Molecular weight effects on the phase morphology of PS/P4VP blend films on homogeneous SAM and heterogeneous SAM/Au substrates

The effects of the molecular weight of polystyrene (PS) component on the phase separation of PS/poly(4-vinylpyridine) (PS/P4VP) blend films on homogeneous alkanethiol self-assembled monolayer (SAM) and heterogeneous SAM/Au substrates have been investigated by means of atomic force microscopy (AFM). For the PS (22.4k)/P4VP (60k) system, owing to the molecular weight of PS component is relatively small, the well-aligned PS and P4VP stripes with good thermal stability are directed by the patterned SAM/Au surfaces. With the increase of the molecular weight of PS component (for the PS (582k)/P4VP (60k) system), the diffusion of P4VP is hindered by the high viscosity of PS during the fast spin-coating process. The phase separation behavior of PS/P4VP on the SAM/Au patterned substrates is similar to that on the homogeneous SAM and cannot be easily directed by the patterned SAM surfaces even though the characteristic length of the lateral domain morphology is commensurate with the stripe width. This indicates that the relative viscosity of the PS is one of the dominant factors in obtaining well-aligned pattern by the phase separation of polymer blends.     

Rubbed films of isomeric poly(4-vinylpyridine) and poly(2-vinylpyridine): surface morphology, molecular orientation, and liquid crystal alignability

Films of poly(4-vinylpyridine) (P4VP) and poly(2-vinylpyridine) (P2VP) were characterized before and after they were rubbed with a rayon velvet, and their liquid crystal (LC) aligning abilities were investigated. Atomic force microscopy images showed that microgrooves developed along the rubbing direction in the surfaces of the rubbed films of both polymers. Retardation and linearly polarized infrared spectroscopy analyses revealed that in both polymers the vinyl backbones are oriented along the rubbing direction, while the pyridine side groups are oriented perpendicular to the rubbing direction; the para-directions of the pyridine rings in the P4VP film have a tilt angle of about 45° in the plane perpendicular to the rubbing direction but the para-directions of the pyridine rings in the P2VP film align nearly in the film surface. These rubbed films were found to induce uniform, homogeneous LC alignment along the rubbing direction. Both LC alignments were, however, found to have low anchoring energies that are due to the inherently weak interactions of the LCs with the film surfaces. Moreover, LC cells prepared using these films were found to have only limited stability. These results lead to the conclusion that the microgrooves generated along the rubbing direction play a critical role in governing the alignment of LCs that weakly interact with the parallel oriented vinyl main chains in competition with the perpendicularly oriented pyridine side groups, despite their dimensions, which are larger than the LC molecules and thus limit their effectiveness. In addition, the zero degree pre-tilting behavior of the LCs on these films was investigated in detail, taking into account both the rubbing-induced orientations of the polymer segments and their anisotropic interactions with the LC molecules.     

A simple method for creating nanoporous block-copolymer thin films

We introduce a simple method to create block copolymer films with controlled porosity. We show that the pore structure can be varied over a broad range of length scales not obtainable in homopolymer blend films. The morphology is a random two phase kinetically trapped structure that is not limited by the equilibrium block copolymer structure. The morphology is obtained through blending homopolymer poly(4-vinylpyridine) (P4VP) with block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and then removing the homopolymer P4VP by washing with ethanol. The structure obtained prior to washing (which templates the nanoporous structure) is stabilized in the kinetically trapped morphology during spincoating and is not obtainable from either homopolymer blends or the pure block copolymer. When PS/P4VP blend solutions in tetrahydrofuran were spincoated at 25% relative humidity, continuous films with raised P4VP nanodomains were formed due to a preferential affinity of the spinning solvent for polystyrene. In a similar manner, when PS-b-P4VP/P4VP block copolymer/homopolymer solutions were spincoated, the P4VP homopolymer was solubilized in the P4VP block domains during spincoating, suppressing macro-phase separation. The film morphology is generated at the air surface and then propagates through the film, resulting in P4VP nanodomains oriented vertically to the substrate. In the resulting films, the size of P4VP nanodomains were varied by increasing the amount of P4VP homopolymer. The subsequent extraction of P4VP homopolymer from the PS-b-P4VP/P4VP blend films in ethanol resulted in nanopores with a distribution of length scales. The morphology of these materials makes the films potentially suitable for a range of applications such as anti-reflective coatings, nanoporous membranes and low-k materials. An illustrative example of an anti-reflective coating will be presented.     

The study of hydrogen bonding and miscibility in poly(vinylpyridines) with phenolic resin

The hydrogen bonding and miscibility behaviors of poly(2-vinylpyridine) (P2VP) or poly(4-vinylpyridine) (P4VP) with phenolic resin were investigated by differential scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). These blends have a single glass transition over the entire composition range indicating that these blends are able to form a miscible phase due to the formation of inter-molecular hydrogen bonding between hydroxyl of phenolic and pyridine ring of poly(vinylpyridines). Furthermore, FTIR studies on the hydrogen-bonding interaction between the hydroxyl group of phenolic and pyridine ring of poly(vinylpyridines) at various compositions and temperatures indicate that the greater inter-association for P4VP than P2VP due to the steric hindrance effect on specific interaction between these two polymers. Finally, inter-association equilibrium constants of phenolic/P2VP and phenolic/P4VP blends were determined by model compounds.     

High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films

A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.     

Anisotropic Conductivity of Diblock Copolymer Films

The first part of this article reviews the orientation of the surface and the in-bulk microdomain structures of diblock copolymers. Well-defined poly(styrene-b-2-vinylpyridine) diblock copolymers (about 50 wt% polystyrene blocks) formed horizontally oriented lamellar microdomains when these copolymers were cast from a nonselective solvent by means of the air–copolymer and substrate–copolymer interactions. The second section reviews the preparation of semiconducting materials by the exposure of these films to alkyl dihalide vapor. This film had an anisotropic conductivity with about 8 orders of magnitude. The third section reviews the construction of ionic complex phases by an ion-exchange reaction of quaternized poly(2-vinylpyridine) (P2VP) layers with lithium perchlorate. Finally, the introduction of colloidal silver into quaternized P2VP layers by reduction of silver iodide is reported. High electrical anisotropy originated in the orientation of microphase-separated structure of diblock copolymer films.     

Block copolymers containing pyridine moieties: Precise synthesis and applications

This review highlights the precise synthesis and application of various well-defined rod–coil and coil–coil block copolymers composed of poly(2-(or 4-)vinylpyridine) (P2VP or P4VP) block(s) with pyridine moieties. These polymers were synthesized by means of living anionic polymerization. Poly(hexyl isocyanate) (PHIC) was used as the rod-like segment, because hexyl isocyanate undergoes living anionic polymerization under carefully selected conditions. This review describes the syntheses of the block copolymers, polystyrene-b-P2VP, polystyrene-b-P4VP, polyisoprene-b-P2VP, P2VP-b-poly(methyl methacrylate), P2VP-b-poly(ethylene oxide), P2VP-b-poly(2-(N-carbazolyl)ethyl methacrylate), P2VP-b-PHIC, P2VP-b-PHIC-b-P2VP, and PHIC-b-P2VP-b-PHIC. The formation of self-organized nanostructured materials and molecular assemblies by such block copolymers and their possible applications are also described. These assemblies include monolayers, microphase-separated periodic-ordered nanostructures, micelles, polymer–metal complexes, nanoparticles, inorganic and metal layers, and nanoporous films with nanoparticles.     

室温可见光引发聚合诱导自组装制备P2VP-b-PSt纳米材料

针对苯乙烯（St）的常温聚合速率缓慢影响了其在常温聚合诱导自组装（PISA）中的应用问题,提出了一种无需添加光引发剂或光催化剂,以蓝光LED为光源,聚2-乙烯基吡啶（P2VP）为大分子链转移剂,常温下在甲醇中实现St的PISA的方法。通过可见光引发的PISA制备了聚2-乙烯基吡啶-b-聚苯乙烯（P2VP-b-PSt）纳米材料,考察了St/P2VP的比例、聚合时间及P2VP的链长对聚集体形貌的影响,结果表明,当P2VP的分子量为4000、St/P2VP的摩尔比从400/1变化到4000/1、聚合时间从3h变化到24h,均可以实现聚集体从球形胶束到囊泡的转变;当P2VP的分子量为8300时,仅能得到球形胶束。     

Permeability of Ibuprofen in Various Polyelectrolyte Multilayers

Ibuprofen microcrystals sized between 25–45 μm have been encapsulated with various types of polyelectrolyte multilayers (PEMs) constructed with polyallylamine (PAH), polyethylenimine (PEI) or poly(4‐vinylpyridine) (P4VP) as polycations and polystyrenesulfonate (PSS), polyanetholesulfonate (PAS) and dextran sulfate (DEXS) as polyanions. The release of ibuprofen from the microcapsules was monitored in situ by UV‐vis spectroscopy for the quantitative characterization of PEM permeability. Our results revealed that PEMs formed by PAH/DEXS, PEI/PSS, P4VP/PSS and P4VP/PAS are highly permeable to ibuprofen because their film cavities are much larger than the size of ibuprofen molecules. The PEMs formed by PAH/PSS and PAH/PAS are less permeable to ibuprofen due to their smaller film cavities. It is believed that the high charge density and well‐matched charge interactions between the coupling polyions in PAH/PSS and PAH/PAS multilayers allow the films to form small cavities. In addition, it was found that the permeability coefficient of PEMs decreases with increasing multilayer thickness before the film reaches a certain number and achieves structural homogeneity. Above that, the permeability coefficient remains constant with further increase of film thickness.     

Transport Behavior of Electrolytes Through Charged Mosaic Composite Membranes

The first part of this article reviews the strong acid/strong base type charged mosaic composite membrane. A template pattern with alternating poly(4-vinylpvridine) (P4VP)/poly(vinyl alcohol) (PVA) lamellae was fabricated upon a microporous membrane by casting of poly[4-vinylpyridine (4VP)-g-vinyl alcohol (VA)] graft copolymer from a water/l-propanol mixture. After a treatment involving the binding of the microporous membrane with the graft copolymer and also domain fixing of the PVA phases, a dilute solution of poly[sodium p-styrenesulfonate (SSS)-g-VA] graft co-polymer/P4VP binary blend was cast on this template surface. After chemical treatments (introduction of a positive charge and domain fixing of ion-exchange regions), we examined the transport of KCl and selective transport of a KCl-sucrose mixture through the charged mosaic composite membrane. The second section reviews the weak acid strong base type charged mosaic composite membrane. In this type, the charged mosaic regions were composed of poly(acrylic acid) (PAA) and quaternized P4VP microdomains. The microstructure of binary blend was observed from scanning electron microscopy (SEM) by wet-etching of films after domain fixing of one component of the binary blend. We examined the transport of KCl and L-phenylalanine through the charged mosaic composite membranes.     

Tailoring block copolymer nanoporous thin films with acetic acid as a small guest molecule

Block copolymers offer the fabrication of mesoporous thin films with distinct nanoscale structural features. In this contribution, we present the use of acetic acid (CH₃COOH) as a low‐molecular‐weight guest molecule to tune the supramolecular assembly of poly[styrene‐block‐(4‐vinylpyridine)] (PS‐b‐P4VP), offering a versatile and straightforward method to obtain tailored nanostructured films with controlled topography and pore size. Spin‐coating toluene solutions of PS‐b‐P4VP, with a variable amount of CH₃COOH, leads to micellar thin films, where the micelles contain the carboxylic acid as a guest molecule. The size can be conveniently modified in these films (from 48 to 75 nm) by varying the amount of organic acid in the starting solutions. Subsequent surface reconstruction of micellar films using ethanol leads to ring‐shaped copolymer nanoporous films with modulated diameter. Controlling the micelle reconstruction process, cylindrical porous films are also obtained. Interestingly, changing the type of aliphatic carboxylic acid leads to a modification of the observed film morphology from micelles to out‐of‐plane P4VP cylinders (or lamellae) in a PS matrix. © 2019 Society of Chemical Industry     

Preparation of pH‐Sensitive Networks by Ultraviolet Induced Crosslinking of Poly(ethylene oxide)‐Poly(2‐vinylpyridine) Blends

Blends of poly(ethylene oxide) of molecular weight 1 000 000 and poly(2‐vinylpyridine) of molecular weight 300 000 were crosslinked by exposure to ultraviolet radiation at 25, 75 and 115°C in the presence of benzophenone as a hydrogen‐abstracting agent. The crosslinking efficiency as well as the pH sensitivity strongly depend on the blend composition, the concentration of benzophenone and the irradiation temperature. The equilibrium swelling behavior of the mixed networks in aqueous solution was studied as a function of pH at constant ionic strength. A more pronounced swelling transition upon pH changes from 2 to 7 is observed at greater content of P2VP in the networks. The addition of poly(propylene oxide) to the P2VP‐PEO networks leads to enhanced mechanical strength and to much greater swelling dependence on pH, due to the hydrophobic and elastic nature of PPO.     

Stimuli responsive associative polyampholytes based on ABCBA pentablock terpolymer architecture

A poly(methyl methacrylate)–poly(acrylic acid)–poly(2-vinyl pyridine)–poly(acrylic acid)–poly(methyl methacrylate) (PMMA–PAA–P2VP–PAA–PMMA), ABCBA pentablock terpolymer was synthesized by “living” anionic polymerization and was studied in aqueous media at different pH conditions in the presence of MeOH. By tuning the pH and/or the solvent selectivity and dielectric constant of the medium, reversible hydrogels of different nature were formed. At low pH the hydrogel is based on a three dimensional network comprising PMMA hydrophobic cores (physical crosslinks) interconnected by complex bridging (elastically active) chains constituted of positively charged P2VP and non-ionic PAA segments. At high pH the hydrogel is transformed reversibly to a negatively charged network the bridging chains of which comprise ionized PAA segments interrupted by hydrophobic P2VP blocks, swellable on MeOH addition. Furthermore, we found conditions for the formation of flower-like micelles of different topologies and nature like core–shell–corona micelles with positively charged corona (pH < 2), multicompartment micelles comprising P2VP and PMMA hydrophobic domains (pH 8.3, low MeOH content), micelles constituted of a centrosymmetric compartmentalized core and PAA negatively charged corona (pH 8.3, 30%, 40% MeOH), and core–shell micelles of PMMA cores (pH 8.3, 50% MeOH).     

Temperature-dependent interaction parameters of poly(methyl methacrylate)/poly(2-vinyl pyridine) and poly(methyl methacrylate)/poly(4-vinyl pyridine) pairs

Temperature-dependent interaction parameters (α) of poly(methyl methacrylate)/poly(2-vinyl pyridine) (PMMA/P2VP) pair and PMMA/poly(4-vinyl pyridine) (PMMA/P4VP) pair were obtained from the SAXS profiles at various temperatures, and curve fitting to the random phase approximation theory. For this purpose, symmetric P2VP-block-PMMA and P4VP-block-PMMA copolymers were synthesized anionically. The molecular weights of both block copolymers were controlled to exhibit the disordered state over the entire experimental temperatures. We found that the value of α for PMMA/P4VP was larger than PMMA/P2VP, similar to polystyrene (PS)/poly(vinyl pyridine) pairs. However, the difference between in α between PMMA/P2VP and PMMA/P4VP was much smaller than that between PS/P2VP and PS/P4VP. This might be attributed to the hydrophilic PMMA block compared with hydrophobic PS block. Finally, the order-to-disorder transition temperature for symmetric P2VP-block-PMMA copolymers was determined by small angle X-ray scattering and birefringence methods.     

Self-assembly of segmented polyurethane and poly(4-vinylpyridine) in solution

Summary Poly(tetrahydrofuran) (PTHF) reacted with toluene diisocyanate (TDI) to form a prepolymer. Such a prepolymer was extended by 2,2-hydroxymethyl butanoic acid (DMBA) to form a segmented polyurethane with carboxyl (PUc) consisting of alternating soft and hard segments, where carboxyls are distributed only along the hard segments. By using static and dynamic laser light scattering (LLS) as well as atomic force microscopy (AFM), we have investigated the self-assembly of the PUc and poly(4-vinylpyridine) (P4VP) in tetrahydrofuran/chloroform mixed solvent. Our experiments show that the PUc and P4VP form a stable assembly with a size of 59–122 nm due to the H-bonding, depending upon the PUc (COOH) concentration. The LLS and AFM measurements demonstrate the assembly is spherical.     

Preparation and morphology of amphiphilic polystyrene–poly (2‐vinylpyridine) heteroarm star copolymers prepared by ATRP

BACKGROUND: The self‐assembly of amphiphilic copolymers has been demonstrated to be a powerful route towards supramolecular objects with novel architectures, functions and physical properties. In this study, the synthesis and morphology of amphiphilic linear polystyrene (PS)‐block‐poly(2‐vinylpyridine) (P2VP) and heteroarm star PS‐star‐P2VP copolymers are studied. The dispersion of silver nanoparticles with the prepared PS‐block‐P2VP and PS‐star‐P2VP copolymers is also discussed. RESULTS: Amphiphilic copolymers with different P2VP chain lengths were successfully synthesized using atom transfer radical polymerization (ATRP). The copolymers prepared had low polydispersity indices. Various aggregate morphologies, including spheres, vesicles, rods, large compound micelles, two‐dimensional ring‐like and three‐dimensional hollow structures, were formed by varying the hydrophilic coil length and the selective solvent content. Silver nanoparticles showed good dispersion behavior in both types of copolymers. CONCLUSION: Based on this study, it will be possible to prepare metal/copolymer nanocomposites by direct mixing. Further, the PS‐block‐P2VP and PS‐star‐P2VP copolymers prepared can be used in the preparation of nanoporous films as templates and nanoparticles as nanoreactors. They can also be applied in terms of oil recovery, paints and cosmetics formulations, as well as in pharmaceutical and medical applications as rheological agents. Copyright © 2008 Society of Chemical Industry     

Synthesis and characterization of styrene-based microbeads possessing amine functionality

Microbeads possessing amine functionality at the surface have been prepared by two methods: In the first method, poly(4-vinylpridine/styrene) P(4VP/S) copolymer microbeads containing 13–69 mol % 4-vinylpridine (4VP) were synthesized from the monomers. In the second method, animated polystyrene (PS) particles were prepared by postpolymerization reactions on cross-linked PS and polychloromethylstyrene particles to obtain poly(aminomethylstyrene/styrene) and polydiethylaminomethylstyrene particles, respectively. Scanning electronic microscopy of P(4VP/S) microbeads showed regular and spherical particles having a diameter between 80 and 200 nm depending on 4VP content. The chemical structure of the various particles made was studied using Fourier transform infrared spectroscopy, electron spectroscopy for chemical analysis (ESCA), and elemental analysis, whereas thermal properties were determined by differential scanning calorimetry and thermogravimetric analysis. © 1994 John Wiley & Sons, Inc.     

Selective hydrogen bonding and hierarchical nanostructures in poly(hydroxyether of bisphenol A)/poly(?-caprolactone)-block-poly(2-vinyl pyridine) blends

The phase behavior, hydrogen bonding interactions and morphology of poly(hydroxyether of bisphenol A) (phenoxy) and poly(?-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP) were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy and atomic force microscopy (AFM). In this A-b-B/C type block copolymer/homopolymer system, both P2VP and PCL blocks have favorable intermolecular interaction towards phenoxy via hydrogen bonding. However, the hydrogen bonding between P2VP and phenoxy is significantly stronger than that between PCL and phenoxy. Selective hydrogen bonding between phenoxy/P2VP pair at lower phenoxy contents and co-existence of two competitive hydrogen bonding interactions between phenoxy/P2VP and phenoxy/PCL pairs at higher phenoxy contents were observed in the blends. This leads to the formation of a variety of composition dependent nanostructures including wormlike, hierarchical and core-shell morphologies. The blends became homogeneous at 95 wt% phenoxy where both blocks of the PCL-b-P2VP were miscible with phenoxy due to hydrogen bonding. In the end, a model was proposed to explain the microphase morphology of blends based on the experimental results obtained. The swelling of the PCL-b-P2VP block copolymer by phenoxy due to selective hydrogen bonding causes formation of different microphases.     

Phase behavior of linear polystyrene-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) triblock terpolymers

Using sequential living anionic polymerization we synthesized well-defined linear ABC triblock terpolymers from polystyrene (PS), poly(2-vinylpyridine) (P2VP), and poly(tert-butyl methacrylate) (PtBMA). The length of the PtBMA block was systematically increased at constant block length ratios of the PS and P2VP blocks. The microdomain structures were characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). With increasing PtBMA block size we observe a systematic change in the bulk structure of the block copolymers.     

Temperature-responsive multilayered micelles formed from the complexation of PNIPAM-b-P4VP block-copolymer and PS-b-PAA core–shell micelles

Multilayered micelles with a polystyrene (PS) core, a swollen poly(acrylic acid) (PAA)/poly(4-vinyl pyridine) (P4VP) complex shell and a poly(4-vinyl pyridine)-block-poly(isopropyl acryl amide) (P4VP-b-PNIPAM) block-copolymer corona was synthesized by complexation between PNIPAM₅₃-b-P4VP₁₀₉ block-copolymers and the PS₁₂₀-b-PAA₄₇ diblock-copolymer core–shell micelles in ethanol due to the hydrogen bonding between the AA units and 4VP units. The surface of the micelle has been modified and a temperature sensitive block PNIPAM was introduced into the corona of the micelles. After being dialyzed against acidic water, PNIPAM corona would collapse onto the PAA/P4VP shell and the excessive P4VP shell would extend into the acidic solution to form the corona reversed micelles when the micelle aqueous solution was heated to 45 °C. The whole process was performed using dynamic light scattering (DLS), static light scattering (SLS), atom force microscope (AFM) and nuclear magnetic resonance (NMR).