Block Copolymer Brushes Research Articles

Thermoresponsive anionic block copolymer brushes with a strongly anionic bottom segment for effective interactions with biomolecules

Thermoresponsive anionic block copolymer brushes were prepared on silica bead surfaces by multistep surface-initiated atom-transfer radical polymerization. The anionic properties of the prepared brushes changed with temperature changes.

Morphological and mechanical behavior of montmorillonite grafted block copolymer brushes

ABSTRACTHere we report the phase behavior of a family of montmorillonite (MMT) block copolymer brushes (MBBs), a novel class of polymer nanocomposites. MBBs are comprised of discrete MMT platelets encapsulated with block copolymer brushes. These MBBs were synthesized via surface‐initiated atom transfer radical polymerization using halogenated alkylammonium surfactants to localize initiation sites on the clay surfaces. Two styreninc MBB systems—poly(styrene‐b‐n‐butyl acrylate) and poly(styrene‐b‐t‐butyl acrylate)—were prepared varying the composition and total 80–250 kDa. MBB materials were compared with their non‐clay bulk block copolymer counterparts via electron microscopy and a host of mechanical tests in both the solid and melt states. Notably, MBBs have similar melt‐state rheological properties compared to neat block copolymers and are thus amenable to current processing techniques. MBBs were found to self‐assemble into single grain morphologies across incredibly large areas (>3 μm) which resulted in extremely well‐ordered, defect‐free lamellar structures with applications in microelectronics. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 353–361

Cylindrical brush copolymer bearing polystyrene-block-poly(ε-caprolactone) diblock side chains: Synthesis via a sequential grafting-from polymerization approach and its formation of fibrillar nanophases in epoxy thermosets

In this contribution, we reported the synthesis of a core-shell cylindrical brush copolymer with poly(2-hydroxyethyl methacrylate) (PHEMA) backbone and polystyrene-block-poly(ε-caprolactone) (PS-b-PCL) diblock side chains [denoted PHEMA-g-(PS-b-PCL)n] with the combination of atom transfer radical polymerization, the Huisgen 1,3-dipolar cycloaddition between azido and alkynyl groups and the ring-opening polymerization via a sequential “grafting from” polymerization approach. The cylindrical brush block copolymer was characterized by means of 1H nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). It is found that the fibrillar nanophases were formed with the length of about 400 nm and the diameter of about 15 nm via reaction-induced microphase separation mechanism while this cylindrical block copolymer brush was incorporated into epoxy thermosets. The fibrillar nanophases were characterized by means of transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). The formation of the fibrillar nanophases was interpreted on the basis of the constraint of cylindrical brush architecture of copolymer on reaction-induced microphase separation behavior.

Brush polymer ion gels

ABSTRACTThe structure, rheological response, and ionic conductivity of ABA brush block copolymer (BBCP) ion gels containing 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMI][TFSI]) at polymer concentrations spanning 5‐50 wt % (Φgel) were studied by small angle X‐ray scattering, dynamic mechanical analysis, and AC impedance spectroscopy. Application of a hard sphere form factor and Percus‐Yevick structure factor reveals trends in gel micellar structure as a function of BBCP molecular weight, A block volume fraction (ΦA), and Φgel. Viscoelastic properties are strongly dependent on end‐block molar mass, with storage moduli ≤103 Pa at 25 °C. Impedance measurements reveal near liquid‐like dynamics in the matrix phase as evidenced by conductivities near 1 mS/cm at 25 °C that decrease with increasing Φgel and ΦA. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 292–300

Large-Volume Self-Organization of Polymer/Nanoparticle Hybrids with Millimeter-Scale Grain Sizes Using Brush Block Copolymers.

We report that an exceptionally large volume of highly ordered arrays (single grains) on the order of millimeters in scale can be rapidly created through a unique innate guiding mechanism of brush block copolymers (BBCPs). The grain volume is over 10(9) times larger than that of typical self-assembled linear BCPs (LBCPs). The use of strong interactions between nanoparticles (NPs) and BBCPs enables high loadings of functional materials, up to 76 wt % (46 vol %) in the target domain, while maintaining excellent long-range order. Overall, this work provides a simple method to precisely control the spatial orientation of functionalities at nanometer length scales over macroscopic volumes, thereby enabling the production of hybrid materials for many important applications.

Preparation of Nitroxide Polymer Brushes and Their Applications in the Synthesis of an Epoxidized Soybean Oil Acrylate as an Inhibitor

With polystyrene (PS) microspheres as the matrix and glycidyl methacrylate (GMA) and methyl methacrylate (MMA) as monomers, two polymer brushes including a homopolymer brush of PS–PGMA and a block copolymer brush of PS–P(MMA-b-GMA) were synthesized via surface-initiated activators regenerated by electron-transfer atom-transfer radical polymerization. Furthermore, a ring-opening reaction between epoxy groups in these brushes and hydroxyl groups in 4-hydroxy-2,2,6,6-tetramethylpiperidinooxy (4-OH-TEMPO) was carried out, consequently obtaining nitroxide polymer brushes of PS–PGMA–TEMPO and PS–P(MMA-b-GMA)–TEMPO. The obtained nitroxide polymer brushes were characterized using a variety of analytical techniques. The nitroxide polymer brush as a supported inhibitor was successfully applied in the synthesis of epoxidized soybean oil acrylate (AESO), showing a good inhibiting effect and easy recyclability. Then the supported TEMPO inhibitor (nitroxide polymer brush) and free TEMPO inhibitor (4-OH-TEMPO) were comb...

Thermally Tunable Metallodielectric Photonic Crystals from the Self‐Assembly of Brush Block Copolymers and Gold Nanoparticles

A robust strategy for the rapid and scalable fabrication of well-ordered metallodielectric 1D photonic crystals through the self-assembly of brush block copolymers and gold nanoparticles is demonstrated. The optical properties of the photonic crystals containing ultrahigh loadings of the gold nanoparticles are thermally tunable through the creation of a network structure of the nanoparticles.

Patchy micelles based on coassembly of block copolymer chains and block copolymer brushes on silica particles.

Patchy particles are a type of colloidal particles with one or more well-defined patches on the surfaces. The patchy particles with multiple compositions and functionalities have found wide applications from the fundamental studies to practical uses. In this research patchy micelles with thiol groups in the patches were prepared based on coassembly of free block copolymer chains and block copolymer brushes on silica particles. Thiol-terminated and cyanoisopropyl-capped polystyrene-block-poly(N-isopropylacrylamide) block copolymers (PS-b-PNIPAM-SH and PS-b-PNIPAM-CIP) were synthesized by reversible addition-fragmentation chain transfer polymerization and chemical modifications. Pyridyl disulfide-functionalized silica particles (SiO2-SS-Py) were prepared by four-step surface chemical reactions. PS-b-PNIPAM brushes on silica particles were prepared by thiol-disulfide exchange reaction between PS-b-PNIPAM-SH and SiO2-SS-Py. Surface micelles on silica particles were prepared by coassembly of PS-b-PNIPAM-CIP and block copolymer brushes. Upon cleavage of the surface micelles from silica particles, patchy micelles with thiol groups in the patches were obtained. Dynamic light scattering, transmission electron microscopy, and zeta-potential measurements demonstrate the preparation of patchy micelles. Gold nanoparticles can be anchored onto the patchy micelles through S-Au bonds, and asymmetric hybrid structures are formed. The thiol groups can be oxidized to disulfides, which results in directional assembly of the patchy micelles. The self-assembly behavior of the patchy micelles was studied experimentally and by computer simulation.

Controlled supramolecular self-assembly of large nanoparticles in amphiphilic brush block copolymers.

To date the self-assembly of ordered metal nanoparticle (NP)/block copolymer hybrid materials has been limited to NPs with core diameters (D(core)) of less than 10 nm, which represents only a very small fraction of NPs with attractive size-dependent physical properties. Here this limitation has been circumvented using amphiphilic brush block copolymers as templates for the self-assembly of ordered, periodic hybrid materials containing large NPs beyond 10 nm. Gold NPs (D(core) = 15.8 ± 1.3 nm) bearing poly(4-vinylphenol) ligands were selectively incorporated within the hydrophilic domains of a phase-separated (polynorbornene-g-polystyrene)-b-(polynorbornene-g-poly(ethylene oxide)) copolymer via hydrogen bonding between the phenol groups on gold and the PEO side chains of the brush block copolymer. Well-ordered NP arrays with an inverse cylindrical morphology were readily generated through an NP-driven order-order transition of the brush block copolymer.

Cleavage of diblock copolymer brushes in a selective solvent and fusion of vesicles self-assembled by pinned micelles.

Lipid membrane fusion is a fundamental process in nature. In the fusion process two distinct bilayers merge the hydrophobic layers, and an interconnected structure is produced. In this research, the fusion of polymer membrane self-assembled by cleaved pinned micelles is investigated. Disulfide-tethered poly(tert-butyl acrylate-block-styrene) diblock copolymer brushes on the surfaces of silica particles were prepared by the "grafting to" or "grafting from" method. In acetone, the diblock copolymer brushes self-assemble into pinned micelles. Upon cleavage from the surfaces of the silica particles with n-tributylphosphine, the pinned micelles self-assemble into vesicles. In the meanwhile, thiol groups at the ends of the block copolymer brushes were produced in the cleavage reaction. Because of the oxidation of the thiol groups and the formation of the disulfide bonds, the vesicle structures are fused into bigger hollow structures and fiber-like structures. The further fusion of the fiber-like structures results in precipitation of the polymer from the solution.

Thermo- and glucose-responsive micelles self-assembled from phenylborate ester-containing brush block copolymer for controlled release of insulin at physiological pH

The micelles present temperature- and glucose-responses, and can achieve the controlled release of insulin by altering temperature and glucose concentration.

Improving brush polymer infrared one-dimensional photonic crystals via linear polymer additives.

Brush block copolymers (BBCPs) enable the rapid fabrication of self-assembled one-dimensional photonic crystals with photonic band gaps that are tunable in the UV-vis-IR, where the peak wavelength of reflection scales with the molecular weight of the BBCPs. Due to the difficulty in synthesizing very large BBCPs, the fidelity of the assembled lamellar nanostructures drastically erodes as the domains become large enough to reflect IR light, severely limiting their performance as optical filters. To overcome this challenge, short linear homopolymers are used to swell the arrays to ∼180% of the initial domain spacing, allowing for photonic band gaps up to ∼1410 nm without significant opacity in the visible, demonstrating improved ordering of the arrays. Additionally, blending BBCPs with random copolymers enables functional groups to be incorporated into the BBCP array without attaching them directly to the BBCPs. The addition of short linear polymers to the BBCP arrays thus offers a facile means of improving the self-assembly and optical properties of these materials, as well as adding a route to achieving films with greater functionality and tailorability, without the need to develop or optimize the processing conditions for each new brush polymer synthesized.

Stereoblock-like Brush Copolymers Consisting of Poly(l-lactide) and Poly(d-lactide) Side Chains along Poly(norbornene) Backbone: Synthesis, Stereocomplex Formation, and Structure–Property Relationship

Random and block copolymerizations of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) macromonomers having an exo-norbornene group at the α- or ω-chain end (D/L ratio = 1/1, Mn = ca. 5000 g mol–1) were performed via ring-opening metathesis polymerization to produce the brush random and block copolymers consisting of parallel or antiparallel aligned PLLA and PDLA side chains on a poly(norbornene) backbone. The molecular weight and polydispersity index of the brush copolymers were in the range of 40 300–458 000 g mol–1 and 1.03–1.14, respectively. Despite such high molecular weights, these brush copolymers formed a stereocomplex without homochiral crystallization. The melting temperature (Tm) and crystallinity (X) of the resulting stereocomplex varied depending on the backbone length, relative chain direction, and distribution of the PLLA/PDLA side chains. The parallel brush copolymers showed significantly higher Tm and X values than the antiparallel ones.

Gradient Crystallization-Driven Self-Assembly: Cylindrical Micelles with “Patchy” Segmented Coronas via the Coassembly of Linear and Brush Block Copolymers

Block copolymers (BCPs) with a short crystallizable poly(ferrocenyldimethylsilane) (PFS) core-forming block self-assemble in selective solvents to afford cylindrical micelles, the ends of which are active to further growth via a process termed living crystallization-driven self-assembly (CDSA). We now report studies of the CDSA of a series of crystalline-brush BCPs with C6 (BCP(6)), C12 (BCP(12)), and C18 (BCP(18)) n-alkyl branches that were prepared by the thiol-ene functionalization of PFS-b-PMVS (PMVS = poly(methylvinylsiloxane)). Although the increased n-alkyl brush length of BCP(12) and BCP(18) hindered micelle growth, the increased intercoronal chain repulsion could be alleviated by their coassembly with linear PFS-b-PMVS. When the coassembly was initiated by short cylindrical seed micelles, monodisperse block comicelles of controllable length with "patchy" coronal nanodomains were accessible. TEM and AFM analysis of micelles prepared from BCP(18) and PFS-b-PMVS were found to provide complementary characterization in that the OsO4-stained PMVS coronal domains were observed by TEM, whereas the brush block domains of BCP(18) (which displayed greater height) were detected by tapping mode AFM. The results showed that the coassembly afforded a gradient structure, with an initial bias for the growth of the linear BCP over that of the more sterically demanding brush BCP, which was gradually reversed as the linear material was consumed. This represents the first example of living gradient CDSA, a process reminiscent of a living covalent gradient copolymerization of two different monomers. Although other possible explanations exist, simulations based on a statistical model indicated that the coronal nanodomains detected likely result from a segmented, gradient comicelle architecture that arises as a consequence of: (i) different rates of addition of BCP unimer to the micelle termini, and (ii) a cumulative effect resulting from steric hindrance associated with the brush block.

Photodegradable neutral-cationic brush block copolymers for nonviral gene delivery.

We report on the fabrication of a photodegradable gene-delivery vector based on PEO-b-P(GMA-g-PDMAEMA) neutral-cationic brush block copolymers that possess cationic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) brushes for DNA compaction, poly(ethylene oxide) (PEO) as a hydrophilic block, and poly(glycidyl methacrylate) (PGMA) as the backbone. The PEO-b-P(GMA-g-PDMAEMA) copolymers were synthesized through the combination of reversible addition-fragmentation transfer (RAFT) polymerization and postmodification. A photocleavable PEO-based macroRAFT agent was first synthesized; next, the PEO-b-PGMA block copolymer was prepared by RAFT polymerization of GMA; this was followed by a click reaction to introduce the RAFT initiators on the side chains of the PGMA block; then, RAFT polymerization of DMAEMA afforded the PEO-b-P(GMA-g-PDMAEMA) copolymer. The obtained neutral-cationic brush block copolymer could effectively complex plasmid DNA (pDNA) into nanoparticles at an N/P ratio (i.e., the number of nitrogen residues per DNA phosphate) of 4. Upon UV irradiation, pDNA could be released owing to cleavage of the pDNA-binding cationic PDMAEMA side chains as well as the nitrobenzyl ester linkages at the diblock junction point. In addition, in vitro gene transfection results demonstrated that the polyplexes could be effectively internalized by cells with good transfection efficiency, and the UV irradiation protocol could considerably enhance the efficiency of gene transfection.

Self-assembled nanoparticles from thiol functionalized liquid crystalline brush block copolymers for dual encapsulation of doxorubicin and gold nanoparticles

A facile approach to synthesize new thiol functionalized liquid crystalline brush block copolymers for dual encapsulation of an anticancer drug and inorganic nanoparticles.

Tumor‐Targeted Redox‐Responsive Nonviral Gene Delivery Nanocarriers Based on Neutral‐Cationic Brush Block Copolymers

Novel neutral-cationic brush block copolymer, poly[oligo(ethylene glycol) monomethyl ether methacrylate-co-folic acid methacrylate]-b-poly[2-(2-(2-(2-bromo-2-methylpropanoyloxy)-ethyl) disulfanyl) ethyl methacrylate-g-2-dimethylaminoethyl methacrylate], P(OEGMA-co-FAMA)-b-P(BSSMA-g-PDMAEMA), is synthesized via consecutive controlled radical polymerizations. Containing disulfide linkages bridging backbone and side chains in the cationic brush block and cancer cell-targeting ligands (folic acid) in the neutral hydrophilic block, the diblock copolymer is employed as a tumor-targeted redox-responsive degradable nonviral gene delivery vector. P(OEGMA-co-FAMA)-b-P(BSSMA-g-PDMAEMA) brush block copolymers can condense plasmid DNA (pDNA) efficiently via the formation of electrostatic polyplex micelles. Under reductive milieu, pDNA can be released due to the cleavage of disulfide linkages and accordingly pDNA-binding cationic PDMAEMA side chains. In addition, the brush block copolymer exhibits low cytotoxicity and the corresponding polyplex micelles show relatively high gene transfection efficiency.

Synthesis of Polyolefin/Layered Silicate Nanocomposites via Surface-Initiated Ring-Opening Metathesis Polymerization

Here we report the synthesis and characterization of block copolymer/layered silicate (BCPLS) nanocomposites via the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene and cyclopentene from montmorillonite clay (MMT). The MMT particle surfaces were functionalized with a norbornene-terminated alkylammonium surfactant through ion exchange. Block copolymer brushes of norbornene and cyclopentene were polymerized directly from the surface of these functionalized clay platelets, yielding highly exfoliated nanocomposites. A fraction of the polymer brushes were removed from their substrate by reverse ion exchange and characterized in parallel with their corresponding nanocomposite analogues. The thermal, mechanical, and morphological characteristics of the BCPLSs and their neat analogues were then compared directly. This enabled us to assess the role of the MMT filler in the thermal properties, solid/melt state rheology, and morphology.

On the Self-Assembly of Brush Block Copolymers in Thin Films

We describe a simple route to fabricate two dimensionally well-ordered, periodic nanopatterns using the self-assembly of brush block copolymers (brush BCPs). Well-developed lamellar microdomains oriented perpendicular to the substrate are achieved, without modification of the underlying substrates, and structures with feature sizes greater than 200 nm are generated due to the reduced degree of chain entanglements of brush BCPs. A near-perfect linear scaling law was found for the period, L, as a function of backbone degree of polymerization (DP) for two series of brush BCPs. The exponent increases slightly from 0.99 to 1.03 as the side chain molecular weight increases from ∼2.4 to ∼4.5 kg/mol(-1) and saturated with further increase in the side chain molecular weight due to the entropic penalty associated with the packing of the side chains. Porous templates and scaffolds from brush BCP thin films are also obtained by selective etching of one component.

Interplay between Liquid Crystalline Order and Microphase Segregation on the Self-Assembly of Side-Chain Liquid Crystalline Brush Block Copolymers

Herein we investigate the influence of competing self-organizing phenomena on the hierarchical self-assembly of liquid crystalline brush block copolymers (LCBBCs). A library of LCBBCs are synthesized using ring-opening metathesis polymerization (ROMP) of norbornene side-chain functionalized monomers comprising (1) cholesteryl mesogen with nine methylene spacer and (2) semicrystalline poly(ethylene glycol) (PEG). The self-assembly of LCBBCs with variations in LC block content (7–80 wt %) are investigated in their melt state. All LCBBCs show two distinct thermal transitions corresponding to PEG semicrystalline phase and LC mesophases. Interestingly, the LCBBCs display a multilevel hierarchical structure evidenced by the results from X-ray scattering and transmission electron microscopy (TEM): (1) smectic A (SmA) mesophases (d = 3–7 nm) by the assembly of cholesteryl side chains and (2) microphase segregation into lamellar or cylinder (d = 40–75 nm) resulting from the incompatibility between LC moieties and ...