Molecular Brushes Research Articles

Synthesis of Loop Poly(Methyl Methacrylate) Brushes via Chain-End Postpolymerization Modification

Polymer brushes are typically densely grafted assemblies of polymer chains that are tethered via one end group to a solid substrate. Anchoring linear polymer chains via both end groups to a surface results in loop-type polymer brushes. Although loop polymer brushes have been shown to be able to outperform their linear, single-chain-end tethered analogues, for example, with respect to the prevention of biofouling or reducing friction, this brush architecture has received only relatively limited attention. Loop-type polymer brushes are mostly prepared following grafting-onto approaches using α,ω-heterobifunctional polymers. Grafting-from strategies, so far, have been rarely explored, but could further expand the range of accessible polymer molecular weights and brush grafting densities and allow the preparation of surface-attached polymer loops from a wider scope of monomers. This manuscript reports an alternative grafting-from strategy for the preparation of loop-type poly(methyl methacrylate) (PMMA) brush...

Stable Omniphobic Anisotropic Covalently Grafted Slippery Surfaces for Directional Transportation of Drops and Bubbles

AbstractDirectional transportation and collection of liquids and bubbles are highly desirable in human life and industrial production. As one of the most promising types of functional surfaces, the reported anisotropic slippery liquid‐infused porous surfaces (SLIPSs) demonstrate unique advantages in liquid directional transportation. However, anisotropic SLIPSs readily suffer from the depletion of lubricant when used to manipulate droplets and bubbles, which leads to unstable surface properties. Therefore, fabricating stable anisotropic slippery surfaces for the directional transportation of drops and bubbles remains a challenge. Here, stable anisotropic covalently grafted slippery surfaces are fabricated by grafting polydimethylsiloxane molecular brushes onto directional microgrooved surfaces. The fabricated surfaces show remarkable anisotropic omniphobic sliding behaviors towards droplets with different surface tensions ranging from 72.8 to 37.7 mN m−1 in air and towards bubbles underwater. Impressively, the surface maintains outstanding stability for the transportation of droplets (in air) and air bubbles (underwater) even after 240 d. Furthermore, anisotropic self‐cleaning towards various dust particles in air and directional bubble collection underwater are achieved on this surface. This stable anisotropic slippery surface has great potential for applications in the directional transportation of liquids and bubbles, microfluidic devices, directional drag reduction, directional antifouling, and beyond.

Molecular brushes with poly-2-ethyl-2-oxazoline side chains and aromatic polyester backbone manifesting double stimuli responsiveness

Behavior of grafted copolymers composed of aromatic polyester (PAPE) backbone and poly-2-ethyl-2-oxazoline (PEOZ) side chains differing in grafting density in aqueous solutions was studied when heated at various concentrations and pH using static and dynamic light scattering and turbidimetry. Aggregates and individual macromolecules were registered in solutions at all times. It was shown that the aggregates of the brush with higher PEOZ side chains’ grafting density undergo compaction on heating below phase separation, whereas the size of the loose polymer brush aggregates continuously increases with the increase of temperature. Phase separation temperatures of both copolymers decreased with dilution. Strong influence of pH on the thermosensitivity of both samples was shown, the copolymer solubility being decreased with the acidity decrease. The nature of the pH effect is under discussion.

Molecular Bottle Brushes with Positioned Selenols: Extending the Toolbox of Oxidative Single Polymer Chain Folding with Conformation Analysis by Atomic Force Microscopy

ABSTRACTA synthesis route to controlled and dynamic single polymer chain folding is reported. Sequence‐controlled macromolecules containing precisely located selenol moieties within a polymer chain are synthesized. Oxidation of selenol functionalities lead to diselenide bridges and induces controlled intramolecular crosslinking to generate single chain collapse. The cyclization process is successfully characterized by SEC as well as by 1H NMR and 2D HSQC NMR spectroscopies. In order to gain insight on the molecular level to reveal the degree of structural control, the folded polymers are transformed into folded molecular brushes that are known to be visualizable as single molecule structures by AFM. The “grafting onto” approach is performed by using triazolinedione−diene reaction to graft the side chain polymers. A series of folded molecular brushes as well as the corresponding linear controls are synthesized. AFM visualization is proving the cyclization of the folded backbone by showing globular objects, where non‐folded brushes show typical worm‐like structures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 154–162

Molecular Brush with Dense PEG Side Chains: Design of a Well-Defined Polymer Electrolyte for Lithium-Ion Batteries

Herein, we designed a series of well-defined bottlebrush-like macromolecules with short and densely grafted poly(ethylene oxide) (PEO) side chains through several controlled radical polymerization ...

Stimuli-Induced Star-Globule Shape Transitions of Dually Responsive Binary Heterografted Three-Arm Star Molecular Brushes in Aqueous Solution

This article reports on the synthesis of doubly responsive binary heterografted, three-arm star molecular brushes and the study of their stimuli-induced star-to-globule shape transitions in aqueous...

On the interdigitation of molecular brushes and solvation force upon adsorption of water in slit-like pores with grafted chains. Density functional approach

We have explored adsorption of a single waterlike model in slitlike pores with walls chemically modified by tethered chains that form molecular brushes. Principal focus of the present study is in the evolution of the microscopic structure of fluid species and of a system of chain molecules upon adsorption. A density functional approach is used. Various projections of the vapor–liquid coexistence envelope, including brushes interdigitation coefficient, are obtained and discussed. We have discovered that the molecular brushes can shrink or “swell” upon phase transition in confined water dependent on the attraction between fluid molecules and chains segments. Trends of behavior of the solvation force between pore walls are investigated dependent on the parameters of the system. Particular attention is paid to the appearance of the effective attraction between pore walls.

Biofilm Disruption Utilizing α/β Chimeric Polypeptide Molecular Brushes

Gram-negative bacteria can cause serious infections and are well known problems in biomedical practices. Biofilms of gram-negative bacteria are notorious for their frequently encountered resistance toward antibiotics. We demonstrate that α/β chimeric polypeptide molecular brush (α/β CPMB) exerts potent activities against antibiotic-resistant gram-negative bacteria. MTT viability assay, bacterial colony counting, and live/dead staining all indicate that α/β CPMB not only inhibits biofilm formation of gram-negative Pseudomonas aeruginosa and Acinetobacter baumannii, but also effectively disrupts mature biofilms that are highly resistant to one of the most active antibiotics—colistin. The superior antibacterial performance of the α/β CPMB implies its potential topical applications in treating biofilms.

Two-dimensional molecular brush-functionalized porous bilayer composite separators toward ultrastable high-current density lithium metal anodes

Lithium metal batteries have been considerably limited by the problems of uncontrolled dendritic lithium formation and the highly reactive nature of lithium with electrolytes. Herein, we have developed functional porous bilayer composite separators by simply blade-coating polyacrylamide-grafted graphene oxide molecular brushes onto commercial polypropylene separators. Our functional porous bilayer composite separators integrate the lithiophilic feature of hairy polyacrylamide chains and fast electrolyte diffusion pathways with the excellent mechanical strength of graphene oxide nanosheets and thus enable molecular-level homogeneous and fast lithium ionic flux on the surfaces of electrodes. As a result, dendrite-free uniform lithium deposition with a high Coulombic efficiency (98%) and ultralong-term reversible lithium plating/stripping (over 2600 h) at a high current density (2 mA cm−2) are achieved for lithium metal anodes. Remarkably, lithium metal anodes with an unprecedented stability of more than 1900 h cycling at an ultrahigh current density of 20 mA cm−2 are demonstrated.

Grubbs' and Schrock's Catalysts, Ring Opening Metathesis Polymerization and Molecular Brushes-Synthesis, Characterization, Properties and Applications.

In this review, molecular brushes and other macromolecular architectures bearing a bottlebrush segment where the main chain is synthesized by ring opening metathesis polymerization (ROMP) mediated by Mo or Ru metal complexes are considered. A brief review of metathesis and ROMP is presented in order to understand the problems and the solutions provided through the years. The synthetic strategies towards bottlebrush copolymers are demonstrated and each one discussed separately. The initiators/catalysts for the synthesis of the backbone with ROMP are discussed. Syntheses of molecular brushes are presented. The most interesting properties of the bottlebrushes are detailed. Finally, the applications studied by different groups are presented.

Synthesis of Polypeptoid-Polycaprolactone-Polytetrahydrofuran Heterograft Molecular Polymer Brushes via a Combination of Janus Polymerization and ROMP.

Janus polymerization is a novel and efficient way to synthesize diblock and multiblock copolymers in one step by using Lu(OTf)3 and propylene epoxide as a catalytic system. By modifying the epoxide initiator, which is located at the block junction with various functional groups, the possibility for future topological design is provided. Herein, 2-bicyclo[2.2.1]hept-5-en-2-yl oxirane (NB-EO) is used as an alternative for propylene epoxide to synthesize a poly(THF-co-CL)-b-PCL diblock copolymer featuring a norbornene group at this position. This also results in multiblock [poly(THF-co-CL)-b-PCL]m copolymers carrying multiple norbornene moieties through Janus polymerization. Subsequent ring-opening metathesis copolymerization (ROMP) of the resulting poly(THF-co-CL)-b-PCL macromonomers with norbornenyl-terminated polysarcosine (PSar-NB) allows the facile preparation of heterograft molecular polymer brushes (MPBs). The MPBs feature three heterografts of PCL, P(CL-co-THF) and PSar, potentially equipping these structures with biocompatibility, biodegradability, semi-crystallinity, and amphiphilicity. A phase separation is observed after annealing in both TEM and AFM analysis. Due to their amphiphilic nature, the MPBs also undergo self-assembly into micelles in aqueous solution. Such materials combining polypeptoids, polyesters, and polyethers segments are expected to attract wide attention in drug delivery applications.

Dynamics in hydrophilic and hydrophobic molecular chains tethered to MCM41-type mesoporous silica upon wetting and dehydration processes

Surface modified mesoporous silica materials are important materials for heterogeneous catalysis and are attracting attention as potential drug carriers. The functionality of these materials relies on the physical and chemical properties of the tethers attached to MCM41 silica surface. These chemically linked tails act as molecular brushes, that can capture pollutant molecules, anchor points for catalysts and can host drug molecules. To utilize the full potential of the tailored silica surfaces, one should infer their properties at different levels of solvation. Here, 1H MAS NMR spectroscopy is used to monitor the dynamic properties of two modified MCM41 materials, an aminopropyl tethered MCM41 and an octyl tethered MCM41, through the process of controlled hydration. The surface site resolved measurements demonstrate how the chemical nature of the two tethers governs the way water molecules are directed to the different sites in the porous materials.

Characterization and Synthesis of This Comb Type Copolymer with Styrene Using A Macromonomer Containing Polyethylmethacrylate

In this study, firstly 7-hydroxy-4-chloromethyl coumarin (CMHC) was synthesized from reaction of ethyl 4-chloroacetoasetate with resorcinol. Then, the poly(ethyl methacrylate) coumarin end grouped having hydroxyl (CEMA) was prepared by ethyl methacrylate with using (CMHC) as initiator by atom transfer radical polymerization (ATRP) method. A macromonomer (CMEMA) was synthesized from reaction of methacryloyl chloride and poly(EMA) ended coumarin having OH group (CEMA). Molecular brush of P(CMEMA-comb-%16St) was synthesized by reaction of macromonomer CMEMA and styrene by free radical polymerization method (SRP). The structures of the prepared macromonomer and molecular brush were characterized by FT-IR and 1H-NMR techniques. The thermal behavior of P(CMEMA-comb-%St) has been investigated by TGA, and the glass transition temperatures have been measured on DSC. The average molecular weights and polydispersity were determined by GPC. The dielectric behavior of P(CMEMA-comb-%16St) was investigated as a function of temperature and frequency. The intrinsic viscosity [] of P(CMEMA-comb-%16St) was determinated.

Intelligent antibacterial surface based on ionic liquid molecular brushes for bacterial killing and release.

The prevention of bacteria-induced infections has been increasing in importance in both clinical surgery and biomedical engineering. Although great attention has been paid to designing intelligent antibacterial surfaces, the fabrication processes are still not facile and universal enough, and the antibacterial efficiencies of these surfaces are also not ideal. Herein, ionic liquid (IL) molecules of 3-(12-mercaptododecyl)-1-methyl-1H-imidazol-3-ium bromide (IL(Br)) were synthesized with the minimum inhibitory concentrations as low as 4 and 8 μg mL-1 against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), respectively. By simply immersing a polymeric substrate into the IL(Br) solution, an antibacterial surface with high killing efficiency of 99% against S. aureus (94% against E. coli) was achieved via a mussel-inspired approach. Subsequently, 97% S. aureus and 95% E. coli on the substrate could be released by simple ion-exchange of Br- with (CF3SO2)2N- due to the ion sensitivity of the IL molecular brushes. Thus, the proposed facile strategy towards a superior efficiency surface could be potentially used in intelligent antibacterial fields.

Realization of the Li+ domain diffusion effect via constructing molecular brushes on the LLZTO surface and its application in all-solid-state lithium batteries

Realization of the fast Li+ domain diffusion effect via constructing molecular brushes on the LLZTO improves the ionic conductivity of electrolytes and electrochemical performance of solid-state lithium batteries.

Towards the description of adsorption of water in slit-like pores with walls covered by molecular brushes.

The density profiles, adsorption isotherms, and phase behavior of a water model in a slit-like pore with walls modified by pre-adsorbed tethered chain molecules have been studied in the framework of a density functional theory. Each chain is bonded to the surface by its terminal segment, and the surface density of grafted chains is the same for each wall. The model for water taken from the work of Clark et al. [Mol. Phys. 104, 3561 (2006)] reproduces successfully a bulk equation of state. The mean field approach has been used to describe the effects of attractive interactions. The chemical association effects are taken into account by using the first-order thermodynamic perturbation theory of Wertheim. We have found that the presence of molecular brushes on the pore walls has important consequences for the adsorption and phase behavior of confined water. If the brush segments do not attract water molecules strongly, the vapor-liquid coexistence envelope shrinks upon increasing brush density, but the critical temperature is weakly affected. Alteration from capillary condensation to evaporation is observed with changes in the brush density, number of segments of tethered chains, and/or chemical identity of segments. The crossover temperature is affected by all these factors. Moreover, we have shown that affinity of water to segments of tethers is an important factor determining adsorption of water vapor and the entire phase diagram.

Structural Organization of Interpolymer Complexes Formed by Poly(N-vinylamides) and Poly(methacrylic acid) Chains Regularly Grafted to Polyimide in Aqueous Solutions

The formation and structural organization of interpolymer complexes formed by poly(methacrylic acid) chains regularly grafted to polyimide (molecular brushes) and macromolecules of poly(N-vinylamides) with different molecular masses are studied by polarized luminescence. The luminescent label of the anthracene structure is covalently bound to poly(methacrylic acid) chains in a brush. It is shown that in aqueous solutions the complexes under study are stabilized by hydrogen bonds formed between proton donor and proton acceptor groups of interacting chains. The formation of these complexes depends not only on the nature of poly(N-vinylamide) but also especially on its molecular mass. An increase in the molecular mass of polyamide is followed by the formation of a more compact less hydrated structure, as proved by an increase in the time of nanosecond relaxation and enhanced binding of the diphilic organic ion. The hindrance of poly(methacrylic acid) grafted chains complexed with polyvinylamide is lower than that of corresponding linear chains. This can be explained by a higher imperfection of the formed double-stranded structures. The ionization of carboxyl groups leads to the dissociation of complexes. The pH range corresponding to the highest degree of binding of acridine orange by poly(methacrylic acid) grafted chains is broader than that corresponding to the highest degree of dye binding by the linear polyacid.

The Behavior of Amphiphilic Molecular Brushes with Polyimide Backbone and Poly(methyl methacrylate) and Polystyrene Side Chains in the Vicinity of Θ Point

The behavior of amphiphilic molecular brushes in the vicinity of the Θ point has been studied by the methods of molecular hydrodynamics and optics upon variation of temperature. As objects of investigation, graft copolymers with polyimide main chain and poly(methyl methacrylate) and polystyrene side chains were chosen. The samples studied differed in the backbone and side chain lengths at a similar degree of grafting. The molecular mass of the samples under investigation was varied in a sevenfold range. For comparison, linear poly(methyl methacrylate) and polystyrene have been studied. It has been shown that the behavior of molecular brushes and linear polymers in the vicinity of the Θ point differs significantly. A more rapid gain in intrinsic viscosity of the solutions of graft copolymers in the vicinity of the Θ point is explained by the simultaneous increase in the volume of macromolecules and in their shape asymmetry.

Fabrication of Porous Functional Nanonetwork-Structured Polymers with Enhanced Adsorption Performance from Well-Defined Molecular Brush Building Blocks

We report the fabrication of porous functional nanonetwork-structured polymers (FNSPs) consisting of poly(acrylic acid) functional cores surrounded by a microporous shell network, via a combination of atom transfer radical polymerization (ATRP) and Friedel–Crafts hyper-cross-linking chemistry. Well-defined molecular brushes with diblock poly(tert-butyl acrylate)-block-polystyrene (PtBA-b-PS) side chains serve as tunable building blocks to synthesize porous networks. The prepared FNSPs demonstrated significantly enhanced adsorption toward basic dyes, up to 767 mg g–1.

High-hydrophilic and salt rejecting PA-g/co-PVP RO membrane via bionic sand-fixing grass for pharmaceutical wastewater treatment

In this study, a novel PA-g/co-PVP reverse osmosis (RO) composite membrane with high-hydrophilic, antifouling, high salt rejection properties, was prepared according to the principle of sand-fixing grass effect for pharmaceutical wastewater treatment. N-vinyl-2-pyrrolidone (NVP) was used as a “seed agent” that was seeped into a low cross-linked polyamide (PA) film. A hydrophilic molecular brush of polyvinylpyrrolidone (PVP) grafted on the PA surface (PA-g-PVP) similar to grass growing on sand and a cross-linked copolymer layer of PA and NVP (PA-co-NVP) similar to grass roots distributed in sand, as well as an interlayer cross-linking between PA separation layer and PES ultrafiltration membrane with a highly stable interfacial structure, synchronously occurred through γ-ray radiation. Upon incorporation of 1.0% of NVP, the resultant PA-g/co-PVP membrane achieved 18.8° water contact angle and high flux recovery ratio (FRR) values of 91.23%, 96.28%, and 93.67% for the foulants of bovine serum albumin (BSA), sodium alginate (SA), and sodium dodecyl sulfate (SDS), respectively. The FRR value of pharmaceutical wastewater-polluted membrane after cleaning was 94.30%. The PA-g/co-PVP RO membrane showed outstanding separation stability due to the radiation cross-linking reactions, which limit matrix swelling and interface delamination similar to the action principle of sand-fixing grass. These merits prove that the RO membrane developed in this study can be used in many applications, including small organic molecular wastewater separation.