Design, Synthesis, and Self-Assembly of Janus Bottlebrush Polymers

Photonic Pigments of Polystyrene-block-Polyvinylpyrrolidone Bottlebrush Block Copolymers via Sustainable Organized Spontaneous Emulsification

Prior studies on photonic pigments of amphiphilic bottlebrush block copolymers (BBCPs) through an organized spontaneous emulsification (OSE) mechanism have been limited to using polyethylene glycol (PEG) as the hydrophilic side chains and toluene as the organic phase. Herein, a family of polystyrene-block-polyvinylpyrrolidone (PS-b-PVP) BBCPs are synthesized with PVP as the hydrophilic block. Biocompatible and sustainable anisole is employed for dissolving the obtained BBCPs followed by emulsification of the solutions in water. Subsequent evaporation of oil-in-water emulsion droplets triggers the OSE mechanism, producing thermodynamically stable water-in-oil-in-water (w/o/w) multiple emulsions with uniform and closely packed internal droplet arrays through the assembly of the BBCPs at the w/o interface. Upon solidification, the homogeneous porous structures are formed within the photonic microparticles that exhibit visible structural colors. The pore diameter is widely tunable (150∼314 nm) by changing the degree of polymerization of BBCP (69∼110), resulting in tunable colors across the whole visible spectrum. This work demonstrates useful knowledge that OSE can be generally used in the fabrication of ordered porous materials with tunable internal functional groups, not only for photonic applications, but also offers a potential platform for catalysis, sensing, separation, encapsulation, etc.

Self-assembly of amphiphilic asymmetric comb-like copolymers with responsive rigid side chains

Amphiphilic asymmetric comb-like copolymers (AACCs) exhibit distinct self-assembly behaviours due to their unique architecture. However, the synthetic difficulties of well-defined AACCs have prohibited a systematic understanding of the architecture-morphology relationship. In this work, we conducted dissipative particle dynamics simulations to investigate the self-assembly behaviours of AACCs with responsive rigid side chains in selective solvents. The effects of side chain length, number of branches, and spacers on the morphology of aggregates were investigated by mapping out morphology diagrams. Besides, the numbers and surface areas of aggregates clearly depicted the morphological transitions during the self-assembly process. Moreover, the rod-to-coil conformation transitions were simulated to explore the stimuli-responsive behaviour of the AACCs with responsive rigid side chains by adjusting the bond angle parameter of the rigid chains. The results indicated that without the support of the rigid chains, the assembly structure collapsed, leading to the tube-to-channelized micelles and one-compartment-to-multicompartment vesicle morphology transformations. The simulation results are consistent with earlier experimental results, which can provide theoretical guidance for assembly toward desired nanostructures.

One-Pot Synthesis, Circularly Polarized Luminescence, and Controlled Self-Assembly of Janus-Type Miktoarm Star Copolymers

With the aim of broadening the scope of Janus-type polymers with new functionalities, Janus-type miktoarm star copolymers comprising helical poly(phenyl isocyanide) (PPI) and a vinyl polymer were designed and synthesized via a combination of Pd(II)-initiated isocyanide polymerization and atom transfer radical polymerization (ATRP). A functional β-cyclodextrin bearing 7 Pd(II) complexes at one side and 14 bromine groups at the other side ((Pd(II))7-CD-(Br)14) was prepared and used as an initiator for the one-pot polymerization of phenyl isocyanide and the ATRP of vinyl monomers in a living and controlled manner. A variety of Janus-type copolymers with different structures and tunable compositions were facilely obtained by using this method. Thus, Janus-type copolymers composed of helical PPIs and tetraphenylethylene-modified vinyl polymers exhibited a significant circularly polarized luminescence performance in both soluble and aggregated states. Meanwhile, Janus-type copolymers containing PPIs and hydrophilic vinyl polymers presented amphiphilicity and self-assembled into diverse morphologies.

Marriage of Organic and Grubbs Catalysts for Tandem Synthesis of Bottlebrush Polyesters

Bottlebrush polymers (BBPs) have gained wide attention for their special characters, such as rigid main/side chains, stemming from the exceedingly high graft density. This study aims to provide a simple synthetic approach to BBPs with polyester side chains by merging ring-opening alternating copolymerization (ROAP) and ring-opening metathesis polymerization (ROMP). A simple phosphazene base (tBuP1) is employed for the ROAP of phthalic anhydride and epoxide, after which Grubbs third-generation catalyst (G3) is added to in situ switch on ROMP of the macromonomer, i.e., norbornenyl-ended alternating polyester. The compatibility of tBuP1 with G3 and well-controlled ROMP is evidenced by DOSY-NMR of mixed catalysts, characterization of BBPs, and side-chain degradation. The method can also be extended to BBPs with one-step synthesized block copolyesters side chains. These results highlight the strength of the non-nucleophilic organobase catalyst for convenient construction of complex (degradable) polymers with compositional diversity.

Preparation of Non-Spherical Janus Particles via an Orthogonal Dissolution Approach

Post-synthesis modifications are valuable tools to alter functionalities and induce morphology changes in colloidal particles. Non-spherical polymer particles with Janus characteristics are prepared by combining seeded growth polymerization and selective dissolution. First, spherical polystyrene (PS) particles have been swollen with methyl methacrylate (MMA) with an activated swelling method. This is followed by polymerization that led to particles with two well-separated faces: one made of PS and the second of polymethyl methacrylate (PMMA). Subsequently, non-spherical particles are obtained by exposing the Janus colloids to various solvents. Using the two polymers' orthogonal solubility, solvents are identified to selectively dissolve only one face, leading to hemispherical PS or PMMA particles. It is further investigated how changing the composition of the PMMA face - by either co-polymerization with glycidyl methacrylate or by adding a cross-linker - affects the particles' morphology. The poly-methacrylate face can gain total or partial resistance towards the solvents, resulting in intriguing shapes, such as mushroom-like and Janus dimpled particles. The dissolution mechanisms are investigated via optical microscopy, where total or partial dissolutions can be directly observed. Lastly, prematurely quenching the dissolution of the particle's lobes with water can be used to control the Janus mushroom-like particle aspect ratio.

Tailored Morphology in Polystyrene/Poly(lactic acid) Blend Particles: Solvent's Effect on Controlled Janus/Core-Shell Structures

Controlling the morphology of polymeric particles is vital for their diverse applications. In this study, we explored how solvent composition influences the morphology of poly(styrene)/poly(lactic acid) (PS/PLA) particles prepared via the emulsion solvent evaporation method. We used toluene, dichloromethane (DCM), and various mixtures to prepare these particles. We investigated phase separation within the PS/PLA/solvent system using the Flory-Huggins ternary phase diagram and MesoDyn simulation, revealing pronounced immiscibility and phase separation in both PS/PLA/DCM and PS/PLA/toluene systems. We employed scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to characterize the resulting morphologies. Our study unveiled the substantial impact of solvent composition on particle structure. Using pure toluene resulted in acorn-shaped Janus particles. However, incorporating DCM into the solvent induced a transition from Janus to core-shell morphology. Remarkably, core-shell particles exhibited a single-core structure in a mixed toluene/DCM solvent, indicating thermodynamic stability. In contrast, pure DCM favored kinetically controlled multicore morphology, leading to lower PLA crystallinity due to increased PS-PLA interfaces. Samples with high Janus balance formed a self-assembled, two-dimensional (2-D) monolayer film, demonstrating the interfacial activity of the Janus particles. This 2-D monolayer film exhibits desirable emulsification properties with potential applications in various fields. Our study combines theoretical and experimental analyses, shedding light on the profound impact of solvent composition on the PS/PLA particle morphology. We observed transitions from Janus to core-shell structures, highlighted the influence of solvent viscosity on particle size, and uncovered the formation of self-assembled 2-D monolayer films. These insights are pivotal for tailoring polymeric particle structures. Furthermore, our findings advance macromolecular science in interface design, offering promising prospects for innovative materials development.

Simultaneous Synthesis and Self-Assembly of Bottlebrush Block Copolymers at Room Temperature via Photoinitiated RAFT Dispersion Polymerization

Bottlebrush polymers exhibiting unique properties have attracted considerable attention for applications in many research areas. Herein, we report the first simultaneous synthesis and self-assembly of bottlebrush block copolymers at room temperature via photoinitiated polymerization-induced self-assembly (photo-PISA) using multifunctional macromolecular chain transfer agents (macro-CTAs). Compare with linear block copolymers, the bottlebrush block copolymers could promote the formation of higher-order morphologies (e.g. vesicles) when targeting similar degrees of polymerization (DPs). Moreover, a higher polymerization rate was observed in the case of bottlebrush block copolymers. Gel permeation chromatography (GPC) analysis showed that good polymerization control was maintained when synthesizing bottlebrush block copolymers by photo-PISA. Finally, the obtained bottlebrush block copolymer vesicles were used as seeds for further chain extension and multicomponent nanoparticles with a sponge internal structure were formed. We expect this study will not only expand polymer architectures employed in PISA, but also provides a new strategy to synthesize polymer nanoparticles with unique structures. This article is protected by copyright. All rights reserved.

Interaction potential for coarse-grained models of bottlebrush polymers

Bottlebrush polymers are a class of highly branched macromolecules that show promise for applications such as self-assembled photonic materials and tunable elastomers. However, computational studies of bottlebrush polymer solutions and melts remain challenging due to the high computational cost involved in explicitly accounting for the presence of side chains. Here, we consider a coarse-grained molecular model of bottlebrush polymers where the side chains are modeled implicitly, with the aim of expediting simulations by accessing longer length and time scales. The key ingredients of this model are the size of a coarse-grained segment and a suitably coarse-grained interaction potential between the non-bonded segments. Prior studies have not focused on developing explicit forms of such potentials, instead, relying on scaling arguments to model non-bonded interactions. Here, we show how to systematically calculate an interaction potential between the coarse-grained segments of bottlebrush from finer grained explicit side chain models using Monte Carlo and Brownian dynamics and then incorporate it into an implicit side chain model. We compare the predictions from our coarse-grained implicit side chain model with those obtained from models with explicit side chains in terms of the potential of mean force, the osmotic second virial coefficient, and the interpenetration function, highlighting the range of applicability and limitations of the coarse-grained representation. Although presented in the context of homopolymer bottlebrushes in athermal solvents, our proposed method can be extended to other solvent conditions as well as to different monomer chemistries. We expect that our implicit side chain model will prove useful for accelerating large-scale simulations of bottlebrush solutions and assembly.

Recent advances in the self-assembly of sparsely grafted amphiphilic copolymers in aqueous solution

This review describes the self-assembly of sparsely grafted amphiphilic copolymers and highlights the effects of structural factors and solvents on their self-assembly behaviour.

Well-Defined Thermo- and pH-Responsive Double Hydrophilic Graft Copolymer Bearing a Pyridine-Containing Backbone

Graft copolymers have extensive applications in material science because of their tunable composition of backbone and side chains and diverse morphologies of aggregates. Recent studies mainly focused on the amphiphilic...

Janus Micelles by Crystallization-Driven Self-Assembly of an Amphiphilic, Double-Crystalline Triblock Terpolymer

Surface-compartmentalized micellar nanostructures (Janus and patchy micelles) have gained increasing interest due to their unique properties opening highly relevant applications, e.g., as efficient particulate surfactants, compatibilizers in polymer blends, or templates for catalytically active nanoparticles. We present a facile method for the production of worm-like Janus micelles based on crystallization-driven self-assembly of a double-crystalline triblock terpolymer with a crystallizable polyethylene middle block and two highly incompatible corona blocks, polystyrene and poly(ethylene oxide). This approach enables the production of amphiphilic Janus micelles with excellent interfacial activity by a comparably simple heating and cooling protocol directly in solution.

Synthesis and Self-Assembly of Thermoresponsive Biohybrid Graft Copolymers Based on a Combination of Passerini Multicomponent Reaction and Molecular Recognition

Amphiphilic graft copolymers exhibit fascinating self-assembly behaviors. Their molecular architectures significantly affect the morphology and functionality of the self-assemblies. Considering the potential application of amphiphilic graft copolymers in the fabrication of nanocarriers, it is essential to synthesize well-defined graft copolymers with desired functional groups. Herein, the Passerini reaction and molecular recognition are introduced to the synthesis of functional thermoresponsive graft copolymers. A bifunctional monomer 2-((adamantan-1-yl)amino)-1-(4-((2-bromo-2-methylpropanoyl)oxy)phenyl)-2-oxoethyl methacrylate (ABMA) with a bromo group for atom transfer radical polymerization (ATRP) and an adamantyl group for molecular recognition is synthesized through the Passerini reaction. The graft copolymers are prepared by reversible addition-fragmentation transfer (RAFT) copolymerization of ABMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) followed by RAFT end group removal and ATRP of di(ethylene glycol)methyl ether methacrylate (DEGMA) initiated by the ABMA units. The graft copolymer P(OEGMA-co-ABMA)-g-PDEGMA can be functionalized with β-cyclodextrin modified peptides, affording a thermoresponsive biohybrid graft copolymer. At a temperature above its lower critical solution temperature, the biohybrid graft copolymer self-assembles into peptide-modified polymersomes.

Dumbbell-Shaped, Graft and Bottlebrush Polymers with All-Siloxane Nature: Synthetic Methodology, Thermal, and Rheological Behavior

A methodology for synthesizing a wide range of dumbbell-shaped, graft and bottlebrush polymers with all-siloxane nature (without carbosilane linkers) is suggested. These macroarchitectures are synthesized from SiOH-containing compounds-silanol (Et₃ SiOH) and siloxanol dendrons of the first and second generations, with various peripheral substituents (Me or Et)-and from linear siloxanes comprising terminal and internal SiH groups by the Piers-Rubinsztajn reaction. Products and key building blocks are obtained in yields up to 95%. These polymers are heat and frost-resistant siloxanes. As it turns out, the product physical properties are determined not only by the macromolecular structure, the linear chain length, the size and frequency of branched pendant, but also by the type of peripheral substituents-Me or Et-in the pendant. Thus, the viscosity of the graft polymers with branched pendant groups comprising peripheral Me-groups is more than ≈3-5 fold lower than that of analogous polymers with peripheral Et-groups.