Tunable Arrangement of Gold Nanoparticles in Epoxidated Poly(styrene‐block‐butadiene) Diblock Copolymer Matrices

A new approach to synthesize block‐copolymer‐mediated/gold nanoparticle (Au NP) composites is developed. Stable and narrowly distributed Au NPs modified with a 2‐phenylethanethiol ligand are prepared by a two‐phase liquid–liquid method. A new epoxidation of a poly(styrene‐block‐butadiene) diblock copolymer, to form poly(styrene‐block‐vinyl oxirane) (PS‐b‐PBO), is achieved through chemical modification. It is found that the Au NPs disperse well in the PS block segment by partially crosslinking the PBO block segment with poly(ethylene oxide bisamine) (D230), a curing agent. The aggregation of Au NPs leads to a red‐shift of the plasmon absorption with the increase in the D230 content. However, without crosslinking the PBO block segment with D230, Au NPs distributes in both the PS and PBO segments.     

Tunable Morphologies From Bulk Self‐Assemblies of Poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) Triblock Copolymers

Reactive poly(acryloxypropyl triethoxysilane)‐b‐poly(styrene)‐b‐poly(acryloxypropyl triethoxysilane) (PAPTES‐b‐PS‐b‐PAPTES) triblock copolymers are prepared through nitroxide‐mediated polymerization (NMP). The bulk morphologies formed by this class of copolymers cast into films are examined by small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). The films morphology can be tuned from spherical structures to lamellar structures by increasing the volume fraction of PS in the copolymer. Thermal annealing at temperatures above 100 °C provides sufficient PS mobility to improve ordering.     

Small‐Angle Neutron Scattering Study of Onion‐Type Micelles

Onion‐type block copolymer micelles were prepared from polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐PVP) inner micelles in an acidic solution by basifying in the presence of poly(2‐vinylpyridine)‐block‐poly‐(ethylene oxide) (PVP‐b‐PEO). This has the effect of depositing the PVP‐b‐PEO onto the collapsed corona of the PS‐b‐PVP micelle. These core PS‐b‐PVP micelles, the small micelles formed by PVP‐b‐PEO, and the resulting onion micelles were studied by small angle neutron scattering (SANS) techniques. Two recently developed evaluation techniques were employed: 1.Bare‐core approximation, which utilizes the data at larger scattering angles and provided information about the size and polydispersity of the micelle cores. 2. Application of the Pedersen and Gerstenberg micelle model, which utilizes the whole scattering curve. Due to their polyelectrolyte nature, the core micelles had very extended coronas corresponding to rather large statistical segment lengths. The SANS data at large scattering angles for the solution of onion‐type micelles revealed the presence of a significant number of the small PVP‐b‐PEO micelles. The contribution of the small micelles to the total scattering was subtracted and the properties and polydispersities of onion cores and stabilizing PEO coronas were obtained.     

Thin Films of Semifluorinated Block Copolymers Prepared by ATRP

A symmetric diblock copolymer, poly(pentafluorostyrene‐b‐styrene) (PPFS‐b‐PS), is synthesized by atom transfer radical polymerization (ATRP). The behavior of PPFS‐b‐PS thin films on silicon wafers is investigated. Lamellar microdomains oriented parallel to the film surface are formed when the thin films are heated to 220 °C for 24 h, due to preferential interfacial interactions and the low surface energy of the PPFS. An electric field is used to overcome the low surface energy of the fluorinated block and preferential interactions with the substrate so as to force the lamellar microdomains to orient normal to the surface.     

Block Copolymer Micelle Nanotubes by the Solvent‐Annealing‐Induced Nanowetting in Anodic Aluminum Oxide Templates

Block copolymer micelles are generally formed by the self‐assembly of amphiphilic copolymer molecules in aqueous medium. Although different types of block copolymer micelles have been studied, the self‐assembly behavior of block copolymer micelles in confined geometries have been rarely studied. In this work, the fabrication of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) micelle nanotubes in the cylindrical nanopores of anodic aluminum oxide templates using a solvent‐annealing‐assisted wetting method is presented. The PS‐b‐P4VP chains wet the pore walls in the form of micelles when the sample is annealed in the vapor of toluene, a good solvent for PS and a nonsolvent for P4VP. The formation of the PS‐b‐P4VP micelle nanotubes instead of nanorods implies that the micelles wet the nanopores in the complete wetting regime. This study not only contributes to a deeper understanding of the self‐assembly behavior of block polymer micelles in confined geometries, but also provides more possible variations and design freedoms in the application of block copolymer micelles.

     

Functionalized Nanoporous Thin Films From Blends of Block Copolymers and Homopolymers Interacting via Hydrogen Bonding

Blends of poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) copolymers and poly(ethylene oxide) (PEO) homopolymers in which PAA and PEO interact via hydrogen bonds were used as precursors of nanoporous PS thin films with cavities decorated by PAA blocks. The presence of free carboxylic acid groups inside the pores was evidenced by fluorescence spectroscopy after reacting them with a diazomethane functionalized fluorescent dye. These nanoporous thin films were then used as templates for the preparation of dense arrays of silica nanodots.     

Fiber‐Like Micelles from the Crystallization‐Driven Self‐Assembly of Poly(3‐heptylselenophene)‐block‐Polystyrene

The crystallization‐driven self‐assembly (CDSA) of crystalline‐coil polyselenophene diblock copolymers represents a facile approach to nanofibers with distinct optoelectronic properties relative to those of their polythiophene analogs. The synthesis of an asymmetric diblock copolymer with a crystallizable, π‐conjugated poly(3‐heptylselenophene) (P3C7Se) block and an amorphous polystyrene (PS) coblock is described. CDSA was performed in solvents selective for the PS block. Based on transmission electron microscopy (TEM) analysis, P3C7Se₁₈‐b‐PS₁₂₅ formed very long (up to 5 μm), highly aggregated nanofibers in n‐butyl acetate (nBuOAc) whereas shorter (ca. 500 nm) micelles of low polydispersity were obtained in cyclohexane. The micelle core widths in both solvents determined from TEM analysis (≈ 8 nm) were commensurate with fully‐extended P3C7Se₁₈ chains (estimated length = 7.1 nm). Atomic force microscopy (AFM) analysis provided characterization of the micelle cross‐section including the PS corona (overall micelle width ≈ 60 nm). The crystallinity of the micelle cores was probed by UV–vis and photoluminescence (PL) spectroscopy and wide‐angle X‐ray scattering (WAXS).     

One‐Step Approach for the Preparation of Organic‐Inorganic Janus‐Like Particles by Alkalization of Polystyrene‐block‐Poly(2‐vinylpyridine)/FeCl3 Complex Micelles

A novel approach to organic‐inorganic Janus‐like particles based on the alkalization process of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) micelles containing FeCl₃ precursors in the P2VP cores in toluene is presented. It is found that by addition of a small amount of NaOH solution to a solution of the spherical PS‐b‐P2VP/FeCl₃ micelles, organic‐inorganic Janus‐like particles with a produced α‐FeOOH domain on one side and PS‐b‐P2VP block copolymers on the other can be prepared. The Janus‐like nanoparticles obtained by this facile approach may have potential application in biomedical areas.     

Folate‐Conjugated Poly(N‐(2‐hydroxypropyl) methacrylamide)‐block‐Poly(benzyl methacrylate): Synthesis,Self‐Assembly,and Drug Release

Well‐defined amphiphilic diblock copolymers of poly(N‐(2‐hydroxypropyl)methacrylamide)‐block‐poly(benzyl methacrylate) (PHPMA‐b‐PBnMA) are synthesized using reversible addition–fragmentation chain transfer polymerization. The terminal dithiobenzoate groups are converted into carboxylic acids. The copolymers self‐assemble into micelles with a PBnMA core and PHPMA shell. Their mean size is <30 nm, and can be regulated by the length of the hydrophilic chain. The compatibility between the hydrophobic segment and the drug doxorubicin (DOX) affords more interaction of the cores with DOX. Fluorescence spectra are used to determine the critical micelle concentration of the folate‐conjugated amphiphilic block copolymer. Dynamic light scattering measurements reveal the stability of the micelles with or without DOX. Drug release experiments show that the DOX‐loaded micelles are stable under simulated circulation conditions and the DOX can be quickly released under acidic endosome pH.     

A Bifunctional Diblock Copolymer from Consecutive RAFT Polymerizations and its Functionalization

Poly(glycidyl methacrylate)‐block‐poly(4‐vinylbenzyl chloride), or P(GMA)‐b‐P(VBC), is synthesized via consecutive reversible addition‐fragmentation chain transfer (RAFT) polymerizations. Subsequent functionalization via atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and styrene (St) gives rise to two functional brush‐type diblock graft copolymers, P(GMA)‐b‐(P(VBC)‐g‐P(MMA)) and P(GMA)‐b‐(P(VBC)‐g‐PS). These graft copolymers are further functionalized by a ring‐opening reaction of the P(GMA) block with diethylamine (DEA) to produce two diblock copolymer brushes, P(DEAHPMA)‐b‐(P(VBC)‐g‐P(MMA) and P(DEAHPMA)‐b‐(P(VBC)‐g‐PS (Brush‐2A). Single molecules of the copolymers are imaged by atomic force microscopy (AFM). Brush‐2A can be cast into porous membranes with well‐defined micropores from tetrahydrofuran (THF) solutions by phase inversion in an aqueous medium.     

Solution Self‐Assembly of Poly(ferrocenylphenylphosphine)‐block‐polydimethylsiloxane: Formation of Spherical Micelles with an Organometallic Poly(ferrocenylphenylphosphine) Core

The novel organometallic‐inorganic diblock copolymer, poly(ferrocenylphenylphosphine)‐block‐polydimethylsiloxane (PFP‐b‐PDMS), with narrow molecular weight distribution has been synthesized by living anionic polymerization through sequential monomer addition. These block copolymers self‐assemble into “star‐like” spherical micelles in hexane with a dense organometallic PFP core surrounded by a swollen corona of the PDMS chains. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to characterize these micellar aggregates. It was found that the block copolymer micelles have a relatively narrow core size distribution, but an overall broader distribution of hydrodynamic size in hexane. Significantly, the preparation method of the micelle solution was also found to have an influence on the size and size distribution of the resulting micellar structures.     

Role of High‐Molecular‐Weight Homopolymers on Block Copolymer Self‐Assembly: From Morphology Modifier to Template

For block copolymer (BCP)/homopolymer self‐assembly systems, the molecular weight of homopolymers is usually lower than that of BCPs. Herein, the cooperative self‐assembly of polystyrene‐b‐poly(ethylene glycol) (PS‐b‐PEG) BCPs with high‐molecular‐weight polystyrene (PS) homopolymers is reported. The molecular weight of PS homopolymers is 3–63 times that of the PS blocks. Typically, a spherical micelle–vesicle–large sphere morphology transition is observed by increasing the weight fraction of PS homopolymers in the polymer mixtures (f _HP). Dynamic process studies reveal that with adding water to the solution of polymer mixtures in organic solvent, the homopolymers first collapse into globules, and their size increases with f _HP and the molecular weight. Then these PS globules cooperatively self‐assemble with the PS‐b‐PEG BCPs. Depending on their size, these PS globules play different roles in the self‐assembly process. Small PS globules act as morphology modifiers inducing the micelle–vesicle transition, while large PS globules serve as self‐assembly templates for PS‐b‐PEG resulting in large spheres.     

Inversion of Phase Morphology in Polymer‐Blend Thin Films on Glass Substrates

Summary: The phase‐morphology inversion in two blend systems of polystyrene/poly(methyl methacrylate) (PS/PMMA) and polystyrene/poly(ε‐caprolactone) (PS/PCL) has been studied after their thin films were prepared on glass substrates by spin‐coating from a co‐solvent tetrahydrofuran (THF). Phase‐contrast microscopy (PCM), scanning‐electron microscopy (SEM) equipped with energy dispersive X‐ray spectroscopy (EDS), and atomic force microscopy (AFM) were used to obtain information on the morphology of the thin films during heat treatment. It was found that the PMMA‐rich and PCL‐rich phases are always continuous after annealing in either of the PS/PMMA and PS/PCL blend thin films, even though the PMMA and PCL are minor components in the blends. This should result from the better wetting abilities of PMMA and PCL on a glass substrate than PS in the blends. The effect of the viscosity in the evolution of the phase structure was also investigated by changing the molecular weight of PS in the PS/PCL blend thin films. Further more, it is found that the phase‐separation process and the wetting phenomenon of the blends on the glass substrate can be strongly suppressed after adding PS‐block‐PMMA diblock copolymer to the PS/PMMA blend system as a compatibilizer.

Scheme of the longitudinal section of the evolution of the phase structure of a PS:PMMA (70:30 w:w) blend film.     

SET‐LRP Synthesis of Well‐Defined Light‐Responsible Block Copolymer Micelles

Herein, the synthesis of well‐defined light‐sensitive amphiphilic diblock copolymers consisting of UV‐responsive poly(2‐nitrobenzyl acrylate) (PNBA) and hydrophilic poly(ethylene oxide) (PEO) blocks is reported. This is achieved by a single electron transfer living radical polymerization (SET‐LRP) of 2‐nitrobenzyl acrylate monomer initiated by PEO‐containing macroinitiator. Despite several reports on PEO‐b‐PNBA copolymers, this is the first time the PNBA block is synthesized by a controlled radical polymerization leading to the copolymers with low dispersity (Ð = 1.10). In water, the copolymers self‐assemble into well‐defined micelles with a hydrodynamic diameter of 25 nm. Upon irradiation with UV‐light, the PNBA units degrade to hydrophilic poly(acrylate) resulting in disassembly of the micelles. Considering the robustness of the reported synthetic protocol, the prepared polymers represent an interesting platform for the construction of new stimuli‐responsive drug delivery systems.     

A New Approach for the Synthesis of pH‐Responsive Cross‐Linked Micelles from a Poly(glycidyl methacrylate)‐Based Functional Copolymer

An amphiphilic poly(ethylene glycol)methyl ether‐block‐poly(glycidyl methacrylate) (MPEG‐b‐PGMA) diblock copolymer is first synthesized via atom transfer radical polymerization. Epoxy groups of this precursor block copolymer are converted to hydroxyl and tertiary amine residues by reacting with diethyl amine over a ring‐opening reaction. The resulting diblock copolymer is poly(ethylene glycol)methyl ether‐block‐poly(3‐diethylamino‐2‐hydroxypropyl methacrylate) (MPEG‐b‐PDEAHPMA). Micellar solution of this diblock copolymer is prepared at pH 12.0 in aqueous media. At high pH (12.0), core – shell micelles are formed with PDEAHPMA‐core and MPEG‐shell. PDEAHPMA blocks have both hydroxyl and tertiary amine groups that provide reactivity against divinyl sulfone (DVS) and a response to solution pH, respectively. Cross‐linking of hydroxyl groups of PDEAHPMA chains in the micelle core is successfully achieved by adding DVS. At pH 2.0, the DEAHPMA‐core of core cross‐linked (CCL) micelles becomes protonated and hence swelling is observed. The effect of varying the DVS concentrations is also studied. The micelle formation of diblock copolymer and its response to solution pH are investigated by using surface tensiometer, ¹H NMR spectroscopy, and dynamic light scattering (DLS) techniques. CCL micellar structure and its response to solution conditions are investigated with transmission electron microscopy and DLS studies, respectively.

     

A Novel Crystallization Scheme in Poly[styrene‐block‐(ferrocenyl dimethylsilane)] Diblock Copolymers

Isothermal crystallization of the poly(ferrocenyl dimethylsilane) (PFDMS) segments in a poly[styrene‐block‐(ferrocenyl dimethylsilane)] (PS‐b‐PFDMS) diblock copolymer of lamellar micro‐morphology has been investigated. The PFDMS is shown to crystallize in a confined and grain‐by‐grain fashion. Here a ‘grain’ is defined as an ensemble of stacked lamellae wherein the PFDMS crystallization spreads quickly but stops at its surroundings. Such crystallization propagates not only along the PFDMS lamellae but across the amorphous PS layers as well. We suggest that conformational changes in the PS as induced by the PFDMS crystallization (‘squeezing transfer’) are responsible for the latter pathway of the crystallization's spread.

     

Gold nanoparticles with a monolayer of doxorubicin-conjugated amphiphilic block copolymer for tumor-targeted drug delivery

Gold (Au) nanoparticles (NPs) stabilized with a monolayer of folate-conjugated poly(l-aspartate-doxorubicin)-b-poly(ethylene glycol) copolymer (Au-P(LA-DOX)-b-PEG-OH/FA) was synthesized as a tumor-targeted drug delivery carrier. The Au-P(LA-DOX)-b-PEG-OH/FA NPs consist of an Au core, a hydrophobic poly(l-aspartate-doxorubicin) (P(LA-DOX)) inner shell, and a hydrophilic poly(ethylene glycol) and folate-conjugated poly(ethylene glycol) outer shell (PEG-OH/FA). The anticancer drug, doxorubicin (DOX), was covalently conjugated onto the hydrophobic inner shell by acid-cleavable hydrazone linkage. The DOX loading level was determined to be 17 wt%. The Au-P(LA-DOX)-b-PEG-OH/FA NPs formed stable unimolecular micelles in aqueous solution. The size of the Au-P(LA-DOX)-b-PEG-OH/FA micelles were determined as 24–52 and 10–25 nm by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The conjugated DOX was released from the Au-P(LA-DOX)-b-PEG-OH/FA micelles much more rapidly at pH 5.3 and 6.6 than at pH 7.4, which is a desirable characteristic for tumor-targeted drug delivery. Cellular uptake of the Au-P(LA-DOX)-b-PEG-OH/FA micelles facilitated by the folate-receptor-mediated endocytosis process was higher than that of the micelles without folate. This was consistent with the higher cytotoxicity observed with the Au-P(LA-DOX)-b-PEG-OH/FA micelles against the 4T1 mouse mammary carcinoma cell line. These results suggest that Au-P(LA-DOX)-b-PEG-OH/FA NPs could be used as a carrier with pH-triggered drug releasing properties for tumor-targeted drug delivery.     

Transforming the Self‐Assembled Structures of Diblock Copolymer/POSS Nanoparticle Composites Through Complementary Multiple Hydrogen Bonding Interactions

Well‐defined self‐assembled structures are obtained in the form of block copolymer (BCP) nanocomposites, prepared by blending octuply adenine (A)‐functionalized polyhedral oligomeric silsesquioxane (OBA‐POSS) nanoparticles (NPs) with a thymine (T)‐containing BCP (PS‐b‐PVBT); these nanocomposites are stabilized through complementary multiple hydrogen bonding interactions between the A and T units. A transition from one ordered morphology to another occurs upon increasing the content of OBA‐POSS NPs in the PS‐b‐PVBT diblock copolymer, namely lamellar structures at relatively low OBA‐POSS NP contents (<25 wt%) and cylindrical structures at higher OBA‐POSS NP contents (>25 wt%), with concomitant variations in the effective interaction parameter and the overall volume fractions of the two microphase‐separated domains.

     

Controlled synthesis and solution behavior of macrocyclic poly[(styrene)‐b‐(ethylene oxide)] copolymers

A series of cyclic poly[(styrene)‐b‐(ethylene oxide)] diblock copolymers 4 (1.5 kg/mol < M_n < 1.1 kg/mol) with narrow molecular weight distributions (I ≤ 1.12) have been synthesized. They were obtained by intramolecular cyclization of linear α‐diethyl acetal‐ω‐styrenyl poly(styrene ethylene oxide) 3 , under high dilution conditions. The use of well‐defined linear precursors in association with a cyclization process based on an unimolecular end‐to‐end coupling reaction allows the formation of macrocyclic diblocks in high yield (more than 90%). The structural characterization and the solution behavior of both the linear and cyclic amphipathic diblock copolymers have been investigated by means of NMR, size exclusion chromatography, and viscosimetry.     

Synthesis of Novel Linear PEO‐b‐PS‐b‐PCL Triblock Copolymers by the Combination of ATRP,ROP, and a Click Reaction

A new strategy to synthesize a series of well‐defined amphiphilic PEO‐b‐PS‐b‐PCL block copolymers is presented. First, bromine‐terminated diblock copolymers PEO‐b‐PS‐Br are prepared by ATRP of styrene, and converted into azido‐terminated PEO‐b‐PS‐N₃ diblock copolymers. Then propargyl‐terminated PCL is prepared by ROP of ε‐caprolactone. The PEO‐b‐PS‐b‐PCL triblock copolymers with from 1.62 × 10⁴ to 1.96 × 10⁴ and a narrow PDI from 1.09 to 1.19 are finally synthesized from these precursors. The structures of these triblock copolymers and their precursors have been characterized by NMR, IR, and GPC analysis.