Formation of Core‐Shell‐Corona Micellar Complexes through Adsorption of Double Hydrophilic Diblock Copolymers into Core‐Shell Micelles

Summary: The complexation between polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles and poly(ethylene glycol)‐block‐poly(4‐vinyl pyridine) (PEG‐b‐P4VP) is studied, and a facile strategy is proposed to prepare core‐shell‐corona micellar complexes. Micellization of PS‐b‐PAA in ethanol forms spherical core‐shell micelles with PS block as core and PAA block as shell. When PEG‐b‐P4VP is added into the core‐shell micellar solution, the P4VP block is absorbed into the core‐shell micelles to form spherical core‐shell‐corona micellar complexes with the PS block as core, the combined PAA/P4VP blocks as shell and the PEG block as corona. A model is suggested to characterize the core‐shell‐corona micellar complexes.

Schematic formation of core‐shell‐corona (CSC) micellar complexes by adsorption of PEG‐b‐P4VP into core‐shell PS‐b‐PAA micelles.     

Hollow nanoparticles prepared from pH‐responsive template polymer micelles

Water‐soluble crosslinked hollow nanoparticles were prepared using pH‐responsive anionic polymer micelles as templates. The template micelles were formed from pH‐responsive diblock copolymers (PAMPS‐PAaH) composed of the poly(sodium 2‐(acrylamido)‐2‐methylpropanesulfonate) and poly(6‐(acrylamido)hexanoic acid) blocks in an aqueous acidic solution. The PAMPS and PAaH blocks form a hydrophilic anionic shell and hydrophobic core of the core‐shell polymer micelle, respectively. A cationic diblock copolymer (PEG‐P(APTAC/CEA)) with the poly(ethylene glycol) block and random copolymer block composed of poly((3‐acrylamidopropyl)trimethylammonium chloride) containing a small amount of the 2‐(cinnamoyl)ethylacrylate photo‐crosslinkable unit can be adsorbed to the anionic shell of the template micelle due to electrostatic interaction, which form a core‐shell‐corona three‐layered micelle. The shell of the core‐shell‐corona micelle is formed from a polyion complex with anionic PAMPS and cationic P(APTAC/CEA) chains. The P(APTAC/CEA) chains in the shell of the core‐shell‐corona micelle can be photo‐crosslinked with UV irradiation. The template micelle can be dissociated using NaOH, because the PAaH blocks are ionized. Furthermore, electrostatic interactions between PAMPS and PAPTAC in the shell are screened by adding excess NaCl in water. The template micelles can be completely removed by dialysis against water containing NaOH and NaCl to prepare the crosslinked hollow nanoparticles. Transmission electron microscopy observations confirmed the hollow structure. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) with blended polystyrene core and their application to the synthesis of hollow silica nanospheres

Core-shell-corona (CSC) micelles of asymmetric triblock copolymer, poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-PVP-PEO), containing polystyrene homopolymer (homo-PS) in the core were successfully prepared in aqueous media. The influence of homo-PS contents over the formation of the micelles was investigated thoroughly by various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. It was found that the size of the PS core of the micelle was increased by the addition of homo-PS as observed by DLS and TEM techniques. The SEM and TEM measurements confirm the spherical morphology of the micelles and enlargement of PS core over the addition of homo-PS. The increase in the PS core volume of the PS-PVP-PEO micelles is attributed to the insertion of homo-PS in the PS core. The micelles have also been demonstrated as facile soft templates for synthesis of hollow silica nanospheres. The average diameter of the spherical hollow particles could be tuned between 30.6 and 38.8 nm with cavity sizes ranging from 20.7 to 28.5 nm using tetramethoxysilane as silica precursors under mild acidic conditions. The facile synthesis of hollow silica using the CSC micelles with different homo-PS contents indicates that the hollow void size can be controlled within a range of several nanometers.     

Hollow capsules prepared from all block copolymer micelle multilayers

We introduce a novel and versatile approach for preparing hollow multilayer capsules containing functional hydrophobic components. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films onto polystyrene (PS) colloids. After removing the PS colloids, the stabilities of the formed BCM hollow capsules were found to be strongly dependent on the charge density of the hydrophilic corona segments (i.e., P4VP and PAA block segments) as well as the relative molecular weight ratio of hydrophobic core (i.e., PS segments) blocks and hydrophilic corona shells. Furthermore, in the case of incorporating hydrophobic fluorescent dyes into the PS core blocks of micelles, the hairy/hairy BCM multilayers showed well-defined fluorescent images after colloidal template removal process. These phenomena are mainly caused by the relatively high degree of electrostatic interdigitation between the protonated and anionic corona block shells.     

Nanometer‐Scaled Hollow Spherical Micelles with Hydrophilic Channels and the Controlled Release of Ibuprofen

PS‐b‐PAA spherical micelles with a liquid core and a PAA shell are prepared with the assistance of 1,2‐dichloroethane. During the process of adding a mixture of PNIPAM‐b‐P4VP and PEG‐b‐P4VP, multi‐layered micelles with a mixed corona that consists of both PNIPAM and PEG chains are constructed through the electrostatic interaction and hydrogen bonding between the PAA block and the P4VP block. When heating above the LCST, the PNIPAM chains collapse onto the PAA/P4VP complex layer while the PEG chains still stretch into the solution through the collapsed PNIPAM layer, which leads to the formation of hydrophilic channels around the PEG chains. The ibuprofen encapsulated in the hollow space can diffuse through the channels and its release rate can be controlled by changing the ratio of PEG chains to PNIPAM chains in the corona.

     

Tunable fabrication on iron oxide/Au/Ag nanostructures for surface enhanced Raman spectroscopy and magnetic enrichment

Novel lanthanum borate (LaBO₃) hollow nanospheres of size 34 ± 2 nm have been reported for the first time by soft-template self-assembly process. Poly(styrene-b-acrylic acid-b-ethylene oxide) (PS-PAA-PEO) micelle with core–shell–corona architecture serves as an efficient soft template for fabrication of LaBO₃ hollow particles using sodium borohydride (NaBH₄) and LaCl₃?7H₂O as the precursors. In this template, the PS block (core) acts as a template of the void space of hollow particle, the anionic PAA block (shell) serves as reaction field for metal ion interactions, and the PEO block (corona) stabilizes the polymer/lanthana composite particles. The PS-PAA-PEO micelles and the resulting LaBO₃ hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscope (TEM), X-ray diffraction, magic angle spinning-nuclear magnetic resonance (¹¹B MAS NMR), energy dispersive X-ray analysis, thermal analyses, Fourier transform infra red spectroscopy, and nitrogen adsorption/desorption analyses. The nitrogen adsorption/desorption analyses and TEM observation of the hollow particles confirmed the presence of disordered mesopores in the LaBO₃ shell domain. The solid state ¹¹B MAS NMR spectra of LaBO₃ hollow nanospheres revealed that the shell part contains both trigonal and tetrahedral boron species. The LaBO₃ hollow particles were applied to anode materials in lithium-ion rechargeable batteries (LIBs). The hollow particles exhibited high coulombic efficiency and charge–discharge cycling capacities of up to 100 cycles in the LIBs.     

Fabrication of polymeric micelles with core–shell–corona structure for applications in controlled drug release

Thermo-responsive polymeric micelles of poly (ethylene glycol)-b-poly(2-hydroxyethyl methacrylate-g-lactide)-b-poly(N-isopropylacrylamide) (PEG-P(HEMA-PLA)-PNIPAM) with core–shell–corona structure were fabricated for applications in controlled drug release. The graft copolymer of PEG-P(HEMA-PLA)-PNIPAM was self-assembled into core–shell micelles with a densely PLA core and mixed PEG/PNIPAM shells at 25 °C in aqueous media. By increasing the temperature above the lower critical solution temperature of PNIPAM, these core–shell micelles could be converted into core–shell–corona micelles because of the collapse of PNIPAM block on the PLA core as the inner shell and the soluble PEG block stretching outside as the outer corona. Anticancer drug doxorubicin (DOX) was loaded in the polymeric micelles as a model drug. Compared with polymeric micelles formed by liner PEG-b-PLA-b-PNIPAM triblock copolymer, these polymeric micelles exhibited higher loading capacity, and release of DOX from the polymeric micelles with core–shell–corona structure was well-controlled.     

New approaches to stimuli-responsive polymeric micelles and hollow spheres

This article briefly describes some new approaches to stimuli-sensitive polymeric micelles and hollow spheres, which were developed in the authors’ laboratory in recent years. (1) Self-assembly of component polymers to non-covalently connected micelles (NCCM) driven by specific interactions. For example, in water, PCL and PAA formed core-shell nanospheres due to interpolymer hydrogen bonding. After crosslinking the PAA shell and removing the PCL core, “nanocages” made of PAA network were obtained. This hollow structure shows perfect reversible size-pH dependence. (2) Simultaneous in-situ polymerization of monomers and self-assembly of the polymers. In this approach, PNIPAM network was formed by radical polymerization covering PCL particles. Hollow spheres of PNIPAM network were then obtained by biodegradation of the PCL core. Both the core-shell spheres and hollow spheres show reversible size dependence on temperature change because of the phase transition of PNIPAM around 32°C. (3) Complexation-induced micellization and transition between the micelles and hollow spheres. Graft copolymers of hydroxylethyl cellulose (HEC) and PAA were prepared by free radical polymerization. The copolymers showed pH dependent micellization, i.e., micelles formed when pH of the graft copolymer solution decreased to around 3. The micellar structure could be locked by crosslinking the PAA grafts. The resultant cross-linked micelles undergo pH-dependent transition between the micelles and hollow spheres, which accompanies a remarkable particle size change. Both the micellization and the structure transition were found to be reversible and associated with H-bonding complexation between the main chain and grafts. __________ Translated from Acta Polymerica Sinica, 2005, 650(5) (in Chinese)     

Modulating the catalytic activity of Au/micelles by tunable hydrophilic channels

Polymeric micelles with a polystyrene core, poly(acrylic acid)/poly(4-vinyl pyridine) (PAA/P4VP) complex shell and poly(ethylene glycol) & poly(N-isopropylacrylamide) (PEG & PNIPAM) mixed corona were synthesized and used as the supporter for the gold nanoparticles (GNs). It was concluded from the result of ¹H NMR characterization that hydrophilic channels formed around PEG chains when PNIPAM collapsed above its lower critical solution temperature. The density of the channels in the corona can be tuned by changing the weight ratios of PEG chains to PNIPAM chains. The GNs were set in the PAA/P4VP complex layer and the catalytic activity of the GNs can be modulated by the channels. The catalytic activity increased with increasing the density of the channels in the corona. Meanwhile, the whole Au/micelle nanoparticles were stabilized by the extended PEG chains.     

Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.     

Reorganization of hydrogen-bonded block copolymer complexes

Poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) have been mixed in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Those insoluble complexes aggregate to form the core of micelles surrounded by a corona of PS chains. Reorganization of these structures occurs upon addition of acidic or basic water, which results in the breaking of the hydrogen bonds between the P4VP and PAA blocks. After transfer of the initial complexes in acidic water, micelles consisting of a PS core and a protonated P4VP corona are observed. In basic water, well-defined nanoparticles formed by the PS-b-P4VP copolymers are obtained. It is demonstrated that these nanoparticles are stabilized by the negatively charged PAA chains. Finally, thermally induced disintegration of the micelles is investigated in organic solvents.     

Polymerizable Molecular Silsesquioxane Cage Armored Hybrid Microcapsules with In Situ Shell Functionalization

We prepared core–shell polymer–silsesquioxane hybrid microcapsules from cage‐like methacryloxypropyl silsesquioxanes (CMSQs) and styrene (St). The presence of CMSQ can moderately reduce the interfacial tension between St and water and help to emulsify the monomer prior to polymerization. Dynamic light scattering (DLS) and TEM analysis demonstrated that uniform core–shell latex particles were achieved. The polymer latex particles were subsequently transformed into well‐defined hollow nanospheres by removing the polystyrene (PS) core with 1:1 ethanol/cyclohexane. High‐resolution TEM and nitrogen adsorption–desorption analysis showed that the final nanospheres possessed hollow cavities and had porous shells; the pore size was approximately 2–3 nm. The nanospheres exhibited large surface areas (up to 486 m² g^?1) and preferential adsorption, and they demonstrated the highest reported methylene blue adsorption capacity (95.1 mg g^?1). Moreover, the uniform distribution of the methacryloyl moiety on the hollow nanospheres endowed them with more potential properties. These results could provide a new benchmark for preparing hollow microspheres by a facile one‐step template‐free method for various applications.     

Preparation and Unique Electrical Behaviors of Monodispersed Hybrid Nanorattles of Metal Nanocores with Hairy Electroactive Polymer Shells

A versatile template‐assisted strategy for the preparation of monodispersed rattle‐type hybrid nanospheres, encapsulating a movable Au nanocore in the hollow cavity of a hairy electroactive polymer shell (Au@air@PTEMA‐g‐P3HT hybrid nanorattles; PTEMA: poly(2‐(thiophen‐3‐yl)ethyl methacrylate; P3HT: poly(3‐hexylthiophene), was reported. The Au@silica core‐shell nanoparticles, prepared by the modified Stöber sol–gel process on Au nanoparticle seeds, were used as templates for the synthesis of Au@silica@PTEMA core‐double shell nanospheres. Subsequent oxidative graft polymerization of 3‐hexylthiophene from the exterior surface of the Au@silica@PTEMA core‐double shell nanospheres allowed the tailoring of surface functionality with electroactive P3HT brushes (Au@silica@PTEMA‐g‐P3HT nanospheres). The Au@air@ PTEMA‐g‐P3HT hybrid nanorattles were obtained after etching of the silica interlayer by HF. The as‐prepared nanorattles were dispersed into an electrically insulating polystyrene matrix and for the first time used to fabricate nonvolatile memory devices. As a result, unique electrical behaviors, including insulator behavior, write‐once‐read‐many‐times and rewritable memory effects, and conductor behavior as well, were observed in the Al/Au@air@PTEMA‐g‐P3HT+PS/ITO (ITO: indium‐tin oxide) sandwich thin‐film devices.     

Structural evolution of mixed micelles due to interchain complexation and segregation investigated by laser light scattering

Polystyrene-b-poly(acrylic acid) (PS-b-PAA) diblock copolymers form micelles in toluene with PAA as the core and PS as the corona. The introduction of poly(methyl methacrylate)-b-poly(ethylene oxide) (PMMA-b-PEO) solution in toluene leads to mixed micelles due to the hydrogen-bonding complexation between PAA and PEO. By using a combination of static and dynamic laser light scattering, we have investigated the evolution of the mixed micelles. Our results revealed that the complexation between PAA and PEO in the core and the segregation between PS and PMMA in the corona as a function of the molar ratio (r) of PEO to PAA manipulate the evolution. At r < approximately 1.0, the mixed micelles hold a spherical structure after a long-time standing. However, at r > approximately 1.0, the average radius of gyration Rg, the average hydrodynamic radius , and the ratio / of the mixed micelles increase with time, whereas the molar mass (Mw) does not change. The facts indicate that the mixed micelle has evolved from a spherical structure to a hyperbranched structure.     

Polymeric nanospheres with tunable sizes,water dispersibility,and thermostability from heating‐enabled micellization of polysulfone‐block‐polyethylene glycol

Polymeric nanospheres with uniform sizes, functional surfaces, and high mechanical strength and thermostability are attracting wide interest in different applications. Here, a new kind of polysulfone micellar spheres with PEGylated surfaces is prepared via directly heating the solution of an amphiphilic block copolymer, polysulfone‐b‐polyethylene glycol (PSF‐b‐PEG). The sizes of the micelles are uniform and tunable between ∼42 and ∼443 nm. TEM characterizations show that the micelles are core‐shell structures with PEG as the corona and PSF as the core. PEG endows the micelles with dispersibility in water and good biocompatibility, while PSF provides the mechanical strength and thermostability. The effects of PEG contents, polymer solution concentrations, solvent types, and heating temperatures are systematically investigated. Furthermore, heat resistance tests show that the micelles are stable at 150–180 °C. These PSF‐b‐PEG micellar spheres are expected to be applied in demanding environmental conditions such as heating involved surface modification process. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 769–777     

Facile strategy for synthesis of silica/polymer hybrid hollow nanoparticles with channels

The silica/polymer hybrid hollow nanoparticles with channels and gatekeepers were successfully fabricated with a facile strategy by using thermoresponsive complex micelles of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) and poly(N-isopropylacrylamide)-b-poly(4-vinylpyridine) (PNIPAM-b-P4VP) as the template. In aqueous solution, the complex micelles (PEG-b-PNIPAM/PNIPAM-b-P4VP) formed with the PNIPAM block as the core and the PEG/P4VP blocks as the mixed shell at 45 °C and pH 4.0. After shell cross-linking by 1,2-bis(2-iodoethoxyl)ethane (BIEE), tetraethylorthosilicate (TEOS) selectively well-deposited on the P4VP block and processed the sol-gel reaction. When the temperature was decreased to 4 °C, the PNIPAM block became swollen and further soluble, and the PEG-b-PNIPAM block copolymer escaped from the hybrid nanoparticles as a result of swelled PNIPAM and weak interaction between PEG and silica at pH 4.0. Therefore, the hybrid hollow silica nanoparticles with inner thermoresponsive PNIPAM as gatekeepers and channels in the silica shell were successfully obtained, which could be used for switchable controlled drug release. In the system, the complex micelles, as a template, could avoid the formation of larger aggregates during the preparation of the hybrid hollow silica nanoparticles. The thermoresponsive core (PNIPAM) could conveniently control the hollow space through the stimuli-responsive phase transition instead of calcination or chemical etching. In the meantime, the channel in the hybrid silica shell could be achieved because of the escape of PEG chains from the hybrid nanoparticles.     

Synthesis of Mesoporous Transition‐Metal Phosphates by Polymeric Micelle Assembly

Mesoporous iron phosphate (FePO₄) was synthesized through assembly of polymeric micelles made of asymmetric triblock co‐polymer (polystyrene‐b‐poly‐2‐vinylpyridine‐b‐ethylene oxide; PS‐PVP‐PEO). The phosphoric acid solution stimulates the formation of micelles with core–shell‐corona architecture. The negatively charged PO₄^3? ions dissolved in the solution strongly interact with the positively charged PVP⁺ units through an electrostatic attraction. Also, the presence of PO₄^3? ions realizes a bridge between the micelle surface and the metal ions. The removal of polymeric template forms the robust framework of iron phosphate with 30 nm pore diameter and 15 nm wall thickness. Our method is applicable to other mesoporous metal phosphates by changing metal sources. The obtained materials were fully characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), N₂ adsorption–desorption, Raman spectroscope, and other techniques.     

A NOVEL METHOD TO PREPARE CROSSLINKED POLYETHYLENEIMINE HOLLOW NANOSPHERES

A novel method to prepare crosslinked polyethyleneimine(CPEI)hollow nanospheres was reported.Uniform silica nanospheres were used as templates,3-aminopropyl trimethoxysilane(APS)was immobilized on the surface of silica nanospheres as couple agent.Aziridine was initiated ring-opening polymerization with the amino groups in APS to form polyethyleneimine(PEI)shell layer.1,4-Butanediol diacrylate was utilized to crosslink PEI polymeric shell.The silica nanospheres in core were etched by hydrofluoric acid to obtain hollow CPEI nanospheres.The hollow nanospheres were characterized by X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),and thermogravimetric analysis(TGA).     

Bioinspired crystallization of CaCO3 coatings on electrospun cellulose acetate fiber scaffolds and corresponding CaCO3 microtube networks

This article describes the mineralization behavior of CaCO(3) crystals on electrospun cellulose acetate (CA) fibers by using poly(acrylic acid) (PAA) as a crystal growth modifier and further templating synthesis of CaCO(3) microtubes. Calcite film coatings composed of nanoneedles can form on the surfaces of CA fibers while maintaining the fibrous and macroporous structures if the concentration of PAA is in a suitable range. In the presence of a suitable concentration of PAA, the acidic PAA molecules will first adsorb onto the surface of CA fibers by the interaction between the OH moieties of CA and the carboxylic groups of PAA, and then the redundant carboxylic groups of PAA can ionically bind Ca(2+) ions on the surfaces of CA fibers, resulting in the local supersaturation of Ca(2+) ions on and near the fiber surface, which can induce the nucleation of CaCO(3) on the CA fibers instead of in bulk solution. Calcite microtube networks on the macroscale can be prepared by the removal of CA fibers after the CA@CaCO(3) composite is treated with acetone. When the CA fiber scaffold is immersed in CaCl(2) solution with an extended incubation time, the first deposited calcite coatings can act as secondary substrate, leading to the formation of smaller calcite mesocrystal fibers. The present work proves that inorganic crystal growth can occur even at an organic interface without the need for commensurability between the lattices of the organic and inorganic counterparts.     

Formation of thin calcium carbonate films with aragonite and vaterite forms coexisting with polyacrylic acids and chitosan membranes

CaCO3 crystallization on a chitosan membrane was studied using diffusion of (NH4)2CO3 vapors into a CaCl2 solution containing differing added amounts of two polyacrylic acids (PAAs) with molecular weights of ca. 2.0 x 10(3) and ca. 4.5 x 10(4). The coexistence of PAA and the chitosan membranes produced thin CaCO3 island crystals, which developed into a continuous CaCO3 film on the membranes. Continuous CaCO3 films consisting of only aragonite formed on the chitosan membranes at the optimum amount of PAA. When the amount of PAA is not optimum, the polymorph of CaCO3 switches from aragonite to vaterite, and the morphology has a tendency to become an isolated island structure. The formation of the aragonite and vaterite island crystals and the appearance of a range of added PAA suitable for their formation are explained by the action of two parallel phenomena: (a) the high concentration of Ca2+ ions in the chitosan membrane vicinity is achieved by the interaction between the -COO- groups of PAA adsorbed by the -NH3+ groups of the chitosan membrane through an electrostatic force and free Ca2+ ions in the CaCl2 solution, which produces the high supersaturation with CaCO3 in the membrane vicinity during CO2 diffusion; (b) PAA, remaining as mobile carboxylic anions in the CaCO3 solution, inhibits the growth of the CaCO3 island crystals by its adsorption. The CaCO3 supersaturation in the membrane vicinity is controlled by regulating the balance of these phenomena, which leads to the formation of the desired CaCO3 polymorph.