Pure Block Copolymer Research Articles

Reorientation of Crystalline Block Copolymer Membranes by Phospholipid Hybridization

Block copolymer (BCP) self-assembly and crystallization determine their fundamental mechanical, optical, and transport properties. Multiple physical and chemical routes to control BCP self-assembly have been developed over the years. In contrast, modulating the crystallization behavior, particularly crystallite size and orientation, has received considerably less attention. This paper underpins that 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipid additives enable precise control of BCP crystallization via a combination of interfacial and confinement effects. The assembly and crystallization behavior of methoxy-poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-b-PCL) hybridized with DPPC was elucidated in solid-supported dry-film forms. mPEG-b-PCL/DPPC hybrid films coassemble into multilamellar structures with BCP and lipid domains stacked in registry across the film thickness. With small amounts of DPPC (3 wt %), mPEG-b-PCL/DPPC hybrid films unexpectedly exhibit nonadditive thermal conductivity, reaching ∼0.1 W m–1 K–1, a value considerably lower than pure BCP or DPPC films. Hybridization alters DPPC chain packing and induces specific PCL crystallite orientation at the nanoscale. PCL chains on the folding plane of an orthorhombic lattice optimize molecular interactions with vertically aligned DPPC alkyl chains by orienting PCL crystallites at a 20° tilt. These results enable new applications of polymeric systems in which switchable crystallization routes are used to tune heat transport.

Blending Linear and Cyclic Block Copolymers to Manipulate Nanolithographic Feature Dimensions.

Block copolymers (BCPs) consist of two or more covalently bound chemically distinct homopolymer blocks. These macromolecules have emerging applications in photonics, membrane separations, and nanolithography stemming from their self-assembly into regular nanoscale structures. Theory suggests that cyclic BCPs should form features up to 40% smaller than their linear analogs while also exhibiting superior thin-film stability and assembly dynamics. However, the complex syntheses required to produce cyclic polymers mean that a need for pure cyclic BCPs would present a challenge to large-scale manufacturing. Here, we employ dissipative particle dynamics simulations to probe the self-assembly behavior of cyclic/linear BCP blends, focusing on nanofeature size and interfacial width as these qualities are critical to nanopatterning applications. We find that for mixtures of symmetric cyclic and linear polymers with equivalent lengths, up to 10% synthetic impurity has a minimal impact on cyclic BCP feature dimensions and interfacial roughness. On the other hand, blending with cyclic BCPs provides a route to “fine-tune” linear BCP feature sizes. We analyze simulated blend domain spacings within the context of strong segregation theory and find significant deviations between simulation and theory that arise from molecular-level packing motifs not included in theory. These insights into blend self-assembly will assist experimentalists in rationally designing BCP materials for advanced nanolithography applications.

Synthesis of polymer nanoparticles via electrohydrodynamic emulsification-mediated self-assembly

HypothesisElectrospray can rapidly produce fine, organic solvent-in-water emulsions in the absence of surfactant via electrohydrodynamic emulsification (EE), a reverse configuration of traditional electrospray. This paper investigates whether EE can produce high-quality nanocomposites comprised of block co-polymers and organic nanoparticles (NPs) via the interfacial instability (IS) self-assembly method. Surfactant-free approaches may increase encapsulation efficiency and product uniformity, process speed, and ease of downstream product purification. ExperimentsAll particles were produced using EE-mediated self-assembly (SA) (EE-SA). Particles were produced using poly(lactic-co-glycolic acid) (PLGA) polymers as proof of concept. Then, block copolymer (BCP) micelles were synthesized from polystyrene-block-poly(ethylene oxide) (PS-b-PEO) (PS 9.5 kDa:PEO 18.0 kDa) in the presence and absence of superparamagnetic iron oxide nanoparticles (SPIONs) or quantum dots (QDs). Encapsulant concentration was varied, and the effect of encapsulant NP ligands on final particle size was investigated. FindingsEE-SA generated both pure polymer NPs and nanocomposites containing SPIONs and QDs. PLGA particles spanned from sub- to super-micron sizes. PS-b-PEO NPs and nanocomposites were highly monodisperse, and more highly loaded than those made via a conventional, surfactant-rich IS process. Free ligands decreased the size of pure BCP particles. Increasing encapsulant levels led to a morphological transition from spherical to worm-like to densely loaded structures.

Toughened polymer electrolyte membranes composed of sulfonated poly(arylene ether ketone) block copolymer and organosiloxane network for fuel cell

The semi-interpenetrating polymer network (semi-IPN) based electrolyte membrane was synthesized from the poly(arylene ether ketone)-b-ketone sulfonated poly(arylene ether ketone) multi-block copolymer (PAEK-b-KSPAEK) and the organosiloxane organic-inorganic hybrid polymer network (OSPN) pre-synthesized. The chemical structure of the synthesized PAEK-b-KSPAEK and semi-IPN was identified using 1H and 19F nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy, and the dimension of the phase separated ionic clusters was examined by small angle X-ray scattering spectroscopy. Introduction of OSPN to PAEK-b-KSPAEK improved not only the thermal and mechanical stability (toughness) but also the oxidative stability. The performance of the membrane electrode assembly fabricated with the semi-IPN electrolyte membranes was superior to that of the pure block copolymer membrane because of the enhanced proton conductivity and toughness. While the semi-IPN24 membrane showed the comparable proton conductivity and cell performance to Nafion 115 membrane, its methanol permeability was significantly lower than that of Nafion 115 membrane.

Copolymerization of 2,3,4,5,6‐Pentafluorostyrene and Methacrylic Acid by Nitroxide‐Mediated Polymerization: The Importance of Reactivity Ratios

Amphiphilic block copolymers of 2,3,4,5,6‐pentafluorostyrene (PFS) and methacrylic acid (MAA) are synthesized via nitroxide‐mediated polymerization (NMP). It is established that to obtain a controlled copolymerization a minimum of 40 mol% of PFS is required, which is significantly greater than other copolymerization systems such as using 4.5–8 mol% styrene or 1 mol% of 9‐(4‐vinylbenzyl)‐9H‐carbazole to control the copolymerization of methacrylates. It is surmised that this lack of control is due to the reactivity ratios that favor the addition of MAA rather than PFS (rPFS = 0.14, rMAA = 6.97). However this reactivity ratio pair suggests that a one‐shot delayed injection approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)‐b‐(PFS‐ran‐MAA) block copolymers are synthesized by a one‐shot delayed addition of MAA. While the concentration of irreversibly terminated chains is evident these results suggest a promising route to the synthesis of fluorinated amphiphilic block copolymers by NMP. image

Compatibilization of All-Conjugated Polymer Blends for Organic Photovoltaics

Compatibilization of an immiscible binary blend comprising a conjugated electron donor and a conjugated electron acceptor polymer with suitable electronic properties upon addition of a block copolymer (BCP) composed of the same building blocks is demonstrated. Efficient compatibilization during melt-annealing is feasible when the two polymers are immiscible in the melt, i.e. above the melting point of ∼250 °C of the semicrystalline donor polymer P3HT. To generate immiscibility at these high temperatures, the acceptor polymer PCDTBT is equipped with fluorinated side chains leading to an increased Flory-Huggins interaction parameter. Compatibilization in bulk and thin films is demonstrated, showing that the photovoltaic performance of pristine microphase separated and nanostructured BCPs can also be obtained for compatibilized blend films containing low contents of 10-20 wt % BCP. Thermodynamically stable domain sizes range between several tens of microns for pure blends and ∼10 nm for pure block copolymers. In addition to controlling domain size, the amount of block copolymer added dictates the ratio of edge-on and face-on P3HT crystals, with compatibilized films showing an increasing amount of face-on P3HT crystals with increasing amount of compatibilizer. This study demonstrates the prerequisites and benefits of compatibilizing all-conjugated semicrystalline polymer blends for organic photovoltaics.

Hybrid Starlike Block Copolymer POSS–(PDMAEMA-b-PNIPAm)8: Thermal Gelation and Its Blends with Poly(vinyl alcohol)

A novel thermogelling polyhedral oligomeric silsesquioxane–poly(2-(dimethylamino)ethyl methacrylate-b-N-isopropylacrylamide), POSS–(PDMAEMA-b-PNIPAm)8, star-shaped block copolymer was synthesized by using RAFT polymerization. In aqueous solution this copolymer (≥10 wt %) underwent sol-to-gel transition as the temperature increased. The network structure and rheology properties of POSS–(PDMAEMA-b-PNIPAm)8 block copolymers could be facilely tuned by blending the poly(vinyl alcohol) into the in situ forming gel system. The presence of PVA could enhance not only the rheological properties but also the thermal sensitivity of the hydrogels. It was observed that the highest storage modulus G′, which is 25 times larger than that of pure star-shaped block copolymer gel, was achieved with 3 wt % content of PVA in the mixture. Moreover, it was found that the addition of PVA could markedly counteract the effect of intramolecular interaction of “arms”. Network structures formed by physically close-packed star-shaped p...

Block Copolymer Nanocomposites with High Refractive Index Contrast for One-Step Photonics.

Photonic crystals (PhCs) prepared using the self-assembly of block copolymers (BCPs) offer the potential for simple and rapid device fabrication but typically suffer from low refractive index contrast (Δn ≤ 0.1) between the phase-segregated domains. Here, we report the simple fabrication of BCP-based photonic nanocomposites with large differences in refractive index (Δn > 0.27). Zirconium oxide (ZrO2) nanoparticles coated with gallic acid are used to tune the optical constants of the target domains of self-assembled (polynorbornene-graft-poly(tert-butyl acrylate))-block-(polynorbornene-graft-poly(ethylene oxide)) (PtBA-b-PEO) brush block copolymers (BBCPs). Strong hydrogen-bonding interactions between the ligands on ZrO2 and PEO brushes of the BBCPs enable selective incorporation and high loading of up to 70 wt % (42 vol %) of the ZrO2 nanoparticles within the PEO domain, resulting in a significant increase of refractive index from 1.45 to up to 1.70. Consequently, greatly enhanced reflection at approximately 398 nm (increases of ∼250%) was observed for the photonic nanocomposites (domain spacing = 137 nm) relative to that of the unmodified BBCPs, which is consistent with numeric modeling results using transfer matrix methods. This work provides a simple strategy for a wide range tuning of optical constants of BCP domains, thereby enabling the design and creation of high-performance photonic coatings for various applications. The large refractive index contrast enables high reflectivity while simultaneously reducing the coating thickness necessary, compared to pure BCP systems.

Stress-strain behavior of block-copolymers and their nanocomposites filled with uniform or Janus nanoparticles under shear: a molecular dynamics simulation.

Although numerous research studies have been focused on studying the self-assembled morphologies of block-copolymers (BCPs) and their nanocomposites, little attention has been directed to explore the relation between their ordered structures and the resulting mechanical properties. We adopt coarse-grained molecular dynamics simulation to study the influence of the morphologies on the stress-strain behavior of pure block copolymers and block copolymers filled with uniform or Janus nanoparticles (NPs). At first, we examine the effect of the arrangement (di-block, tri-block, alternating-block) and the components of the pure block copolymers, and by varying the component ratio between A and B blocks, spherical, cylindrical and lamellar phases are all formed, showing that spherical domains bring the largest reinforcing effect. Then by studying BCPs filled with NPs, the Janus NPs induce stronger bond orientation of polymer chains and greater mechanical properties than the uniform NPs, when these two kinds of NPs are both located in the interface region. Meanwhile, some other anisotropic Janus NPs, such as Janus rods and Janus sheets, are incorporated to examine the effect on the morphology and the stress-strain behavior. These findings deepen our understanding of the morphology-mechanics relation of BCPs and their nanocomposites, opening up a vast number of approaches such as designing the arrangement and components of BCPs, positioning uniform or Janus NPs with different shapes and shear flow to tailor their stress-strain performance.

Brownian dynamics simulation of amphiphilic block copolymers with different tail lengths, comparison with theory and comicelles

Study on the effect of amphiphilic copolymers structure on their self assembly is an interesting subject, with important applications in the area of drug delivery and biological system treatments. Brownian dynamics simulations were performed to study self-assembly of the linear amphiphilic block copolymers with the same hydrophilic head, but hydrophobic tails of different lengths. Critical micelle concentration (CMC), gyration radius distribution, micelle size distribution, density profiles of micelles, shape anisotropy, and dynamics of micellization were investigated as a function of tail length. Simulation results were compared with predictions from theory and simulation for mixed systems of block copolymers with long and short hydrophobic tail, reported in our previous work. Interestingly, the equilibrium structural and dynamic parameters of pure and mixed block copolymers were similarly dependant on the intrinsic/apparent hydrophobic block length. Log (CMC) was, however; proportional to the tail length and had a different behavior compared to the mixed system. The power law scaling relation of equilibrium structural parameters for amphiphilic block copolymers predicts the same dependence for similar hydrophobic tail lengths, but the power law prediction of CMC is different, which is due to its simplifying assumptions as discussed here.

Ionic liquids as self-assembly guide for the formation of nanostructured block copolymer membranes

Nanostructured block copolymer membranes were manufactured by water induced phase inversion, using ionic liquids (ILs) as cosolvents. The effect of ionic liquids on the morphology was investigated, by using polystyrene-b-poly(4-vinyl pyridine) (PS-b-PV4P) diblock as membrane copolymer matrix and imidazolium and pyridinium based ILs. The effect of IL concentration and chemical composition was evident with particular interaction with P4VP blocks. The order of block copolymer/ILs solutions previous to the membrane casting was confirmed by cryo scanning electron microscopy and the morphologies of the manufactured nanostructured membranes were characterized by transmission and scanning electron microscopy. Non-protic ionic liquids facilitate the formation of hexagonal nanoporous block copolymer structure, while protic ILs led to a lamella-structured membrane. The rheology of the IL/block copolymer solutions was investigated, evaluating the storage and loss moduli. Most membranes prepared with ionic liquid had higher water flux than pure block copolymer membranes without additives.

Large compound vesicles from amphiphilic block copolymer/rigid-rod conjugated polymer complexes.

Morphology evolution in complexes of amphiphilic block copolymers poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) and poly(styrene)-b-poly(ethylene oxide) (PS-b-PEO) in the presence of polyaniline (PANI) in aqueous solution is reported. Transmission electron microscopy, atomic force microscopy, and dynamic light scattering techniques were used to study the morphologies at various PANI contents [aniline]/[acrylic acid] ([ANI]/[AA]) ranging from 0.1 to 0.7. The interpolyelectrolyte complex formed between PAA and PANI plays a key role in the morphology transformation. Spherical micelles formed from pure block copolymers were transformed into large compound vesicles upon increasing PANI concentration due to internal block copolymer segregation. In addition to varying PANI content, the kinetic pathway of nanoparticle formation was controlled through different water addition methods and was critical in the formation of multigeometry nanoparticles.

Role of Nanoparticle Selectivity in the Symmetry Breaking of Cylindrically Confined Block Copolymers

We have comprehensively studied the effect of nanoparticle selectivity on the self-assembly of symmetrical block copolymer (BCP) under cylindrical confinement using simulation and experiment. For the simulation, a coarse-grained molecular dynamics (CGMD) simulation has been utilized, and we investigated the confined assembly using nanoparticles with three different interactions with block copolymer: (i) neutral to both A (wall-attractive) and B (wall-repulsive) phases, (ii) B domain selective, and (iii) A domain selective. It is predicted that nonselective (neutral) nanoparticles (NPs) tend to be placed near the interface between radially alternating layers of A or B domains, while selective (A or B) NPs swell the corresponding phase, inducing discrete asymmetrical morphologies. We also find that pure asymmetrical BCP forms more radially perforated morphologies, while symmetrical BCP/NP forms more discrete morphologies. Experimentally, we have incorporated gold or magnetite NPs with the matching three types of selectivity toward symmetrical diblock PS-b-PI and electrospun them. The morphologies observed from our study have been quantified by morphological classification numbers to identify the degree of asymmetry formed. The qualitative and quantitative comparisons between experiment and simulation confirm the validity of the simulation tool and shed light on the NP’s role on breaking the symmetry of BCP under cylindrical confinement.

Improvement of Piezoelectricity of Poly(L-lactide) Film by Using Acrylic Symmetric Block Copolymer as Additive

By using additives to change the higher-order structure of a poly(L-lactide) (PLLA) film, an improvement in its piezoelectricity was realized. The additive used was a triblock copolymer, which is a pure acrylic symmetric block copolymer consisting of a center block of poly(butyl acrylate) (PBA), corresponding to its soft part, and two side blocks of poly(methyl methacrylate) (PMMA), corresponding to its hard part. The triblock copolymer is hereafter denoted as PMMA-b-PBA-b-PMMA. The piezoelectric e-constant of the PLLA film with added PMMA-b-PBA-b-PMMA (PLLA/PMMA–PBA–PMMA film) was over two times higher than that of the PLLA film without adding PMMA-b-PBA-b-PMMA (reference PLLA film). Also, we found that the glass transition temperature increases with increasing PMMA-b-PBA-b-PMMA content. From atomic force microscopy (AFM) images, it was found that a new higher-order structure was formed in the PLLA/PMMA–PBA–PMMA film with high piezoelectricity. The method of using PMMA-b-PBA-b-PMMA has high productivity and its promising for industrial use.

Nanoreactors based on self-assembled amphiphilic diblock copolymers for the preparation of ZnO nanoparticles

A self-assembled diblock copolymer containing styrene (S), methyl methacrylate and a certain percentage of hydrophilic segment of poly(methacrylic acid) (i.e., poly(styrene)-block-poly(methyl methacrylate/methacrylic acid) was synthesized via the ATRP method in two steps. This was followed by a partial hydrolysis of the methyl ester linkages of the methyl methacrylate block under acidic conditions. The resultant block copolymer had a narrow molecular weight dispersity (Ð<1.3) and was characterized using FT-IR and Raman spectroscopy as well as size exclusion chromatography. The block copolymer was used as a nanoreactor for inorganic nanoparticles (ZnO). The incorporation of a single source precursor, such as ZnCl2, into the self-assembled copolymer matrix and the conversion into ZnO nanostructures was carried out in the liquid phase using wet chemical processing techniques. We report the synthesis and characterization of nanocomposites with dual characteristics due to the functionalities incorporated into the matrix. The optical properties were determined by UV–Vis and fluorescence, the crystallinity was studied using X-ray diffraction, and the thermal stability and studies of the cyclic voltammetry were obtained by thermogravimetric analyzes and potentiodynamic electrochemical measurements, respectively. The structural, topographical and morphological characterizations of the ZnO composite in relation to the precursor block copolymer were analyzed via scanning electron microscopy, transmission electron microscopy and atomic force microscopy.According to the results, the block copolymer shows good transparency in the visible region (when containing 20, 30 and 50wt.% nanoparticles) and was able to absorb UV irradiation below 350nm, indicating good UV-screening effects. The thermo gravimetric analysis data showed that the block copolymer composite is more thermally stable compared to the pure block copolymer. The self-assembled nanoscale morphology of the diblock copolymer results in the formation of uniformly distributed spherical nano particles within the polymer matrix.

PEGylation of HPMA-based block copolymers enhances tumor accumulation in vivo: A quantitative study using radiolabeling and positron emission tomography

This paper reports the body distribution of block copolymers (made by controlled radical polymerization) with N-(2-hydroxypropyl)methacrylamide (HPMA) as hydrophilic block and lauryl methacrylate (LMA) as hydrophobic block. They form micellar aggregates in aqueous solution. For this study the hydrophilic/hydrophobic balance was varied by incorporation of differing amounts of poly(ethylene glycol) (PEG) side chains into the hydrophilic block, while keeping the degree of polymerization of both blocks constant. PEGylation reduced the size of the micellar aggregates (Rh=113 to 38nm) and led to a minimum size of 7% PEG side chains. Polymers were labeled with the positron emitter 18F, which enables to monitor their biodistribution pattern for up to 4h with high spatial resolution. These block copolymers were investigated in Sprague–Dawley rats bearing the Walker 256 mammary carcinoma in vivo. Organ/tumor uptake was quantified by ex vivo biodistribution as well as small animal positron emission tomography (PET).All polymers showed renal clearance with time. Their uptake in liver and spleen decreased with size of the aggregates. This made PEGylated polymers – which form smaller aggregates – attractive as they show a higher blood pool concentration. Within the studied polymers, the block copolymer of 7% PEGylation exhibited the most favorable organ distribution pattern, showing highest blood-circulation level as well as lowest hepatic and splenic uptake. Most remarkably, the in vivo results revealed a continuous increase in tumor accumulation with PEGylation (independent of the blood pool concentration) — starting from lowest tumor uptake for the pure block copolymer to highest enrichment with 11% PEG side chains. These findings emphasize the need for reliable (non-invasive) in vivo techniques revealing overall polymer distribution and helping to identify drug carrier systems for efficient therapy.

Selective control over the lamellar thickness of one domain in thin binary blends of block copolymer films

ABSTRACTThin binary blends of poly(styrene‐b‐methyl methacrylate) (PS‐PMMA) block copolymers in films where the lamellar thickness of one domain is controlled while preserving the thickness of the other domain were demonstrated without microphase separation. One of the block copolymers used here was short and symmetric, and the other was long and asymmetric; the molecular weights of the PMMA block chains in the constituents were similar. A random copolymer brush was introduced and film thickness and composition of brush were adjusted to induce perpendicular orientation in thin film. As the blend composition of the long asymmetric block copolymer increased, the PS lamellar thickness increased from 15.8 to 25.1 nm, whereas the PMMA lamellar thickness remained constant at approximately 14 nm (the thickness decreased slightly from 14.0 to 13.3 nm). The domain spacing behavior in thin film was consistent in the bulk. These results were compared with the Birshtein, Zhulina, and Lyatskaya model and the theories for pure block copolymers in the strong segregation limit and in the intermediate segregation regime. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1393–1399

Tuning self-assembly and photo-responsive behavior of azobenzene-containing triblock copolymers by combining homopolymers

The self-assembly behavior of azobenzene-based triblock copolymers poly(ethylene oxide)-block-polystyrene-block-poly[6-(4-methoxy-4′-oxy-azobenzene) hexyl methacrylate] (PEO-b-PS-b-PMMAZO) and their mixtures with PS or PMMAZO homopolymers was studied by means of transmission electron microscopy, scanning electron microscopy, laser light scattering and UV–vis spectrophotometry. It was found that pure block copolymers self-assembled into spherical micelles with core–shell structures. The addition of PS or PMMAZO homopolymers can not only increase the aggregate size but also have a significant influence on the photo-isomerization behavior and photo-deformation behavior of the aggregate. The photo-isomerization study revealed that a complete trans–cis or cis–trans isomerization of azobenzene chromophores can be acquired when irradiated with UV or visible light for polymers both in organic solutions and in micelles. The photo-isomerization rate of azobenzene chromophores increases when PS homopolymers were incorporated into micelles, while with the addition of PMMAZO homopolymers, it decreases. The photo-induced elongation of the aggregates by irradiation of a linearly polarized laser was observed for all the samples, and the deformation degree increases with the weight fraction of azobenzene groups in the parent copolymers, as well as the PMMAZO content for the mixture micelles.

Revisited Block Copolymer/Nanoparticle Composites: Extension of Interfacial Statistical Associating Fluid Theory

The mean-field intermolecular interaction contribution in interfacial statistical associating fluid theory (iSAFT) is extended to include correlation functions, which could be evaluated from molecular simulation and the density functional theory (DFT) itself. Order–disorder transitions (ODTs) between lamellar and disordered phases for pure block copolymers and copolymer nanoparticle composites are reported, and the extended theory has been shown to give good agreement with molecular simulations and considerable improvement over the previous mean-field dispersion description. The interaction parameters at ODT are also correlated with the length of copolymers. Concentration profiles of different species are then calculated and compared quantitatively with simulation. The scaled microstructures predicted by the theory agree with simulation for all the nanoparticle size and surface chemistry investigated. Improvements over previous DFT reports have also been observed for large selective nanoparticles. iSAFT has been shown to be capable of modeling BCP from different segregation regimes using a single framework and predicting characteristic exponent for chain length dependence of lamellar spacing, in good agreement with other theories in all segregation regimes.

Self-Assembly of a Mixture System Containing Polypeptide Graft and Block Copolymers: Experimental Studies and Self-Consistent Field Theory Simulations

Self-assembly behavior of mixture systems containing poly(γ-benzyl-L-glutamate)-poly(ethylene glycol) graft (PBLG-g-PEG) and block (PBLG-b-PEG) copolymers in aqueous solution was investigated by both experiments and computer simulations. Pure graft copolymers self-assembled into vesicles, and pure block copolymers aggregated into spherical micelles or vesicles, while, for the mixture systems, hybrid cylindrical micelles were observed. In addition to the experimental observations, self-consistent field theory (SCFT) simulations were performed on the self-assembly behavior of graft/block copolymer mixtures. Simulation results reproduced the morphological transitions observed in the experiments. Moreover, from the SCFT simulations, the chain distributions of copolymers in the aggregates were obtained. For the hybrid cylindrical micelles, block copolymers were found to mainly locate at the ends of aggregates, which prevents the fusion of cylinders to vesicles. By combining experimental findings with simulation results, the mechanism regarding the morphological transition of the aggregates formed by graft/block copolymer mixtures is proposed.