Diblock Copolymer Systems Research Articles

Poly(dimethylsiloxane-b-methyl methacrylate): A Promising Candidate for Sub-10 nm Patterning

We report herein the modular synthesis and nanolithographic potential of poly(dimethylsiloxane-block-methyl methacrylate) (PDMS-b-PMMA) with self-assembled domains approaching sub-10 nm periods. A straightforward and modular coupling strategy, optimized for low molecular weight diblocks and using copper-catalyzed azide–alkyne “click” cycloaddition, was employed to obtain a library of PDMS-b-PMMA and poly(dimethylsiloxane-block-styrene) (PDMS-b-PS) diblock copolymers. Flory–Huggins interaction parameters, determined from small-angle X-ray scattering experiments, were high for PDMS-b-PMMA (χ ∼ 0.2 at 150 °C), suggesting this diblock copolymer system has promise for sub-10 nm lithographic applications when compared to the corresponding PDMS-b-PS diblock copolymers (χ ∼ 0.1 at 150 °C). Performance evaluation in thin film self-assembly experiments allowed domain periods as small as 12.1 nm to be obtained, which is among the smallest highly ordered nanoscale patterns reported hitherto for thermally annealed mat...

Influence of Composition Fluctuations on the Linear Viscoelastic Properties of Symmetric Diblock Copolymers near the Order-Disorder Transition.

Rheological evidence of composition fluctuations in disordered diblock copolymers near the order-disorder transition (ODT) has been documented in the literature over the past three decades, characterized by a failure of time-temperature superposition (tTS) to reduce linear dynamic mechanical spectroscopy (DMS) data in the terminal viscoelastic regime to a temperature-independent form. However, for some materials, most notably poly(styrene-b-isoprene) (PS-PI), no signature of these rheological features has been found. We present small-angle X-ray scattering (SAXS) results on symmetric poly(cyclohexylethylene-b-ethylene) (PCHE-PE) diblock copolymers that confirm the presence of fluctuations in the disordered state and DMS measurements that also show no sign of the features ascribed to composition fluctuations. Assessment of DMS results published on five different diblock copolymer systems leads us to conclude that the effects of composition fluctuations can be masked by highly asymmetric block dynamics, thereby resolving a long-standing disagreement in the literature and reinforcing the importance of mechanical contrast in understanding the dynamics of ordered and disordered block polymers.

Communication: Effect of solvophobic block length on critical micelle concentration in model surfactant systems.

Experimental measurements of the Critical Micelle Concentration (CMC) in diblock copolymer and molecular surfactant systems have shown a cross-over from the exponential decrease at short chain lengths to a much more shallow decay of the CMC when the solvophobic block length was increased. This effect was observed for a wide variety of surfactants, and has been attributed to the collapse of the solvophobic tail group. In order to study this peculiar effect in more detail, we performed grand canonical Monte Carlo simulations of model surfactants in combination with histogram reweighting to obtain the CMC as a function of solvophobic block length. We found that the CMC decreases exponentially with increasing solvophobic block length; no cross-over to a slower decay has been observed, as also expected based on theoretical considerations. These findings suggest that the experimentally measured CMCs may not be true equilibrium values, but that kinetic effects may be influencing the observed cross-over.

Morphology, Modulus, and Conductivity of a Triblock Terpolymer/Ionic Liquid Electrolyte Membrane

Block polymers are ideally suited for polymer electrolytes exhibiting both high ionic conductivity and superior mechanical robustness because they self-assemble into well-defined nanostructures. Network morphologies exhibiting long-range continuity of both the mechanically robust and conductive domains maximize the macroscopic composite properties but are difficult to achieve in commonly studied diblock copolymer systems. We therefore investigated a polymer electrolyte comprising the triblock terpolymer poly[isoprene-b-(styrene-co-norbornenylethylstyrene)-b-ethylene oxide] (INSO) and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) because INSO self-assembles into equilibrium network morphologies in which each domain is continuous throughout the sample. Small-angle X-ray scattering and transmission electron microscopy revealed the bulk morphology of INSO to be the O70 network prior to cross-linking. The material remained microphase-separated but without long-range order after solvent-casting from dichloromethane, a morphology that was retained after cross-linking and the addition of ionic liquid. Cross-linking had the effect of increasing the elastic modulus by 4 orders of magnitude, from 104 to 108 Pa, and importantly, a high modulus was retained well above the Tg of linear polystyrene. The conductivity was somewhat lower than that expected for a heterogeneous electrolyte, but the results suggest that refinements to the solvent-casting procedure could increase connectivity of the conductive domain and thus macroscopic conductivity.

The Γ-Limit of the Two-Dimensional Ohta–Kawasaki Energy. Droplet Arrangement via the Renormalized Energy

This is the second in a series of papers in which we derive a Γ-expansion for the two-dimensional non-local Ginzburg–Landau energy with Coulomb repulsion known as the Ohta–Kawasaki model in connection with diblock copolymer systems. In this model, two phases appear, which interact via a nonlocal Coulomb type energy. Here we focus on the sharp interface version of this energy in the regime where one of the phases has very small volume fraction, thus creating small “droplets” of the minority phase in a “sea” of the majority phase. In our previous paper, we computed the Γ-limit of the leading order energy, which yields the averaged behavior for almost minimizers, namely that the density of droplets should be uniform. Here we go to the next order and derive a next order Γ-limit energy, which is exactly the Coulombian renormalized energy obtained by Sandier and Serfaty as a limiting interaction energy for vortices in the magnetic Ginzburg–Landau model. The derivation is based on the abstract scheme of Sandier-Serfaty that serves to obtain lower bounds for 2-scale energies and express them through some probabilities on patterns via the multiparameter ergodic theorem. Thus, without appealing to the Euler–Lagrange equation, we establish for all configurations which have “almost minimal energy” the asymptotic roundness and radius of the droplets, and the fact that they asymptotically shrink to points whose arrangement minimizes the renormalized energy in some averaged sense. Via a kind of Γ-equivalence, the obtained results also yield an expansion of the minimal energy and a characterization of the zero super-level sets of the minimizers for the original Ohta–Kawasaki energy. This leads to the expectation of seeing triangular lattices of droplets as energy minimizers.

Effects of molecular geometry on the self-assembly of giant polymer–dendron conjugates in condensed state

A series of giant polymer-dendron conjugates with a dendron head and a linear polymer tail were synthesized via"click" chemistry between azide-functionalized polystyrene (PS(N), N: degree-of-polymerization) and t-butyl protected, alkyne-functionalized second generation dendron (tD), followed by a deprotection process to generate a dendron termini possessing nine carboxylic acid groups. The molecular structures were confirmed by nuclear magnetic resonance, size-exclusion chromatographic analyses, and matrix-assisted laser desorption ionization time-of-flight mass spectra. These well-defined conjugates can serve as a model system to study the effects of the molecular geometries on the self-assembly behaviour, as compared with their linear analogues. Four phase morphologies found in flexible linear diblock copolymer systems, including lamellae, bicontinuous double gyroids, hexagonal packed cylinders, and body-centred cubic packed spheres, were observed in this series of conjugates based on the results of small angle X-ray scattering and transmission electron microscopy. All of the domain sizes in these phase separated structures were around or less than 10 nm. A 'half' phase diagram was constructed based on the experimental results. The geometrical effect was found not only to enhance the immiscibility between the PS(N) tail and dendron head, but also systematically shift all of the phase boundaries towards higher volume fractions of the PS(N) tails, resulting in an asymmetrical phase diagram. This study may provide a pathway to the construction of ordered patterns of sub-10 nm feature size using polymer-dendron conjugates.

Directed Assembly of Lamellae Forming Block Copolymer Thin Films near the Order–Disorder Transition

The impact of thin film confinement on the ordering of lamellae was investigated using symmetric poly(styrene-b-[isoprene-ran-epoxyisoprene]) diblock copolymers bound by nonpreferential wetting interfaces. The order-disorder transition temperature (TODT) and the occurrence of composition fluctuations in the disordered state are not significantly affected by two-dimensional confinement. Directed self-assembly using chemical patterning is demonstrated near TODT. These results establish the minimum feature size attainable using directed self-assembly of a given diblock copolymer system.

Fluctuation effects on the order-disorder transition in polydisperse copolymer melts

Using single chain in mean field simulation approach, we examine the influence of fluctuation effects on the order-disorder transition (ODT) of polydisperse copolymer systems. We consider two model systems: (i) molecular weight polydisperse systems represented by AB diblock copolymer melts having monodisperse A blocks and polydisperse B blocks; and (ii) compositionally polydisperse symmetric diblock copolymer systems. In each case, we present results for the fluctuation-induced shift in the ODT from the corresponding mean-field predictions. In both models, an increase in polydispersity enhances the influence of fluctuations. Moreover, for compositionally polydisperse systems, we observe that the effects of fluctuations show similar trends in systems containing quenched and annealed representation of sequences.

Controlling the Physical and Biological Properties of Highly Fluorescent Aqueous Quantum Dots Using Block Copolymers of Different Size and Shape

The phase transfer of fluorescent CdSe based quantum dots (QDs) while retaining their properties and offering some advantages concerning the stability and functionalization characteristics is an important and intensively investigated field of research. Here we report how to tune and control the properties of CdSe/CdS/ZnS core-shell-shell QDs in water, using poly(isoprene-block-ethylene oxide) (PI-b-PEO) as a versatile system of amphiphilic diblock copolymers for the micellular encapsulation of nanoparticles (NPs). We show the synthesis of a novel PI-b-(PEO)2 miktoarm star polymer and how this different architecture besides the variation of the polymers' molecular weight gives us the opportunity to control the size of the built constructs in water between 24 and 53 nm. Because of this size control, an upper limit of the construct's diameter for the cellular uptake could be determined by a systemic study with human alveolar epithelial cells (A549) and murine macrophage leukemia cell (RAW-264.7). Furthermore, fluorescence quenching experiments with copper(II) and iron(III) ions show a strong influence of the used polymer on the shielding against these ions. This enables us to control the permeability of the polymer shell from very porous shells, which allow an almost complete cation exchange up to very dense shells. These even offer the possibility to perform copper(I) catalyzed click reactions while keeping the fluorescence of the QDs. All these results underline the huge variability and controllability of the PI-b-PEO diblock copolymer system for the encapsulation and functionalization of nanoparticles for biological applications. As a general trend, it can be stated that those coatings, which were most stable against quenchers, also showed the best resistivity with respect to unspecific cellular uptake.

The Γ-Limit of the Two-Dimensional Ohta–Kawasaki Energy. I. Droplet Density

This is the first in a series of two papers in which we derive a $\Gamma$-expansion for a two-dimensional non-local Ginzburg-Landau energy with Coulomb repulsion, also known as the Ohta-Kawasaki model in connection with diblock copolymer systems. In that model, two phases appear, which interact via a nonlocal Coulomb type energy. We focus on the regime where one of the phases has very small volume fraction, thus creating small "droplets" of the minority phase in a "sea" of the majority phase. In this paper we show that an appropriate setting for $\Gamma$-convergence in the considered parameter regime is via weak convergence of the suitably normalized charge density in the sense of measures. We prove that, after a suitable rescaling, the Ohta-Kawasaki energy functional $\Gamma$-converges to a quadratic energy functional of the limit charge density generated by the screened Coulomb kernel. A consequence of our results is that minimizers (or almost minimizers) of the energy have droplets which are almost all asymptotically round, have the same radius and are uniformly distributed in the domain. The proof relies mainly on the analysis of the sharp interface version of the energy, with the connection to the original diffuse interface model obtained via matching upper and lower bounds for the energy. We thus also obtain a characterization of the limit charge density for the energy minimizers in the diffuse interface model.

Nano tools for macro problems: multiscale molecular modeling of nanostructured polymer systems

A current challenge of physical, chemical, and engineering sciences is to develop theoretical tools for predicting structure and properties of complex materials from the knowledge of a few input parameters. In this work, we present a general multiscale molecular simulation protocol for predicting morphologies and properties of nanostructured polymer systems and we apply it to three examples of industrial relevance. The first example is of general importance for the polymer industry and is related to the enhancement of mechanical and barrier properties, if a nanofiller is dispersed into a polymer matrix: the role of multiscale modeling for the development of the material in the stage of screening, the best design is evidenced. The second example, important for the optoelectronic industry, is related to the prediction of the dispersion of gold nanoparticles into a diblock copolymer system forming different nanostructures (lamellae, cylinders, …). In this case, it is relevant to understand how it is possible to influence the self-assembly of the nanoparticles in different regions of the diblock copolymer structure. The third example is of interest to automotive and polymer industries and involves inorganic nanoparticles grafted with organic side chains. The assembly is dispersed in a polymeric matrix and it is interesting to predict the effect of the chain length and grafting density on the nanostructure.

Hierarchical self-assembly of miktoarm star polymers containing a polycationic segment: A general concept

We recently introduced a concept for the counterion-mediated hierarchical self-assembly of an amphiphilic ABC miktoarm star terpolymer in aqueous media into micrometer-sized compartmentalized particles with a highly periodic lamellar fine structure (“woodlice”). Herein, we extend this concept to different miktoarm star polymer systems containing a polycationic segment. The presence of a poly(N-methyl-2-vinylpyridinium) (P2VPq) block and its interaction with iodide/triiodide counterions is crucial. In analogy to linear diblock copolymer systems the hydrophilic/hydrophobic balance of polybutadiene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene miktoarm star terpolymers determines the morphology of the primary building blocks (spherical micelles and cylindrical micelles/vesicles) and the obtained superstructures (stacked lamellar structures and multilamellar vesicles) during this hierarchical process. When an ABA' miktoarm star copolymer (polystyrene-arm-poly(N-methyl-2-vinylpyridinium iodide)-arm-polystyrene) without a dynamic core-forming block was investigated, a different mechanism into “woodlouse” structured aggregates via aggregation and deformation of intermediate vesicles was found. The individual steps of the different self-assembly processes were investigated by transmission electron microscopy and additionally supported by dynamic light scattering, differential scanning calorimetry, and small-angle X-ray scattering.

Simultaneous Determination of Critical Micelle Temperature and Micelle Core Glass Transition Temperature of Block Copolymer–Solvent Systems via Pyrene-Label Fluorescence

The critical micelle temperature (CMT) and micelle core glass transition temperature (Tg) for a poly(methyl methacrylate) (PMMA)-poly(tert-butyl methacrylate) (PtBMA) diblock copolymer system were measured by fluorescence via single temperature (T) ramps. Synthesis yielded identical block lengths in unlabeled and pyrene-labeled diblocks, the latter with dye at the PMMA block terminus. Studies were conducted at 5–18 wt % diblock in 2-ethylhexanol (2EH) with a trace of labeled diblock (0.2 wt % of total copolymer). The T dependence of pyrene-label fluorescence intensity yielded the CMT and micelle core Tg in systems where the PMMA-block and the 2EH within the cores constituted 1.9–7.8% of sample mass. While the CMT can be measured by many methods, this is the first direct measurement of micelle core Tg at low core content (e.g., 1.9 wt %) in a block copolymer/solvent system. Differential scanning calorimetry was done on diblock samples, showing severe limitations for sensing and characterizing core Tg. Fluorescence from trace levels of labeled diblock was used with 5–20 wt % PMMA–poly(n-butyl acrylate)–PMMA triblocks in 2EH. The micelle core Tg is important in triblock systems that form thermoreversible gels because it fundamentally underlies the viscoelastic to elastic gel transition. Fluorescence results demonstrated the dependence of the CMT and the near invariance of the micelle core Tg on core-block molecular weight in these diblock and triblock systems for PMMA blocks with Mn = 15–25 kg/mol and solvent in the micelle core.

Micro- and nanophase separations in hierarchical self-assembly of strongly amphiphilic block copolymer-based ionic supramolecules

By a selective complexation between different alkyltrimethylammonium amphiphiles (C8, C12 and C16) and three different diblock copolymer systems of poly(styrene)-b-poly(methacrylic acid) at various grafting densities X (X = number of alkyl chains per acidic group of the poly(methacrylic acid) PMAA block), a class of ionic supramolecules are successfully synthesized whose molecular architecture consists of a poly(styrene) PS block (Linear block) covalently connected to a strongly amphiphilic comb-like block (AmphComb block), i.e. Linear-b-AmphComb. In the melt state, these ionic supramolecules can show simultaneous microphase (between Linear and AmphComb blocks) and nanophase (within the AmphComb blocks) separations. This leads to the formation of various structure-in-structure two-scale hierarchical self-assemblies, including S-in-SLL, S-in-SBCC, S-in-C, S-in-L and C-in-L, where S, SLL, SBCC, C and L stand for spherical, spherical in liquid-like state, spherical in body-centered-cubic arrangement, cylindrical and lamellar, respectively. Synchrotron small angle X-ray scattering (SAXS) and crossed polarizers, together with SAXS modelling analysis, were used for a detailed structural study of the samples. The morphology of the microphase separated state was mapped out on ‘master’ microdomain morphology diagrams as a function of the volume fraction of the AmphComb blocks (ΦAmphComb) and the compositional window of each microdomain morphology was determined. It was observed that, (i) within samples based on the same parent diblock copolymer system, the occurrence of a specific microdomain morphology is only dependent on the value of ΦAmphComb, regardless of the grafting density X and the length of the alkyl side-chains, and (ii) microdomain morphological boundaries occur at ΦAmphComb values of ∼0.20 (SLL/C and SBCC/C) and ∼0.28 (C/L). Finally, the specific influences of the strongly amphiphilic nature of the AmphComb blocks on the observed morphological and hierarchical behaviours of our system are discussed. For reference, stoichiometric strongly amphiphilic comb-like (AmphComb) ionic supramolecules, based on complexation between a homopolymer of PMAA and the various alkyltrimethylammonium amphiphiles, were prepared, which nanophase separated into S (C8) or C (C12 and C16) domains.

Block Copolymers for Drug Delivery Nano Systems (DDnSs)

The application of polymers in medicine, as components of drug carriers, as well as their synthetic strategies are considered essential for producing and developing new drug formulations against human deceases. The synthesis of block copolymers is a timeconsuming process with a high cost of the final product, although several block copolymer systems have been already commercialized successfully. The biocompatibility, the biodegradability and the non toxic profile of newly synthesized polymers towards healthy tissues, should be taken into account in order to be acceptable for biomedical applications. In this review article, focus is placed on new approaches and synthetic strategies for preparing novel block copolymers and their utilization as parts of new and advanced Drug Delivery nanoSystems (aDDnSs) with a Modulatory Controlled Release profile (MCR). Such complex and advanced nanosystems can alter the pharmacokinetic properties of the encapsulated drug and consequently its effectiveness. Emphasis is given to the use of living polymerization methodologies and post polymerization chemical transformation reactions for the synthesis of mainly diblock copolymers for novel drug delivery nanosystems. Issues related to self-assembly of block copolymers in solution toward formation of colloidal functional nanostructures that can serve as nanocontainers and nanocarriers, and strategies for controlling encapsulation of specific drugs are also discussed. Specific examples are reported mainly on diblock copolymer systems, including authors' recent work.

Crystallization of Isotactic Polypropylene under the Spatial Confinement Templated by Block Copolymer Microdomains

We investigate the crystallization behavior of isotactic polypropylene (iPP) under the influence of nanoscale confinement templated by the microphase-separated structure of an iPP-based diblock copolymer system, isotactic polypropylene-block-atactic polystyrene (iPP-b-aPS). Three types of iPP microdomains, i.e., lamellae, cylinder, and sphere, were generated by controlling the composition of the diblock. The effect of microdomain morphology on the nucleation mechanism, crystallization kinetics, self-nucleation behavior, the population of the helical sequence of iPP block in the melt state, and crystal orientation have been systematically studied. It was found that the crystallization rate of iPP was predominantly controlled by homogeneous nucleation when the crystallization process was largely confined within the individual cylindrical and spherical microdomains. Such a nucleation mechanism and the highly frustrated crystal growth in the isolated microdomains led to the absence of Domain II and atypical crystallization kinetics in Domain III in the self-nucleation study. The population of the longer helical sequence of iPP block revealed by infrared spectroscopy was found to be affected by temperature but not by the spatial confinement, chain stretching, and junction point constraint imposed by the microdomains. Finally, the orientation of α-form iPP crystals in the lamellae-forming iPP-b-aPS was identified over a broad range of crystallization temperatures (T(c)). Different from other crystalline-amorphous diblocks, a lamellar branching of α-form iPP was observed in the lamellar microdomains at T(c) lying between 15 and 80 °C, where the daughter lamellae developed from the perpendicularly orientated parent iPP crystals with a specific angle of 80° or 100°. Once the sample was crystallized at T(c) ≤ 10 °C, the iPP crystals became randomly oriented.

Magnetic Properties of Cobalt-Containing Diblock Copolymers with Cylindrical Morphology of Different Domain Sizes

Previously, we have synthesized a cobalt-containing diblock copolymer system which exhibited room temperature ferromagnetic properties after phase separation and heat treatment. We have also shown that the morphology and cobalt density in the nanostructured domains both influenced the magnetic properties of these materials due to nanoconfinement which enhanced the dipolar interactions between otherwise superparamagnetic cobalt nanoparticles. Here, we investigated the effect of domain size on the magnetic properties of these room temperature ferromagnetic materials (RTFMs) using a series of five cobalt-containing diblock copolymers with various molecular weights and constant block ratios. The diblock copolymers self-assembled into cylindrical morphologies with different domain sizes upon solvent annealing, and then were converted to RTFMs upon a simple heat treatment. The domain sizes of these RTFMs did not show a significant impact on their coercivity values, possibly because the domain size range investigated was not large enough and the cobalt–cobalt dipolar interactions were nearly constant throughout. At the same time, this study confirms that the RTFMs generated from these novel block copolymers are robust.

Thermoresponsive Self-Assemblies of Cyclic and Branched Oligosaccharide-block-poly(N-isopropylacrylamide) Diblock Copolymers into Nanoparticles

This paper discusses the thermoresponsive nanoparticles obtained by self-assemblies of nonlinear oligosaccharide-based diblock copolymer systems. These diblock copolymers were synthesized by Cu(I)-catalyzed 1,3-dipolar azide/alkyne cycloaddition ("click" reaction) of propargyl-functionalized β-cyclodextrin (βCyD) and xyloglucooligosaccharide (XGO) with poly(N-isopropylacrylamide) (PNIPAM) having a terminal azido group prepared by atom transfer radical polymerization (ATRP). Elastic and quasi-elastic light scattering analysis of the dibock copolymers in H(2)O indicated that thermodynamic phase transitions of the PNIPAM blocks at their cloud points (T(cp)s ≈ 34 °C), around lower critical solution temperatures (LCSTs), triggered their self-assemblies into the nanoparticles. These nanoparticles had narrow size distributions and small interphases (i.e., sharp boundaries). The mean hydrodynamic radii (R(h)s) of the βCyD and XGO-based nanoparticles were determined to be around 150 and 250 nm upon slow heating (i.e., step-by-step heating), and 364 and 91.5 nm upon fast heating, respectively, depending on a predominance of the interchain association or the intrachain contraction. Transmission electron microscope (TEM) and field emission gun-scanning electron microscopy (FEG-SEM) images of the nanoparticles clearly showed compact spherical nanoparticles whose cores are mainly made with the PNIPAM blocks, whereas the rough shells consist in the oligosaccharidic blocks.

Triply Triggered Doxorubicin Release From Supramolecular Nanocontainers

The synthesis of a supramolecular double hydrophilic block copolymer (DHBC) held together by cucurbit[8]uril (CB[8]) ternary complexation and its subsequent self-assembly into micelles is described. This system is responsive to multiple external triggers including temperature, pH and the addition of a competitive guest. The supramolecular block copolymer assembly consists of poly(N-isopropylacrylamide) (PNIPAAm) as a thermoresponsive block and poly(dimethylaminoethylmethacrylate) (PDMAEMA) as a pH-responsive block. Moreover, encapsulation and controlled drug release was demonstrated with this system using the chemotherapeutic drug doxorubicin (DOX). This triple stimuli-responsive DHBC micelle system represents an evolution over conventional double stimuli-responsive covalent diblock copolymer systems and displayed a significant reduction in the viability of HeLa cells upon triggered release of DOX from the supramolecular micellar nanocontainers.

Multiple Vesicular Morphologies in AB/AC Diblock Copolymer Complexes through Hydrogen Bonding Interactions

We report for the first time multiple vesicular morphologies in block copolymer complexes formed in aqueous media via hydrogen bonding interactions. A model AB/AC diblock copolymer system consisting of polystyrene-block-poly(acrylic acid) (PS-b-PAA) and polystyrene-block-poly(ethylene oxide) (PS-b-PEO) was examined using transmission electron microscopy, small-angle X-ray scattering, and dynamic light scattering. The complexation and morphological transitions were driven by the hydrogen bonding between the complementary binding sites on PAA and PEO blocks of the two diblock copolymers. Upon the addition of PS-b-PEO, a variety of bilayer aggregates were formed in PS-b-PAA/PS-b-PEO complexes including vesicles, multilamellar vesicles (MLVs), thick-walled vesicles (TWVs), interconnected compound vesicles (ICCVs), and irregular aggregates. Among these aggregates, ICCVs were observed as a new morphology. The morphology of aggregates was correlated with respect to the molar ratio of PEO to PAA. At [EO]/[AA] = 0.5, vesicles were observed, while MLVs were obtained at [EO]/[AA] = 1. TWVs and ICCVs were formed at [EO]/[AA] = 2 and 6, respectively. When [EO]/[AA] reached 8 and above, only irregular aggregates appeared. These findings suggest that complexation between two amphiphilic diblock copolymers is a viable approach to prepare polymer vesicles in aqueous media.