Diblock Copolymers Of Polystyrene Research Articles

Reversible switching of supramolecular self‐assembly between nanofibers and nanorings based on perylene‐terminated star elastomers

AbstractPerylene‐terminated star elastomers (PSE) containing the diblock copolymers of polystyrene (PS) and polyisoprene (PI) segments were designed and synthesized by anionic polymerization. The PSE exhibits good fluorescence performances in solution, self‐assembled aggregates, and solid state. Different supramolecular self‐assemblies in tetrahydrofuran (THF) solution based on the π−π stacking of perylene and interactions in PS can be observed from nanofibers to twisted multi‐nanoropes. Moreover, the twisted nanoropes under ultrasonic can transform spontaneously into nanorings in the stationary state, and reversibly switch between twisted nanoropes and nanorings via the manipulation of ultrasonic force. The terminating methods will offer considerable scope for the design and synthesis of new star elastomers. Meanwhile, a new insight into π−π stacking and interactions is provided for understanding multistep and cooperative self‐assembly in supramolecular self‐assembly.

PH-responsive size- and charge-selective block copolymer membrane for the separation of small proteins

Blue-light-induced RAFT polymerization was utilized to synthesize poly(N,N-dimethylacrylamide)–block–polystyrene (PDMA–b–PS) diblock copolymers to obtain 40 g per batch for membrane fabrication. Using a combination of self-assembly and non-solvent induced phase separation (SNIPS), larger isoporous membranes (≈ 0.5 m · 0.3 m) were fabricated with pore diameters of ≈ 25 nm in the dry state and around 4 nm in the wet state. These membranes were post-modified with hydrochloric acid to impart negatively charged, pH-responsive poly(acrylic acid)–block–polystyrene (PAA–b–PS) membranes. While all proteins like cytochrome C, insulin, lysozyme, myoglobin, and ovalbumin were fully rejected by the pristine PDMA–b–PS membrane, the PAA–b–PS membrane demonstrated selective rejection based on protein size and charge, effectively rejecting the proteins with a hydrodynamic radius Rh ≥ 1.9 nm. The PAA–b–PS membrane showed a real selectivity of 4.1 for the positively charged protein cytochrome C compared to the similarly sized, but negatively charged insulin, as well as a real selectivity of 16.1 towards the negatively charged ovalbumin. This illustrates the size- and charge-selective characteristics of the PAA–b–PS membrane for protein separation.

Influence of the Grain Size on the Mechanical Behavior of a Nanostructured Poly(butyl methacrylate)–Polystyrene Diblock Copolymer

The morphology and mechanical properties of solution-cast poly(butyl methacrylate)–polystyrene (PBMA–PS) diblock copolymer films (Mn = 270 kg mol−1, 70 Vol.-% PS) prepared by using different solvents (cyclohexane, toluene, chloroform, and dioxane) are investigated in this study. All solvents except dioxane, which leads to PBMA cylinders in the PS matrix, result in lamellar morphologies. The grain size, however, by using cyclohexane, is —two to three times smaller compared to toluene and chloroform. The grain boundaries in PBMA–PS formed by the soft thermoplastic PBMA phase cause flaws in the material, which results in both small values of the tensile strength of cyclohexane-cast films (23 MPa) compared to toluene- and chloroform-cast ones (31–32 MPa) and low ductility.

Intermittent-contact local dielectric spectroscopy of nanostructured interfaces

Local dielectric spectroscopy (LDS) is a scanning probe method, based on dynamic-mode atomic force microscopy (AFM), to discriminate dielectric properties at surfaces with nanometer-scale lateral resolution. Until now a sub-10 nm resolution for LDS has not been documented, that would give access to the length scale of fundamental physical phenomena such as the cooperativity length related to structural arrest in glass formers (2–3 nm). In this work, LDS performed by a peculiar variant of intermittent-contact mode of AFM, named constant-excitation frequency modulation, was introduced and extensively explored in order to assess its best resolution capability. Dependence of resolution and contrast of dielectric imaging and spectroscopy on operation parameters like probe oscillation amplitude and free amplitude, the resulting frequency shift, and probe/surface distance-regulation feedback gain, were explored. By using thin films of a diblock copolymer of polystyrene (PS) and polymethylmethacrylate (PMMA), exhibiting phase separation on the nanometer scale, lateral resolution of at least 3 nm was demonstrated in both dielectric imaging and localized spectroscopy, by operating with optimized parameters. The interface within lamellar PS/PMMA was mapped, with a best width in the range between 1 and 3 nm. Changes of characteristic time of the secondary (β) relaxation process of PMMA could be tracked across the interface with PS.

The Effect of Poly(ethylene glycol) (PEG) Length on the Wettability and Surface Chemistry of PEG-Fluoroalkyl-Modified Polystyrene Diblock Copolymers and Their Two-Layer Films with Elastomer Matrix.

Diblock copolymers composed of a polystyrene first block and a PEG-fluoroalkyl chain-modified polystyrene second block were synthesized by controlled atom transfer radical polymerization (ATRP), starting from the same polystyrene macroinitiator. The wettability of the polymer film surfaces was investigated by measurements of static and dynamic contact angles. An increase in advancing water contact angle was evident for all the films after immersion in water for short times (10 and 1000 s), consistent with an unusual contraphilic switch of the PEG-fluoroalkyl side chains. Such a contraphilic response also accounted for the retained wettability of the polymer films upon prolonged contact with water, without an anticipated increase in the hydrophilic character. The copolymers were then used as surface-active modifiers of elastomer poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS)-based two-layer films. The elastomeric behavior of the films was varied by using SEBS matrices with different amounts of polystyrene. Whereas the mechanical properties strictly resembled those of the nature of the SEBS matrix, the surface properties were imposed by the additive. The contraphilic switch of the PEG-fluoroalkyl side chains resulted in an exceptionally high enrichment in fluorine of the film surface after immersion in water for seven days.

Surface-Induced Ordering Depresses Through-Film Ionic Conductivity in Lamellar Block Copolymer Electrolytes.

Lamellar block copolymers based on polymeric ionic liquids (PILs) show promise as electrolytes in electrochemical devices. However, these systems often display structural anisotropy that depresses the through-film ionic conductivity. This work hypothesizes that structural anisotropy is a consequence of surface-induced ordering, where preferential adsorption of one block at the electrode drives a short-range stacking of the lamellae. This point was examined with lamellar diblock copolymers of polystyrene (PS) and poly(1-(2-acryloyloxyethyl)-3-butylimidazolium bis(trifluoromethanesulfonyl)imide) (PIL). The bulk PS-PIL structure was comprised of randomly oriented lamellar grains. However, in thin PS-PIL films (100-400 nm), the lamellae were stacked normal to the plane of the film, and islands/holes were observed when the as-prepared film thickness was incommensurate with the natural lamellar periodicity. Both of these attributes are well-known consequences of preferential wetting at surfaces. The ionic conductivity of thick PS-PIL films (50-100 μm) was approximately 20× higher in the in-plane direction than in the through-plane direction, consistent with a mixed structure comprised of randomly oriented lamellae throughout the interior of the film and highly oriented lamellae at the electrode surface. Therefore, to fully optimize the performance of a block copolymer electrolyte, it is important to consider the effects of surface interactions on the ordering of domains.

Aggregated Solution Morphology of Poly(acrylic acid)-Poly(styrene) Block Copolymers Improves Drug Supersaturation Maintenance and Caco-2 Cell Membrane Permeation.

Amorphous solid dispersions of polymers and drugs have been shown to improve supersaturation maintenance of poorly water-soluble drugs. Herein, amorphous spray-dried dispersions (SDDs) of poly(acrylic acid)-polystyrene (PS-b-PAA) diblock copolymers with differing degrees of polymerization were prepared in aggregated and nonaggregated states with the Biopharmaceutical Classification System Class II drug, probucol (PBC). Specifically, PS90-b-PAA15, PS90-b-PAA80, PS38-b-PAA220, and PS38-b-PAA320 amphiphilic block polymers that covered a compositional range in the area of oral drug delivery were prepared to examine the role of molecular weight and controlled aggregation in promoting drug supersaturation and maintenance. In addition, hydrophilic homopolymers PAA20, PAA96, PAA226, and PAA392 were prepared as controls to evaluate the role of the block copolymer-based SDDs in PBC solubilization. Characterization such as powder X-ray diffraction, scanning electron microscopy, and dissolution tests under nonsink conditions were then performed to evaluate the SDDs. When comparing the block copolymer systems, polymers that were preaggregated into micellular structures prior to spray drying with the drug promoted higher drug solubility and maintenance than when the drug was formulated with molecularly dissolved PS-PAA block polymer. Interestingly, the aggregated PS90-b-PAA80 SDD with 25 wt % PBC achieved 100% burst release and maintained full supersaturation of PBC at pH 6.5 (physiological pH in the small intestine). Dissolution studies conducted at the pH of the stomach (pH = 1.2) show that a minimal amount of drug (∼10 μg/mL) was released, which could be used for protecting drugs from acidic environments (stomach) before reaching the small intestine. To evaluate drug bioavailability, in vitro Caco-2 cell assays were performed, which reveal that PAA-based excipients do not hinder drug permeation across the epithelial membrane and that PS90-b-PAA80 SDD with 25 wt % PBC achieved the highest membrane permeability coefficient. This work demonstrates that block copolymer-based SDDs capable of preaggregating into nanostructures may be a tunable drug-delivery platform that can improve solubility and supersaturation maintenance of Class II pharmaceutics while also not prohibiting bioavailability through model intestinal membranes. Indeed, this concept may be extended to accommodate a myriad of pharmaceutical and excipient structures.

DNA-Functionalized 100 nm Polymer Nanoparticles from Block Copolymer Micelles.

DNA-mediated self-assembly of colloidal particles is one of the most promising approaches for constructing colloidal superstructures. For nanophotonic materials and devices, DNA-functionalized colloids with diameters of around 100 nm are essential building blocks. Here, we demonstrate a strategy for synthesizing DNA-functionalized polymer nanoparticles (DNA-polyNPs) in the size range of 55-150 nm using block copolymer micelles as a template. Diblock copolymers of polystyrene- b-poly(ethylene oxide) with an azide end group (PS- b-PEO-N3) are first formed into spherical micelles. Then, the micelle cores are swollen with the styrene monomer and polymerized, thus producing PS NPs with PEO brushes and azide functional end groups. DNA strands are conjugated onto the ends of the PEO brushes through a strain-promoted alkyne-azide cycloaddition reaction, resulting in a DNA density of more than one DNA strand per 12.6 nm2 for 70 nm particles. The DNA-polyNPs with complementary sequences enable the formation of CsCl-type colloidal superstructure by DNA binding.

Effects of Spreading Conditions on the Aggregation Behavior of a Symmetric Diblock Copolymer Polystyrene- block-poly(methyl methacrylate) at the Air/Water Interface.

Langmuir monolayers and Langmuir-Blodgett (LB) films of a symmetric diblock copolymer polystyrene- block-poly(methyl methacrylate) (PS- b-PMMA) were characterized by the film balance technique and tapping mode atomic force microscopy, respectively. Effects of both the spreading solution concentration and the surface concentration on the aggregation behavior of PS- b-PMMA at the air/water interface and the morphologies of its LB films were studied in detail. When the monolayers spread in different concentrations (≤0.50 mg/mL), all their initial morphologies exhibit tiny circular micelles because of the long hydrophilic PMMA block in the copolymer. The initial tiny circular micelles form spontaneously and then aggregate into small ones upon compression, which can further coalesce into rodlike aggregates or large micelles depending on the spreading concentrations. The LB films of PS- b-PMMA usually exhibit various mixed structures of rodlike aggregates and circular micelles, which can further transform into labyrinth patterns under some special spreading conditions. Besides spreading concentration and volume, we discover that the detailed spreading process should also be responsible for the initial and final morphologies of the LB films. Furthermore, the LB films prepared under different spreading conditions can be regarded as in the equilibrium or nonequilibrium structures because of the kinetic effect difference resulting from the different PS chain entanglement degrees.

Solubilization of Phenol Derivatives in Polymer Micelles Formed by Cationic Block Copolymer

The aggregation of cationic block copolymers formed by polystyrene (PS) and poly(ethyl-4-vinylpyridine) (PS-b-PE4VP) was studied in aqueous solution. Diblock copolymers of PS and poly(4-vinylpyridine) were synthesized by sequential anionic polymerization using BuLi as initiator. Subsequently, the 4-vinylpyridine units were quaternized with ethyl bromide to obtain cationic PS-b-PE4VP block copolymers with different quaternization degree. The self-aggregation of cationic block copolymers was studied by fluorescence probing, whereas the morphology and size of polymer micelles were determined by transmission electronic microscopy. Results indicate that spherical micelles with sizes lower than 100 nm were formed, whereas their micropolarity decreases with increasing quaternization degree. The partition of phenols between the micellar and aqueous phase was studied by using the pseudo-phase model, and the results show that the partition coefficients increase with increasing length of the side alkyl chain and are larger for star micelles. These results are discussed in terms of three-region model.

Diblock copolymers of polystyrene‐b‐poly(1,3‐cyclohexadiene) exhibiting unique three‐phase microdomain morphologies

ABSTRACTThe synthesis and molecular characterization of a series of conformationally asymmetric polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐b‐PCHD) diblock copolymers (PCHD: ∼90% 1,4 and ∼10% 1,2), by sequential anionic copolymerization high vacuum techniques, is reported. A wide range of volume fractions (0.27 ≤ ϕPS ≤ 0.91) was studied by transmission electron microscopy and small‐angle X‐ray scattering in order to explore in detail the microphase separation behavior of these flexible/semiflexible diblock copolymers. Unusual morphologies, consisting of PCHD core(PCHD‐1,4)–shell(PCHD‐1,2) cylinders in PS matrix and three‐phase (PS, PCHD‐1,4, PCHD‐1,2) four‐layer lamellae, were observed suggesting that the chain stiffness of the PCHD block and the strong dependence of the interaction parameter χ on the PCHD microstructures are important factors for the formation of this unusual microphase separation behavior in PS‐b‐PCHD diblock copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1564–1572

In Situ Photocontrol of Block Copolymer Morphology During Dip-Coating of Thin Films.

We demonstrate a unique combination of simultaneous top-down and bottom-up control of the morphology of block copolymer films by application of in situ optical irradiation during dip-coating. A light-addressable and block-selective small molecule, 4-butyl-4'-hydroxyazobenzene (BHAB), is introduced into a diblock copolymer of polystyrene and poly(4-vinylpyridine) (PS-P4VP) of 28.4 wt % P4VP via supramolecular chemistry, notably by hydrogen bonding to P4VP. We show that the spherical morphology of thin films dip-coated from a THF solution at slow withdrawal rates in the dark convert to cylindrical morphology when dip-coated under illumination. This is attributed to volume expansion of the P4VP/BHAB phase due to trans-cis photoisomerization combined with a light-induced increase in BHAB uptake in the film. The demonstrated photocontrol highlights the potential of dip-coating as a scalable film preparation method that can be easily coupled with external stimuli to direct nanostructured self-assembly in the films as solvent evaporates.

Photopatterning of cross-linkable epoxide-functionalized block copolymers and dual-tone nanostructure development for fabrication across the nano- and microscales.

The self-assembly of block copolymers in thin films provides an attractive approach to patterning 5-100 nm structures. Cross-linking and photopatterning of the self-assembled block copolymer morphologies provide further opportunities to structure such materials for lithographic applications, and to also enhance the thermal, chemical, or mechanical stability of such nanostructures to achieve robust templates for subsequent fabrication processes. Here, model lamellar-forming diblock copolymers of polystyrene and poly(methyl methacrylate) with an epoxide functionality are synthesized by atom transfer radical polymerization. We demonstrate that self-assembly and cross-linking of the reactive block copolymer materials in thin films can be decoupled into distinct, controlled process steps using solvent annealing and thermal treatment/ultraviolet exposure, respectively. Conventional optical lithography approaches can also be applied to the cross-linkable block copolymer materials in thin films and enable simultaneous structure formation across scales-micrometer scale patterns achieved by photolithography and nanostructures via self-assembly of the block copolymer. Such materials and processes are thus shown to be capable of self-assembling distinct block copolymers (e.g., lamellae of significantly different periodicity) in adjacent regions of a continuous thin film.

Rapid synthesis of ultrahigh molecular weight and low polydispersity polystyrene diblock copolymers by RAFT-mediated emulsion polymerization

An environmentally friendly emulsion technique produces uniform nanoparticles with precise control over molecular weight and particle size.

Facile synthesis of block copolymers from a cinnamate derivative by combination of AGET ATRP and click chemistry

An azido- and bromo-containing compound derived from naturally occurring ethyl cinnamate was used successfully to prepare block copolymers by a combination of ‘activator generated by electron transfer atom transfer radical polymerization’ (AGET ATRP) and Huisgen “click” reactions in emulsion. First, azido-end poly(methyl methacrylate) and alkyne-end polystyrene were prepared under AGET ATRP conditions, then, poly(methyl methacrylate) block polystyrene (PMMA-b-PS) diblock copolymer was formed by Huisgen 1,3-dipolar cycloaddition. Finally, polystyrene block poly(methyl methacrylate) block polystyrene (PS-b-PMMA-b-PS) triblock copolymer was synthesized via simultaneous AGET ATRP and click reactions, catalyzed by the same copper-based catalyst. The polymers were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), which confirmed the successful synthesis of the corresponding polymers.

High angular-resolution automated visible-wavelength scanning angle Raman microscopy

A scanning angle (SA) Raman microscope with 532-nm excitation is reported for probing chemical content perpendicular to a sample interface. The instrument is fully automated to collect Raman spectra across a range of incident angles from 20.50 to 79.50° with an angular spread of 0.4±0.2° and an angular uncertainty of 0.09°. Instrumental controls drive a rotational stage with a fixed axis of rotation relative to a prism-based sample interface mounted on an inverted microscope stage. Three benefits of SA Raman microscopy using visible wavelengths, compared to near infrared wavelengths are: (i) better surface sensitivity; (ii) increased signal due to the frequency to the fourth power dependence of the Raman signal, and the possibility for resonant enhancement; (iii) the need to scan a reduced angular range to shorten data collection times. These benefits were demonstrated with SA Raman measurements of thin polymer films of polystyrene or a diblock copolymer of polystyrene and poly(3-hexylthiophene-2,5-diyl). Thin film spectra were collected with a signal-to-noise ratio of 30 using a 0.25s acquisition time.

Polystyrene-poly(2-ethylhexylmethacrylate) block copolymers: Synthesis, bulk phase behavior, and thin film structure

Anionic polymerization was employed to synthesize well-defined diblock copolymers of polystyrene and poly(2-ethylhexylmethacrylate), PS-PEHMA. Diblock morphologies in bulk and in substrate-supported thin films were characterized by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM), respectively. PS-PEHMA diblocks exhibited thermotropic order-disorder transitions; one diblock showed a thermoreversible transition between lamellae and a higher-temperature morphology assigned as perforated lamellae. Unlike PS-poly(alkylmethacrylate) diblocks where the alkyl group is n-butyl or n-pentyl, PS-PEHMA diblocks showed a typical decreasing Flory interaction parameter with increasing temperature. Thin films of PS-cylinder-forming PS-PEHMA diblocks showed a strong preference for the cylinders to lie in the plane of the film; films of incommensurate thickness readily formed terraces. Films of commensurate thickness were easily aligned over macroscopic areas through the application of mechanical shear.

HPLC Characterization of Hydrogenous Polystyrene-block-deuterated polystyrene Utilizing the Isotope Effect

HPLC elution behavior of isotopically different block copolymers was investigated. A series of three diblock copolymers of hydrogenous polystyrene and deuterated polystyrene (hPS-b-dPS), in which the length of hPS-block is fixed at 18 kg/mol and the length of dPS-block is varied from 17 kg/mol to 80 kg/mol, was synthesized and their retention behavior in liquid chromatography at critical condition (LCCC) was investigated using a C18 coated silica stationary phase and a mixed solvent of CH2Cl2 and CH3CN. At this LC separation condition, hPS is retained slightly longer than dPS. The LCCC separations were performed at both LCCC conditions of dPS and hPS established with the same stationary and mobile phases, but at different column temperatures. Since the chromatographic retention difference between dPS and hPS is very small, it was possible to elute the block copolymers at both exclusion and interaction modes at the critical condition of each individual block. We found that the block at its critical condition is not fully invisible in both cases. In the LCCC separation at the critical condition of dPS, hPS-b-dPS elutes after the injection solvent peak (interaction mode) due to the stronger interaction of the hPS block. Although they have the same hPS block, they do not coelute but elute in the order of decreasing total molecular weight like an elution in exclusion mode. It clearly demonstrates that the dPS block is not invisible at the critical condition but influences the retention of the block copolymers. Monte Carlo simulations of the partition coefficient of A-b-B into a slit pore were performed to give insight on the elution behavior of A-b-B at the critical condition of the B block. The simulation shows that a block under the critical condition influences the retention of the other visible block whether the visible block is eluted in exclusion or interaction mode. When A is eluted in the interaction mode and B is at its critical condition, the partition coefficient is found to decrease with the increase of the invisible B block length, conforming to the observed elution behavior in experiments.

Selective localization of multi-wall carbon nanotubes in homopolymer blends and a diblock copolymer. Rheological orientation studies of the final nanocomposites

In this study, pristine as well as polystyrene (PS) and poly(2-vinylpyridine) (P2VP) functionalized multi-wall carbon nanotubes (MWCNTs) were selectively incorporated in homopolymer binary blends of PS/P2VP and diblock copolymer (BCP) of the PS-b-P4VP type [P4VP: poly(4-vinylpyridine)]. Studies on the blends verified the chemical affinity of PS and P2VP grafted MWCNTs to the corresponding phase. Based on the results obtained from the blend systems, MWCNTs were incorporated in a PS-b-P4VP copolymer matrix with lamellar morphology and large amplitude oscillatory shear (LAOS) experiments were performed to achieve orientation of the BCP lamellae. The PS grafted MWCNTs (MWCNT-g-PS) were selectively sequestered in the PS phase and the P2VP grafted MWCNTs (MWCNT-g-P2VP) in the P4VP phase of the diblock copolymer. Unfunctionalized pristine MWCNTs were localized on the PS phase of the blend system and no special preference was observed towards the diblock copolymer PS domains. Small angle X-ray scattering (SAXS) analysis revealed the orientation of the alternating lamellae formed by the diblock copolymer when studied by LAOS. The localization of PS and P2VP grafted MWCNTs on the corresponding blend and BCP phase was also verified by transmission electron microscopy (TEM) studies.

Original route to polylactide–polystyrene diblock copolymers containing a sulfonyl group at the junction between both blocks as precursors to functional nanoporous materials

Novel functionalized nanoporous polymeric materials could be derived from poly(D,L-lactide)-block-polystyrene (PLA-b-PS) diblock copolymers with a sulfonyl group at the junction between both blocks were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) using a synthetic difunctional initiator through a three-step sequential methodology. Different ω-bromo PLA polymers with various molar masses ranging from 3640 to 11,440gmol−1 were first produced by coupling ω-hydroxy PLA precursors to a chlorosulfonyl-functionalized ATRP initiator previously prepared, thus leading to the formation of suitable macroinitiators for the subsequent ATRP polymerization of styrene. Consequently, PLA-b-PS diblock copolymers were obtained with a finely tuned PLA volume fraction (fPLA) in order to develop a microphased-separation morphology. The resulting copolymers as well as the intermediate compounds were carefully analyzed by size exclusion chromatography and 1H NMR. Upon shear flow induced by a channel die processing, oriented copolymers were generally afforded as characterized by small-angle-X-ray scattering (SAXS). Such copolymers were finally submitted to mild alkaline conditions so as to hydrolyze the sacrificial PLA block, and the presence of the sulfonic acid functionality on the pore walls of the resulting nanoporous materials was evidenced by means of a post-modification reaction consisting in the corresponding sulfonamide formation.