Functionalization of Gold and Silicon Surfaces by Copolymer Brushes Using Surface‐Initiated ATRP

Surface‐initiated ATRP was used for step‐by‐step growth of poly(butyl methacrylate)‐co‐poly(2,2‐dimethylaminoethyl methacrylate) (PBMA‐co‐PDMAEMA) brushes from gold and silicon substrates. A one‐step procedure was found to have high efficiency for initiator anchoring. The polymer brushes were characterized in situ by contact angle measurements, ellipsometry, and X‐ray photoelectron spectroscopy (XPS). Detachment of the polymer brushes from both substrates allowed an exact determination of molecular weight and polydispersity indexes given by GPC. ¹H NMR confirmed the chemical structure of the detached brushes. Comparison of theoretical predictions and experimental data showed that the first PBMA block had a folded conformation while copolymerization of the second DMAEMA induced stretching of the brushes.

     

Double Hydrophilic Block Copolymer Self‐Assembly in Aqueous Solution

Self‐assembly of double hydrophilic block copolymers (DHBCs) in water is an emerging area of research. The self‐assembly process can be derived from aqueous two‐phase systems that are composed of hydrophilic homopolymers at elevated concentration. Consecutively, DHBCs form self‐assembled structures like micelles, vesicles, or particles at high concentrations in water and without the use of external triggers that would change solubility of individual blocks. Careful choice of the two hydrophilic blocks and design of the polymer structure allows formation of self‐assembled structures with high efficiency. The present contribution highlights recent research in the area of DHBC self‐assembly, including the polymer types employed and strategies for crosslinking of the self‐assembled structures. Moreover, an overview of aqueous multiphase systems and theoretical considerations of DHBC self‐assembly are presented, as well as an outlook regarding potential future applications in areas such as the biomedical field.     

Self‐Assembly of Carbon Nanotubes Modified by Amphiphilic Block Polymers in Selective Solvent

Block copolymers of polystyrene and poly(tert‐butyl methyacrylate) were prepared by ATRP. Halogen atoms at the chain ends were transformed into azide groups to obtain  N₃ terminated block copolymers, which were connected to the surface of multi‐walled carbon nanotubes (MWNTs) by reacting  N₃ with MWNT's surface. Amphiphilic diblock copolymer modified MWNTs were obtained after PtBMA blocks were hydrolyzed to polymethyacrylic acid (PMAA). Results showed that the amphiphilic diblock copolymer was grafted onto MWNTs by covalent bonds. TEM showed that they formed self‐assembly structures by hydrophilic/hydrophobic interaction in good solvents. As the block length of PMAA increased, the self‐assembly structures of amphiphilic MWNTs became increasingly ordered and uniform.

     

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.     

Two Non‐covalent Methods to Decorate Nanoparticles with Block Copolymers

The physical adsorption of block copolymers is a simple and reliable approach to functionalize the surface of organic or inorganic nanoparticles. This article presents two novel methods of particle coating with block copolymers that may apply to various aqueous colloidal dispersions. The first method relies on the use of charged block copolymers having two adsorbing blocks, which can adopt a typical anchor‐buoy conformation at the particle surface when proper conditions are used. The second approach consists of self‐assembling a bilayer of amphiphilic block copolymers around charged nanoparticles. In both cases, a special emphasis is placed on the process used to control and orient the molecular interactions between the copolymer and the particles.

     

Self‐Assembly of Globular‐Protein‐Containing Block Copolymers

Self‐assembly has emerged as a powerful approach to control nanostructure in materials containing globular proteins, both through templated self‐assembly and direct self‐assembly of globular protein‐polymer conjugates or fusion proteins. The folded structures of globular proteins that are critical to their function introduce complex shapes and interactions into block copolymers that significantly alter the physics of self‐assembly. This article discusses the different methods for controlling the nanostructure of globular proteins using block copolymers, highlighting efforts at understanding the physics of self‐assembly in concentrated solution and solid‐state bioconjugate copolymers.

     

Poly(ethylene imine)‐Triggered Morphological Change of Anisotropic Micelles from Direct Aqueous Self‐Assembly of an Amphiphilic Diblock Copolymer

In this paper, “star anise”‐like anisotropic micelle (AM) from direct aqueous self‐assembly of poly(ethylene oxide)‐block‐poly(p‐dioxanone) amphiphilic diblock copolymer is presented. By adding poly(ethylene imine) (PEI), the AM shows morphological change from “star anise” to swollen sphere. The mechanism of PEI‐triggered morphological transition involving complexation and weakening of crystallizability is revealed.

     

Multivalent (Nitrilotriacetic Acid)‐End‐Functionalized Polystyrenes by ATRP and Their Self‐Assembly

The synthesis of tri‐(nitrilotriacetic acid) (NTA)‐end‐functionalized polystyrenes using an initiator containing tert‐butyl protected NTA moieties, by atom transfer radical polymerization (ATRP) of styrene is described. First, a suitable ATRP initiator is prepared and subsequently characterized by ¹H and ¹³C NMR spectroscopy, gel‐permeation chromatography (GPC), and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) mass spectro­scopy. The structures of the tri‐NTA‐end‐functionalized polystyrenes (tri‐NTA‐PS) are confirmed by ¹H and ¹³C NMR spectroscopy. Tri‐NTA‐PS itself produces self‐assembled spherical aggregates with ≈40–60 nm diameters in water/THF, whereas nickel‐complexed tri‐NTA‐PS produces spherical core–shell hybrid aggregates with ≈90–115 nm diameters with His‐tagged GFP in water/DMF (DMF 4 vol%), as confirmed by transmission electron microscopy and dynamic light scattering measurements.

     

Solution Self‐Assembly of Core‐Labeled Block Random‐Copolymers Prepared by Ring Opening Metathesis Polymerization

Herein, the synthesis of block random‐copolymers via ring opening metathesis polymerization (ROMP) is presented. A random‐copolymer of norbornene dimethyl ester with different xanthen‐functionalized norbornene derivatives was used as a hydrophobic block while, the hydrophilic part was built from an ethylene glycol‐substituted monomer. The self‐association of these block random‐copolymers in MeOH was strongly influenced by the ionization state of the dye molecules, as shown by a combination of UV–Vis absorption and dynamic light scattering measurements. Aggregate sizes were significantly smaller for samples with charged dye molecules in the core of the aggregate. These findings were attributed to ion pair formation of the charged dye molecules and the according counter ions, thus, inducing strongly attractive dipole–dipole interactions. The optical properties of the dyes under investigation, however, were preserved within the polymer aggregates.

     

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.     

Free‐Standing Films of Semifluorinated Block Copolymer Brushes from Layer‐by‐Layer Polyelectrolyte Macroinitiators

Free‐standing semifluorinated polymer brushes from layer‐by‐layer (LbL) macroinitiators are demonstrated. LbL deposition of macroinitiators is followed by surface‐initiated atom transfer radical polymerization (SI‐ATRP). Increasing the number of LbL macroinitiator layers increases grafting density and thickness. The SI‐ATRP is conducted by first polymerizing a block of polystyrene followed by the semifluorinated poly‐2,2,2‐trifluoroethyl methacrylate block. Solvent selective response is investigated by AFM imaging and water contact angle measurements. Specifically, the solvent response of the semifluorinated block copolymer brushes exhibits alternate selectivity to cyclohexane and trifluorotoluene. Solvent responsive free‐standing films are also demonstrated.

     

Poly(hydroxyl propyl methacrylate)‐b‐Poly(oligo ethylene glycol methacrylate) Thermoresponsive Block Copolymers by RAFT Polymerization

Thermoresponsive amphiphilic poly(hydroxyl propyl methacrylate)‐b‐poly(oligo ethylene glycol methacrylate) block copolymers (PHPMA‐b‐POEGMA) are synthesized by RAFT polymerization, with different compositions and molecular weights. The copolymers are molecularly characterized by size‐exclusion chromophotography, and ¹H NMR spectroscopy. Dynamic light scattering (DLS) and static light scattering (SLS) experiments in aqueous solutions show that the copolymers respond to temperature variations via formation of self‐organized nanoscale aggregates. Aggregate structural characteristics depend on copolymer composition, molecular weight, and ionic strength of the solution. Fluorescence spectroscopy experiments confirm the presence of less hydrophilic domains within the aggregates at higher temperatures. The thermoresponsive behavior of the PHPMA‐b‐POEGMA block copolymers is attributed to the particular solubility characteristics of the hydrophilic, water insoluble PHPMA block that are modulated by the presence of the water soluble POEGMA block.     

Synthesis and Self‐Assembly of Functionalized Cyclooctene Block Copolymers via ROMP

A novel block copolymer consisted of MACIT and HCO segments was synthesized via ROMP in the ionic liquid [bmim][PF₆] with good control over the polymerization process. The molecular weight of the block copolymer was estimated by ¹H NMR, and the molar composition ratio of repeating units in the MACIT block to those in the HCO block was 100:120 (120:120 in feed). The micellar characterization was carried out by DLS, AFM, and TEM. The hydrodynamic diameter of the micelles, measured by DLS, was 129 ± 0.09 nm with a narrow distribution (PDI = 0.034). The TEM image showed spherical micelles.

     

Dot Nanopattern Self‐Assembled from Rod‐Coil Block Copolymer on Substrate

Nanoscale dot patterns are important in various fields. However, it is still a challenge to fabricate ordered nanopatterns on substrates through a polymer self‐assembly approach. In this work, it is reported that polypeptide‐based rod‐coil block copolymers can self‐assemble into surface micelles on substrates, thus forming dot nanopatterns. The size of the surface micelles is readily adjusted by the degree of the polymerization of the block copolymers. It is found that most of the surface micelles are in a sixfold coordinated lattice, indicating an ordered array feature. Defects such as fivefold coordination arrays and sevenfold coordination arrays are also observed, which are derived from the nonuniform size of the micelles and the existence of nonspherical micelles. The experimental findings are well modelled by dissipative particle dynamics theoretical simulations, and the simulations provide more detailed information, such as the packing manner of the polymer chain in the surface micelles.     

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.     

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

Polyisoprene‐block‐poly(ferrocenylmethylsilane) (PI‐b‐PFMS) copolymers, containing the atactic but semicrystalline PFMS block, have been prepared by sequential anionic polymerization of isoprene and methyl[1]silaferrocenophane. The reaction to form the metalloblock is not living in nature, but still enabled three block copolymers to be prepared (PI₃₅‐b‐PFMS₅, PI₂₀₀‐b‐PFMS₁₀, and PI₂₄₇‐b‐PFMS₂₃) with relative narrow molar mass distributions (polydispersity < 1.3). The self‐assembly of all three materials was studied in PI selective n‐alkanes and found to afford lenticular platelets, tapered cylindrical micelles, and regular cylinders, as the length of the PFMS block increased. PI₂₀₀‐b‐PFMS₁₀ micelles could be increased in length by self‐seeding a sample of short micelles at temperatures of 90 °C and above; however, this process also resulted in an increase in width. Addition of a solution of PI₂₄₇‐b‐PFMS₂₃ copolymer to preformed seed micelles also resulted in an increase in length, although growth is not linearly related to the amount of copolymer added beyond ≈600 nm.

     

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).     

Double‐Gyroid Morphology of a Polystyrene‐block‐Poly(ferrocenylethylmethylsilane) Diblock Copolymer: A Route to Ordered Bicontinuous Nanoscale Architectures

A polystyrene‐block‐poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double‐gyroid morphology when self‐assembled in the solid state, has been prepared with a PFEMS volume fraction ?_PFEMS = 0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal‐containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self‐assembly of the diblock copolymer in the bulk showed a stable, double‐gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia d space group.

     

Self‐Assembled Structures in Block Copolymer Blends: SAXS,SANS and TEM Study

Phenomena associated with the order‐disorder transition, microdomain morphology and phase behavior of a deuterated block copolymer (BCP) blend I / II (where I is dPS‐block‐dPMMA and II is dPS‐block‐PI) were studied by SAXS, SANS and TEM. The studied, almost symmetric, copolymers differ essentially in microdomain morphology. One of them ( I ) is in disordered microdomain state, while the other ( II ) displays lamellar morphology at ordinary temperatures. Self‐assembled structures in blends were investigated as a function of concentration of the added microphase‐separated copolymer and temperature. The ODT positions were located in all the blends, the position of ODT depending only slightly on the concentration of the ordered copolymer. A systematic increase in long period D of the lamellar phase is observed with the growing content of the disordered copolymer. The evaluation of TEM shows the gradual diminishing of macrophase separated regions of disordered copolymer I with growing content of the lamellar copolymer II .

     

Poly(2‐vinylnaphthalene)‐block‐poly(acrylic acid) Block Copolymer: Self‐Assembled Pattern Formation,Alignment, and Transfer into Silicon via Plasma Etching

P2VN‐b‐PAA is a novel diblock copolymer which has potential as a self‐assembled nanoscale patterning material. Thin spin cast P2VN‐b‐PAA films rapidly reorganize to vertical lamellar with exposure to acetone vapor. P2VN‐b‐PAA lamellar morphology was aligned by electric field under acetone vapor at a significantly faster rate and at lower electric field strengths than other polymer systems. Observed dry etching selectivity for P2VN to PAA were comparatively high for a variety of etch gases, consistent with estimations from Ohnishi and ring parameters. Block copolymer self assembled patterns were transferred to silicon via two‐step CF₄ and SF₆ etching.