Effect of Degree of Branching on the Self-Assembly of Amphiphilic Hyperbranched Multiarm Copolymers

Aqueous RAFT Dispersion Polymerization Mediated by an ω,ω-Macromolecular Chain Transfer Monomer: An Efficient Approach for Amphiphilic Branched Block Copolymers and the Assemblies

Herein, an ω,ω-macromolecular chain transfer monomer (macro-CTM) containing a RAFT (reversible addition-fragmentation chain transfer) group and a methacryloyl group was synthesized and used to mediate photoinitiated RAFT dispersion polymerization of hydroxypropyl methacrylate (HPMA) in water. The macro-CTM undergoes a self-condensing vinyl polymerization (SCVP) mechanism under RAFT dispersion polymerization conditions, leading to the formation of amphiphilic branched block copolymers and the assemblies. Compared with RAFT solution polymerization, it was found that the SCVP process was promoted under RAFT dispersion polymerization conditions. Morphologies of branched block copolymer assemblies could be controlled by varying the monomer concentration and the [HPMA]/[macro-CTM] ratio. The branched block copolymer vesicles could be used as seeds for seeded RAFT emulsion polymerization, and framboidal vesicles were successfully obtained. Finally, degrees of branching of branched block copolymers could be further controlled by using a binary mixture of the macro-CTM and a linear macro-RAFT agent or a small molecule CTM. We believe that this study not only provides a versatile strategy for the preparation of branched block copolymer assemblies but also offers important insights into polymer synthesis via heterogeneous RAFT polymerization.

A novel route to improve the mechanical and rheological properties of HTPE/AP/Al propellant by adding a modified hyperbranched polyester

Both better mechanical and rheological properties are pursued for composite solid propellant. In this work, varying proportions of a modified hyperbranched polyester (MHBPE) were added to HTPE/AP/Al propellant. The static tensile property as one kind of mechanical properties of MHBPE/HTPE/AP/Al propellant were found to be superior to those of blank HTPE/AP/Al propellant as a result of the entanglement and interpenetration of molecular chains caused by the introduction of the hyperbranched structure. Evaluations on the related improved creep resistance and stress relaxation performance further demonstrated the advantages of introduction of MHBPE to HTPE/AP/Al propellant. Rheological properties of HTPE/AP/Al propellant with and without MHBPE during the casting process were investigated and compared and the results confirmed the improvement benefiting from low viscosity and loose void structure. Thus, modified hyperbranched polyester provided a novel route to potentially meet the requirements for propellant manufacturing and applications.

Defects and defect engineering in Soft Matter

Soft matter covers a wide range of materials based on linear or branched polymers, gels and rubbers, amphiphilic (macro)molecules, colloids, and self-assembled structures. These materials have applications in various industries, all highly important for our daily life, and they control all biological functions; therefore, controlling and tailoring their properties is crucial. One way to approach this target is defect engineering, which aims to control defects in the material's structure, and/or to purposely add defects into it to trigger specific functions. While this approach has been a striking success story in crystalline inorganic hard matter, both for mechanical and electronic properties, and has also been applied to organic hard materials, defect engineering is rarely used in soft matter design. In this review, we present a survey on investigations on defects and/or defect engineering in nine classes of soft matter composed of liquid crystals, colloids, linear polymers with moderate degree of branching, hyperbranched polymers and dendrimers, conjugated polymers, polymeric networks, self-assembled amphiphiles and proteins, block copolymers and supramolecular polymers. This overview proposes a promising role of this approach for tuning the properties of soft matter.

Self-assembly of Organic Nanomaterials and Biomaterials: The Bottom-Up Approach for Functional Nanostructures Formation and Advanced Applications

In this paper, we survey recent advances in the self-assembly processes of novel functional platforms for nanomaterials and biomaterials applications. We provide an organized overview, by analyzing the main factors that influence the formation of organic nanostructured systems, while putting into evidence the main challenges, limitations and emerging approaches in the various fields of nanotechology and biotechnology. We outline how the building blocks properties, the mutual and cooperative interactions, as well as the initial spatial configuration (and environment conditions) play a fundamental role in the construction of efficient nanostructured materials with desired functional properties. The insertion of functional endgroups (such as polymers, peptides or DNA) within the nanostructured units has enormously increased the complexity of morphologies and functions that can be designed in the fabrication of bio-inspired materials capable of mimicking biological activity. However, unwanted or uncontrollable effects originating from unexpected thermodynamic perturbations or complex cooperative interactions interfere at the molecular level with the designed assembly process. Correction and harmonization of unwanted processes is one of the major challenges of the next decades and requires a deeper knowledge and understanding of the key factors that drive the formation of nanomaterials. Self-assembly of nanomaterials still remains a central topic of current research located at the interface between material science and engineering, biotechnology and nanomedicine, and it will continue to stimulate the renewed interest of biologist, physicists and materials engineers by combining the principles of molecular self-assembly with the concept of supramolecular chemistry.

Amphiphilic hyperbranched polymers: synthesis, characterization and self-assembly performance

Abstract

A series of amphiphilic hyperbranched polymers (AHP-s, the “s” refers to the algebra of AHP) were synthesized by the reaction between hydroxyl-terminated hyperbranched polymers (HBP-s, the “s” refers to the algebra of HBP) and palmitoyl chloride. FTIR, NMR and GPC were used to determine the structure of AHP-s, the results showed that AHP-s exhibits core-shell structure. The thermal properties of polymers were investigated by DSC and TGA. It was found that AHP-2, AHP-3 and AHP-4 display higher thermal stability than AHP-1 (AHP-1, AHP-2, AHP-3 and AHP-4 represent the first, second, third and fourth generation AHP, respectively). Furthermore, the self-assembly performance of AHP-s in THF solvent was investigated by TEM and SEM. Finally, the encapsulation capacity of the AHP-s for methyl orange (MO) was explored at different concentrations of AHP-s and pH conditions. It was found that AHP-s is capable of accommodating hydrophilic guest MO. Moreover, the higher generation of AHP-s, the stronger encapsulation capacity obtained. And the encapsulation capacity closely associated with the pH of encapsulation system.

Graphical abstract

Stearoyl-appended pendant amino acid-based hyperbranched polymers for selective gelation of oil from oil/water mixtures

Stearic acid-appended pendant amino acid-based poly(methacrylate) hyperbranched polymers were developed for the phase-selective organogelation of crude oil from a binary mixture of oil/water.

Investigations on the micellization of amphiphilic dendritic copolymers: From unimers to micelles

Since the micellization kinetics is influenced by polymer structure, the spherical three-dimensional topology of amphiphilic dendritic copolymers (ADPs) which hinders the phase separation during micellization is assumed to make the micellization kinetics different. In the literatures, most of the attention has been paid to the morphology transition or the morphology at equilibrium and the micellization kinetics of ADPs is rarely reported. In this study, the micellization processes of amphiphilic dendritic copolymers from unimers to the final equilibrium micelles were monitored by laser light scattering. Based on the closed association mechanism, the thermodynamics of micellization was analysed. The negative thermodynamic quantities indicate that the micellization of ADPs is driven by enthalpy. Based on the change of scattering intensity and hydrodynamic radius (R_h) with time, the detailed micellization kinetics was analysed, which contains two steps. By controlling the temperature and type of solvent, a system in which the concentration has little influence on R_h is obtained. The relaxation times of the two steps decrease with concentration, indicating that at higher concentration the rate of micellization is quicker. With the increasing mass fraction of the hydrophobic part, the relaxation times decrease and the driving force of micellization increases.

A dissipative particle dynamics simulation study on phase diagrams for the self-assembly of amphiphilic hyperbranched multiarm copolymers in various solvents

Self-assembly of amphiphilic hyperbranched multiarm copolymers (HMCs) has shown great potential for preparing all kinds of delicate supramolecular structures in all scales and dimensions in solution. However, theoretical studies on the influencing factors for the self-assembly of HMCs have been greatly lagging behind. The phase diagram of HMCs in selective solvents is very necessary but has not been disclosed up to now. Here, the self-assembly of HMCs with different hydrophilic fractions in various solvents was studied systematically by using dissipative particle dynamics (DPD) simulations. Three morphological phase diagrams are constructed and a rich variety of morphologies, ranging from spherical micelles, worm-like micelles, membranes, vesicles, vesosomes, small micellar aggregates (SMAs), and aggregates of spherical and worm-like micelles to helical micelles, are obtained. In addition, both the self-assembly mechanisms and the dynamic processes for the formation of these self-assemblies have been systematically investigated. The simulation results are consistent with available experimental observations. Besides, several novel structures, like aggregates of spherical and worm-like micelles, vesosomes and helical micelles, are firstly discovered for HMC self-assembly. We believe the current work will extend the knowledge on the self-assembly of HMCs, especially on the control of supramolecular structures and on fabricating novel self-assemblies.

Worm-Like Superparamagnetic Nanoparticle Clusters for Enhanced Adhesion and Magnetic Resonance Relaxivity

Nanosized bioprobes that can highlight diseased tissue can be powerful diagnostic tools. However, a major unmet need is a tool with adequate adhesive properties and contrast-to-dose ratio. To this end, this study demonstrates that targeted superparamagnetic nanoprobes engineered to present a worm-like shape and hydrophilic packaging enhance both adhesion efficiency to target substrates and magnetic resonance (MR) sensitivity. These nanoprobes were prepared by the controlled self-assembly of superparamagnetic iron oxide nanoparticles (SPIONs) into worm-like superstructures using glycogen-like amphiphilic hyperbranched polyglycerols functionalized with peptides capable of binding to defective vasculature. The resulting worm-like SPION clusters presented binding affinity to the target substrate 10-fold higher than that of spherical ones and T2 molar MR relaxivity 3.5-fold higher than that of conventional, single SPIONs. The design principles discovered for these nanoprobes should be applicable to a range of other diseases where improved diagnostics are needed.

Janus long-chain hyperbranched copolymers of PSt and POEGMA from a self-assembly mediated click reaction

A Janus hyperbranched POEGMA/PSt copolymer with long sub-chains was prepared through a self-assembly mediated click reaction in selective solvents.

Hydrodynamic behaviors of amphiphilic dendritic polymers with different degrees of amidation

This work highlights the structure evolution and the response to solvent quality of ADPs.

Control-synthesized multilayer hyperbranched–hyperbranched polyethers with a tunable molecular weight and an invariant degree of branching

Multilayer hyperbranched–hyperbranched polyethers with a tunable M_n and an invariant DB were reported for the first time.

Effect of Topological Structures on the Self-Assembly Behavior of Supramolecular Amphiphiles

Three types of azobenzene-based telechelic guest polymers, PEG-azo, azo-PEG-azo, and PEG-azo4, were synthesized by a facile method. Subsequently, a series supramolecular amphiphiles with three distinct topological structures (hemitelechelic, ditelechelic, and quadritelechelic) were constructed through coupling with host polymer β-cyclodextrin-poly(l-lactide) (β-CD-PLLA) by combined host-guest complexation. Research on the self-assembly behavior of these amphiphiles demonstrated that the variation in self-assembly was tuned by the synergistic interaction of hydrophilicity and the curvature of the polymer chains, and very importantly, the topological structure of amphiphiles demonstrated effective control of the self-assembly behavior.

Supramolecular Architectures of Dendritic Amphiphiles in Water

Dendritic molecules are an exciting research topic because of their highly branched architecture, multiple functional groups on the periphery, and very pertinent features for various applications. Self-assembling dendritic amphiphiles have produced different nanostructures with unique morphologies and properties. Since their self-assembly in water is greatly relevant for biomedical applications, researchers have been looking for a way to rationally design dendritic amphiphiles for the last few decades. We review here some recent developments from investigations on the self-assembly of dendritic amphiphiles into various nanostructures in water on the molecular level. The main content of the review is divided into sections according to the different nanostructure morphologies resulting from the dendritic amphiphiles' self-assembly. Finally, we conclude with some remarks that highlight the self-assembling features of these dendritic amphiphiles.

Dissipative particle dynamics simulation study on self-assembly of amphiphilic hyperbranched multiarm copolymers with different degrees of branching

Hyperbranched multiarm copolymers (HMCs) have shown great potential to be excellent precursors in self-assembly to form various supramolecular structures in all scales and dimensions in solution. However, theoretical studies on the self-assembly of HMCs, especially the self-assembly dynamics and mechanisms, have been greatly lagging behind the experimental progress. Herein, we investigate the effect of degree of branching (DB) on the self-assembly structures of HMCs by dissipative particle dynamics (DPD) simulation. Our simulation results demonstrate that the self-assembly morphologies of HMCs can be changed from spherical micelles, wormlike micelles, to vesicles with the increase of DBs, which are qualitatively consistent with the experimental observations. In addition, both the self-assembly mechanisms and the dynamic processes for the formation of these three aggregates have been systematically disclosed through the simulations. These self-assembly details are difficult to be shown by experiments and are very useful to fully understand the self-assembly behaviors of HMCs.

Hyperbranched polymer vesicles: from self-assembly, characterization, mechanisms, and properties to applications

This tutorial review summarizes the first 10 years of work on hyperbranched polymer vesicles from syntheses, self-assembly, and properties to applications.

Organic nanospheres with an internal bicontinuous structure and their responsive phase inversion

Responsive nanospheres with an internal bicontinuous structure and shape changing ability through phase inversion were obtained through hierarchical self-assembly of a dendritic block terpolymer in selective solvents.

Studies on the orthogonal assembly of β-cyclodextrin-poly (ε-caprolactone) and ferrocene-poly (ethylene oxide)

A biodegradable multi-arm polymer β-cyclodextrin-poly (ε-caprolactone) (CD-PCL) with a ``jellyfish-like'' structure was obtained, in which flexible and hydrophobic PCL arms were selectively grafted to the wide side of the hydrophilic torus-shaped β-CD. The amphiphilic "jellyfish-like'' polymer with a hollow cavity and hydrophobic tails could orthogonally self-assemble into a new amphiphilic supramolecular copolymer CD-PCL/FcPEG with poly (ethylene oxide) end-decorated by ferrocene (FcPEG) in aqueous solution based on terminal hydrophobic interactions. The chemical structures of CD-PCL and CD-PCL/FcPEG were characterized by IR, NMR and UV and their self-assembled structures in water were investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). CD-PCL alone self-assembled into nano vesicles in water, while CD-PCL/FcPEG into nanospheres. The supramolecular nanospheres were further investigated by cyclic voltammogram. The results indicated that the ferrocenyl groups which were embedded into the hydrophobic core of the supramolecular nanospheres could not transmit electrons or carry out electrochemical oxidation and reduction reaction.

Poly (ethylene glycol)-armed hyperbranched polyoxetanes for anticancer drug delivery

A facile method for synthesis of polyethylene glycol (PEG)-armed hyperbranched polyoxetanes is presented as well as characterization and use in drug delivery. A series of hyperbranched polyoxetanes with multiple PEG arms were synthesized via a one-pot cationic ring-opening polymerization of 3-ethyl-3-hydroxymethyloxetane (EHMO) and its PEGylated derivative (EPMO), in which the feed mass ratio of EHMO to EPMO was 98:2, 96:4, 74:26, or 17:83. Characterization methods included NMR, DLS, FT-IR, DSC, and SEM. Toxicity of the synthesized polymers to human dermal fibroblasts was evaluated using the MTT assay. Formulation into particles was carried out to encapsulate the anticancer drug camptothecin using the single oil-in-water (o/w) solvent evaporation method. The resulting drug encapsulated particles were evaluated for antitumor activity using HN12 cells.

Polymer nanoassemblies for cancer treatment and imaging

Amphiphilic polymers represented by block copolymers self-assemble into well-defined nanostructures capable of incorporating therapeutics. Polymer nanoassemblies currently developed for cancer treatment and imaging are reviewed in this article. Particular attention is paid to three representative polymer nanoassemblies: polymer micelles, polymer micellar aggregates and polymer vesicles. Rationales, design and performance of these polymer nanoassemblies are addressed, focusing on increasing the solubility and chemical stability of drugs. Also discussed are polymer nanoassembly formation, the distribution of polymer materials in the human body and applications of polymer nanoassemblies for combined therapy and imaging of cancer. Updates on tumor-targeting approaches, based on preclinical and clinical results are provided, as well as solutions for current issues that drug-delivery systems have, such as in vivo stability, tissue penetration and therapeutic efficacy. These are discussed to provide insights on the future development of more effective polymer nanoassemblies for the delivery of therapeutics in the body.