计算聚合物宏观相分离体系时,需要将正则系综与巨正则系综结合使用。 通过将正则系综与巨正则系综之间的变量进行转化,只在正则系综下计算即可得到巨正则系综下的相应变量的值,在很大程度上减少了计算量。 本文利用这种简化方法计算了A-b-B两嵌段共聚物与均聚物A在不同均聚物聚合度下随着均聚物含量变化的相图,其结果与巨正则系综下的计算结果相同。 该结果表明,在嵌段共聚物与均聚物的共混体系中,增加嵌段共聚物组成fA或者减小均聚物的聚合度,将有效阻止体系发生宏观相分离。     

接枝共聚物聚苯乙烯－g－聚氧乙烯的微相分离形态研究

 本文利用透射电子显微镜技术，以两性接校共聚物聚苯乙烯－ｇ－聚氧乙烯为研究对象，研究了接枝共聚物的微相分离形态结构，发现聚苯乙烯－ｇ－聚氧乙烯能形成微相分离结构，微区的形状和尺寸与共聚物的组成和侧链长度有关．文中还讨论了嵌段共聚物和接枝共聚物在形成微相分离结构时的共性和个性．     

接枝共聚物聚苯乙烯－g－聚氧乙烯的微相分离形态研究

本文利用透射电子显微镜技术，以两性接校共聚物聚苯乙烯－ｇ－聚氧乙烯为研究对象，研究了接枝共聚物的微相分离形态结构，发现聚苯乙烯－ｇ－聚氧乙烯能形成微相分离结构，微区的形状和尺寸与共聚物的组成和侧链长度有关．文中还讨论了嵌段共聚物和接枝共聚物在形成微相分离结构时的共性和个性．     

Surface segregation of polypeptide-based block copolymer micelles: An approach to engineer nanostructured and stimuli responsive surfaces

We describe the surface segregation of polypeptide-based block copolymer micelles to produce stimuli-responsive nanostructures at the polymer blend/air interface. Such structures were obtained by simultaneous surface migration and self assembly at the surface of diblock copolymer/homopolymer blends. We employed blends composed of homopolymer (PS) and an amphiphilic block copolymer polystyrene-b-poly(l-glutamic acid) (PS-b-PGA). The surface was functionalized based on the preferential segregation to the polymer blend/air interface of the hydrophilic PGA block of the diblock copolymer upon annealing to water vapor. The surface migration of the diblock copolymer to the interface was demonstrated both by XPS and contact angle measurements. As a consequence, the PGA interfacial attraction leads to a large surface excess on diblock copolymer which in turn, through macrophase and microphase separation, produced separated domains at the surface with regions composed either of homo or block copolymer. Herein we demonstrate that the use of asymmetric diblock copolymers with a higher content in PS lead to spherical micellar assemblies randomly distributed at the surface. As observed by AFM imaging the blend composition, i.e. the amount of block copolymer within the blend influences the density of micelles at the surface. Finally, when exposed to water, the pH affects the surface morphology. The PGA segments are collapsed at low pH values and extended at pH values above 4.8, thus inducing variations on the topography of the films at the nanometer scale.     

Integral equation theory of randomly coupled multiblock copolymer melts: effect of block size on the phase behavior

The phase behavior of randomly coupled multiblock copolymer melts is studied using the polymer reference interaction site model integral equation theory. The molecules are modeled as flexible chains with random sequences of two types of blocks, each of which consists of the same number (R) of monomer beads. In the random copolymer (R=1) limit the theory predicts macrophase separation as the temperature is decreased for all values of the monomer correlation length lambda. For R>2, however, the theory predicts a microphase separation for values of lambda less than some critical value which increases as the block size increases.     

Poly(3-alkylthiophene) diblock copolymers with ordered microstructures and continuous semiconducting pathways

Conjugated rod-coil diblock copolymers self-assemble due to a balance of liquid crystalline (rod-rod) and enthalpic (rod-coil) interactions. Previous work has shown that while classical block copolymers self-assemble into a wide variety of nanostructures, when rod-rod interactions dominate self-assembly in rod-coil block copolymers, lamellar structures are preferred. Here, it is demonstrated that other, potentially more useful, nanostructures can be formed when these two interactions are more closely balanced. In particular, hexagonally packed polylactide (PLA) cylinders embedded in a semiconducting poly(3-alkylthiophene) (P3AT) matrix can be formed. This microstructure has been long-sought as it provides an opportunity to incorporate additional functionalities into a majority phase nanostructured conjugated polymer, for example in organic photovoltaic applications. Previous efforts to generate this phase in polythiophene-based block copolymers have failed due to the high driving force for P3AT crystallization. Here, we demonstrate that careful design of the P3AT moiety allows for a balance between crystallization and microphase separation due to chemical dissimilarity between copolymer blocks. In addition to hexagonally packed cylinders, P3AT-PLA block copolymers form nanostructures with long-range order at all block copolymer compositions. Importantly, the conjugated moiety of the P3AT-PLA block copolymers retains the crystalline packing structure and characteristic high time-of-flight charge transport of the homopolymer polythiophene (μ(h) ~10(-4) cm(2) V(-1) s(-1)) in the confined geometry of the block copolymer domains.     

嵌段共聚物／均聚物共混体系的微相分离和形态结构研究

着重介绍嵌段共聚物／均聚物共混体系的微相分离，微胶束的形成，微区的形态结构以及形态的控制。     

聚甲基丙烯酸甲酯－聚四氢呋喃两嵌段共聚物／聚四氢呋喃共混体系的相容性和结晶行为

报道了对嵌段共聚物结晶型共混体系结晶行为的研究．通过对聚甲基丙烯酸甲酯－聚四氢呋喃两嵌段共聚物／聚四氢呋喃共混体系的研究，我们发现１．微相分离结构的存在，可使相容的这类体系形成多种特殊的结晶形态；２．共混体系的相容性可以方便地由其结晶行为来判断；３．共混体系中共聚物的结晶能力显著提高．这些特点都明显不同于一般的聚合物共混体系．     

线性ABC三嵌段共聚物在均聚物C中自组装的自洽平均场模拟

应用实空间的自洽平均场理论研究了线性ABC三嵌段共聚物在均聚物C中的自组装. 模拟结果表明, 共聚物在均聚物中形成的分散相主要为核壳结构. 通过降低A与C之间的相互作用, 可以使核壳结构的成核嵌段发生从嵌段A向嵌段B的转变, 并且在转变过程中观察到了多种过渡结构, 包括带有凸起表面的盘状结构和柱状结构以及相互缠绕的柱状结构. 另外, 降低嵌段共聚物中A嵌段在共混体系中的含量有利于形成以B为核的核壳结构.     

尼龙6/多单体接枝聚丙烯合金中的微相分离结构

近年来,有关高聚物微相分离结构的研究不断深入,发现了许多新的微相分离形态.但这些研究几乎全部集中在嵌段或接枝共聚物上,即共聚物本身具有的链结构导致了微相分离结构.     

SOME ASPECTS OF MORPHOLOGIES AND INTERFACES IN COPOLYMER/HOMOPOLYMER BLENDS

Based on a series of morphological studies of blends of homopolymer (Homo) and a variety of block and graft copolymers (Cop), the nature of phase separation, interface, emulsification and inner morphology of copolymer-dispersed phase etc. in the blends are discussed. In the cases of Cop AB/Homo A/Homo B systems, in which one homopolymer forms matrix, it is observed that the dispersed homopolymer phase is exclusively associated with Cop AB, i.e. no Homo A-Homo B interface exists. This phenomenon is believed to be caused by minimizing the interfacial energy of the systems. Meanwhile, preferential solubilization or anchoring of the like chains of copolymer into homopolymer matrix leads to stabilization of the dispersed phase in the matrix. In addition, regular variation of the inner morphology of the dispersed copolymer phase with the composition and molecular parameters of the component polymers is observed. When the two components have comparable proportions, alternating concentric shells are the most common feature which is associated with minimizing the interfacial energy in the Cop/Homo systems.     

Oil-continuous microemulsions mixed with an amphiphilic graft copolymer or with the parent homopolymer Polymer–droplet interactions as revealed by phase behavior and light scattering

Polymer–droplet interactions have been studied in AOT/water/isooctane oil-continuous microemulsions mixed with an amphiphilic graft copolymer, or with the parent homopolymer (AOT = sodium bis(2-ethylhexyl) sulfosuccinate). The graft copolymer has an oil-soluble poly(dodecyl methacrylate) backbone and water-soluble poly(ethylene glycol) side chains. Pseudo-ternary polymer/droplet/isooctane phase diagrams have been established for both the parent homopolymer and the graft copolymer, and the two types of mixture display entirely different phase behavior. The homopolymer–droplet interaction is repulsive, and a segregative phase separation occurs at high droplet concentrations. By contrast, the graft copolymer–droplet interaction is attractive: the polymer is insoluble in the pure oil, but dissolves in the microemulsion. A comparatively high concentration of droplets is required to solubilize even small amounts of polymer. Static and dynamic light scattering has been performed in order to obtain information on structure and dynamics in the two types of mixture. For optically matched microemulsions, with a vanishing excess polarizability of the droplets, the polymer dominates the intensity of scattered light. The absolute intensity of scattered light increases as phase separation is approached owing to large-scale concentration fluctuations. Dynamic light scattering shows two populations of diffusion coefficients; one population originates from “free” microemulsion droplets and the other from the polymer (for homopolymer mixtures) or from polymer–droplet aggregates (for mixtures with the graft copolymer). The graft copolymer forms large polymer–droplet aggregates with a broad size distribution, which coexist with a significant fraction of free droplets.     

Phase behavior of a blend of polymer-tethered nanoparticles with diblock copolymers

Using the self-consistent field theory (SCFT), we investigate the phase behavior of a mixture of diblock copolymers and nanoparticles with monodisperse polymer chains tethered to their surfaces. We assume the size of the nanoparticles to be much smaller than that of the attached polymer chains and therefore model the particles with their grafted polymer "shell" as star polymers. The polymer chains attached to the particles are of the same species as one of the blocks of the symmetric diblock copolymer. Of primary interest is how to tune the shell of the particle by changing both the length and number of tethered polymers in order to achieve higher loading of nanoparticles within an ordered structure without macrophase separation occurring. We find that the phase behavior of the system is very sensitive to the size of the particle including its tethered shell. The region of microphase separation is increased upon decreasing the star polymer size, which may be achieved by shortening and/or removing tethered polymer chains. To explore the possible structures in these systems we employ SCFT simulations that provide insight into the arrangement of the different species in these complex composites.     

聚丁二烯－b－甲基丙烯酸甲酯共聚物的聚集态研究

聚丁二烯－ｂ－甲基丙烯酸甲酯共聚物的聚集态研究周庆业,张邦华,宋谋道,何炳林（南开大学高分子化学研究所,天津,３０００７１）关键词共聚物,相分离,聚集态结构嵌段共聚物按其组成、合成及成型条件的不同可形成丰富的相结构［１］,其动态力学性能,如在损耗模量...     

Phase behavior of compressible melts of multiblock polydisperse copolymers

In terms of the previously proposed model, specific features of the phase behavior of Markovian polydisperse copolymers with allowance for their compressibility have been investigated via bifurcation analysis followed by continuation with respect to a parameter that characterizes the deviation of the temperature of the system from its value on the spinodal. These features above all include competition between microphase separation and macrophase separation under conditions when the local instability of the homogeneous state appearing at the spinodal corresponds to the macrophase separation only. Nevertheless, it was shown that depending on the structural parameters, the global instability characterized by a cloud-point hypersurface can result in either macrophase or microphase separation, with the microphase separation occurring in the vicinity of the critical point. In this case, the results are consistent with the conclusions of the Landau theory of phase transitions, whose applicability limits with respect to deviation from the critical point have been evaluated in this study. Outside the range of applicability of this theory, cloud-point curves that correspond to macrophase separation and microphase separation are very similar. These conclusions remain valid over a wide range of compressibility whose influence has been assessed for the first time. It has been found that the type of copolymers under consideration has a characteristic feature that was not noticed previously: Namely, the distribution of density in the nucleus of a new phase in this case will look like a spatially localized solitonlike profile.     

Tuning block copolymer phase behavior with a selectively associating homopolymer additive

We use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A ? B segmental interaction parameter (χ_ABN)_S to significantly lower values [i.e., (χ_ABN)_S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χ_ABN)_S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χ_ABN)_S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009     

Self-Assembly of Rod-Coil Block Copolymers for Photovoltaic Applications

Summary: Two different approaches to obtain electron donor-acceptor interfaces via self-assembly of block copolymer systems are discussed, where the donor domains are formed by a π-conjugated rod-like polymer and the acceptor domains result from a coiled polymer modified by C₆₀ fullerenes. In the first strategy, C₆₀ is chemically grafted onto the coil polymer, typically a statistical copolymer of styrene and chloromethyl styrene. This has as major effect the increase in molecular weight and volume fraction of the coil block, which can markedly perturb the self-assembled block copolymer final morphologies and eventually suppress any microseparated nanostructure in favour of fully isotropic homogeneous phases. We discuss how the presence of free homopolymer rods in the system can help recovering a microphase separated morphology suitable for photovoltaic applications. In the second approach we discuss the poly(diethylhexyl-p-phenylenevinylene-b-4-vinylpyridine) (PPV-P4VP) rod-coil block copolymer system and we argue how supramolecular interactions among P4VP and free C₆₀ can be exploited to blend rod-coil block copolymers and C₆₀ preserving the original lamellar phase.     

Modification of the morphology of P(S-b-EO) templated thin TiO2 films by swelling with PS homopolymer

For the controlled modification of sol-gel-templated polymer nanocomposites, which are transferred to a nanostructured, crystalline TiO2 phase by a calcination process, the addition of a single homopolymer was investigated. For the preparation, the homopolymer polystyrene (PS) is added in different amounts to the diblock copolymer P(S-b-EO) acting as a templating agent. The homopolymer/diblock copolymer blend system is combined with sol-gel chemistry to provide and attach the TiO2 nanoparticles to the diblock copolymer. So-called good-poor solvent-pair-induced phase separation leads to the formation of nanostructures by film preparation via spin coating. The fabricated morphologies are studied as a function of added homopolymer before and after calcination with atomic force microscopy, field emission scanning electron microscopy, and grazing incidence small-angle X-ray scattering. The observed behavior is discussed in the framework of controlling the block copolymer morphologies by the addition of homopolymers. At small homopolymer concentrations, the increase in homopolymer concentration changes the structure size, whereas at high homopolymer concentrations, a change in morphology is triggered. Thus, the behavior of a pure polymer system is transferred to a more complex hybrid system.