Probing into Homopolymer Self-Assembly: How Does Hydrogen Bonding Influence Morphology?

Polymeric Bowl-Shaped Nanoparticles: Hollow Structures with a Large Opening on the Surface

Polymeric bowl-shaped nanoparticles (BNPs) are anisotropic hollow structures with large openings on the surface, which have shown advantages such as high specific area and efficient encapsulation, delivery and release of large-sized cargoes on demand compared to solid nanoparticles or closed hollow structures. Several strategies have been developed to prepare BNPs based on either template or template-free methods. For instance, despite the widely used self-assembly strategy, alternative methods including emulsion polymerization, swelling and freeze-drying of polymeric spheres, and template-assisted approaches have also been developed. It is attractive but still challenging to fabricate BNPs due to their unique structural features. However, there is still no comprehensive summary of BNPs up to now, which significantly hinders the further development of this field. In this review, the recent progress of BNPs will be highlighted from the perspectives of design strategies, preparation methods, formation mechanisms, and emerging applications. Moreover, the future perspectives of BNPs will also be proposed.

Self-Assembled Plasmonic Nanojunctions Mediated by Host-Guest Interaction for Ultrasensitive Dual-Mode Detection of Cholesterol

Herein, a fluorescence and surface-enhanced Raman spectroscopy dual-mode system was designed for cholesterol detection based on self-assembled plasmonic nanojunctions mediated by the competition of rhodamine 6G (R6G) and cholesterol with β-cyclodextrin modified on gold nanoparticles (HS-β-CD@Au). The fluorescence of R6G was quenched by HS-β-CD@Au due to the fluorescence resonance energy transfer effect. When cholesterol was introduced as the competitive guest, R6G in the cavities of HS-β-CD@Au was displaced to recover its fluorescence. Moreover, two of HS-β-CD@Au can be linked by one cholesterol to form a more stable 2:1 complex, and then, plasmonic nanojunctions were generated, which resulted in the increasing SERS signal of R6G. In addition, fluorescence and SERS intensity of R6G increased linearly with the increase in the cholesterol concentrations with the limits of detection of 95 and 74 nM, respectively. Furthermore, the dual-mode strategy can realize the reliable and sensitive detection of cholesterol in the serum with good accuracy, and two sets of data can mutually validate each other, which demonstrated great application prospects in the surveillance of diseases related with cholesterol.

The effect of hydration and dehydration on the conformation, assembling behavior and photoluminescence of PBLG

Hydration and dehydration play crucial roles in hydrophobic effects (HEs) and are yet to be understood. Poly(γ-benzyl-L-glutamate) (PBLG) homopolymers in THF/water with various water contents were investigated. We discovered that PBLG was hydrated at low water contents and adopted a helical conformation. The chain became dehydrated with increasing water content, which converted the PBLG₁₀₀ helix to a PPII-helix. The variation in the conformation resulted in an alteration of the self-assembled morphologies from fibers to particles. For PBLG₁₂ with a shorter chain, the chain underwent an α-to-β transition in the conformation due to dehydration as the water content increased, and correspondingly the morphologies varied from tapes to helical ribbons, and eventually to toroids at a higher water content. We also observed that this α-to-β transition is accompanied by an increase in intensity of the fluorescence, which is attributed to the through-space-conjugation of tightly packed phenyl groups within the β-sheet. The discovered effect of hydration and dehydration on the PBLG chain conformation, self-assembling behavior and optical function is essential for the innovation of polypeptide materials and understanding of water-mediated biological systems.

End-Terminated Poly(urethane-urea) Hybrid Approach toward Nanoporous/Microfilament Morphology

In the present work, the effect of heteroatomic hydrogen bonding on the properties of -OH/-NH-terminated soft-segment-free polymers, viz, polyurethane (P-UT), polyurea (P-UR), and their hybrid (P-UT-UR), is explored. P-UT was synthesized from phloroglucinol and P-UR was synthesized from 1,3,5-triazine-2,4,6-triamine by employing hexamethylene diisocyanate as a counterpart. P-UT exhibited a spherulitic structure with varying sizes, whereas P-UR displayed a fibrillar structure characteristic as that of crystalline hard segments. The P-UT-UR hybrid exhibited a fine nanospherulitic structure with a high order of interconnectivity. Negative surface skewness values of -0.47 and -0.18 were measured (by AFM) for P-UT and P-UT-UR, respectively, which revealed that the surface is not smooth and is covered with features. Due to the increased H-bonding (-N-H···O-H) in P-UT-UR, its transparency decreased. A block copolymer hybrid of urethane-urea was synthesized, which preferred homoatomic H-bonding, whereas random urethane/urea bridges favored hetreoheteroatom H-bonding. A pentafluorophenyl end-functional hybrid (PFI-P-UT-UR) was synthesized, which displayed filaments of ∼2-3 μm length in contrast to the interconnected nanospherulitic structure observed for P-UT-UR. The self-aggregation and end folding led to the formation of a filament structure. By altering the chemical structure slightly, nano-ordered polyurethanes or their hybrids can be achieved.

Self-assembly of hydrophobic-amphiphilic diblock copolymers in solution

Thermoresponsive polymers are usually characterized by a locally amphiphilic chain structure and their self-assembly in solution is controlled, in particular, by the surface activity of the monomer units or side chains. We theoretically study the condensed state of a single diblock copolymer molecule consisting of a hydrophobic block and amphiphilic block with hydrophobic groups in the backbone and pendant polar groups. The equilibrium parameters of the polymer globules of different shapes are determined using the mean-field approach to determine the most favorable structure. Morphological diagrams of condensed macromolecules are presented depending on the chain length, amphiphilic block fraction, interaction parameters, and pendant volume and length. The diagrams are compared with those of a copolymer molecule with the same fraction of amphiphilic monomer units which are regularly distributed along the chain. The diblock copolymer molecule is found to form a single spherical or flattened particle, with the core from the hydrophobic block, or a granular micelle consisting of spherical or nearly spherical particles, in agreement with the experimental data in the literature. The optimal chain parameters for self-assembly into a stable single core-shell particle are predicted.

Homopolymer nanobowls with controlled size and denting degree

Homopolymer nanobowls hold promising potential applications in many fields because of their designability, large specific surface area and high packing density. However, it is still challenging to prepare nanobowls with...

Self-Assembled Polymeric Materials: Design, Morphology, and Functional-Oriented Applications

This Review focuses on the current research advances of the synthesis of various amphiphilic block copolymers (ABCs), such as conventional ABCs and newly-presented polyprodrug amphiphiles (PPAs), and the development of corresponding self-assemblies in selective solvents driven by the intermolecular interactions, like noncovalent hydrophobic interactions, π-π interactions, and hydrogen bonds, between ABCs or preformed small polymeric nanoparticles. The design of these assemblies is systematically introduced, and the diverse examples concerning the unique assembly structures along with the fast development of their exclusive properties and various applications in different fields were discussed. Possible perspectives on the existential challenges and glorious future were elucidated finally. We hope this review will provide a convenient way for readers to motivate more evolutional innovative concepts and methods to design next generation of novel polymeric nanoassemblies, and fill the gap between material design and practical applications. This article is protected by copyright. All rights reserved.

Self-Assembled Nanosized Vehicles from Amino Acid-Based Amphiphilic Polymers with Pendent Carboxyl Groups for Efficient Drug Delivery

Developing safe and efficient delivery vehicles for chemotherapeutic drugs has been a long-standing demanding. Amino acid-based polymers are promising candidates to address this challenge due to their excellent biocompatibility and biodegradation. Herein, a series of well-defined amphiphilic block copolymers were prepared by PET-RAFT polymerization of N-acryloyl amino acid monomers. By altering monomer types and the block ratio of the copolymers, the copolymers self-assembled into nanostructures with various morphologies, including spheres, rod-like, fibers, and lamellae via hydrophobic and hydrogen bonding interactions. Significantly, the nanoparticles (NPs) assembled from amphiphilic block copolymers poly(N-acryloyl-valine)-b-poly(N-acryloyl-aspartic acid) (PV-b-PD) displayed an appealing cargo loading efficiency (21.8-32.6%) for a broad range of drugs (paclitaxel, doxorubicin (DOX), cisplatin, etc.) due to strong interactions. The DOX-loaded PV-b-PD NPs exhibited rapid cellular uptake (within 1 min) and a great therapeutic performance. These drug delivery systems provide new insights for regulating the controlled morphologies and improving the efficiency of drug delivery.

Giant Polymer Vesicles with a Latticelike Membrane

Hierarchical self-assembly offers great possibilities to mimic biological systems with finely arranged complex structures. Herein, we demonstrate the preparation and formation mechanism of an unusual giant polymer vesicle with a latticelike membrane (GVLM). This GVLM is formed by fusion-induced particle assembly (FIPA) of small vesicles that are self-assembled from poly(ethylene oxide)-block-poly[(2-(tetrahydrofuranyloxy)ethyl methacrylate)-stat-(6-(3,3-diphenylnaphthopyranyloxy)hexyl methacrylate)] [PEO₄₃-b-P(TMA₂₂-stat-NMA₄)]. Flexible TMA units with high chain mobility and relatively rigid NMA units with intrinsic π-π stacking form the hydrophobic block. These units act as "antifusion" and "profusion" components, respectively. The latticelike membrane of the final GVLM consists of hundreds of small polymer vesicles that are interconnected via multiple interactions. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) studies show that the diameter of the GVLMs is 800-1000 nm. Overall, we provide a new insight into the judicious preparation of hierarchical nanostructures via chemical synthesis and FIPA.

Functionalization and metathesis polymerization induced self-assembly of an alternating copolymer into giant vesicles

A facile fabrication of spherical vesicles and micelles by acyclic diene metathesis (ADMET) polymerization and alternative metathesis polymerization (ALTMET) was investigated. We utilize fluorine (FL) and perylene diimide-based (PDI) α,ω-dienes and α,ω-diacrylates to provide a series of homopolymers and alternating copolymers. When using α,ω-dienes as model monomers, TEM measurement indicates that the aromatic FL and PDI building block induced polymers to generate medium-sized (30-50 nm and 90-120 nm, respectively) micelles and vesicles. It was amazing that alternating copolymers derived from PDI α,ω-dienes and FL α,ω-diacrylates spontaneously form giant vesicles with sizes in the range of 0.7 μm to 2.5 μm. The controlled self-assembly of the organic polymer mediated by ADMET and ALTMET techniques avoided extremely annoying post treatment. Therefore, this work establishes a new, versatile synthetic strategy to create nanoparticles having tunable morphologies with potential application as molecular payload delivery vehicles.

Cholesteroled polymer (Chol-b-Lys)-based nanoparticles (CL-NPs) confer antibacterial efficacy without resistance

The nanoparticles CL-NPs assembled by polymer Chol-b-Lys confer antibacterial efficacy without resistance.

Self-assembly behavior of oligo(ethylene glycol) substituted polycaprolactone homopolymers

In this work, non-ionic amphiphilic oligo(ethylene glycol)-substituted polycaprolactone homopolymers readily self-assembled to form micelles in a polar environment, which allowed the encapsulation of a hydrophobic molecule.

Dual Biochemically Breakable Drug Carriers from Programmed Telechelic Homopolymers

Well-defined hydrophilic telechelic dibromo poly(triethylene glycol monomethyl ether acrylate)s were prepared by single-electron transfer living radical polymerization employing a hydrophobic difunctional initiator containing acetal and disulfide linkages. Although the resulting homopolymers have low hydrophobic contents (<8.5 wt % of the entire structure), they are able to self-assemble in water into nanoscale micellelike particles via chain folding. Acetal and disulfide linkages were demonstrated to be "keystone" units for their dual stimuli-responsive behavior under biochemically relevant conditions. Their site-selective middle-chain cleavage under both acidic pH and reductive conditions splits the homopolymer into two equal-sized fragments and results in the breakdown of the nanoassemblies. The drug loading/delivery potential of these nanoparticles was investigated using curcumine combining in vitro drug release, cytotoxicity, and cellular uptake studies with human cancer cell lines (HT-29 and HeLa). Importantly, this strategy may be extended to prepare innovative nanoplatforms based on hydrophilic homopolymers or random copolymers for intelligent drug delivery.

Orthogonal functionalization of alternating polyesters: selective patterning of (AB) n sequences

Precision functionalized polyesters, with defined monomer sequences, are prepared using an orthogonal post-polymerization strategy. These polyesters can be synthesized from bio-derived monomers and are targeted to degrade, by hydrolysis processes, to biocompatible diols and diacids; the new structures enabled by this methodology would be very difficult to synthesize by alternative strategies. A series of 9 well-defined highly alternating AB-type copolyesters, containing terminal and internal alkene functionalities, are synthesized in high conversions by the ring-opening copolymerization of epoxides and cyclic anhydrides. Firstly, the polyesters are functionalized by a selective hydroboration-oxidation reaction to exclusively and quantitatively hydroxylate the terminal alkenes, leaving the alternating internal alkenes unreacted. Subsequently, the internal alkenes are quantitatively transformed into carboxylic acid, amine, alkyl and oligo-ether groups, by thiol-ene reactions, to afford AB polyesters with alternating functional substituents. Three polyesters showing alternating hydrophilic/hydrophobic side-chain sequences self-assemble in solution to form nanostructures that are characterized using transmission electron microscopy and dynamic light scattering methods (R h = 100-300 nm). The selective patterning methodology provides facile, efficient and orthogonal functionalization of alternating polyesters with near-quantitative (AB) n repeat sequences. The method is expected to be generalizable to other polymers and provides access to completely new AB alternating structures with the potential to exploit ligand multi-valency and adjacency to enhance properties.

Lamellae and parking garage structures in amphiphilic homopolymer brushes with different grafting densities

This article is devoted to the study of polymer layers of amphiphilic homopolymers tightly grafted to a flat surface at the nodes of a square lattice. It was shown that, due to the amphiphilicity of monomer units containing groups with different affinities, in a selective solvent, such layers form lamellae perpendicular to the grafting surface. The period of the lamellae depends on the grafting density and the quality of the solvent. The results are presented in the form of a state diagram in variables "the energy of attraction of the side groups" (effective solvent quality) and "the distance between the grafting points" (inversely proportional to the square root of the grafting density). The diagram contains the regions of stability of lamellae with significantly different periods, and a transitional area with a parking garage structure. The diagram is constructed by calculating the layer-by-layer structure factor and the angle of inclination of the lamellae in the slice. The calculations were performed for different sizes of the simulation box, and the most commensurate size was determined by a special procedure for each grafting density. The results may be interesting not only to specialists in polymer science but also to all those who investigate the processes of self-organization and rearrangement in dense systems.

Water-guided synthesis of well-defined inorganic micro-/nanostructures

Water is one of the most commonplace solvents employed in wet chemical synthesis; however, it can sometimes play important roles such as an effective inducer or morphology-directing agent when introduced into a special reaction system, resulting in the formation of inorganic micro-/nanostructures with well-defined configurations. A better understanding of the key roles of water in the chemical synthesis will unlock a door to the design of many more novel single-component and hybrid nanocomposite architectures. Therefore, it is imperative to comprehensively review the topic of water-guided synthesis of well-defined micro-/nanostructures. Unfortunately, the significance of water has been underestimated and an in-depth study about the exact action of water in morphology-control is still lacking. In this review, we focus on the recent advances made in the development of the shape-controlled synthesis of inorganic micro-/nanostructures achieved by only adjusting the amount of water through some typical examples, including noble metals, metal oxides, perovskites, metal sulfides and oxysalts. In particular, the theory principles, synthesis strategies and growth mechanisms of the water-guided synthesis of well-defined inorganic micro-/nanostructures have been mainly highlighted. Finally, several current issues and challenges of this topic that need to be addressed in future investigations are briefly presented.

Enantioselective cytotoxicity of chiral polymer vesicles with linear and hyperbranched structures

Herein, we study the enantioselective cytotoxicity of vesicles self-assembled by optically active linear polymers (LNPs) and hyperbranched polymers (HBPs). Compared to HBP vesicles, LNP vesicles exhibit properties such as a higher surface charge density and more violent interaction with simulated biomembranes which results in larger cytotoxicity against HeLa cells. Specifically, racemic-LNP vesicles exhibit the largest cytotoxicity of all. More interestingly, there is no significant enantioselective dependence of HBP vesicles on the abovementioned properties. Overall, we proved that the cytotoxicity of vesicles is deeply related to chirality and topological-structures. This research is of great fundamental value for the design of novel bio-interface materials.

Self-Assembling Nonconjugated Poly(amide-imide) into Thermoresponsive Nanovesicles with Unexpected Red Fluorescence for Bioimaging

Nonconjugated red fluorescent polymers have been increasingly studied to improve the biocompatibility and penetration depth over conventional fluorescent materials. However, the accessibility of such polymers remains challenging due to the scarcity of nonconjugated fluorophores and lacking relevant mechanism of red-shifted fluorescence. Herein, we discovered that the combination of hydrogen bonding and π-π stacking interactions provides nonconjugated poly(amide-imide) with a large bathochromic shift (>100 nm) from blue-green fluorescence to red emission. The amphiphilic PEGylated poly(amide-imide) derived from in situ PEGylation self-assembled into nanovesicles in water, which isolated the aminosuccinimide fluorophore from the solvents and suppressed the hydrogen bonds formation between aminosuccinimide fluorophores and water. Therefore, the fluorescence of PEGylated poly(amide-imide) in water was soundly retained. Furthermore, the strong hydrogen bonding and hydrophobic interactions with water provided PEGylated poly(amide-imide) with a reversible thermoresponsiveness and presented a concentration-dependent behavior. Finally, accompanied by the excellent biostability and photostability, PEGylated poly(amide-imide) exhibited as a good candidate for cell imaging.

Nanobowls with controlled openings and interior holes driven by the synergy of hydrogen bonding and π-π interaction

Asymmetric nanoparticles such as nanobowls have promising potential in many fields due to their interior asymmetric cavities and specific concave structure. However, the fabrication of nanobowls and control over their openings and interior holes are still challenging. Herein we demonstrate a versatile strategy for preparing nanobowls with precisely controlled openings and interior holes based on the synergy of hydrogen bonding and π-π interaction of homopolymers. We designed and synthesized a series of amphiphilic homopolymers with an amino alcohol moiety and azobenzene pendant (poly(2-hydroxy-3-((4-(phenyldiazenyl)phenyl)amino)propyl methacrylate) (PHAzoMA)). The homopolymers can self-assemble into nanobowls due to the heterogeneous shrinkage of the preformed spheres. Upon increasing the molecular weight of the homopolymers from 10.1 to 76.9 kg mol-1, the sizes of the openings of nanobowls can be precisely controlled from 242 to 423 nm with a linear relationship as a result of the enhancement of the hydrogen bonding and π-π interaction between homopolymer chains. Overall, we have prepared finely controlled nanobowls by the synergy of non-covalent interactions such as hydrogen bonding and π-π interaction of polymers, which opens a new avenue for the preparation of asymmetric nanoparticles.

Photoluminescent poly(4-vinylpyridine)-based ionic liquids coded with l- and d-histidine: a supramolecular self-assembly leading to the formation of red-shifted photoluminescent helical aggregates

Herein, photoluminescent poly(4-vinylpyridine)-based ionic liquids including d- and l-histidine were synthesized. The chiral PILs self-assembled into helical aggregates.

Construction, mechanism, and antibacterial resistance insight into polypeptide-based nanoparticles

Demonstration of the bactericidal mechanism of self-assembled nanoparticles.

Plasmonic vesicles with tailored collective properties

Plasmonic nanoparticle assemblies have been exhibiting unique collective properties absent in their individual counterparts. However, it is an important challenge to manipulate those properties due to the difficulty in controlling the arrangement and distance between plasmonic nanoparticles. Herein, we propose an alternative strategy for manipulating the distance between gold nanoparticles on the plasmonic vesicles to afford tunable collective properties by changing the temperature. To reach this goal, a thermally responsive vesicle is self-assembled from an azobenzene-terminated homopolymer, poly(2-(2-ethoxyethoxy)ethyl acrylate) (Azo-PEEA). Gold nanoparticles are then decorated on its membrane to afford plasmonic vesicles, which can be grouped and fused into larger plasmonic vesicles when heated. Consequently, the gold nanoparticles come closer, creating local hot spots in the gap between adjacent gold nanoparticles, leading to the red shift of local surface plasmon resonance (LSPR) peaks and better surface-enhanced Raman scattering (SERS). Besides, the structure and the collective optical properties of the plasmonic vesicles can be reserved under various conditions, e.g., different pH values, high salt concentration and relatively high temperature once they are heated up to 35 °C.

A Pseudopeptide Polymer Micelle Used for Asymmetric Catalysis of the Aldol Reaction in Water

Micelles assembled from amphiphilic molecules have proved to be ideal scaffolds to construct artificial catalysts mimicking enzymatic catalytic behavior. In this paper, we describe the synthesis of amphiphilic poly(2-oxazoline) derivatives with l-prolinamide units in the side chain and their application in asymmetric aldol reactions. Upon dissolution in water, the pseudopeptide polymers self-assembled into particles with different sizes, relying on the copolymer composition and distribution of hydrophilic/hydrophobic segments in the polymer chain. A preliminary study has demonstrated that the catalytic activity of these polymeric organocatalysts are strongly dependent on the aggregated architecture. The micelle-type assemblies can act as nanoreactors to efficiently promote the direct aldolisation of cyclohexanone with aromatic aldehydes in aqueous media, affording anti-aldol products in excellent yields (88⁻99%) and higher stereoselectivities (90/10 dr, 86% ee) compared to their nonmicellar systems under identical conditions.

Aqueous self-assembly of hydrophobic macromolecules with adjustable rigidity of the backbone

P(FpC₃P) (Fp: CpFe(CO)₂; C₃P: propyl diphenyl phosphine) has a helical backbone, resulting from piano stool metal coordination geometry, which is rigid with intramolecular aromatic interaction of the phenyl groups. The macromolecule is hydrophobic, but the polarized CO groups can interact with water for aqueous self-assembly. The stiffness of P(FpC₃P), which is adjustable by temperature, is an important factor influencing the morphologies of kinetically trapped assemblies. P(FpC₃P)₇ self-assembles in DMSO/water (10/90 by volume) into lamellae at 25 °C, vesicles at 40 °C and irregular aggregates at higher temperatures (60 and 70 °C). The colloidal stability decreases in the order of lamellae, vesicles and irregular aggregates. Dissipative particle dynamics (DPD) simulation reveals the same temperature-dependent self-assembled morphologies with an interior of hydrophobic aromatic groups covered with the metal coordination units. The rigid backbone at 25 °C accounts for the formation of the layered morphology, while the reduced rigidity of the same P(FpC₃P)₇ at 40 °C curves up the lamellae into vesicles. At a higher temperature (60 or 70 °C), P(FpC₃P)₇ behaves as a random coil without obvious amphiphilic segregation, resulting in irregular aggregates. The stiffness is, therefore, a crucial factor for the aqueous assembly of macromolecules without obvious amphiphilic segregation, which is reminiscent of the solution behavior observed for many hydrophobic biological macromolecules such as proteins.

Synthesis and self-assembly of a dual-responsive monocleavable ABCD star quaterpolymer

A modularly synthesized core-functionalized PEG-PSt-PCL-PAA miktoarm star can self-assemble into hollow nanocapsules that are sensitive to pH/redox stimuli and H-bond/polyion complexation.

Vesicles of double hydrophilic pullulan and poly(acrylamide) block copolymers: a combination of synthetic- and bio-derived blocks

The formation of vesicular structures with average diameters from 200 to 300 nm consisting of double hydrophilic diblock copolymers pullulan-b-poly(N,N-dimethylacrylamide) and pullulan-b-poly(N-ethylacrylamide) in aqueous solution is described.

Triple-stimuli-responsive ferrocene-containing homopolymers by RAFT polymerization

This article presents a new type of well-defined ferrocene-containing homopolymer obtained from RAFT polymerization, showing pH/CO₂ and redox responsiveness.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

One-, two-, and three-dimensional hierarchical self-assembly of non-amphiphilic low-entropy chains from nanotubes to nanoribbons and porous net-sheets

The association of some small molecules such as benzene and phthalimide with non-amphiphilic homopolymeric low-entropy chains such as PVAc, PVA, PVP, and PNIPAM has been realized by reversible addition–fragmentation chain transfer reaction (RAFT) method.