Hydrophilic-hydrophobic Block Copolymers Research Articles

Using Grazing-Incidence Small-Angle Neutron Scattering to Study the Orientation of Block Copolymer Morphologies in Thin Films

We used grazing-incidence small-angle neutron scattering (GISANS) to probe the depth-dependent orientation of self-assembled morphologies of block copolymers. A hydrophobic–hydrophobic block copolymer, poly(solketal methacrylate)-block-polystyrene (PSM-b-PS), was synthesized and spin-coated into films tens of nanometers in thickness where the polymers adopted a disordered state. PSM-b-PS was then hydrolyzed by exposing the polymer thin film to trifluoroacetic acid vapor or embedding a photoacid generator in the film during spin coating, followed by exposure to UV light. The hydrolysis converted the block copolymer into a hydrophilic–hydrophobic block copolymer, poly(glycerol monomethacrylate)-block-polystyrene (PGM-b-PS), significantly increasing the segmental interaction parameter (χ) and causing microphase separation of the copolymers. GISANS was used to study the depth-dependent structure of the films and revealed that the orientation of the microphase-separated structure differed at the polymer–air and polymer–substrate interfaces. In the regions where the lamellae were parallel to the interfaces, the orientation propagated into the film from the interfaces. However, in the areas where the lamellae were perpendicular to the interfaces, the orientation did not persist with increasing distance from the interfaces.

Assembly of polyelectrolyte star block copolymers at the oil-water interface.

To understand and resolve adsorption, reconfiguration, and equilibrium conformations of charged star copolymers, we carried out an integrated experimental and coarse-grained molecular dynamics simulation study of the assembly process at the oil-water interface. This is important to guide development of novel surfactants or amphiphiles for chemical transformations and separations. The star block copolymer consisted of arms that are comprised of hydrophilic-hydrophobic block copolymers that are covalently tethered via the hydrophobic blocks to one point. The hydrophobic core represents polystyrene (PS) chains, while the hydrophilic corona represents quaternized poly(2-vinylpyridine) (P2VP) chains. The P2VP is modeled to become protonated when in contact with an acidic aqueous phase, thereby massively increasing the hydrophilicity of this block, and changing the nature of the star at the oil-water interface. This results in a configurational change whereby the chains comprising the hydrophilic corona are significantly stretched into the aqueous phase, while the hydrophobic core remains solubilized in the oil phase. In the simulations, we followed the kinetics of the anchoring and assembly of the star block copolymer at the interface, monitoring the lateral assembly, and the subsequent reconfiguration of the star via changes in the interfacial tension that varies as the degree-of-protonation increases. At low fractions of protonation, the arm cannot fully partition into the aqueous side of the interface and instead interacts with other arms in the oil phase forming a network near the interface. These insights were used to interpret the non-monotonic dependence of pH with the asymptotic interfacial tension from pendant drop tensiometry experiments and spectral signatures of aromatic stretches seen in vibrational sum frequency generation (SFG) spectroscopy. We describe the relationship of interfacial tension to the star assembly via the Frumkin isotherm, which phenomenologically describes anti-cooperativity in adsorbing stars to the interface due to crowding. Although our model explicitly considers long-range electrostatics, the contribution of electrostatics to interfacial tension is small and brought about by strong counterion condensation at the interface. These results provide key insights into resolving the adsorption, reconfiguration, and equilibrium conformations of charged star block copolymers as surfactants.

Novel hydrophilic-hydrophobic block copolymer based on cardo poly(arylene ether sulfone)s with bis-quaternary ammonium moieties for anion exchange membranes

Two types of phenolphthalein-based copolymers, random and block cardo poly(aryl ether sulfone)s with pendant tertiary amine groups were synthesized via copolycondensation. Both of the copolymers were grafted with (3-bromopropyl) trimethylammonium bromide to prepare anion exchange membranes with bis-quaternary ammonium groups for hydroxide ion conductivity measurements. The block anion exchange membrane QBPES-60 with an ion exchange capacity (IEC) of 1.93mmolg−1 exhibited higher ionic conductivity (40.5mScm−1) in water at 60°C than the random copolymer QRPES-60 (30.0mScm−1) under the same conditions. Small-angle X-ray scattering and transmission electron microscopy suggested the membrane constructed from the block polymer exhibited a more obvious phase-separated structure and formed ion clusters which would be responsible for the high conductivity. Moreover, the block anion exchange membrane with bis-quaternary ammonium groups showed better alkaline stability than the random membrane where degradation could be recognized by 1H NMR spectra as well as ion conductivities. In conclusion, integrating the block hydrophilic bis-quaternary ammonium ion groups along with the long aliphatic side chains, and the hydrophobic copolymer backbone, this synthetic strategy is promising to prepare AEMs with high conductivity and good alkaline stability.

Controlled release bevacizumab in thermoresponsive hydrogel found to inhibit angiogenesis.

Age-related macular degeneration (ARMD) and intraocular neovascular diseases have been treated clinically by anti-VEGF antibody drug bevacizumab. However, the use of bevacizumab in the treatment of retinal neovascular diseases has been limited due to the short half-life and frequent injections. In this research, novel amphiphilic hydrophilic-hydrophobic block copolymers of methoxy-poly (ethylene glycol)-block-poly (lactic-co-glycolic acid) were synthesized with ring-opening polymerization, and cross-linked with 2,2-bis (2-oxazoline) (BOX). The aqueous solution of the block copolymers can reverse the sol-gel-sol phase transition. After 1 month of intravitreal injection, the histomorphology of a rabbit's retina was preserved, which indicated the mPEG-PLGA-BOX hydrogel had no cytotoxicity in vivo. Released bevacizumab from the mPEG-PLGA-BOX hydrogel inhibited the RF/6A (Maraca mulatta retina epithelial cell) and HUVEC cell growth, and anti-angiogenesis in 3-D cultures, which showed the bioactivity of the anti-VEGF agent, were maintained in the hydrogel within the release process. In conclusion, the mPEG-PLGA-BOX hydrogel had a sol-gel behavior phase transition, and its intraocular biocompatibility and the characteristics of biodegradability and bioactivity appear to be a promising intravitreal injection carrier for bevacizumab delivery.

High Stability Aggregation Obtained Using Hydrophilic-Hydrophobic Block Copolymer Based on Poly(trimethylene carbonate)

High Stability Aggregation Obtained Using Hydrophilic-Hydrophobic Block Copolymer Based on Poly(trimethylene carbonate)

Stable sol-gel microstructured and microfluidic networks for protein patterning.

We demonstrate the formation of micropatterned sol-gel structures containing active proteins by patterning with polydimethylsiloxane (PDMS) microchannels. To transport sol solution efficiently into the hydrophobic PDMS microchannels, a hydrophilic-hydrophobic block copolymer was used to impart hydrophilicity to the PDMS microchannels. Poor adhesion of the micropatterned gel structure onto glass slides was improved by treating the glass surface with a polymeric substrate. To minimize cracks in the gel microstructure, hybrid matrices of interpenetrating organic and inorganic networks were prepared containing the reactive organic moieties polyvinylalcohol or polyvinylpyrrolidone. Retention of biochemical activity within the micropatterned gel was demonstrated by performing immunobinding assays with immobilized immunoglobulin G (IgG) antibody. The potential application of microfluidics technology to immobilized-enzyme biocatalysis was demonstrated using PDMS-patterned microchannels filled with trypsin-containing sol-gels. This work provides a foundation for the microfabrication of functional protein chips using sol-gel processes.

Polystyrene/wood composites and hydrophobic wood coatings from water-based hydrophilic-hydrophobic block copolymers

The combination of synthetic thermoplastic polymers and wood is normally problematic because wood surfaces are hydrophilic while typical thermoplastic polymers are hydrophobic. A possible solution is to use block copolymer coupling agents. In this work we show the use of a potentially useful synthetic method of producing hydrophilic-hydrophobic block copolymers as hydrophobic coatings and coupling agents in polystyrene/ wood flour composites. In particular, wood veneers are coated with water-based emulsions of hydrophilic-hydro- phobic block copolymers from styrene and methacrylic acid. Dried coated surfaces are shown to become hydro- phobic through dynamic contact angle measurements. When wood flour is coated with the hydrophilic-hydro- phobic block copolymer based on styrene and acrylic acid, significant improvement in the ultimate tensile properties of composites formed from coated wood flour/ polystyrene mixtures is realized. Since no volatile organic compounds (VOCs) are used in coating wood surfaces and subsequent composite production, improvement in mechanical properties of thermoplastic/wood flour composites are shown to occur in environmentally responsible formulations.

Minimized platelet interaction with poly(2-hydroxyethyl methacrylate-block-4-bis(trimethylsilyl)methylstyrene) hydrogel showing anomalously high free water content

Novel hydrophilic-hydrophobic block copolymers - poly(2-hydroxyethyl methacrylate-block-4-bis(trimethylsilyl)methylstyrene) (poly(HEMA-block-BSMS) or BH polymer) - were prepared as materials potentially useful for blood-contacting devices. Among the BH(X) series including poly(HEMA) itself, platelet adhesion and activation are minimum on the surface of BH(10), the block copolymer composed of 10 mol% of the hydrophobic segment. The unique physicochemical characteristics of BH(10) such as the high free water content and the increased mobility of PHEMA segments seem to play an important role in the prevention of platelet adhesion and activation. The water content of BH(10) was twice that of poly(HEMA) itself, even in the presence of 10 mol% of the hydrophobic moiety [poly(BSMS)]. Further, an anomalous increase in free water content was observed for the BH(10) sample measured by DSC. The glass transition temperature of BH(10) in the dry state was determined to be c. 10°C, which was much lower than that observed for each of the homopolymers (c.f.: Tg [poly(HEMA)] = 70°C; Tg [poly(BSMS)] = 160°C), suggesting an increased mobility of tethered PHEMA segments in the BH(10) film.

Adsorption of Hydrophilic-Hydrophobic Block Copolymers on Silica from Aqueous Solutions

Adsorption of a water-soluble diblock copolymer, poly(tert-butylstyrene)-sodium poly(styrenesulfonate) (PtBS-NaPSS), on silica surfaces in aqueous solutions was studied using ellipsometry and atomic-force microscopy (AFM). The block copolymers used were compositionally asymmetric, with large, hydrophilic, PSS blocks and small, hydrophobic, PtBS blocks. Materials with molecular weights of 87 000 and 160 000 were used. Adsorption could not be observed in pure water without added salt (NaCl). When the NaCl concentration was increased to 1 M, adsorption could be readily observed. The measured adsorbed amount at long times was significantly larger for the 87 000 diblock compared with that for a polyelectrolyte homopolymer of comparable molecular size, demonstrating the role played by the uncharged block in anchoring the diblock at the solid surface. The kinetics of adsorption showed a two-stage process: an initial diffusion-limited stage, followed by a slower buildup of surface coverage in a brush-limited stage. The number density of molecules at the surface was smaller for the higher molecular weight species, in agreement with simple scaling arguments

Synthesis and Surface Characterization of Hydrophilic-Hydrophobic Block Copolymers Containing Poly(2,3-dihydroxypropyl methacrylate)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis and Surface Characterization of Hydrophilic-Hydrophobic Block Copolymers Containing Poly(2,3-dihydroxypropyl methacrylate)Hideharu Mori, Akira Hirao, Seiichi Nakahama, and Kazuhisa SenshuCite this: Macromolecules 1994, 27, 15, 4093–4100Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://doi.org/10.1021/ma00093a010RIGHTS & PERMISSIONSArticle Views850Altmetric-Citations68LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

Surface coating of hydrophilic-hydrophobic block co-polymers on a poly(acrylonitrile) haemodialyser reduces platelet adhesion and its transmembrane stimulation

Surface design aimed at reduced adhesion and preserved functions of platelets is of great importance for extracorporeal devices. In this study, a coating technique using hydrophilic-hydrophobic block co-polymers on a hydrophobic poly(acrylonitrile) (PAN) haemodialyser was explored. The hydrophilic block of co-polymers was composed of either poly(methoxy polyethylene glycol methacrylate) or poly(dimethyl acrylamide), and the hydrophobic block was poly(methyl methacrylate). The co-polymers were coated on the dialyser membrane by means of a solution coating method. Upon coating, the hydrophobic block of the co-polymers was anchored on a PAN membrane and the hydrophilic block oriented towards the blood-material interface. This was deduced from water wettability measurements. Significantly reduced transmembrane stimulation of platelets was observed, which was evaluated by determining the intracellular calcium ion concentration of platelets eluted through treated hollow fibres. This suppression was enhanced as the relative fraction of the hydrophilic block of the co-polymers increased. Furthermore, the number of platelets adhering to the co-polymer-coated PAN membrane was drastically reduced. Thus, coating of the hydrophilic-hydrophobic block co-polymers provided better biocompatibility on a hydrophobic PAN dialyser.

Etude des proprietes surfactives des copolymeres sequences

The surfactive properties of block copolymers are reviewed on the bases of studies which we have carried out during the last decade. The solution properties of block copolymers have been studied extensively in terms of their colloid-chemical behavior in selective solvents and their interfacial activity in two-phase systems. Micelle formation has been examined for hydrophilic-hydrophobic block copolymers. The micellar characteristics such as aggregation number have been correlated to the molecular characteristics, e.g. structure, molecular weight, composition, of di- and triblock copolymers based on polystyrene and poly(ethylene oxide). The emulsifying effect of block copolymers and the preparation of oil-water and oil-oil emulsions has been reviewed. In addition the surfactive properties of block copolymers are illustrated in the case of “polymeric oil-oil” and “polymeric water-water” emulsions which are formed by two incompatible polymers in the presence of a common solvent ; an organic solvent or water, respectively. The important factors, e.g. interfacial tension, interfacial thickness, molecular characteristics of the polymers, affecting the interfacial activity of the block copolymers and thus the stability of the “polymeric emulsions” are investigated. By a theoretical approach, and in particular by considering the interfacial characteristics of a liquid-liquid two-phase system, it was possible to define the optimum conditions leading to stable oil-water, oil-oil and to “polymeric emulsions”.

Investigation of the behaviour of random and block copolymers of styrene and methacrylic acid

For the first time hydrophilic-hydrophobic block copolymers of styrene and methacrylic acid have been obtained through a radical mechanism. It is shown that the behaviour of the block copolymers in dioxan-ethyl alcohol solution differs from that of random copolymers of like composition. Curling of the individual blocks into globules in the block copolymer molecules is dependent solely on solvent composition, whereas curling of the random copolymer molecule is also dependent on the styrene content of the copolymer.