Block Copolymers Of Polystyrene Research Articles

Synthesis of Adamantyl Polyphosphazene−Polystyrene Block Copolymers, and β-Cyclodextrin-Adamantyl Side Group Complexation

Hydrophobic block copolymers with adamantyl polyphosphazene and polystyrene blocks were synthesized via the controlled cationic living polymerization of a phosphoranimine at ambient temperature. β-Cyclodextrins (β-CDs) were then complexed with the adamantyl side groups in aqueous media to generate amphiphilic block copolymers. These underwent micelle formation in an aqueous environment. The micellar behavior of these complexes was monitored using fluorescence techniques, transmission electron microscopy (TEM), and dynamic light scattering. The critical micelle concentration of the adamantyl polyphosphazene-polystyrene block copolymer complexes was 0.925 mg/L. TEM imaging revealed spherically shaped micelles. A mean diameter of 193 nm was measured by dynamic light scattering. It was possible to control micelle formation by changing the amount of β-CD in the aqueous medium at constant block copolymer concentration.

Synthesis and Characterization of Well‐Defined Block Copolymers by Combing Controlled Radical and Cationic Polymerization

AbstractA facile synthetic strategy for well‐defined poly(ethyleneimine)‐polystyrene (PEI‐PS) block copolymers utilizing controlled radical polymerization through the macroinitiator approach is presented. Poly(2‐methyl‐2‐oxazoline) containing an alkoxyamine initiating unit at the chain end was prepared by ring opening cationic polymerization of 2‐methyl‐2‐oxazoline through a nitroxide containing initiator. Polymerization of styrene with the poly(2‐methyl‐2‐oxazoline) macroinitiator was carried out under nitroxide‐mediated radical polymerization (NMRP) conditions. GPC and NMR revealed that the polymerization was accurately controlled and well‐defined polystyrene chains were attached to the chain end of the macroinitiator to give the poly(2‐methyl‐2‐oxazoline‐b‐styrene) block copolymers. Hydrolysis of the poly(2‐methyl‐2‐oxazoline) block resulted effectively in poly(ethyleneimine‐b‐styrene) block copolymers.

Improved performances of 36 m small-angle neutron scattering spectrometer BATAN in Serpong Indonesia

SMARTer, a 36 m small-angle neutron scattering (SANS) spectrometer owned by the National Nuclear Energy Agency of Indonesia (BATAN) was installed at the Neutron Scattering Laboratory (NSL) in Serpong, Indonesia. Lots of works on replacing, upgrading and improving the control system, experimental methods, data collection and reduction in the last two years have been carried out to optimize the performance of SMARTer. Some standard samples such as silver behenate, monodisperse polystyrene nanoparticle, porous silica and block copolymer PS-PEP film were measured for the inter-laboratory comparison.

Self‐assembled structures in blends of disordered and lamellar block copolymers: SAXS, SANS and TEM study

AbstractBACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self‐assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS‐block‐dPMMA)1/(dPS‐block‐PMMA)2, were investigated using small‐angle X‐ray scattering, small‐angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature.RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution‐cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with Mn by D ∼ Mn2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene‐block‐polyisoprene copolymers).CONCLUSIONS: The criterion for forming a single‐domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self‐assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene‐block‐polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry

On‐line coupling of liquid chromatography at critical conditions with electrospray ionization tandem mass spectrometry for the characterization of a nitroxide‐mediated poly(ethylene oxide)/polystyrene block copolymer

Coupling of liquid chromatography at critical conditions (LCCC) with on-line mass spectrometry (MS) detection was implemented via an electrospray ionization (ESI) interface, using a mobile phase containing the cationizing agent. Critical conditions established for poly(ethylene oxide) were used to characterize a poly(ethylene oxide)/polystyrene block copolymer (PEO-b-PS) in both MS and MS/MS modes. As co-oligomer molecules were successfully separated according to the PS block size, structural information could be reached from simplified MS spectra. The microstructure of this copolymer, synthesized by nitroxide-mediated polymerization, could further be unambiguously characterized in LCCC/ESI-MS/MS experiments since the PS block size could be reached by both the co-oligomer chromatographic behavior and its MS/MS pattern.

How Are Insoluble Blocks Interacted with and Packed Inside a Micelle Made of Block Copolymers in a Selective Solvent?

It is well-known that block copolymers can form large core−shell micelles in a selective solvent. The ultrafiltration of such polymeric micelles made of polystyrene (PS) and polyisoprene (PI) block copolymers in n-hexane through small pores (20 nm) is possible only when the flow-rate-dependent hydrodynamic force in the range 10−15 to 10−12 N (i.e., 1 fN−1 pN) is sufficiently strong to pull individual copolymer chains out of the core and disintegrate each micelle. Therefore, we are able to find how strong insoluble PS blocks in the core interact with each other from such a critical flow rate. Our results reveal that the micelle retention gradually decreases as the flow rate increases, different from a sharp first-order coil-to-stretch transition of a flexible linear homopolymer chain under the same elongation flow field. As expected, the interaction strength increases as the PS block becomes longer. Each flow-rate dependence of the micelle retention can be converted to a hydrodynamic force distribution f(Fh). For PS-b-PI diblock copolymers, f(Fh) has a single peak in the range 1−200 fN, whereas for PI-b-PS-b-PI triblock copolymers, there are two separated peaks in f(Fh), respectively, in the ranges 3−20 and 30−500 fN, attributing to two kinds of packing of the PS blocks inside the core; namely, the packing of unentangled and entangled insoluble PS blocks.

Nanopatterned Carbon Films with Engineered Morphology by Direct Carbonization of UV-Stabilized Block Copolymer Films

Nanopatterned thin carbon films were prepared by direct and expeditious carbonization of the block copolymer polystyrene- block-poly(2-vinylpyridine) (PS- b-P2VP) without the necessity of slow heating to the process temperature and of addition of further carbon precursors. Carbonaceous films having an ordered "dots-on-film" surface topology were obtained from reverse micelle monolayers. The regular nanoporous morphology of PS- b-P2VP films obtained by subjecting reverse micelle monolayers to swelling-induced surface reconstruction could likewise be transferred to carbon films thus characterized by ordered nanopit arrays. Stabilization of PS- b-P2VP by UV irradiation and the concurrent carbonization of both blocks were key to the conservation of the film topography. The approach reported here may enable the realization of a broad range of nanoscaled architectures for carbonaceous materials using a block copolymer ideally suited as a template because of the pronounced repulsion between its blocks and its capability to form highly ordered microdomain structures.

Surface studies of corona treated polydimethylsiloxane‐block‐polystyrene hybrid copolymer films

AbstractLinear hybrid block copolymers of polydimethylsiloxane (PDMS) and polystyrene (PS) were synthesized using living sequential anionic polymerization. Sample films of these block copolymers were thermally annealed for 48 hr at 120°C to promote phase segregation and allow for the preferential surface segregation of PDMS. The films were then exposed to corona discharge for 30 min. Optical microscopy and scanning electron microscopy (SEM) were used to identify surface cracks due to the formation of a silica‐like glassy layer after corona exposure. Slow positron beam studies were used to evaluate the degradation phenomenon and provide the first evidence of silica‐like degradation layers forming on the surface of PDMS containing hybrid polymer films, after corona exposure. It also allowed determination of the thickness of the glassy layer. Contact angle measurements also showed the first evidence that the same hydrophobic loss and recovery phenomenon for the corona treated hybrid polymer films occurs, as with pure PDMS samples. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Thermoplastic elastomer/polyaniline blends: Evaluation of mechanical and electromechanical properties

Conducting polymer blends whose undiluted components have different properties are promising materials for several technological applications such as electromagnetic shielding, electrostatic charge dissipation, optoelectronic displays, chemical sensors, biosensors and electromechanical sensors. The aim of this study was to obtain and evaluate the electrical conductivity and electromechanical properties of a polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene copolymer (SEBS)/polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA) blends. Electrically conductive elastomeric blends based on SEBS/PAni.DBSA were prepared through a solution casting method, at room temperature, after dissolving both components in toluene as a common solvent. SEBS/PAni.DBSA blends were also prepared through polymerization of aniline in the presence of SEBS solution, using a one-step in situ emulsion polymerization method. The protonation degree of the PAni.DBSA used in this study was determined from X-ray photoelectron spectroscopy (XPS) analysis by calculating the amount of different neutral and positive nitrogen species of the polyaniline chain from the properly curve-fitted N-1s core-level spectrum. The PAni.DBSA used to prepare solution casting blends had a 46% protonation degree, with almost all imine groups protonated and only a small amount of residual DBSA, as expected for an emeraldine salt. This protonation degree is responsible for the high conductivity (2.4 S cm −1) and good solubility of this conducting polymer in toluene. The protonation degree of PAni.DBSA in the blends analyzed was higher than that of undiluted PAni.DBSA, due to an additional protonation during the casting or in situ processes. The insulator–conductor transition was not as sharp as those found in carbon black conducting systems and the percolation threshold was lower than 20 wt.% of PAni.DBSA. Above 20 wt.% PAni.DBSA content, the emulsion-polymerized systems had higher volume conductivity values than the corresponding solution casting blends. The mechanical properties such as tensile strength, elastic modulus and elongation at break of SEBS/PAni.DBSA blends were dependent on the blend preparation method. Blends were also characterized by electromechanical properties and optical microscopy.

Pyrene-containing polystyrene segmented copolymer from nitroxide mediated polymerization and its application for the noncovalent functionalization of as-prepared multiwalled carbon nanotubes

This study reports simple and convenient procedures for the preparation of a novel surface modifier for multiwalled carbon nanotubes (CNTs) having uniform and controlled structure through controlled “living” free-radical polymerization technique. The technique afforded pyrene functionalized polystyrene block copolymers (PMAS) having controlled molecular weight, molecular weight distribution and length of each block for effective surface modification of CNTs. The modified CNTs exhibited much improved and stable dispersion in toluene. PMAS–CNT/polystyrene composites afforded clearer and more homogeneous films compared to those containing non-modified CNTs. The polystyrene films containing 2 wt% and 5 wt% of PMAS–CNTs showed improved AC conductivities of approximately 10 −3 and 10 −2 S/cm, respectively, which were 10 ∼ 10 6 times higher than those of films containing non-modified CNTs. These results demonstrated that PMAS effectively modified the surface of CNTs, which resulted in improved dispersion of CNTs in polystyrene matrices.

Microstructural Study of a Nitroxide-Mediated Poly(Ethylene Oxide)/Polystyrene Block Copolymer (PEO- b-PS) by Electrospray Tandem Mass Spectrometry

Electrospray ionization tandem mass spectrometry has been used to characterize the microstructure of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer, called SG1-capped PEO-b-PS. The main dissociation route of co-oligomers adducted with lithium or silver cation was observed to proceed via the homolytic cleavage of a C-ON bond, aimed at undergoing reversible homolysis during nitroxide mediated polymerization. This cleavage results in the elimination of the terminal SG1 end-group as a radical, inducing a complete depolymerization process of the PS block from the so-formed radical cation. These successive eliminations of styrene molecules allowed a straightforward determination of the PS block size. An alternative fragmentation pathway of the radical cation was shown to provide structural information on the junction group between the two blocks. Proposed dissociation mechanisms were supported by accurate mass measurements. Structural information on the SG1 end-group could be reached from weak abundance fragment ions detected in the low m/z range of the MS/MS spectrum. Amongst fragments typically expected from PS dissociation, only beta ions were produced. Moreover, specific dissociation of the PEO block was not observed to occur in MS/MS, suggesting that these rearrangement reactions do not compete effectively with dissociations of the odd-electron fragment ions. Information about the PEO block length and the initiated end-group were obtained in MS(3) experiments.

Formation and catalytic activity of spherical composites with surfaces coated with gold nanoparticles

Micelle-supported gold composites with a polystyrene core and a poly(4-vinyl pyridine)/Au shell are synthesized using NaBH 4 to reduce a mixture of micelle and HAuCl 4 in acidic aqueous solution (pH ∼2). The template micelle with a polystyrene core and a poly(4-vinyl pyridine) shell is formed by self-assembly of block copolymer polystyrene- block-poly(4-vinyl pyridine). The gold nanoparticles coated onto the surfaces of the composites possess an average diameter of about 15 nm. The composites are applied to catalyze the reduction of p-nitrophenol in the presence of NaBH 4, and the results indicate that the kinetic constant of the reaction increases when the composite concentration and the reaction temperature increase. In addition, research results also indicate that composites with high content of gold show higher catalytic activity and higher catalytic efficiency.

Micellization and the Surface Hydrophobicity of Amphiphilic Poly(vinylphenol)‐block‐Polystyrene Block Copolymers

AbstractThe self‐assembly of PVPh‐b‐PS in different solvents was studied. Upon replacing toluene by THF as the solvent, the morphology of the resulting aggregates change from core‐shell spheres, rod‐like micelles and vesicles to onion‐like aggregates. With increasing block copolymer concentration, morphologies such as honeycomb‐like films, surfaces of aggregated large porous spheres, or pincushion‐like spheres with protruding tubular vesicle aggregates are observed. These surface‐patterned films show significantly enhanced hydrophobicity. The results suggest that a superhydrophobic behavior can be achieved, with a maximum contact angle of 158°, by using the pincushion‐like micellar structure.magnified image

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

AbstractEllipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both ‘soft’ and solid thin films. ‘Soft’ polymer thin films of polystyrene and poly(styrene–ethylene/butylene–styrene) block copolymer were prepared by spin‐coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two‐layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80–130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright © 2007 John Wiley & Sons, Ltd.

Grafting from Surfaces for “Everyone”: ARGET ATRP in the Presence of Air

Atom-transfer radical polymerization (ATRP) is one of the controlled/living radical polymerizations yielding well-defined (co)polymers, nanocomposites, molecular hybrids, and bioconjugates. ATRP, as in any radical process, has to be carried out in rigorously deoxygenated systems to prevent trapping of propagating radicals by oxygen. Herein, we report that ATRP can be performed in the presence of limited amount of air and with a very small (typically ppm) amount of copper catalyst together with an appropriate reducing agent. This technique has been successfully applied to the preparation of densely grafted polymer brushes, poly(n-butyl acrylate) homopolymer, and poly(n-butyl acrylate)-block-polystyrene copolymer from silicon wafers (0.4 chains/nm2). This simple new method of grafting well-defined polymers does not require any special equipment and can be carried out in vials or jars without deoxygenation. The grafting for "everyone" technique is especially useful for wafers and other large objects and may be also applied for molecular hybrids and bioconjugates.

New Preparation and Purification Methods for Metallo-Supramolecular Block Copolymers

The bis-complex formation of two terpyridine-modified polymers using microwave assisted reaction conditions was investigated in detail. In order to construct a heteroleptic block copolymer polystyrene, which was prepared by nitroxide-mediated radical polymerization (NMRP), and a commercial available poly(ethylene oxide) were used. These studies include the influence of temperature, reaction time, concentration and the use of different solvent mixtures on complexation. The conversion was determined by GPC measurements. The amphiphilic metallo-supramolecular block copolymers were investigated towards their formation of micellar aggregates in water. Other characterization techniques include 1H-NMR, UV/vis spectroscopy, dynamic light scattering (DLS), atomic force spectroscopy (AFM) and transmission electron microscopy (TEM) techniques.

Polymer nanostructures in sub-micron lithographically defined channels: film-thickness effects on structural alignment of a small feature size polystyrene-polyisoprene-polystyrene block copolymer.

The use of phase separation in block copolymer systems to generate regular nanopatterns at surfaces may be an alternative to advanced photolithography. Here, substrates with photolithographically defined rectangular channels (of depth 60 nm and widths 166-433 nm) are used to direct nanoscale phase separation of a polystyrene--polyisoprene--polystyrene (PS-PI-PS) block copolymer into aligned periodic superstructures. This nanoscale phase separation results in the rapid formation of parallel and narrow polystyrene (PS) cylinders orientated in a 2D hexagonal arrangement within a polyisoprene (PI) matrix for the polymer composition used here. The PS-PI-PS system is shown to be extremely amenable to simple processing methods allowing precise and homogeneous coating of the substrates. Effects of polymer film thickness are investigated in depth, given that polymer film thickness plays an essential role in the orientation/architecture of the structure formed. It was observed that control of film thickness can determine the orientation of cylinders (parallel or vertical) with respect to the substrate surface. In films where the PS cylinders are aligned parallel to the substrate surface careful control of the processing parameters facilitates the fabrication of regular multi-layer systems ( layers of cylinders) within the channel. The directional effect imposed by the channels is not limited to polymer nanostructures within the channels as long-range order and alignment can be observed at film thicknesses that extend above the channels and onto the outer surface of the substrate. However, as thickness increases, this 'directing' effect conferring alignment is lost.

ABA triblock copolymers with a ring‐opening metathesis polymerization/macromolecular chain‐transfer agent approach

AbstractBlock copolymers containing polystyrene and polycyclooctene were synthesized with a ring‐opening metathesis polymerization/chain‐transfer approach. Polystyrene, containing appropriately placed olefins, was prepared by anionic polymerization and served as a macromolecular chain‐transfer agent for the ring‐opening metathesis polymerization of cyclooctene. These unsaturated polymers were subsequently converted to the corresponding saturated triblock copolymers with a simple heterogeneous catalytic hydrogenation step. The molecular and morphological characterization of the block copolymers was consistent with the absence of significant branching in the central polycyclooctene and polyethylene blocks [high melting temperatures (114–127 °C) and levels of crystallinity (17–42%)]. A dramatic improvement in both the long‐range order and the mechanical properties of a microphase‐separated, symmetric polystyrene–polycyclooctene–polystyrene block copolymer sample was observed after fractionation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 361–373, 2007

Effect of Supercritical CO2 in Modified Polystyrene 3D Latex Arrays

The effect of supercritical CO(2) (scCO(2)) in 3D latex arrays formed by monodispersed particles of polystyrene (PS), PS cross-linked with divinylbenzene (PS-DVB), and PS block copolymers with 2-hydroxyethyl methacrylate (PS-HEMA), methacrylic acid (PS-MA), acrylic acid (PS-AA), itaconic acid (PS-IA), and a mixture of methacrylic and itaconic acid (PS-IA-MA) has been studied. Sorption of CO(2) into the polymer particles leads to a decrease in the glass transition temperature of the polymer and the swelling of the particles and induces their coalescence. 3D-latex arrays of the former compositions were treated in scCO(2) at temperatures and pressures ranging from 40 to 80 degrees C and from 85 to 197 bar, respectively. The effect of CO(2) on the polymeric template was assessed by scanning electron microscopy and N(2) adsorption analysis. Bare PS and PS-HEMA particles sintered readily in scCO(2) at 40 degrees C and 85 bar. On the other hand, particles containing carboxylic acid groups on their surface (PS-MA, PS-AA, PS-IA, and PS-IA-MA) were, at the same temperature and pressure, more resistant to the CO(2) treatment. For a given polymer composition, the sorption of CO(2) inside the polymer particles, the swelling, and the degree of coalescence depend on the pressure, temperature, and time of the CO(2) treatment. Analysis of the pore size distributions from the N(2) adsorption data has allowed us to quantify the degree of coalescence of the particles in the matrix. By careful control of the experimental variables, the coalescence of the 3D latex array could be finely tuned using CO(2).

Biomacromolecular engineering: design, synthesis and characterization. One‐pot synthesis of block copolymers of arborescent polyisobutylene and polystyrene

AbstractNovel arborescent block copolymers comprising of an arborescent rubbery polyisobutylene (PIB) midsegment and glassy polystyrene (PSt) end blocks were prepared by sequential addition of monomers. Synthesis was conducted by the use of 4‐(2‐methoxyisopropyl) styrene as an inimer‐type initiator in conjunction with titanium tetrachloride (TiCl4) in 60:40 (v/v) methylcyclohexane/methyl chloride solvent mixture. Isobutylene was polymerized for 1–2 hr and then prechilled styrene in the same solvent mixture was sequentially added with select additives to the reaction flask. The recovered block copolymers were purified and then characterized by 1H‐NMR, size exclusion chromatograph (SEC), tensile test, atomic force Microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS). Samples with 16.4–32.8 wt% PSt and Mn = 47,600–125,900 g/mol (Mw/Mn = 2.02–4.45) displayed thermoplastic elastomeric properties with 5–9.2 MPa tensile strength and 490–920% elongation. The arborescent block copolymers showed surface morphologies ranging from spherical to cylindrical/lamellar nanometer‐sized discreet PSt phases dispersed in a continuous PIB matrix, with a 10 nm PIB layer on the surface. Drug release profiles of paclitaxel from two arborescent blocks were found to be similar to that measured from Translute®. Copyright © 2006 John Wiley & Sons, Ltd.