Copolymer Brushes Research Articles

Mussel-inspired construction of thermo-responsive double-hydrophilic diblock copolymers-decorated reduced graphene oxide as effective catalyst supports for highly dispersed superfine Pd nanoparticles.

Well-dispersed ultrafine palladium nanoparticles supported by reduced graphene oxide functionalized with catechol-terminated thermo-responsive block copolymer (PdNPs@BPrGO) were successfully constructed for highly efficient heterogeneous catalytic reduction. We first synthesized a novel temperature-responsive episulfide-containing double-hydrophilic diblock copolymer, poly(poly(ethylene glycol) methyl ether methacrylate-co-2,3-epithiopropyl methacrylate)-block-poly(N-isopropylacrylamide) (P(PEGMA-co-ETMA)-b-PNIPAM), through a reversible addition-fragmentation chain transfer (RAFT) polymerization utilizing a chain-transfer agent with a catechol unit as the end group. The obtained block copolymers can be facilely anchored to the surface of GO via mussel-inspired chemistry. The PdNPs were loaded on GO decorated with block copolymer brushes (BPrGO) as a support via the in situ reduction of palladium precursors with the episulfide ligands of the block copolymer as a stabilizer. The resulting PdNPs@BPrGO nanohybrid catalyst had good water dispersibility and stability. Furthermore, a low dosage of PdNPs@BPrGO catalyst exhibited excellent catalytic performance in the reduction of methylene blue and nitrophenols. The performance was attributed to the ability of PdNPs@BPrGO to facilitate the diffusion of reactants compared to PdNPs@GO without polymer modification. PdNPs@BPrGO also possessed an interesting temperature-responsive catalytic property due to the reversible "coil-to-globule" phase transition behaviour of PNIPAM blocks onto the surface of catalyst. The PdNPs@BPrGO catalyst was successfully recovered and reused five times without any detectible loss in catalytic activity, demonstrating its great potential in a wide range of industrial catalytic applications.

Composition, thickness and properties of grafted copolymer brush coatings determined by ellipsometry: calculation and prediction.

The composition, thickness and properties of poly(4-vinylpyridine-co-oligo(ethylene glycol)ethyl ether methacrylate246) [P(4VP-co-OEGMA246)] copolymer grafted brush coatings attached to glass were studied in the dry and swollen states using ellipsometry. These measured data are in good agreement with predicted (estimated) changes in the amount of water, refractive index and thickness of the grafted copolymer brush coatings on swelling. For POEGMA brushes the thickness of the coatings on swelling at 20 °C can be more than double, in contrast to P4VP where those changes are insignificant. The presence of 4VP units in the structure of the P(4VP-co-OEGMA246) copolymer grafted brushes significantly decreases the hydration degree even for coatings with very low concentrations of 4VP units.

Chemoenzymatic Synthesis of Nitrogen Polymers with Biomedical Applications Catalyzed by Lipases.

The application of Candida antarctica lipase B as catalyst in the synthesis of two examples of nitrogen polymers is described. Firstly, we report a novel linear polyamidoamine oligomer, obtained by polymerization of ethyl acrylate and N-methyl-1,3-diaminopropane, catalyzed by Candida antarctica lipase B immobilized on polypropylene. The second part of the chapter describes an efficient route for the synthesis of a novel β-peptoid oligomer with hydroxyalkyl pendant groups in the nitrogen atom, through the polymerization of ethyl N-(2-hydroxyethyl)-β-alaninate catalyzed by Candida antarctica lipase B physically adsorbed within a macroporous poly(methyl methacrylate-co-butyl methacrylate) resin. Moreover, two derivatives of the β-peptoid oligomer were prepared: by acetylation and by grafting polycaprolactone. This last process was performed through ring-opening polymerization of caprolactone from the β-peptoid pendant hydroxyl groups and afforded a brush copolymer. The products were blended with polycaprolactone to make films by solvent casting. The inclusion of the acyl derivatives of the β-peptoid to polycaprolactone affected the morphology of the film yielding micro- and nanostructured patterns. The obtained products showed biomedical applications.

Supramolecular Nanomedicine Constructed from Cucurbit[8]uril-Based Amphiphilic Brush Copolymer for Cancer Therapy.

An amphiphilic supramolecular brush copolymer CB[8]⊃(PEG-Np·PTPE) was constructed on the basis of a novel host-guest molecular recognition model formed by cucurbit[8]uril (CB[8]), 4,4'-bipyridinium derivative, and PEGylated naphthol (PEG-Np). In aqueous solution, the resultant supramolecular brush copolymer self-assembled into supramolecular nanoparticles (SNPs), by which the anticancer drug doxorubicin (DOX) was encapsulated in the hydrophobic core, establishing an artful Förster resonance energy transfer system with dual fluorescence quenched. With the help of intracellular reducing agents and low pH environment, the SNPs disassembled and the loaded drug molecules were released, realizing in situ visualization of the drug release via the location and magnitude of the energy transfer-dependent fluorescence variation. The cytotoxicity evaluation indicated DOX-loaded SNPs effectively inhibited cell proliferation against HeLa cells. Animal experiments demonstrated that these DOX-loaded SNPs highly accumulated in tumor tissues through the enhanced permeability and retention effect and also had a long blood circulation time. These multifunctional supramolecular nanoparticles possessing self-imaging and controllable drug release ability exhibited great potential in cancer therapy.

Dissipative Particle Dynamics Simulations on the pH-responsive Gating of Block Copolymer Brush Modified Nanopores†

Dissipative Particle Dynamics Simulations on the pH-responsive Gating of Block Copolymer Brush Modified Nanopores†

Random binary brush architecture enhances both ionic conductivity and mechanical strength at room temperature

The ionic conductivity and the mechanical strength are two key factors for the performance of poly(ethylene oxide) (PEO) based polyelectrolytes. However, crystallized PEO suppresses ion conductivity at low temperature and melted PEO has low mechanical strength at high temperature. Here, random binary brush copolymer composed of PEO- and polystyrene (PS)-based side chains is synthesized. PEO crystallinity is suppressed by the introduction of PS brushes. Doping with lithium trifluoromethanesulfonate (LiTf) induces microphase separation. Due to a random arrangement of the brushes, the microphase segregation is incomplete even at high salt loading, which provides both high ionic conductivity and high mechanical strength at room temperature. These results provide opportunities for the design of polymeric electrolytes to be used at room temperature.

Enhanced Stability of Surface-Tethered Diblock Copolymer Brushes with a Neutral Polymer Block and a Weak Polyelectrolyte Block: Effects of Molecular Weight and Hydrophobicity of the Neutral Block

We study the stability of diblock copolymer brushes featuring a bottom neutral block, poly(methyl methacrylate) (PMMA) or poly(poly(ethylene glycol) methacrylate) (PPEGMA), and a top poly(acrylic acid) (PAA) block on flat silicon substrate. The polymer brushes are prepared by surface-initiated atom transfer radical polymerization (SI-ATRP). We use a combinatorial design featuring a molecular weight gradient in the bottom neutral block to investigate systematically the effect of the molecular weight of that block on the stability of the copolymer brush. We measure variations in dry thickness of the diblock copolymer brush by ellipsometry after different incubation times in aqueous buffer (pH = 9.0) as a function of thickness of the neutral block, indicating degrafting of the mechanically activated copolymer chains via hydrolysis of ester groups in the initiator and/or Si–O bonds that attach the polymer to the substrate. The stability of the diblock copolymer brushes is higher than that of PAA homopolymer b...

Exploring the wetting properties of diblock copolymer brushes with a hydrophobic block of poly([formula omitted]H,[formula omitted]H,[formula omitted]H,[formula omitted]H-Perfluorodecyl acrylate)-(PPFDA) and a Thermoresponsive block of poly(N-isopropylacrylamide)-(PNiPAM) synthesized by RAFT polymerization

Polymer brushes have a great potential for controlling surface wetting properties. In this work we study the surface wettability in respect to water of diblock copolymer brushes with an outer block of the thermoresponsive poly(N-isopropylacrylamide) (PNiPAM) polymer and an inner hydrophobic block of 1H 1H 2H 2H-perfluorodecyl Acrylate (PPFDA) and with variable block lengths. Block copolymer brushes are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. The conditions of synthesis; polymerization time of NiPAM, grafting density of change transfer agent (CTA) on the surface, amount of initiator and monomers were varied to produce brushes with different ratios of PNiPAM and PPFDA. Diblock copolymer brushes are characterized by Raman, XPS and Atomic Force Microscopy. Brushes with contact angles from 28 to 85 degrees are produced. The brushes with longer PPFDA blocks are the more hydrophobic. Contact angle values increase when raising temperature from 20 °C to 40 °C as for PNiPAM but always to higher contact angles than for the PNiPAM brush.

Fabrication of device with poly(N-isopropylacrylamide)-b-ssDNA copolymer brush for resistivity study

In this study, we grafted bromo-terminated poly(N-isopropylacrylamide) (PNIPAAm) brushes onto thin gold films deposited on silicon, and then reacted with NaN3 to produce azido-terminated PNIPAAm brushes. A probe sequence of single-stranded DNA (ssDNA) with a 4-pentynoic acid succinimidyl ester unit was grafted onto the azido-terminated PNIPAAm brushes through a click reaction, resulting in the formation of block copolymer brushes. The PNIPAAm-b-ssDNA copolymer brushes formed supramolecular complexes stabilized by bio-multiple hydrogen bonds (BMHBs), which enhanced the proton transfer and thereby decreased the resistivity of the structures. In addition, the optimal operation window for DNA detection ranges from 0 to 0.2 M of NaCl concentration. Therefore, the specimens were prepared in the PBS solution at 150 mM NaCl concentration for target hybridization. The supramolecular complex state of the PNIPAAm-b-ssDNA copolymer brushes transformed into the phase-separated state after the hybridization with 0.5 ng/µL of its target DNA sequence owing to the competition between BMHBs and complementary hydrogen bonds. This phase transformation of the PNIPAAm and probe segments inhibited the proton transfer and significantly increased the resistivity at 25 °C. Moreover, there were no significant changes in the resistivity of the copolymer brushes after hybridization with the target sequence at 45 °C. These results indicated that the phase-separated state of the PNIPAAm-b-ssDNA copolymer brushes, which was generally occurred above the LCST, can be substantially generated after hybridization with its target DNA sequence. By performing the controlled experiments, in the same manner, using another sequence with lengths similar to that of the target sequence without complementarity. In addition, the sequences featuring various degrees of complementarity were exploited to verify the phase separation behavior inside the PNIPAAm-b-ssDNA copolymer thin film.

Synthesis and microphase separation behavior of random, mixed cylindrical brush copolymers bearing polystyrene and poly(ε-caprolactone) side chains

A series of mixed, random cylindrical brush copolymers bearing polystyrene (PS) and poly(ε-caprolactone) (PCL) side chains were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). These novel cylindrical brush copolymers have been characterized by means of nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). It was found that the mikto-armed cylindrical brush copolymers were microphase-separated in bulks and that the morphologies were dependent on the mass ratios of PS to PCL side chains. One of the cylindrical brush copolymers was employed to incorporate into epoxy thermoset to investigate effect of the mikto-armed cylindrical brush architecture on the reaction-induced microphase separation behavior. Depending on the concentration of the cylindrical brush in epoxy, the thermosets can display the morphologies with the spherical, worm-like and lamellar PS microdomains dispersing in continuous thermosetting matrices.

Bioactive zwitterionic polymer brushes grafted from silicon wafers via SI-ATRP for enhancement of antifouling properties and endothelial cell selectivity

Zwitterionic copolymers keep good resistance to platelet adhesion and nonspecific protein adsorption. In this study, A block copolymer brushes consisting of carboxybetaine methacrylate (CBMA) and glycidyl methacrylate (GMA) were grafted from silicon wafers via surface-initiated atom transfer radical polymerization, and then the Arg-Glu-Asp-Val (REDV) peptide was attached to the polymer brush via an reactive epoxy group of the P(GMA) unit to improve endothelial cells (ECs) selectivity. These modified surfaces were evaluated with scanning electron microscopy, atomic force microscopy, attenuated total reflectance-Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and static water contact angle measurement. The results showed that REDV-modified zwitterionic brushes were successfully constructed on silicon wafers. The biocompatibility of the membrane was determined by plasma recalcification time assay and platelet adhesion test. The results showed that the modified substrate exhibited good blood compatibility. Moreover, the proliferation of ECs and smooth muscle cells onto the REDV-modified copolymer brushes were examined to demonstrate the synergistic effect of CBMA with antifouling property and REDV peptide with ECs selectivity. All assays showed that the silicon wafers displayed excellent EC selectivity after modification. In summary, REDV-modified zwitterionic brushes had great potential for cardiovascular stent implantation.

Nanoparticles of a polyaspartamide-based brush copolymer for modified release of sorafenib: In vitro and in vivo evaluation

In this paper, we describe the preparation of polymeric nanoparticles (NPs) loaded with sorafenib for the treatment of hepatocellular carcinoma (HCC). A synthetic brush copolymer, named PHEA-BIB-ButMA (PBB), was synthesized by Atom Trasnfer Radical Polymerization (ATRP) starting from the α-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) and poly butyl methacrylate (ButMA). Empty and sorafenib loaded PBB NPs were, then, produced by using a dialysis method and showed spherical morphology, colloidal size, negative ζ potential and the ability to allow a sustained sorafenib release in physiological environment.Sorafenib loaded PBB NPs were tested in vitro on HCC cells in order to evaluate their cytocompatibility and anticancer efficacy if compared to free drug. Furthermore, the enhanced anticancer effect of sorafenib loaded PBB NPs was demonstrated in vivo by using a xenograft model, by first allowing Hep3B cells to grow subcutaneously into nude mice and then administering sorafenib as free drug or incorporated into NPs via intraperitoneal injection. Finally, in vivo biodistribution studies were performed, showing the ability of the produced drug delivery system to accumulate in a significant manner in the solid tumor by passive targeting, thanks to the enhanced permeability and retention effect.

Synthesis of naringin‐based polymer brushes via seATRP

The flavonoid‐based macromolecule initiator was prepared for the first time by the transesterification reaction of naringin with 2‐bromoisobutyryl bromide. In accordance with the “grafting from” methodology, a naringin‐based copolymer brush with a polar naringenine‐7‐rhamnosidoglucoside core and an amphiphilic poly(methyl methacrylate)‐block‐poly(N‐isopropylacrylamide) (PMMA‐b‐PNIPAM) side chains was synthesized for the first time via a simplified electrochemically mediated ATRP (seATRP), utilizing only 40 ppm of catalytic complex. The rate of the polymerizations was controlled by applying optimal potential or current values during preparative electrolysis to prevent the possibility of intermolecular coupling of the growing polymer brushes. Naturally derived polymer brushes showed narrow molecular weight distributions (Đ = 1.06−1.08). 1H NMR spectral results confirm the formation of citrus‐based polymer brushes. These new naringin‐based polymer materials may find biomedical applications as thermo‐sensitive drug delivery systems, membranes, and biologically active thin films in tissue engineering.

Construction of Hierarchical Polymer Brushes on Upconversion Nanoparticles via NIR-Light-Initiated RAFT Polymerization

Photoinduced reversible addition-fragmentation chain transfer (RAFT) polymerization generally adopts high-energy ultraviolet (UV) or blue light. In combination with photoredox catalyst, the excitation light wavelength was extended to the visible and even near-infrared (NIR) region for photoinduced electron transfer RAFT polymerization. In this report, we introduce for the first time a surface NIR-light-initiated RAFT polymerization on upconversion nanoparticles (UCNPs) without adding any photocatalyst and construct a functional inorganic core/polymer shell nanohybrid for application in cancer theranostics. The multilayer core-shell UCNPs (NaYF4:Yb/Tm@NaYbF4:Gd@NaNdF4:Yb@NaYF4), with surface anchorings of chain transfer agents, can serve as efficient NIR-to-UV light transducers for initiating the RAFT polymerization. A hierarchical double block copolymer brush, consisting of poly(acrylic acid) (PAA) and poly(oligo(ethylene oxide)methacrylate-co-2-(2-methoxy-ethoxy)ethyl methacrylate) (PEG for short), was grafted from the surface in sequence. The targeting arginine-glycine-aspartic (RGD) peptide was modified at the end of the copolymer through the trithiolcarbonate end group. After loading of doxorubicin, the UCNPs@PAA-b-PEG-RGD exhibited an enhanced U87MG cancer cell uptake efficiency and cytotoxicity. Besides, the unique upconversion luminescence of the nanohybrids was used for the autofluoresence-free cell imaging and labeling. Therefore, our strategy verified that UCNPs could efficiently activate RAFT polymerization by NIR photoirradiation and construct the complex nanohybrids, exhibiting prospective biomedical applications due to the low phototoxicity and deep penetration of NIR light.

Sustainable thermoplastic elastomers derived from cellulose, fatty acid and furfural via ATRP and click chemistry

Cellulose-based thermoplastic elastomers (TPEs) have attracted considerable attention because of their rigid backbone, good mechanical properties, renewable nature and abundance. In the present study, sustainable TPEs based on ethyl cellulose (EC), fatty acid and furfural were generated by the combination of ATRP and “click chemistry”. To fabricate sustainable TPEs with higher toughness, a range of polymers, including mono random-copolymer poly(tetrahydrofurfuryl methacrylate-co-lauryl methacrylate) (P(THFMA-co-LMA), dual polymer side chains PTHFMA and PLMA, and mono-block copolymer PTHFMA-b-PLMA, were designed as side chains to fabricate EC brush copolymers with random, dual or block side chain architectures using the “grafting from” and “grafting onto” methods. The multi-armed structures, chemical compositions and phase separation of these EC brush copolymers were confirmed by FT-IR, 1H NMR, GPC, DSC, TEM and SEM. Overall, three types of EC brush copolymers all exhibited the desired mechanical properties of TPEs. In addition, the EC brush copolymers with dual/block side chain architectures showed higher tensile strength than that of the random polymers with similar compositions.

A rapid approach to prepare poly(2-methyl-2-oxazoline)-based antifouling coating by UV irradiation

A series of brush copolymers, poly[(2-methyl-2-oxazoline)-random-4-vinylpyridine] (PMOXA-r-4VP), with a variety of compositions was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of the poly(2-methyl-2-oxazoline) methacrylate macromonomer (PMOXA-MA) and 4-vinylpyridine (4VP), and then characterized by 1H NMR spectroscopy and gel permeation chromatography (GPC). The PMOXA-based coatings on the surfaces of glass, silicon, gold and polydimethylsiloxane (PDMS) substrates were then produced by short-time ultraviolet (UV) irradiation of PMOXA-r-4VP. Water contact angel (WCA), ellipsometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and ζ-potential techniques were used to characterize the coatings. The results showed that copolymers can be successfully bonded on the surfaces of glass, silicon, gold, and PDMS substrate. Besides, the PMOXA-based coatings displayed a superior resistance to bovine serum albumin, human blood platelets, Human Umbilical Vein Endothelial Cells adsorption and good biocompatibility. Finally, stability test indicated that the stability of coatings can be improved with the content of the 4VP segment. Furthermore, PMOXA-r1/2-4VP immobilized surfaces displayed good antifouling property in long-term applications.

Thermo-responsive polymer brushes on glass plate prepared from a new class of amino acid-derived vinyl monomers and their applications in cell-sheet engineering

In this study, we present a novel thermo-responsive polymer platform that is based on the alanine methyl ester-containing homopolymer (PNAAMe) and the copolymer with glycine methyl ester-based vinyl monomer (P(NAAMe-co-NAGMe)) brushes prepared via surface-initiated atom transfer radical polymerization. Water contact angles for these brushes measured at different temperatures reveal that the polymer brushes collapse and dehydrate around 13°C and 25°C (TTs), respectively, upon elevating the temperature. At 37°C, seeded fibroblasts (NIH/3T3) adhere to and spread well onto these brush surfaces although the copolymer brush of P(NAAMe-co-NAGMe) depresses the number of adherent cells less than half of that for the homopolymer of PNAAMe after 24h of cell culture due to increment in hydrophilicity. To prepare the cell-sheet, the cells are seeded on both polymer brushes and cultured at 37°C in the presence of serum. After 4days, the cells proliferated confluently on these brush surfaces. Lowering the temperature to 4°C and 20°C below TT of each brush led to the cell-sheet detachment as a monolayer form from the polymer brushes accompanying with the switching of surface affinity.

Synthesis and characterization of brush diblock and triblock copolymers bearing polynorbornene backbone and poly(l‐lactide) and/or poly(hexyl isocyanate) side chains by a combination of coordination and ring opening metathesis polymerization

ABSTRACTWe report the synthesis of poly(l‐lactide) and poly(hexyl isocyanate) macromonomers using bischloro‐η5‐cyclopentadienyl(bicyclo[2.2.1]‐hept‐5‐en‐2‐oxy) Titanium (IV), [CpTiCl2(O‐NBE)]. These macromonomers bearing a norbornene end group were polymerized towards brush copolymers employing Grubbs' first generation catalyst. Brush copolymers consisting of blocks with different side chains were synthesized. The polymers were characterized by Size Exclusion Chromatography, Nuclear Magnetic Resonance, and their thermal properties were investigated by Thermogravimetric Analysis, and Differential Scanning Calorimetry analysis. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3455–3465

Effect of Grafting Density of Random Copolymer Brushes on Perpendicular Alignment in PS-b-PMMA Thin Films

We modulated the grafting density (σ) of a random copolymer brush of poly(styrene-r-methyl methacrylate) on substrates to probe its effect on the formation of perpendicularly aligned lamellae of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA). Supported by coarse-grained simulation results, we hypothesized that an increase in σ will allow us to systematically tune the block copolymer interfacial interactions with the substrates from being preferential to one of the blocks to being neutral toward both blocks and will thereby facilitate enhanced regimes of perpendicularly aligned lamellae. We verified such a hypothesis by using a simple grafting-to approach to modify the substrates and characterized the thickness window for perpendicular lamellae as a function of brush thickness (or σ) on the grafted substrates using scanning force microscopy (SFM) images and grazing incidence small-angle X-ray scattering (GISAXS) measurements. The experimental results validated our hypothesis and suggested that the σ o...

Thermo‐Responsive Brush Copolymers by “Grafting Through” Strategy Implemented on the Surface of the Macromonomer Micelles and Their High Emulsifying Performance

In the present study, the synthesis of water‐soluble thermo‐responsive brush copolymers via “graft through” strategy that is conducted on the surfaces of macromonomer micelles and their application as emulsifiers for thermo‐responsive emulsions are reported. Water‐soluble poly(N,N‐dimethylacrylmide)‐block‐poly(N‐isopropylacrylmide) (PDMA‐b‐PNIPAM) diblock copolymers carrying a hydrophobic polymerizable vinyl group at the end of the PDMA block are synthesized by reversible addition‐fragmentation chain transfer polymerization and click functionalization. Increasing the temperature to above the low critical solution temperature of the PNIPAM block, the macromonomers self‐assemble to core–shell structure micelles with the polymerizable vinyl terminals on the surface of the micelles. Instead of being directly and freely exposed in the bulk water as the hydrophilic group, the hydrophobic vinyl terminals are protected by the partially looped PDMA segments. PMA‐g‐(PDMA‐b‐PNIPAM) brush copolymers with a high molecular weight and a narrow distribution are obtained by radical polymerization of the macromonomers using the potassium peroxydisulfate as initiator. The radical polymerization only proceeds within the single micelle, and intermicellar propagation and/or termination reactions are totally excluded. These brush copolymers feature the thermo‐responsive conformation transition property and high emulsifying performances for the formation of thermo‐responsive emulsion. image