Solution Self-assembly Of Block Copolymers Research Articles

Emerging trends in solution self-assembly of block copolymers

Since the foundation of macromolecular science by Staudinger, advances in polymer chemistry have unveiled enormous avenues for controlling chemical structures at the molecular scale. As a typical self-assembling polymer covalently linked by chemically distinct polymer blocks, amphiphilic block copolymers (BCPs) spontaneously form a variety of nanostructures with diverse functional applications, especially in the fields of nanomedicine and biomaterials. Self-assembling processes could occur at single chain level (i.e., intrachain folding) or involve multiple chains with similar and dissimilar chemical structures (i.e., interchain association). This review article discusses recent trends concerning solution self-assembly of BCPs, including the formation of inverted mesophases, self-folding into single-chain nanoparticles (SCNPs), compartmentalized nanoparticles with sophisticated functions, and nanostructures of amphiphilic copolymers with precise chain lengths and predetermined sequences, by highlighting selected examples.

Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures on Ultrathin MoS2 Nanosheets by Block Copolymer Self-Assembly in Solution.

The development of versatile strategies toward two-dimensional (2D) porous nanocomposites with tunable pore structures draws immense scientific attention in view of their attractive physiochemical properties and a wide range of promising applications. This paper describes a self-assembly approach for the directed growth of mesoporous polyaniline (PANi) with tunable pore structures and sizes on ultrathin freestanding MoS2 nanosheets in solution, which produces 2D mesoporous PANi/MoS2 nanocomposites. The strategy employs spherical and cylindrical micelles, which are formed by the controlled solution self-assembly of block copolymers, as the soft templates for the construction of well-defined spherical and cylindrical mesopores in the 2D PANi/MoS2 nanocomposites, respectively. With potential applications as supercapacitor electrode materials, the resultant 2D composites show excellent capacitive performance with a maximum capacitance of 500 F g-1 at a current density of 0.5 A g-1, good rate performance, as well as outstanding stability for charge-discharge cycling. Moreover, the 2D mesoporous nanocomposites offer an opportunity for the study on the influence of different pore structures on their capacitive performance, which helps to understand the pore structure-property relationship of 2D porous electrode materials and to achieve their electrochemical performance control.

50th Anniversary Perspective: Functional Nanoparticles from the Solution Self-Assembly of Block Copolymers

This Perspective outlines recent advances concerning the formation and potential uses of block copolymer micelles, a class of soft-matter-based nanoparticles of growing importance. As a result of rapidly expanding interest since the mid-1990s, substantial advances have been reported in terms of the development of morphological diversity, structural complexity, control over micelle dimensions, scale-up, and applications in a range of areas from nanocomposites to nanomedicine.

Transformation and patterning of supermicelles using dynamic holographic assembly.

Although the solution self-assembly of block copolymers has enabled the fabrication of a broad range of complex, functional nanostructures, their precise manipulation and patterning remain a key challenge. Here we demonstrate that spherical and linear supermicelles, supramolecular structures held together by non-covalent solvophobic and coordination interactions and formed by the hierarchical self-assembly of block copolymer micelle and block comicelle precursors, can be manipulated, transformed and patterned with mediation by dynamic holographic assembly (optical tweezers). This allows the creation of new and stable soft-matter superstructures far from equilibrium. For example, individual spherical supermicelles can be optically held in close proximity and photocrosslinked through controlled coronal chemistry to generate linear oligomeric arrays. The use of optical tweezers also enables the directed deposition and immobilization of supermicelles on surfaces, allowing the precise creation of arrays of soft-matter nano-objects with potentially diverse functionality and a range of applications.

ChemInform Abstract: Self‐Assembly of “Patchy” Nanoparticles: A Versatile Approach to Functional Hierarchical Materials

AbstractReview: 108 refs.

Solution self-assembly of block copolymers containing a branched hydrophilic block into inverse bicontinuous cubic mesophases.

Solution self-assembly of amphiphilic block copolymers into inverse bicontinuous cubic mesophases is an emerging strategy for directly creating highly ordered triply periodic porous polymer nanostructures with large pore networks and desired surface functionalities. Although there have been recent reports on the formation of highly ordered triply periodic minimal surfaces of self-assembled block copolymer bilayers, the structural requirements for block copolymers in order to facilitate the preferential formation of such inverse mesophases in solution have not been fully investigated. In this study, we synthesized a series of model block copolymers, namely, branched poly(ethylene glycol)-block-polystyrene (bPEG-PS), to investigate the effect of the architecture of the block copolymers on their solution self-assembly into inverse mesophases consisting of the block copolymer bilayer. On the basis of the results, we suggest that the branched architecture of the hydrophilic block is a crucial structural requirement for the preferential self-assembly of the resulting block copolymers into inverse bicontinuous cubic phases. The internal crystalline lattice of the inverse bicontinuous cubic structure can be controlled via coassembly of branched and linear block copolymers. The results presented here provide design criteria for amphiphilic block copolymers to allow the formation of inverse bicontinuous cubic mesophases in solution. This may contribute to the direct synthesis of well-defined porous polymers with desired crystalline order in the porous networks and surface functionalities.

Mesoporous monoliths of inverse bicontinuous cubic phases of block copolymer bilayers.

Solution self-assembly of block copolymers into inverse bicontinuous cubic mesophases is a promising new approach for creating porous polymer films and monoliths with highly organized bicontinuous mesoporous networks. Here we report the direct self-assembly of block copolymers with branched hydrophilic blocks into large monoliths consisting of the inverse bicontinuous cubic structures of the block copolymer bilayer. We suggest a facile and scalable method of solution self-assembly by diffusion of water to the block copolymer solution, which results in the unperturbed formation of mesoporous monoliths with large-pore (>25 nm diameter) networks weaved in crystalline lattices. The surface functional groups of the internal large-pore networks are freely accessible for large guest molecules such as protein complexes of which the molecular weight exceeded 100 kDa. The internal double-diamond (Pn3m) networks of large pores within the mesoporous monoliths could be replicated to self-supporting three-dimensional skeletal structures of crystalline titania and mesoporous silica.

Optical nanoimaging for block copolymer self-assembly.

One approach toward optical nanoimaging involves sequential molecular localization of photoswitchable fluorophores to achieve high resolution beyond optical limit of diffraction. Block copolymer micelles assembled from polystryrene-block-poly(ethylene oxide) block copolymers (PSt-b-PEO) are visualized in optical nanoimaging by staining the polystyrene blocks with spiropyrans (SPs). SPs localized in hydrophobic phase of block copolymer micelles exhibit reversible fluorescence on-off switching at alternating irradiation of UV and visible light. Phase-selective distribution of SPs in block copolymer micelles enables optical nanoimaging of microphase structures of block copolymer self-assembly at 50-nm resolution. To date, this is the sturdiest realization of optical nanoimaging with subdiffraction resolution for solution self-assembly of block copolymers.

Crystallization-driven solution self-assembly of block copolymers with a photocleavable junction.

Light-responsive block copolymers have been prepared with a crystallizable core-forming poly(ferrocenyldimethylsilane) (PFS) block, a corona-forming segment of poly(2-vinylpyridine) (P2VP), and a photocleavable o-nitrobenzyl (ONB) junction. These PFS-ONB-P2VP materials form monodisperse cylindrical micelles by living crystallization-driven self-assembly in a selective solvent for P2VP. The P2VP coronas were readily removed by photocleavage at the ONB linker, leading to PFS cylinders with a residual percentage of corona chains dependent on the photoirradiation time. Addition of PFS block copolymer unimers to a solution of the cylinders with ca. 10% residual coronal chains led to the formation of branched rather than linear micelles. The synthetic utility of the PFS-ONB-P2VP materials was further demonstrated by the preparation of nearly monodisperse P2VP nanotubes of tunable length using a strategy that also involved corona cross-linking.

Polyprodrug Amphiphiles: Hierarchical Assemblies for Shape-Regulated Cellular Internalization, Trafficking, and Drug Delivery

Solution self-assembly of block copolymers (BCPs) typically generates spheres, rods, and vesicles. The reproducible bottom-up fabrication of stable planar nanostructures remains elusive due to their tendency to bend into closed bilayers. This morphological vacancy renders the study of shape effects on BCP nanocarrier-cell interactions incomplete. Furthermore, the fabrication of single BCP assemblies with built-in drug delivery functions and geometry-optimized performance remains a major challenge. We demonstrate that PEG-b-PCPTM polyprodrug amphiphiles, where PEG is poly(ethylene glycol) and PCPTM is polymerized block of reduction-cleavable camptothecin (CPT) prodrug monomer, with >50 wt % CPT loading content can self-assemble into four types of uniform nanostructures including spheres, large compound vesicles, smooth disks, and unprecedented staggered lamellae with spiked periphery. Staggered lamellae outperform the other three nanostructure types, exhibiting extended blood circulation duration, the fastest cellular uptake, and unique internalization pathways. We also explore shape-modulated CPT release kinetics, nanostructure degradation, and in vitro cytotoxicities. The controlled hierarchical organization of polyprodrug amphiphiles and shape-tunable biological performance opens up new horizons for exploring next-generation BCP-based drug delivery systems with improved efficacy.

Fiber-like Micelles via the Crystallization-Driven Solution Self-Assembly of Poly(3-hexylthiophene)-block-Poly(methyl methacrylate) Copolymers

The solution self-assembly of block copolymers with a π-conjugated, crystalline, core-forming block represents a facile strategy toward the preparation of semiconducting nanowires with potential for high-tech applications. In this study, two asymmetric block copolymers based on regioregular poly(3-hexylthiophene) (P3HT) and poly(methyl methacrylate) (PMMA), namely P3HT40-b-PMMA520 (6a) and P3HT40-b-PMMA1100 (6b) (block ratios = 1:13 and 1:27.5, respectively) were prepared via atom transfer radical polymerization (ATRP) from a P3HT macroinitiator. The solution self-assembly of the P3HT-b-PMMA block copolymers was subsequently studied under a variety of experimental conditions. Short, fiber-like micelles resulted when THF (common solvent for P3HT and PMMA) solutions of the block copolymer were dialyzed against ethyl acetate and n-butyl acetate (selective solvents for PMMA). The electronic properties of the fiber-like micelles obtained coupled with wide-angle X-ray scattering studies confirmed that the cores...