Control of Self-Assembled Structure through Architecturally and Compositionally Complex Block Copolymer Surfactant Mixtures

Architecture- and Composition-Controlled Self-Assembly of Block Copolymers and Binary Mixtures With Crosslinkable Components: Chain Exchange Between Block Copolymer Nanoparticles

Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.

Tailoring Azlactone-Based Block Copolymers for Stimuli-Responsive Disassembly of Nanocarriers

Stimuli-responsive nanoparticles based on a reactive block copolymers (BCPs) of poly(ethylene glycol)-b-poly(2-vinyl-4,4-dimethylazlactone) (PEG-b-PVDMA) have been fabricated for loading and controlled release of molecular cargoes. Microphase segregation of PEG-b-PVDMA BCPs enables the construction of well-defined nanoparticles in aqueous solutions. The azlactone groups in VDMA repeat units offer active sites for hydrophilization of the BCPs and functionalization by primary amines. The hydrophilization of PEG-b-PVDMA BCPs induces gradual reconstruction and dissociation of the BCP nanoparticles. Functional primary amines can be conjugated to PEG-b-PVDMA BCPs, yielding azobenzene- and pyridine-containing BCPs. The self-assembled nanoparticles made from the functionalized BCPs can disassemble in response to different external stimuli (e.g., addition of β-cyclodextrin and pH changes). The gradual reconstruction of functionalized PEG-b-PVDMA BCP nanoparticles caused by hydrolysis of residual azlactone groups provides a novel method to engineer sub-50 nm, well-dispersed, stimuli-responsive nanoparticles. These nanoparticles can incorporate molecular cargoes and release them upon external stimuli, making the azlactone-containing BCPs attractive platforms for the development of controlled delivery vehicles.

Isotactic-Polypropylene/Atactic-Polystyrene Miktoarm Star Copolymers: Synthesis and Aggregation Morphology

In this work, a series of isotactic-polypropylene/atactic-polystyrene (iPP/aPS) miktoarm star copolymers, PxSy, was synthesized via an arm-first approach. Varied star macromolecule architectures were fabricated by designing the arm length and the arm numbers (x and y). These miktoarm stars were able to form micelles in selective solvent (N,N'-dimethylformamide (DMF)), in which the insoluble iPP arms formed the core and the soluble aPS arms formed the shell. The miktoarm polymers aggregated to micro-nanoscale binary structures (MNBSes) in the casting process, and their morphologies, including the MNBS shape and size, were greatly influenced by the PxSy architectures. The MNBSes endowed the material surface with superhydrophobic performance with a water contact angle of 157.0° and a sliding angle of 1.5°.

The synthesis, self-assembly and pH-responsive fluorescence enhancement of an alternating amphiphilic copolymer with azobenzene pendants

In this work, a novel alternating amphiphilic copolymer (AAC) P(EG₄-a-NAzoOMe) with azobenzene pendants can selfassemble into large compound micelles, and it features fantastic pH-enhanced aggregate induced emission property.

Self-Assembly of Block and Graft Copolymers in Organic Solvents: An Overview of Recent Advances

This review is an attempt to update the recent advances in the self-assembly of amphiphilic block and graft copolymers. Their micellization behavior is highlighted for linear AB, ABC triblock terpolymers, and graft structures in non-aqueous selective polar and non-polar solvents, including solvent mixtures and ionic liquids. The micellar characteristics, such as particle size, aggregation number, and morphology, are examined as a function of the copolymers' architecture and molecular characteristics.

Nano-porous structuresviaself-assembly of amphiphilic triblock copolymers: influence of solvent and molecular weight

Self-assembly of ABA triblock copolymer micelles into porous materials which are subsequently used as filtration membranes.

Perpendicular Structure Formation of Block Copolymer Thin Films during Thermal Solvent Vapor Annealing: Solvent and Thickness Effects

Solvent vapor annealing of block copolymer (BCP) thin films can produce a range of interesting morphologies, especially when the perpendicular orientation of micro-domains with respect to the substrate plays a role. This, for instance, allows BCP thin films to serve as useful templates for nanolithography and hybrid materials preparation. However, precise control of the arising morphologies is essential, but in most cases difficult to achieve. In this work, we investigated the solvent and thickness effects on the morphology of poly(styrene-b-2 vinyl pyridine) (PS-b-P2VP) thin films with a film thickness range from 0.4 L₀ up to 0.8 L₀. Ordered perpendicular structures were achieved. One of the main merits of our work is that the phase behavior of the ultra-high molecular weight BCP thin films, which hold a 100-nm sized domain distance, can be easily monitored via current available techniques, such as scanning electron microscope (SEM), atomic force microscope (AFM), and transmission electron microscope (TEM). Systematic monitoring of the self-assembly behavior during solvent vapor annealing can thus provide an experimental guideline for the optimization of processing conditions of related BCP films systems.

Reversible, voltage-activated formation of biomimetic membranes between triblock copolymer-coated aqueous droplets in good solvents

Biomimetic membranes assembled from block copolymers attract considerable interest because they exhibit greater stability and longetivity compared to lipid bilayers, and some enable the reconstitution of functional transmembrane biomolecules. Yet to-date, block copolymer membranes have not been achieved using the droplet interface bilayer (DIB) method, which uniquely allows assembling single- and multi-membrane networks between water droplets in oil. Herein, we investigate the formation of poly(ethylene oxide)-b-poly(dimethyl siloxane)-b-poly(ethylene oxide) triblock copolymer-stabilized interfaces (CSIs) between polymer-coated aqueous droplets in solutions comprising combinations of decane, hexadecane and AR20 silicone oil. We demonstrate that triblock-coated droplets do not spontaneously adhere in these oils because all are thermodynamically good solvents for the hydrophobic PDMS middle block. However, thinned planar membranes are reversibly formed at the interface between droplets upon the application of a sufficient transmembrane voltage, which removes excess solvent from between droplets through electrocompression. At applied voltages above the threshold required to initiate membrane thinning, electrowetting causes the area of the CSI between droplets to increase while thickness remains constant; the CSI electrowetting response is similar to that encountered with lipid-based DIBs. In combination, these results reveal that stable membranes can be assembled in a manner that is completely reversible when an external pressure is used to overcome a barrier to adhesion caused by solvent-chain interactions, and they demonstrate new capability for connecting and disconnecting aqueous droplets via polymer-stabilized membranes.

Impact of chain microstructure on solution and thin film self-assembly of PCHD-based semi-flexible/flexible diblock copolymers

Self-assembly of semi-flexible/flexible block copolymers in a selective solvent is examined using a set of diblock copolymers where the chain microstructure of the semi-flexible block is manipulated in order to tune chain stiffness. Conceptually, the reduced conformational space of the semi-flexible block is anticipated to alter the way the chains pack, potentially changing the structure of self-assembled aggregates in comparison to flexible diblock copolymer analogs. Semi-flexible/flexible diblock copolymers comprised of poly(styrene)-block-poly(1,3-cyclohexadiene) (PS-b-PCHD) having systematic changes in chain microstructure, as captured by the ratio of 1,4/1,2-linkages between cyclohexenyl repeat units, and molecular weight of the PCHD blocks were synthesized using anionic polymerization. These diblocks were dissolved in tetrahydrofuran (THF), which is a preferential solvent for PS, and the structures formed were examined using laser light scattering and complementary imaging techniques. Results show that PS-b-PCHD copolymers with a chain microstructure of 90% 1,4/10% 1,2 linkages between cyclohexenyl repeat units (referred to simply as 90/10) are able to micellize, forming spherical structures, while diblocks of 70/30 and 50/50 1,4-to-1,2 ratios remain as single chains and ill-defined aggregates, respectively, when dissolved in THF. With inferences drawn from simple structural models, we speculate that this self-assembly behavior arises due to the change in the chain configuration with increasing content of 1,2-links in the backbone. This renders the chain with higher 1,2 content incapable of swelling in response to solvent and unable to pack into well-defined self-assembled structures.

Fine-tuning vitamin E-containing telodendrimers for efficient delivery of gambogic acid in colon cancer treatment

Certain natural products such as gambogic acid (GA) exhibit potent antitumor effects. Unfortunately, administration of these natural products is limited by their poor solubility in conventional pharmaceutical solvents. In this study, a series of telodendrimers, composed of linear polyethylene glycol (PEG)-blocking-dendritic oligomer of cholic acid (CA) and vitamin E (VE), have been designed with architectures optimized for efficient delivery of GA and other natural anticancer compounds. Two of the telodendrimers with segregated CA and VE domains self-assembled into stable cylindrical and/or spherical nanoparticles (NPs) after being loaded with GA as observed under transmission electron microscopy (TEM), which correlated with the dynamic light scattering (DLS) analysis of sub-30 nm particle sizes. A very high GA loading capacity (3:10 drug/polymer w/w) and sustained drug release were achieved with the optimized telodendrimers. These novel nanoformulations of GA were found to exhibit similar in vitro cytotoxic activity against colon cancer cells as the free drug. Near-infrared fluorescence small animal imaging revealed preferential accumulation of GA-loaded NPs into tumor tissue. The optimized nanoformulation of GA achieved superior antitumor efficacy compared to GA-Cremophor EL formulation at equivalent doses in HT-29 human colon cancer xenograft mouse models. Given the mild adverse effects associated with this natural compound and the enhanced anticancer effects via tumor targeted telodendrimer delivery, the optimized GA nanoformulation is a promising alternative to the traditional chemotherapy in colon cancer treatment.

RAFT dispersion polymerization: a method to tune the morphology of thymine-containing self-assemblies

The synthesis and self-assembly of thymine-containing polymers were performed using RAFT dispersion polymerization.

Thermodynamics and kinetic investigation of electron transfer reactions of surfactant cobalt(iii) complexes containing diimine ligands with iron(ii) in the presence of liposome vesicles and amphiphilic salt media

The kinetics of reductions of surfactant cobalt(iii) complexes by iron(ii) in liposome vesicles (DPPC) and amphiphilic salt ((BMIM)Br) were studied at different temperatures by UV-Vis absorption spectroscopy method under pseudo first order conditions using an excess of the reductant.