Self-assembly Of Amphiphilic Copolymers Research Articles

Biofilm microenvironment-responsive polymeric CO releasing micelles for enhanced amikacin efficacy

Biofilm-associated infections (BAI) have posed serious threats to public health. Novel therapy based on carbon monoxide (CO) is being increasingly appreciated. However, CO therapy like inhaled gas treatment was impeded owing to its low bioavailability. Besides, the direct use of CO releasing molecules (CORM) showed low therapeutic efficacy in BAI. Therefore, it is vital to improve the efficiency of CO therapy. Herein, we proposed polymeric CO releasing micelles (pCORM) from self-assembly of amphiphilic copolymers containing CORM bearing block as hydrophobic part and acryloylmorpholine block as hydrophilic part. The catechol modified CORM were conjugated through pH cleavable boronate ester bonds and releasing CO passively under biofilm microenvironment. When combined with subminimal inhibitory concentration antibiotic amikacin, pCORM could significantly enhance its bactericidal efficiency against biofilm-encapsulated multidrug-resistant bacteria, representing a promising approach to combat BAI.

Main Fabrication Methods of Micellar Nanoparticles for Nanoscale Tumor Therapy through the Self-assembly of Amphiphilic Copolymers

Abstract: Micellar nanoparticles synthesized through the self-assembly of amphiphilic copolymers have been widely used to encapsulate various cancer therapeutic agents for preclinical and clinical applications. These drug delivery systems are easy to fabricate and have good biocompatibility in general. In this article, we provide an overview of the advantages and disadvantages of micellar nanoparticles for the fabrication of therapeutic agent-loaded nanoparticles from amphiphilic copolymers, the examples of common polymer materials, and methods used to prepare micellar nanoparticles, including emulsion solvent evaporation method, double emulsion method, nanoprecipitation method, etc. By choosing an appropriate technique, different therapeutic agents with different properties can be incorporated into nanoparticles individually or in combination. We analyzed the parameters of various preparation methods, with particular emphasis on improvements in improved techniques for simultaneous co-loading of hydrophilic/hydrophobic drugs and therapeutic nucleic acids in a single nanoparticle. It will allow researchers to choose the appropriate method to design therapeutic agent-loaded micellar nanoparticles from amphiphilic copolymers.

Nanomicelles co-loaded with doxorubicin and salvianolic acid A for breast cancer chemotherapy

BackgroundMulti-drug delivery system based on polymer carrier is emerging for alleviating dose-limiting toxicities of first-line cytotoxic anticancer drugs, such as doxorubicin (DOX) for breast cancer chemotherapy. By co-loading the premium natural antioxidant salvianolic acid A (SAA) through colloidal self-assembly of amphiphilic copolymer, we herein developed CPMSD, a complex polymeric micellar system to overcome cardiotoxicity associated with DOX.ResultsOptimal formulation was obtained by DOE study and CPMSD micelles were well constructed by using mPEG-PCL for entrapment at a drug–carrier mass ratio of 1:5 and DOX–SAA mass ratio of 1:4. Molecular dynamics simulation revealed the ratiometrical co-encapsulation of SAA into the hydrophobic cavity but DOX to ball-shaped surface of micelles due to hydrophilicity. Characterization study manifested favorable biopharmaceutical properties, such as small and uniform particle size, fairly high drug loading capacity, as well as good colloidal stability and controlled drug release. CPMSD maintained anticancer efficacy of DOX and the action mechanism, which did not be affected by co-administering SAA. More to the point, it was of great benefit to systemic safety and cardioprotective effect against oxidative stress injuries associated with DOX in tumor-bearing mice.ConclusionsAll the findings substantiated that CPMSD would be a promising multifunctional nanosystem of DOX for breast cancer chemotherapy.

Self-Assembled Catalytic Nanoreactors from Molecular Brushes by Utilizing Postpolymerization Modification for Catalyst Attachment

Polymer-based catalytic nanoreactors, with the characteristics of easy preparation, good dispersion, and facile modulation of molecular structures, have been widely applied for various organic transformations. Usually, polymeric nanoreactors are fabricated via the self-assembly of amphiphilic copolymers in water, while the disassembly and instability of the relevant nanoreactors often compromise their potential applicability. Molecular brushes (MBs), as a kind of polymer with high-density grafted side chains on the linear polymer main chain, can be rapidly self-assembled into highly ordered nanostructures even at low concentrations. This study reports the fabrication of catalytic nanoreactors from molecular brushes of poly[norbornene–poly(bromoethyl methacrylate-co-methyl methacrylate)]-co-poly[norbornene polyethylene glycol monomethyl ether] (P[NB-(BEMA-co-MMA)]-co-P[NB-PEG]). The amphiphilic molecular brush was synthesized by combining reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP) techniques. Homogeneous catalysts, such as triethylenediamine and 4-(dimethylamino)pyridine analogues, were introduced by nucleophilic substitution with alkyl bromide on the side chain of molecular brushes. Furthermore, micellar catalytic nanoreactors were fabricated via self-assembly in deionized water. The resulted nanoreactors display high catalytic activities toward the Knoevenagel condensation reaction and acylation reaction of alcohol in water, respectively. This contribution describes a general method for constructing highly efficient molecular brush-based catalytic nanoreactors utilizing postpolymerization modification (PPM) for aqueous catalysis.

The Thermogel Chronicle─From Rational Design of Thermogelling Copolymers to Advanced Thermogel Applications

ConspectusTemperature responsive supramolecular hydrogels, also known as thermogels, are produced by the self-assembly of amphiphilic copolymers in solution following temperature stimulus. They are a class of high caliber novel materials possessing highly attractive properties such as injectability, ability to undergo temperature controlled reversible sol–gel phase transitions, high biocompatibility, and tunable biodegradability. Much research vigor has been dedicated to designing advanced amphiphilic copolymers and investigating their molecular interactions in order to enhance the properties of the thermogelling systems and expand the scope of their applications. As such, thermogelling systems have since become well established in the field of sustained localized drug or protein delivery and have also been demonstrated as high potential materials for niche applications such as three-dimensional cell culture, wound healing patches, and vitreous endotamponades. Recent developments saw the advent of thermogelling systems with advanced biomedical applications ranging from enhanced cancer therapy to radiology imaging to tissue engineering, and these are usually achieved by the conjugating of biologically relevant molecules such as drugs and peptides to the thermogel copolymer or by incorporating nanoparticles into the thermogel systems. New developments in this field see a shift away from employing traditional synthetic polymers such as polypropylene glycol (PPG) and poly(lactic-co-glycolic acid) (PLGA) to utilizing more advanced nature-derived bioactive molecules and also introducing chiral moieties in the thermogelling copolymer backbone.There are currently a few main types of thermogel copolymers such as diblock, triblock, end-capped, graft, and random multiblock polyurethane thermogels. Among these, our lab is specialized in the synthesis and application of polyurethane multiblock thermogels. These thermogels have the advantage of high molecular weights and enhanced intermolecular hydrogen bonding arising from the urethane groups. These generally allow for the formation of thermogelling systems with higher gel stiffness, resilience, and encapsulation efficiency, allowing these polyurethane thermogels to be well suited for niche applications such as sustained drug delivery and vitreous endotamponades. In this Account, we summarize the fundamental polymeric factors influencing the micellar and bulk polyurethane thermogel properties, provide our group’s insights into the rational design of these thermogels for various advanced applications and finally discuss the future possibilities of thermogelling systems. We speculate that there is still much untapped potential of thermogels in the biomedical field and these can possibly be achieved by designing thermogel copolymers with bioactive moieties and exploring more advanced branched architectures. In addition, we also propose the expansion of thermogels beyond biomedical fields, for which our lab has demonstrated thermogels as electrode contacts for noninvasive plant health monitoring.

Direct Access to Polysaccharide-Based Vesicles with a Tunable Membrane Thickness in a Large Concentration Window via Polymerization-Induced Self-Assembly.

Polymersomes are multicompartmental vesicular nano-objects obtained by self-assembly of amphiphilic copolymers. When prepared in the aqueous phase, they are composed of a hydrophobic bilayer enclosing water. Although such fascinating polymeric nano-objects have been widely reported with synthetic block copolymers, their formation from polysaccharide-based copolymers remains a significant challenge. In the present study, the powerful platform technology known as polymerization-induced self-assembly was used to prepare in situ pure vesicles from a polysaccharide-grafted copolymer: dextran-g-poly(2-hydroxypropyl methacrylate) (Dex-g-PHPMA). The growth of the PHPMA grafts was performed with a dextran-based macromolecular chain transfer agent in water at 20 °C using photomediated reversible addition fragmentation chain transfer polymerization at 405 nm. Transmission electron microscopy, cryogenic electron microscopy, small-angle X-ray scattering, atomic force microscopy, and dynamic light scattering revealed that amphiphilic Dex-g-PHPMAX=100-300 (X is the targeted average degree of polymerization, Xn̅, of each graft at full conversion) exhibit remarkable self-assembly behavior. On the one hand, vesicles were obtained over a wide range of solid concentrations (from 2.5% to 13.5% w/w), which can facilitate posterior targeting of such rare morphology. On the other hand, the extension of Xn̅ induces an increase in the vesicle membrane thickness, rather than a morphological evolution (spherical micelles to cylinders to vesicles).

TEMPO-Functionalized Nanoreactors from Bottlebrush Copolymers for the Selective Oxidation of Alcohols in Water.

Polymeric nanoreactors in water fabricated by the self-assembly of amphiphilic copolymers have attracted much attention due to their good catalytic performance without using organic solvents. However, the disassembly and instability of relevant nanostructures often compromise their potential applicability. Herein, the preparation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-containing nanoreactors by the self-assembly of amphiphilic bottlebrush copolymers has been demonstrated. First, a macromonomer having a norbornenyl polymerizable group was prepared by RAFT polymerization of hydrophobic and hydrophilic monomers. The macromonomer was further subjected to ring-opening metathesis polymerization to produce an amphiphilic bottlebrush copolymer. Further, TEMPO, as a catalyst, was introduced into the hydrophobic block through the activated ester strategy. Finally, TEMPO-functionalized polymeric nanoreactors were successfully obtained by self-assembly in water. The nanoreactors exhibited excellent catalytic activities in selective oxidation of alcohols in water. More importantly, the reaction kinetics showed that the turnover frequency is greatly increased compared to that of the similar nanoreactor prepared from liner copolymers under the same conditions. The outstanding catalytic activities of the nanoreactors from bottlebrush copolymers could be attributed to the more stable micellar structure using the substrate concentration effect. This work presents a new strategy to fabricate stable nanoreactors, paving the way for highly efficient organic reactions in aqueous solutions.

Self-Assembly of Amphiphilic Copolymers with Sequence-Controlled Alternating Hydrophilic–Hydrophobic Pendant Side Chains

To design versatile ordered nanomorphologies from the alternating sequence-controlled amphiphilic copolymers, in the current work, we have investigated the self-assembly behavior of a series of alt...

Reversibly Photoswitchable Dual-Color Fluorescence and Controlled Release Properties of Polymeric Nanoparticles

Here, we report a novel polymeric nanoparticle prepared by the self-assembly of amphiphilic copolymers containing a fluorescent naphthalimide (NAPH) and a photochromic spiropyran (SP), which posses...

ABA-type triblock copolymer micellar system with lower critical solution temperature-type sol-gel transition

A temperature sensitive sol-gel transition induced by the self-assembly of amphiphilic copolymers and its application in industry have been the objects of increasing study. We demonstrate here a two-step, reversible addition-fragmentation chain transfer (RAFT) polymerization of an ABA-type copolymer consisting of poly(N,N-dimethylacrylamide)-b-poly(diacetone acrylamide)-b-poly(N,N-dimethylacrylamide) (PDMAA-b-PDAAM-b-PDMAA). This copolymer can be easily dispersed in water, and this dispersion is critical for its lower critical solution temperature (LCST)-type sol-gel transition, which was monitored using dynamic light scattering (DLS), transmission electron microscopy (TEM), and rheology analysis, in addition to temperature-dependent 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Results revealed an abnormal sphere-to-worm micellar transition of this ABA copolymer at the LCST point, which could be affected by the length of the PDAAM block (B-block), the length as well as the distribution of the PDMAA block (A-block), and the concentration of the copolymer dispersion. Thus, copolymer dispersion could be feasibly used for drug loading at a low temperature, which could then be transformed into a gel at an elevated temperature. The loading and controllable release of the model drug of paracetamol into and out of a copolymer gel was further determined. The sustained release behavior was also studied using the Rigter-Peppas model.

The non-equilibrium self-assembly of amphiphilic block copolymers driven by a pH oscillator

Realizing and investigating artificial an non-equilibrium self-assembly is one of the challenging but attractive fields in supramolecular chemistry, because most molecular self-assembly in living organisms are out of thermodynamic equilibrium. In this article, we achieved the non-equilibrium self-assembly of amphiphilic block copolymers that contained polyethylene glycol segment and polyacrylic acid segment (PEG-PAAs) by coupling them with a pH oscillator. The self-assembly of PEG-PAAs varied dynamically and periodically in the pH oscillator. Furthermore, we found that the self-assembly of PEG-PAAs can bring additional influence on the dynamics of the pH oscillator. This line of work not only demonstrates the interrelationship between chemical oscillators and self-assembly of amphiphilic copolymers, but also contributes to develop chemical oscillators into a general driving force to realize and investigate non-equilibrium self-assembly of stimuli-responsive building blocks, and promotes the study of molecular self-assembly one step forward from static self-assembly under thermodynamic equilibrium to a dissipative system like living organisms.

Fabrication and biological imaging of polyhedral oligomeric silsesquioxane cross-linked fluorescent polymeric nanoparticles with aggregation-induced emission feature

Aggregation-induced emission (AIE) dyes based fluorescent polymeric nanoparticles (FNPs) have been intensively explored for biomedical applications. However, many of these AIE-active FNPs are relied on the self-assembly of amphiphilic copolymers, which are not stable in diluted solution. Therefore, the introduction of cross-linkages into these micelles has demonstrated to be an efficient route to overcome this stability problem and endow ultra-low critical micelle concentrations (CMC) of these AIE-active FNPs. In this work, we reported the fabrication of cross-linked AIE-active FNPs through controllable reversible addition fragmentation chain transfer polymerization by using commercially available octavinyl-T8-silsesquioxane (8-vinyl POSS) as the cross-linkage for the first time. The resultant cross-linked amphiphilic copolymers (named as PEG-POSS-PhE) are prone to self-assemble into stable core–shell nanoparticles with well water dispersity, strong red fluorescence and low CMC (0.0069mgmL−1) in aqueous solution. More importantly, PEG-POSS-PhE FNPs possess some other properties such as high water dispersity, uniform morphology and small size, excellent biocompatibility and cellular internalization, providing great potential of PEG-POSS-PhE FNPs for biological imaging application.

Formation of bowl-shaped nanoparticles by self-assembly of cinnamic acid-modified dextran

The self-assembly of amphiphilic copolymers has attracted much attention because of their various morphologies and potential applications. Bowl-shaped nanoparticles could apply in many aspects due to their interior cavity, specific concave structure and high surface area. In this study, dextran (Dex) was hydrophobic modified by cinnamic acid (CINN) via esterification reaction between the hydroxyl group of Dex and the carboxyl group of CINN. The modification degree of CINN could be achieved by changing the feed ratios between Dex, CINN and the coupling agent. The cinnamic acid-modified dextran (Dex–CINN) composed of Dex as hydrophilic segment and CINN as hydrophobic segment could self-assemble into bowl-shaped nanoparticles with a single dimple on the surface. Furthermore, the size of the dimples could be controlled by changing the modification degree of CINN, concentration of Dex–CINN and the rate of water addition. The morphologies of bowl-shaped nanoparticles were characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM).

An airflow-controlled solvent evaporation route to hollow microspheres and colloidosomes

A facile and large-scale method combining airflow-controlled solvent evaporation and amphiphilic copolymer self-assembly has been developed for the generation of hollow polymer microspheres, colloidosomes or even organic–inorganic hybrid colloidosomes. By replacing traditional agitation with the controllable airflow, this surfactant free route showed promising prospect in the fabrication of microcapsules with closed pore morphology. While the hollow polymer microspheres had an adjustable pore structure, the polymer colloidosomes and the hybrid colloidosomes possessed seamless surfaces, making them suitable for the stable encapsulation of small molecules. The hybrid colloidosomes constructed from polymer and Fe3O4 nanoparticles, and the ternary hybrid colloidosomes derived from polymer, polymer nanospheres and Fe3O4 nanoparticles displayed superparamagnetic properties and were excellent contrast agents for magnetic resonance imaging. More importantly, both hybrid colloidosomes and ternary hybrid colloidosomes exhibited a significant evolution of pore morphology from a closed pore structure to an open pore structure in response to the temperature variation, which induced a controllable release of guest molecules.

Multifunctional Dendritic Sialopolymersomes as Potential Antiviral Agents: Their Lectin Binding and Drug Release Properties

Polymer vesicles, commonly referred to as polymersomes, are self-organized materials that result from the self-assembly of amphiphilic copolymers in solution. Recently, there has been increasing interest in biomedical applications of polymersomes due to the different functions that can be imparted through encapsulation of molecules within the core or membrane or through the introduction of bioactive molecules to the polymersome surface. We describe here the development and study of poly(ethylene oxide)-polycaprolactone polymersomes designed to interact with influenza viruses at two different stages in the infection process. First, the conjugation of the sialic acid N-acetylneuraminic acid (Neu5Ac) to the polymersome surface was designed to inhibit the binding of viral hemagglutinin to sialic acids on host cells, thus preventing viral entry. Second, the incorporation of the neuraminidase inhibitor zanamivir into the polymersome core was designed to prevent the release of progeny virus from the host cells, thus inhibiting viral replication. With the aim of maximizing multivalent effects at the polymersome surface, polyester dendrons functionalized with Neu5Ac were synthesized and conjugated to polymersomes. Binding of the resulting dendritic sialopolymersomes to Limax flavus agglutinin was studied and compared to the sialodendron and a monovalent Neu5Ac derivative using an enzyme-linked lectin inhibition assay. It was found that while the sialodendron exhibited a 17-fold enhancement (per sialoside) relative to the small molecule, the dendritic sialopolymersomes resulted in an almost 2000-fold enhancement in binding affinity. It was also demonstrated that encapsulation of zanamivir into the dendritic sialopolymersomes could be performed with the same efficiency as for naked polymersomes to provide a drug loading of ~35 wt %. Drug release rates were similar for both systems with sustained release over a period of 4 days. Overall, these results suggest the promise of using a multifunctional polymersome system for interaction with and inhibition of influenza viruses.

Unexpected behavior of polydimethylsiloxane/poly(2-(dimethylamino)ethyl acrylate) (charged) amphiphilic block copolymers in aqueous solution

We report the synthesis and self assembly of amphiphilic block copolymers based on poly(dimethylsiloxane) and poly(2-(dimethylamino)ethyl acrylate) (PDMS-b-PDMAEA). We consider the self-catalyzed hydrolysis of PDMAEA in aqueous solution, and its effect on the self-assembly of the amphiphilic copolymer by investigating poly(dimethylsiloxane)-b-[poly(2-dimethylamino)ethyl acrylate)-co-poly(acrylic acid)] (PDMS-b-(PDMAEA-co-PAA)), obtained from hydrolysis of PDMAEA, and poly(dimethylsiloxane)-b-poly(2-(trimethylammonium iodide)ethyl acrylate) (PDMS-b-PTMAIEA), obtained from quaternization of PDMAEA. We observe that the thermal properties and self-assembly behavior in water of these amphiphilic diblock copolymers depend on the structure of the hydrophilic block, and are strongly influence by hydrolysis of the PDMAEA block. Self-assembly in aqueous solution leads to the formation of spherical micellar structures with diameters between 40 and 70 nm, which were investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). PDMS-b-(PDMAEA-co-PAA) is shown to be pH responsive, and behaves as a highly negatively charged polymer at high pH values (pH > 10) and as a highly positively charged polymer at low pH values (pH < 2). Critical micelle concentrations (cmc) of the amphiphilic block copolymers were determined by fluorescence measurement with N-phenyl-1-naphthylamine (PNA) as a fluorescence probe. Surprisingly, surface tension measurements suggest that PDMS-b-PTMAIEA is “non-surface active”, forming micelles in bulk solution instead of adsorbing at the air–water interface to form a Gibbs monolayer, even when the polymer concentration was over 100 times above its cmc value. This remarkable behavior is consistent with recent reports that suggest that “non-surface activity” can be observed for both cationic and anionic amphiphilic diblock copolymers due to the effect of image charge repulsion at the air–water interface.

Aggregates and hydrogels prepared by self-assembly of amphiphilic copolymers with surfactants

A series of water-insoluble polylactide/poly(ethylene glycol) (PLA/PEG) block copolymers were synthesized by ring-opening polymerization of lactide in the presence of mono- or dihydroxyl PEG, using nontoxic zinc lactate as catalyst. Interactions between the resulting copolymers and sodium dodecyl sulfate (SDS) in water were studied by varying SDS fraction and copolymer concentration, using ultraviolet–visible spectrometer. Light transmission results show that all the insoluble copolymers strongly interact with SDS, and the solubility of the copolymers is improved with increasing SDS fraction. Copolymers with triblock structures or higher molar masses present larger variation of solubility as compared to those with diblock structures or lower molar masses. Transmission electron microscopy and dynamic light scattering were then employed to examine the microstructure of aggregates in the mixture solutions. Various aggregates such as vesicles, branch-like micelles, spherical micelles, or nanogels were observed, depending on the SDS fraction and copolymer concentration. It is assumed that at low SDS fractions, surfactant molecules attach to PLA segments and make the copolymers more soluble to form various aggregates. At high SDS fractions, junctions composed of SDS aggregates with PLA segments involved inside are formed in the case of triblock copolymers and diblock ones with high molar masses. These junctions lead to cross-linking of copolymer chains to yield a nanogel. Hydrogels can be obtained at high concentrations as confirmed by rheological measurements.

Polymeric Vesicles: From Drug Carriers to Nanoreactors and Artificial Organelles

One strategy in modern medicine is the development of new platforms that combine multifunctional compounds with stable, safe carriers in patient-oriented therapeutic strategies. The simultaneous detection and treatment of pathological events through interactions manipulated at the molecular level offer treatment strategies that can decrease side effects resulting from conventional therapeutic approaches. Several types of nanocarriers have been proposed for biomedical purposes, including inorganic nanoparticles, lipid aggregates, including liposomes, and synthetic polymeric systems, such as vesicles, micelles, or nanotubes. Polymeric vesicles--structures similar to lipid vesicles but created using synthetic block copolymers--represent an excellent candidate for new nanocarriers for medical applications. These structures are more stable than liposomes but retain their low immunogenicity. Significant efforts have been made to improve the size, membrane flexibility, and permeability of polymeric vesicles and to enhance their target specificity. The optimization of these properties will allow researchers to design smart compartments that can co-encapsulate sensitive molecules, such as RNA, enzymes, and proteins, and their membranes allow insertion of membrane proteins rather than simply serving as passive carriers. In this Account, we illustrate the advances that are shifting these molecular systems from simple polymeric carriers to smart-complex protein-polymer assemblies, such as nanoreactors or synthetic organelles. Polymeric vesicles generated by the self-assembly of amphiphilic copolymers (polymersomes) offer the advantage of simultaneous encapsulation of hydrophilic compounds in their aqueous cavities and the insertion of fragile, hydrophobic compounds in their membranes. This strategy has permitted us and others to design and develop new systems such as nanoreactors and artificial organelles in which active compounds are simultaneously protected and allowed to act in situ. In recent years, we have created a variety of multifunctional, proteinpolymersomes combinations for biomedical applications. The insertion of membrane proteins or biopores into the polymer membrane supported the activity of co-encapsulated enzymes that act in tandem inside the cavity or of combinations of drugs and imaging agents. Surface functionalization of these nanocarriers permitted specific targeting of the desired biological compartments. Polymeric vesicles alone are relatively easy to prepare and functionalize. Those features, along with their stability and multifunctionality, promote their use in the development of new theranostic strategies. The combination of polymer vesicles and biological entities will serve as tools to improve the observation and treatment of pathological events and the overall condition of the patient.

Pluronics‐Stabilized Gold Nanoparticles: Investigation of the Structure of the Polymer–Particle Hybrid

Hybrid gold-polymer nanoparticles are obtained by self-assembly of amphiphilic copolymers (Pluronics) in solutions containing preformed gold nanoparticles (diameter ca. 12 nm). Dynamic light scattering, TEM, cryo-TEM, and small-angle neutron scattering experiments with contrast variation are used to characterize the structure of the gold-polymer particles. Five Pluronics (F127, F68, F88, F108, P84) with different molecular weights and hydrophilic/hydrophobic balances are investigated. Gold nanoparticles are individually embedded within globules of polymer, even under conditions for which Pluronics micelles do not form in solution. The hybrid particles are several tens of nanometers in size (larger than micelles of the corresponding Pluronics), and the size can be tuned by changing the temperature.

PbS nanoparticles/polymer composite aggregates through self-assembly of amphiphilic copolymer containing cross-linked hydrophilic block

Poly(methyl methacrylate) macroinitiator and amphiphilic block copolymer poly(methyl methacrylate)-block-poly(lead dimethacrylate) (PMMA -b-PLDMA) were synthesized by two-step sequential atom transfer radical polymerization (ATRP). In this novel amphiphilic block copolymer, the hydrophilic block PLDMA is cross-linked, and the hydrophobic block PMMA is linear. In selective solvent, the copolymers can self-assemble to form crew-cut aggregates comprised of the hydrophobic block PMMA surround by the cross-linked hydrophilic block PLDMA. Through bubbling H 2S into the aggregate solution in the next step, PbS nanoparticles can be synthesized in the aggregates in situ. XPS spectra confirm the successful synthesis of the copolymers. AFM, SEM and TEM are used to characterize the morphologies of these composite aggregates.