Hydrophobic Block Copolymers Research Articles

Vortex-assisted dispersive solid-phase microextraction of cadmium and copper on magnetic polystyrene-b- poly dimethyl siloxane hydrophobic block copolymer for their atomic absorption spectrometric determination in water, soft drink and food samples

The goal of the study was to create an easy-to-use, efficient method for extracting and pre-concentrating copper (Cu) and cadmium (Cd) using vortex assisted dispersive solid phase microextraction (VAdSP-μE) using a magnetic polystyrene-b-poly dimethyl siloxane block copolymer (MPCP) in different food, soft drink and water matrices using FAAS. MPCP was synthesized and characterized using FTIR NMR, Sem-EDAX, DSC, GPC. Multivariate optimization was used to statistically evaluate the various factors. Various factors such as pH, the type and volume of eluent, MPCP mass, and contact time were optimized. The VAdSP-μE method used in this study involves dispersing the MPCP in the sample solution and magnetically separating the MPCP from the sample matrix. The adsorption capacity of MPCP was obtained as 20.1 mg g−1 and 31.4 mg g−1 for Cu and Cd. Under the optimum conditions, it has been achieved 2.5–140 µg L−1 and 5.1–100 µg L−1 linear range, 0.8 and 1.7 µg L−1 LOD, 1.1% and 0.7% RSD, and 50 enhancement factors for Cu and Cd, respectively. A certified set of materials for reference was used to verify the precision of the method. Water, soft drink, and food samples all underwent the current procedure.

Synthesis of Hydrophobic Block Copolymer Nanoparticles in Alcohol/Water Stabilized by Poly(methyl methacrylate) via RAFT Dispersion Polymerization-Induced Self-Assembly

Poly(methyl methacrylate) (PMMA) is an important common polymer widely used in industry. While PMMA has been used as a core-forming block for polymerization-induced self-assembly (PISA), a powerful approach for the synthesis of block copolymer nanoparticles, it has not been utilized as a corona block due to PMMA being insoluble in common solvents for PISA formulations (e.g., water and alcohols). Exploiting the solubility of PMMA-dithiobenzoate (DTB) in ethanol/water mixtures, such macroRAFT agents have in the present work been successfully employed for reversible addition–fragmentation chain transfer (RAFT) PISA in ethanol/water (80/20 by volume). RAFT dispersion polymerization of benzyl methacrylate mediated by PMMA-DTB macroRAFT agents with various degrees of polymerization has been investigated. Transmission electron microscopy analyses revealed well-defined block copolymer nano-objects, including spheres, worms, as well as vesicles. Nanoparticles comprising a PMMA outer layer would have superior compatibility with various hydrophobic polymer matrices, thereby enabling various new applications such as, e.g., use as nanofillers.

Nanoporous thin films of hydrophobic block copolymers enabled by selective swelling for membrane distillation

Membrane distillation (MD) is receiving growing interest because of its >99.9% salt rejection even with low-grade waste heat as the energy supply. However, MD membranes are prone to be wetted and usually require complicated modification strategies to gain sufficient hydrophobicity. In this work, we report a new type of MD membranes with hydrophobic films carrying pores in the ultrafiltration range as the separation layers. Such membranes are prepared by coating an A-B-A triblock copolymer polystyrene-block-polydimethylsiloxane-block-polystyrene (PS-b-PDMS-b-PS, further abbreviated as SDS) on the macroporous PVDF substrate, followed by soaking in alkanes to cavitate the SDS coating layers following the mechanism of selective swelling. The PDMS microdomains in the SDS layers are converted to interconnected nanopores, and the PDMS blocks are enriched along the pore walls and membrane surface, endowing the membranes with intrinsic hydrophobicity. Thus-prepared SDS membranes exhibit stable rejection to NaCl (>99.99%) and high permeate flux up to 32.8 kg m−2 h−1, better than most MD membranes with large pores in the microfiltration range. Moreover, the SDS membranes display excellent wetting resistance, good heat resistance, and long-term stability. This work provides a new strategy to prepare MD membranes enabled by selective swelling of hydrophobic block copolymers, and demonstrates the great potential of hydrophobic ultrafiltration membranes in the long-term use in membrane distillation.

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.

Lactate and glucose induced self‐assembly of hydrophobic boronic acid‐substituted polymers

AbstractAmphiphilic boronic acid (BA)‐substituted block copolymers have been utilized in biomedical applications through binding to saccharides, including to glucose whereas binding to the anaerobically produced metabolite lactate is unreported. Glucose requires basic conditions, while lactate binding occurs at neutral physiological conditions. Herein, BA binding to glucose and lactate is used for the first time to convert solvated hydrophobic homopolymer and hydrophobic block copolymers to amphiphilic core‐shell nanoparticle spheres and worms.

Preparation of hydrophobic block copolymer PCL-b-PFPE: The microsphere-coated fabrics via direct electrostatic spraying and its super-hydrophobicity

In this study, the perfluoropolyether carboxylic acid (PFPE-COOH) was used to react with polycaprolactone (PCL) to synthesise the hydrophobic block copolymer PCL-b-PFPE. The esterification reaction was performed successfully with the terminated hydroxyl group in the PCL-OH after activation of PFPE-COOH with N, N′ -dicyclohexyl carbon diimide. The PCL-b-PFPE was dissolved in various solvents to prepare microspheres using electrostatic spraying technology, and the flow rate, voltage, temperature and humidity parameters were optimised. The findings demonstrated that the solvent and ambient humidity had a substantial influence on the microspheres' surface morphology. Through smooth surface morphology, chloroform (CF) single solvent formed an ideal microsphere and DMF/CF mixed solvent produced a ‘pit’ surface morphology. Furthermore, the surface roughness of microspheres increases with an increase in humidity. The static contact angles of electrostatic spraying polyester fabric were 147.1° ± 1.8°, 150.9° ± 1.5°, 156.3° ± 2.6° and 155.9° ± 3.3°, under 20 %, 40 %, 60 % and 80 % humidity, respectively. The findings demonstrated that during the electrostatic spraying, the PFPE chain's introduction into PCL helped construct the secondary rough morphology on the microsphere surface and substantially enhanced the hydrophobicity of coatings, providing the finished polyester fabric super-hydrophobicity. The PCL-b-PFPE microspheres were directly sprayed and coated with the developed spray solution via electrostatic spraying. The water contact angle of the finished polyester fabric was found to be ≥140°, which provided hydrophobicity after 5 cycles of laundry. Following the sandpaper abrasion and adhesion tests, the contact angle of the fabrics coated with the microspheres remained ≥145°, indicating a good mechanical stability.

Selective Synthesis of Carbon Nanorings via Asymmetric Intramicellar Phase-Transition-Induced Tip-to-Tip Assembly

The selective synthesis of energetically less favorable ring-shaped nanostructures by liquid phase synthetic chemistry is a huge challenge. Herein, we report a precise synthesis of carbon nanorings with a well-defined morphology and tunable thickness based on asymmetric intramicellar phase-transition-induced tip-to-tip assembly via mixing hydrophobic long-chain octadecanol and block copolymer F127. This orientational self-assembly depends on the hydrophobicity difference of the intermediate’s surface, which triggers directional interactions that surpass the entropy cost of undesired connections and help assemble intermediates into defined ringlike structures. Based on a ringlike template, carbon nanorings with adjustable sizes can be attained by changing synthetic variables. More importantly, diverse units including crescentlike, podlike, and garlandlike nanostructures can also be created through controlling the kinetics of the self-assembly process. This discovery lays a solid foundation for the challenging construction of such a precise configuration on the nanoscale, which would not only promote fundamental studies but also pave the way for the development of advanced nanodevices with unique properties.

Membrane Engineering: Phase Separation in Polymeric Giant Vesicles.

Cell membranes exhibit elaborate lipidic patterning to carry out a myriad of functions such as signaling and trafficking. Domain formation in giant unilamellar vesicles (GUVs) is thus of interest for understanding fundamental biological processes and to provide new prospects for biocompatible soft materials. Lipid rearrangements in lipidic GUVs and lipid/polymer GUVs are extensively studied whereas polymer/polymer hybrid GUVs remain evasive. Here, the focus is on the thermodynamically driven phase separation of amphiphilic polymers in GUVs. It is demonstrated that polymer phase separation is entropically dictated by hydrophobic block incompatibilities and that films topology can help to determine the outcome of polymeric phase separation in GUVs. Lastly, Janus-GUVs are obtained and GUVs exhibit a single large domain by using a compatibilizing hydrophobic block copolymer.

Efficiency above 6% in poly(3‐hexylthiophene):phenyl‐C‐butyric acid methyl ester photovoltaics via simultaneous addition of poly(3‐hexylthiophene) based grafted graphene nanosheets and hydrophobic block copolymers

AbstractA combination of reduced graphene oxide (rGO) nanosheets grafted with regioregular poly(3‐hexylthiophene) (P3HT) (rGO‐g‐P3HT) and P3HT‐b‐polystyrene (PS) block copolymers was utilized to modify the morphology of P3HT:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM) active layers in photovoltaic devices. Efficiencies greater than 6% were acquired after a mild thermal annealing. To this end, the assembling of P3HT homopolymers and P3HT‐b‐PS block copolymers onto rGO‐g‐P3HT nanosheets was investigated, showing that the copolymers were assembled from the P3HT side onto the rGO‐g‐P3HT nanosheets. Assembling of P3HT‐b‐PS block copolymers onto the rGO‐g‐P3HT nanosheets developed the net hole and electron highways for charge transport, thereby in addition to photoluminescence quenching the charge mobility (μh and μe) values increased considerably. The best charge mobilities were acquired for the P3HT50000:PC71BM:rGO‐g‐P3HT50000:P3HT7000‐b‐PS1000 system (μh = 1.9 × 10−5 cm2 V–1 s–1 and μe = 0.8 × 10−4 cm2 V–1 s–1). Thermal annealing conducted at 120 °C also further increased the hole and electron mobilities to 9.8 × 10−4 and 2.7 × 10−3 cm2 V–1 s–1, respectively. The thermal annealing acted as a driving force for better assembly of the P3HT‐b‐PS copolymers onto the rGO‐g‐P3HT nanosheets. This phenomenon improved the short circuit current density, fill factor, open circuit voltage and power conversion efficiency parameters from 11.13 mA cm−2, 0.63 V, 62% and 4.35% to 12.98 mA cm−2, 0.69 V, 68% and 6.09%, respectively. © 2019 Society of Chemical Industry

Simple Photochemical Route to Block Copolymers via Two‐Step Sequential Type II Photoinitiation

AbstractA simple method for the preparation of block copolymers by a two‐step sequential Type II photoinitiation is described. In the first step, amine functionalized poly(methyl methacrylate) (PMMA‐N(Et)2) is prepared by photopolymerization of methyl methacrylate at λ = 350 nm using benzophenone and triethyl amine as photosensitizer and hydrogen donor, respectively. Subsequent benzophenone‐sensitized photopolymerization of tert‐butyl acrylate using PMMA‐N(Et)2 as hydrogen donor yielded poly(methyl methacrylate)‐block‐poly(tert‐butyl acrylate). The obtained hydrophobic block copolymer is readily converted to amphiphilic polymer by hydrolysis of the tert‐butyl ester moieties of the block copolymer as demonstrated by contact angle measurements. All polymers are characterized by NMR, Fourier transform infrared and UV–vis spectroscopies, and differential scanning calorimetry (DSC) thermal analyses.

Self‐Assembly of Poly(vinylpyridine‐b‐oligo(ethylene glycol) methyl ether methacrylate) Diblock Copolymers

ABSTRACTPoly(oligoethylene glycol)‐poly(2‐vinylpyridine) is a model diblock for studying the effect of block‐localized charge on block copolymer self‐assembly because in the absence of charge the polymers are perfectly miscible, and upon protonation of the vinylpyridine block the polymer undergoes an order–disorder transition. Seven model block copolymers with molecular weights of approximately 60 kDa containing poly(2‐vinylpyridine) volume fractions spanning 0.069–0.700 were synthesized using reversible addition fragmentation transfer polymerization and then studied to understand the effect of protonation level, diblock composition, and temperature on the location of the ordering transition and the type of nanostructures formed in a charge asymmetric system. All of the polymers displayed lower critical solution‐type behavior, with the order–disorder transition temperature decreasing with increasing acid content. Polymers with symmetric compositions showed the highest degree of incompatibility for a given degree of protonation, and the observed morphologies for all polymers were consistent with those observed at similar compositions for classical hydrophobic block copolymers. The observed protonation‐induced phase transition can be explained by the shift of the Flory–Huggins parameter due to the alternation of the identity of monomers, consistent with the prediction of Nakamura and Wang's theory. The use of polyvalent ions promotes self‐assembly at lower concentrations, consistent with ionic crosslinking effects between polymer chains that are promoted at high concentration due to exchange entropy in crosslinked polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1181–1190

Amphiphilic Polymer Conetworks Based on Interconnected Hydrophobic Star Block Copolymers: Synthesis and Characterization

SummaryHerein we report on the preparation and structural characterization of six amphiphilic polymer conetworks (APCN) based on end‐linked amphiphilic “core‐first” star block copolymers, comprising methyl methacrylate and 2‐(dimethylamino)ethyl methacrylate as the monomer repeating units in the hydrophobic and hydrophilic blocks, respectively. The various APCNs differed either in the arm composition or in the arm molecular weight. APCN synthesis was accomplished via the one‐pot, sequential group transfer polymerization (GTP) of cross‐linker, hydrophobic monomer, hydrophilic monomer, and cross‐linker again. The soluble precursors to the APCNs, i.e., the star homopolymers, the star block copolymers and the initial cross‐linker cores, were characterized in terms of their composition, size and size dispersity. The degrees of swelling in tetrahydrofuran were found to increase with the molecular weight of the arms of the stars of the APCNs, whereas the degrees of swelling in water increased with the content in hydrophilic units in the arms of the constituting stars. Small‐angle neutron scattering (SANS) indicated that most APCNs nanophase separated in D2O. The structure and size of the hydrophobic domains determined by fitting the SANS data to an appropriate model could be correlated with the molecular architecture of the APCNs. Finally, polarized light microscopy showed that all APCNs were birefringent both in water and in the dried state.

Macromolecular metamorphosis via stimulus-induced transformations of polymer architecture.

Macromolecular architecture plays a pivotal role in determining the properties of polymers. When designing polymers for specific applications, it is not only the size of a macromolecule that must be considered, but also its shape. In most cases, the topology of a polymer is a static feature that is inalterable once synthesized. Using reversible-covalent chemistry to prompt the disconnection of chemical bonds and the formation of new linkages in situ, we report polymers that undergo dramatic topological transformations via a process we term macromolecular metamorphosis. Utilizing this technique, a linear amphiphilic block copolymer or hyperbranched polymer undergoes 'metamorphosis' into comb, star and hydrophobic block copolymer architectures. This approach was extended to include a macroscopic gel which transitioned from a densely and covalently crosslinked network to one with larger distances between the covalent crosslinks when heated. These architectural transformations present an entirely new approach to 'smart' materials.

Controlling the aqueous solubility of PNIPAM with hydrophobic molecular units

The effect of co-polymerization of thermo-sensitive polymers with hydrophilic or hydrophobic co-monomers on the LCST and the structure of proximal water remains a fundamental and challenging problem. Here, we employ all-atom molecular dynamics simulations to investigate the aqueous solubility of a thermo-sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), a hydrophobic polymer polystyrene (PS) and block co-polymers of PNIPAM-co-PS. The simulations of pure oligomers of PNIPAM and PS and their co-polymers are conducted below and above the LCST of PNIPAM to elucidate the effect of increase in number of PS units in PNIPAM-co-PS co-polymers on the coil-to-globule transition of PNIPAM and structure of proximal water. Our simulations suggest that while the LCST of pure PNIPAM oligomers is strongly associated with the structural changes in the proximal water molecules present near PNIPAM, inclusion of PS units disrupts the interactions between PNIPAM and water and promotes the faster dehydration of PNIPAM chains above its LCST. This phenomenon is manifested by a coil-to-globule transition in PNIPAM chains present in PNIPAM-co-PS co-polymers at much shorter times as compared to the pure PNIPAM oligomers. Our results also reveal that with increase in the number of PS units in PNIPAM-co-PS co-polymers the coil-to-globule transition is accelerated.

Surface Chemistry of Amphiphilic Polysiloxane/Triethyleneglycol-Modified Poly(pentafluorostyrene) Block Copolymer Films Before and After Water Immersion

New amphiphilic block copolymers Si-EFSx composed of a poly(dimethyl siloxane) (Si) block and a poly(4-(triethyleneglycol monomethyl ether)-2,3,5,6-tetrafluorostyrene) (EFS) block are synthesized by atom transfer radical polymerization (ATRP) starting from a bromo-terminated Si macroinitiator. Similarly, new hydrophobic block copolymers Si-FSy consisting of an Si block and a poly(pentafluorostyrene) (FS) block are prepared for comparison. X-ray photoelectron spectroscopy (XPS) analysis on block copolymer films reveals that the Si block is concentrated at the polymer–air interface, while the EFS block is located in the layers underneath. The same polymer films undergo a marked surface reconstruction after immersion in water for 7 d, as probed by XPS. This phenomenon involves the exposure of the hydrophilic oxyethylenic chains to contact water. Such surface reconstruction is even more drastic when an amphiphilic block copolymer is dispersed in a cross-linked poly(dimethyl siloxane) matrix film.

High‐Internal‐Phase Emulsion Tailoring Polymer Amphiphilicity towards an Efficient NIR‐Sensitive Bacteria Filter

Emulsions having a high internal-phase volume fraction—termed as HIPEs for high internal phase emulsions—are in high demand as templates for functional macroporous materials. Designing molecular surfactants with appropriate amphiphilicity plays a critical role in the HIPE preparation. In this study, successful tailoring of the amphiphilicity of the originally hydrophobic block co-polymer of polystyrene-b-polyvinylpyridine (PS-b-P4VP) is reported. In combination with trifluoroacetic acid, less than 5 wt% of the polymer-CF3COOH system is feasible as a surfactant for HIPE preparation; this is lower than the amounts typically needed for commonly used commercial surfactants. Using the HIPEs as templates, well-defined closed- and open-cell macroporous triacrylate-based monoliths are fabricated simply through the adjustment of the ratio of the water phase to oil phase. After coating the resulting macroporous material with polypyrrole nanoparticles, the system can be exploited as an NIR-sensitive filter for bacteria; it not only excludes oversized bacteria, but it also kills the bacteria with the help of NIR-induced heat.

Preparation of Pickering double emulsions using block copolymer worms.

The rational formulation of Pickering double emulsions is described using a judicious combination of hydrophilic and hydrophobic block copolymer worms as highly anisotropic emulsifiers. More specifically, RAFT dispersion polymerization was utilized to prepare poly(lauryl methacrylate)–poly(benzyl methacrylate) worms at 20% w/w solids in n-dodecane and poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate)–poly(benzyl methacrylate) worms at 13% w/w solids in water by polymerization-induced self-assembly (PISA). Water-in-oil-in-water (w/o/w) double emulsions can be readily prepared with mean droplet diameters ranging from 30 to 80 μm using a two-stage approach. First, a w/o precursor emulsion comprising 25 μm aqueous droplets is prepared using the hydrophobic worms, followed by encapsulation within oil droplets stabilized by the hydrophilic worms. The double emulsion droplet diameter and number of encapsulated water droplets can be readily varied by adjusting the stirring rate employed during the second stage. For each stage, the droplet volume fraction is relatively high at 0.50. The double emulsion nature of the final formulation was confirmed by optical and fluorescence microscopy studies. Such double emulsions are highly stable to coalescence, with little or no change in droplet diameter being detected over storage at 20 °C for 10 weeks as judged by laser diffraction. Preliminary experiments indicate that the complementary o/w/o emulsions can also be prepared using the same pair of worms by changing the order of homogenization, although somewhat lower droplet volume fractions were required in this case. Finally, we demonstrate that triple and even quadruple emulsions can be formulated using these new highly anisotropic Pickering emulsifiers.

Molecular interaction governing solubility and release profiles in supramolecular systems containing fenbufen, pluronics and cyclodextrins

In this work, the combination of two solubilizing agents, methyl-beta-cyclodextrin and Pluronic F68, is proposed and analyzed for a sparingly water soluble drug, fenbufen. Despite the large solubility enhancement achieved, ca. 70-fold, the synergistic effect promoted by the combination of these agents, is only effective over a narrow concentration range, being replaced by a competition between the drug and hydrophobic blocks of the copolymer when the concentration of the latter increases. Moreover, the detailed analysis of the release profiles, resorting to a model dependent approach, shows that the combination of these agents is a strong modulator of the overall profile and also of the total amount of drug that is released. Molecular dynamics simulation indicates a significant change in the cyclodextrin behavior, when alone in solution, situation in which the collapse of the conical structure is relatively frequent, or in the presence of each of the other components, and also shows that copolymer extension is decreased upon introduction of the drug, while there is an increase in extension when the cyclodextrin is added. Inclusion complexes are detected for both drug and copolymer. These play a definite role in solubilization by cyclodextrins, but are also responsible for the competitive behavior observed when polymeric micelles are present. Hydrophobic block copolymers compete with the drug for the cyclodextrin cavity through the formation of polypseudorotaxanes, which in turn modulates drug release. From the fundamental point of view, this work presents an in depth analysis of the molecular behavior in these systems, focusing on the cyclodextrin, inclusion complexes, polymeric micelles and supramolecular systems.

Regulation of the self-assembly morphology of azobenzene-bearing double hydrophobic block copolymers in aqueous solution by shifting the dynamic host–guest complexation

The complexation equilibrium between azo and β-CD can be shifted by various methods, thus the micellar morphology of azo-bearing block copolymers is altered.

Noncanonical Self-Assembly of Highly Asymmetric Genetically Encoded Polypeptide Amphiphiles into Cylindrical Micelles

Elastin-like polypeptides (ELPs) are a class of biopolymers consisting of the pentameric repeat (VPGαG)n based on the sequence of mammalian tropoelastin that display a thermally induced soluble-to-insoluble phase transition in aqueous solution. We have discovered a remarkably simple approach to driving the spontaneous self-assembly of high molecular weight ELPs into nanostructures by genetically fusing a short 1.5 kDa (XGy)z assembly domain to one end of the ELP. Classical theories of self-assembly based on the geometric mass balance of hydrophilic and hydrophobic block copolymers suggest that these highly asymmetric polypeptides should form spherical micelles. Surprisingly, when sufficiently hydrophobic amino acids (X) are presented in a periodic sequence such as (FGG)8 or (YG)8, these highly asymmetric polypeptides self-assemble into cylindrical micelles whose length can be tuned by the sequence of the morphogenic tag. These nanostructures were characterized by light scattering, tunable resistive pulse sensing, fluorescence spectrophotometry, and thermal turbidimetry, as well as by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS). These short assembly domains provide a facile strategy to control the size, shape, and stability of stimuli responsive polypeptide nanostructures.