Diblock Copolymers Of Styrene Research Articles

Polymeric and Low-Molecular Stabilizers for Au Nanoparticles in a Diblock Copolymer Matrix

An effect of several polymeric stabilizers on the composites based on a diblock copolymer of styrene and 2-vinyl pyridine and spherical Au nanoparticles has been studied. Among the tested substances were thiol-terminated polystyrene, thiol-terminated poly(2-vinyl pyridine), diblock copolymers of styrene with 2- and 4-vinyl pyridine, and decanethiol as a typical low molecular mass stabilizer. Thin composite films with a microphase-separated cylindrical morphology have been prepared and characterized by atomic force and scanning electron microscopy to describe the surface morphology and nanoparticle distribution in the block copolymer matrix. In all the cases, the nanoparticles were selectively positioned either within vinyl pyridine domains or at the domain boundaries. The most effective stabilization of Au nanoparticles, both regarding their location and prevention of aggregation, was provided by the diblock copolymers.

Stabilization of Gold Nanospheres and Nanorods in Diblock Copolymers of Styrene and Vinylpyridine

Composites based on microphase-separated diblock copolymers of styrene with vinylpyridine and gold nanoparticles, in which the block copolymers play simultaneously both the role of a stabilizer preventing the aggregation of nanoparticles and a matrix providing their selective arrangement within domains of the predefined type, are obtained for the first time. The suggested approach implies no use of additional stabilizers and is efficient for both initially organic dispersed small (~5 nm) spheres and hydrasols of larger (9 × 30 nm) rodlike nanoparticles. Nanospheres are introduced into the composites via replacement of a labile stabilizer used in synthesis with the diblock copolymer, while nanorods synthesized in aqueous media by the two-stage method are incorporated via phase transfer mediated by the diblock copolymer. Films capable of microphase separation leading to the formation of vinylpyridine cylindrical domains with a diameter of tens nanometers are spin-coated from the obtained composites. The content of nanoparticles in the composites is up to 5 wt %; they are dispersed and arranged predominantly within vinylpyridine domains, with nanospheres being localized near domain boundaries, while nanorods being mainly oriented perpendicularly to the axis of cylinders.

Facile phase transfer of gold nanorods and nanospheres stabilized with block copolymers.

A fast route to transfer Au nanoparticles from aqueous to organic media is proposed based on the use of a high molecular mass diblock copolymer of styrene and 2-vinylpyridine for ligand exchange at the nanoparticle surface. The method enables the preparation of stable sols of Au nanorods with sizes of up to tens of nanometers or Au nanospheres in various organic solvents. By comparing the optical absorbance spectra of Au hydro- and organosols with the data of numerical simulations of the surface plasmon resonance, we find that nanoparticles do not aggregate and confirm the transmission electron microscopy data regarding their shape and size. The proposed approach can be effective in preparing hybrid composites without the use of strong thiol and amine surfactants.

Synthesis of amphiphilic block-gradient copolymers of styrene and acrylic acid by Nitroxide Mediated Polymerization

We present an overview on synthesis of amphiphilic ionic block-gradient copolymers of styrene and acrylic acid by means of one step direct Nitroxide Mediated Polymerization (NMP) and their characterization. The copolymers comprise a block of poly(acrylic acid) and one or two terminal blocks that include co-monomer units of styrene and acrylic acid in variable proportion. Using 1H NMR the gradient sequence of the poly(acrylic acid-co-styrene) copolymer block has been confirmed. In contrast to diblock copolymers of styrene and acrylic acid, that are known to form in aqueous environment “frozen” aggregates with glassy poly(styrene) core, the novel block gradient copolymers exhibit stimuli-responsive aggregation behavior, as was demonstrated by subsequent studies. This feature makes them very promising for design of a large variety of smart functional materials.

Water-Induced Formation of Reverse Micelles from Diblock Copolymer of Styrene and N-Isopropylacrylamide in 1,2-Dichloroethane

Water-induced formation of reverse micelles from polystyrene-b-poly(N-isopropylacrylamide) (PS(x)–PN(y), where x and y were the degrees of polymerization of PS and PN blocks, respectively) in 1,2-dichloroethane (DCE) was investigated mainly by light scattering. Four PS(x)–PN(y) samples with different degrees of polymerization x and y were prepared by the reversible addition–fragmentation chain-transfer (RAFT) radical polymerization technique. While PS(x)–PN(y) was molecularly dispersed in DCE, the addition of water remarkably enhanced scattering light intensity from the DCE solutions of all the PS(x)–PN(y) samples, indicative of the formation of the reverse micelle having a water pool as the micellar core. Static light scattering (SLS) data for PS(x)–PN(y)/water/DCE ternary systems were analyzed using a model of spherical reverse micelle to estimate structural parameters, which were dependent on the hydrophilic–hydrophobic balance, i.e., y/x.

Tandem Metal-Coordination Copolymerization and Organocatalytic Ring-Opening Polymerization via Water To Synthesize Diblock Copolymers of Styrene Oxide/CO2 and Lactide

Selective transformation of carbon dioxide and epoxides into degradable polycarbonates (CO(2)-based copolymer) has been regarded as a most promising green polymerization process. Although tremendous progress has been made during the past decade, very few successful examples have been reported to synthesize well-defined block copolymers to expand the scope of these green copolymers. Herein, we report a tandem strategy combining two living polymerization techniques, salenCo(III)X-catalyzed styrene oxide SO/CO(2) copolymerization and ring-opening polymerization of lactide with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), for the synthesis of poly(styrene carbonate-block-lactide) copolymers. The key to the success of this tandem strategy is the judicious choice of water as the chain transfer and/or chain terminator reagent, which is added at the end of the salenCo(III)X-catalyzed SO/CO(2) copolymerization to in situ generate hydroxyl groups at the end of the polymer chains. The resulting polycarbonates with -OH end groups can thus be directly used as macroinitiators to subsequently initiate ring-opening polymerization of lactide to synthesize the diblock copolymers. Because of the living polymerization nature of both steps in this tandem strategy, we have demonstrated that the diblock copolymers synthesized possess well-defined structures with narrow molecular weight distributions and controllable lengths of both styrene carbonate and lactide blocks.

Styrene-vinyl pyridine diblock copolymers: Synthesis by RAFT polymerization and self-assembly in solution and in the bulk

Reversible addition-fragmentation chain transfer (RAFT) polymerization along with benzyl dithiobenzoate chain transfer agent was employed for the controlled preparation of four diblock copolymers of styrene (St, less polar monomer) and 2- or 4-vinyl pyridine (2VP or 4VP, more polar monomers): St161-b-2VP48, St161-b-2VP121, St161-b-4VP76, and St161-b-4VP107, where the subscripts indicate the experimentally determined degrees of polymerization for each block. These diblock copolymers and their common St homopolymer precursor were characterized in terms of their molecular weights and compositions using gel permeation chromatography and 1H NMR spectroscopy, respectively. All four diblock copolymers self-assembled in dilute toluene solutions to form reverse spherical micelles, which were characterized using atomic force microscopy and cryogenic transmission electron microscopy. Both microscopy techniques revealed that the 4VP-bearing diblock copolymers formed larger micelles than the 2VP-bearing ones, a result of the greater 4VP-toluene incompatibility as compared to the 2VP-toluene one. Finally, films cast from chloroform solutions of the diblocks were investigated in terms of their bulk morphologies using transmission electron microscopy. While the 2VP-containing block copolymer self-assembled into a spherical morphology, the 4VP-containing one with comparable composition and molecular weight formed a cylindrical structure, manifesting the greater 4VP-St incompatibility as compared to that of the 2VP-St pair. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

SAXS and SANS characterization of gelable polystyrene-b-poly(acryloxy propyl triethoxysilane) (PS-b-PAPTES) diblock copolymer micelles before and after hydrolysis–condensation

Diblock copolymers of styrene and gelable acryloxy propyl triethoxysilane (APTES) were successfully prepared through Nitroxide-Mediated Polymerization (NMP). Their micellar behaviour in dioxane–methanol solutions was investigated by Small Angle X-ray Scattering (SAXS) and Neutron Scattering (SANS) measurements. The micelles were found to be spherical whatever the copolymer composition with a PS core size varying from 13.5 nm to 37.8 nm depending on the PS chain length and the swelling ratio. The thickness of the PAPTES corona increased from 6.0 nm to 10.8 nm when increasing the PAPTES polymerization degree from 91 to 336. Two micellar structural regimes were identified, depending on the chain length of the PAPTES soluble block. For PAPTES polymerization degrees higher than 100, the PS core radius in dried state RDC can be consistently described by a scaling relationship RDC α (NPS0.34NPAPTES−0.069) and the aggregation number Nagg obeys the relationship Nagg α (NPS0.021NPAPTES−0.21), consistent with previous studies. For polymerization degrees of the soluble block lower than 100, it was shown that RDC and Nagg do not follow the expected scaling relationships with higher values of Nagg, possibly due to complete chain incorporation in the micelle core. After the cross-linking process, a decrease of the hydrodynamic diameter of 1.6 to 4.7 nm was observed. This is mainly due to the corona shrinkage, the aggregation number and the core radius being directly dependent of the parent non-crosslinked micelles.

Synthesis and Morphological Study of Thick Benzyl Methacrylate–Styrene Diblock Copolymer Brushes

We demonstrate, for the first time, the synthesis of model poly(benzyl methacrylate) [P(BnMA)] brushes of very high thickness (>300 nm) on silicon wafer. P(BnMA) brush is also synthesized from the surface of silica nanoparticles, from a covalently anchored initiator monolayer, using ambient temperature ATRP. The kinetic studies and block copolymerization from the surface anchored P(BnMA)-Br macroinitiator showed that the polymerization was controlled in nature. AFM, ellipsometry, and water contact angle were used for the characterization of the polymer brush. The grafting density of the P(BnMA) brush, formed by immersion in a dilute monomer solution, was relatively less (∼11% less) in comparison to that obtained by immersion in neat monomer under similar conditions. The P(BnMA)-Br macroinitiator brushes were used to synthesize P(BnMA-b-S) diblock copolymer brushes by the ATRP of styrene at 95 °C. The P(BnMA-b-S) brushes showed stimulus response to a selective solvent and various nanopatterns were observed according to the composition of the block copolymer.

Diblock copolymer micellar lithography: 1. Intermicellar interactions and pathways for control of monomicellar film structure

The formation of reverse micelles of amphiphilic diblock copolymers of styrene and 2-vinylpyridine in selective (for one of the blocks) solvent (toluene) is studied by dynamic light scattering and atomic force and transmission electron microscopies, as well as by absorption spectroscopy and X-ray photoelectron spectroscopy techniques. It is revealed that the behavior of micelles of block copolymers with different ratios of block lengths and absolute molecular masses in solution is fundamentally different depending on the amount of added metal salt. The possibility of controlled variations in the characteristic sizes of two-dimensional ordered ensembles of micelles on the surface of silicon wafers is demonstrated. It is shown that, in some cases, the distance between the centers of micelles in ensemble depends on the concentration of copolymer solution and the amount of metal salt preliminarily added to the solution.

Diblock copolymer micellar lithography: 2. Formation of highly ordered nanoparticle ensembles with controlled geometric characteristics

The regularities of the formation of hexagonal ordered ensembles of gold nanoparticles using monomicellar films of amphiphilic diblock copolymers of styrene and vinylpyridine as templates are studied. The possibility of controlling the structure of these ensembles (in particular the particle size and interparticle distance) by varying experimental parameters (characteristics of diblock copolymer molecules, conditions for film formation, procedure for the reduction of precursor, etc.) is demonstrated. The procedure for enlarging the nanoparticles that form ensembles in dilute mixed solution of chloroauric acid and weak reductant (hydroxylamine) is realized. This procedure allows particle size to be increased from 7 to 30 nm, which sub� stantially changes the optical characteristics of synthesized structures. Moreover, a high degree of order of 2D ensemble of nanoparticles is retained. DOI: 10.1134/S1061933X11050164

One‐Pot Synthesis of Lactide–Styrene Diblock Copolymers via Catalytic Immortal Ring‐Opening Polymerization of Lactide and Nitroxide‐Mediated Polymerization of Styrene

An efficient, practical, and industrially relevant procedure for the production of polymer materials, in which a part of the oil-derived polyolefins has been replaced by a renewable, biodegradable, and biocompatible poly(lactide) block, is presented. Binary catalytic systems combining innocuous metals (yttrium, zinc, magnesium, or calcium) and bifunctional alcohols (acting as transfer agents) were developed to promote the immortal ring-opening polymerization of lactide directly in styrene. Up to 20,000 equivalents of lactide were polymerized (metal catalyst loading of 50-100 ppm) in a controlled fashion in the presence of 10-100 equivalents of a double-headed transfer agent to give as many end-functionalized poly(lactide) macromolecules that can be used eventually as macroinitiators for the controlled nitroxide-mediated polymerization of styrene. The specific use of the sterically shielded complex [BDI-iPr]Zn-N(SiMe(3))(2) ([BDI-iPr]=bis(diketiminate) ligand) allowed the efficient, catalytic, and controlled production of poly(lactide)-block-poly(styrene) materials in a one-pot, solvent-free sequential procedure, with nearly 100% atom-efficiency.

Amorphous polystyrene-block-polybutadiene and crystallizable polystyrene-block-(hydrogenated polybutadiene) solutions in compressible near critical propane and propylene – Hydrogenation effects

Polystyrene, polybutadiene, hydrogenated polybutadiene, and styrene diblock copolymers of these homopolymers can form homogenous solutions in compressible solvents, such as propane and propylene, which separate into two bulk phases upon reducing pressure. The cloud and micellization pressures for homopolymer and diblock copolymers are generally found to be higher in propane than in propylene, except for hydrogenated polybutadiene and polystyrene-block-(hydrogenated polybutadiene). Hydrogenated polybutadiene homopolymers and copolymers exhibit relatively pressure-independent crystallization and melting observed in both propane and propylene solutions.

Poly(styrene- b-2-(N,N-dimethylamino)ethyl methacrylate) diblock copolymers: Micellization and application in the synthesis of photoluminescent CdS nanoparticles

Fluorescence studies on amphiphilic diblock copolymers of styrene and 2-(N,N-dimethylamino)ethyl methacrylate using 1,8-anilinonaphthalenesulfonate (ANS) as fluorescent probe revealed the formation of stable micelles at extremely low polymer concentrations of ∼0.05%. The micellar microenvironment was characterized by an average polarity of E T(30) = 44–48 kcal mol −1, similar to the moderately polar solvents, and extremely high microviscosity. Increase in hydrophilic: hydrophobic ratio of the copolymers resulted in an increase in the average polarity and decrease in microviscosity. The micelles proved to be excellent hosts for the synthesis and stabilization of photoluminescent CdS nanoparticles with a high degree of quantum confinement and broad photoluminescence, dominated by trap-state emission. Moreover, the size and size-related steady-state optical properties of CdS nanoparticles were significantly dependent on the microenvironment of the host micelle. In contrast, the photoluminescence dynamics of the nanoparticles, involving time-scales from 100 ps to 100 ns, are similar in all cases. Interestingly, the nanoparticles exhibit a large time-dependent Stokes shift, 75% of which is complete within the first ∼100 ps after the excitation. The extremely rapid Stokes shift is attributed to the decay of the initially formed band-edge excitons in a time-scale too fast to be affected by the microenvironment surrounding the particle.

Synthesis and characterization of diblock copolymers of styrene and N-tert-butylacrylamide and gelation evidenced by rheology

The self-assembly of block copolymers in melt and in solution states is of current interest for the design of hierarchical materials. In this contribution, we report the synthesis of amphiphilic block copolymers of styrene and N-tert-butylacrylamide (SmNtBAMn) with narrow molecular weight distributions by reversible addition–fragmentation chain transfer (RAFT) technique. Block copolymers were characterized by gel permeation chromatography (for distribution width), 1H NMR spectroscopy (for molar mass and composition), thermal analysis and transmission electron microscopy (morphology investigation). These diblock copolymers in 1-octanol, a selective solvent for the N-tert-butylacrylamide block, self assemble to form micelles. At higher concentrations, these diblock copolymers in 1-octanol form glass-clear gels. Dynamic viscoelastic properties of a diblock copolymer, S278NtBAM517, in 1-octanol have been studied as a function of copolymer concentration. Scaling relations for the micelles and gels have been established in the terminal frequency range. Critical gelation concentration (cg) was determined by frequency independence of loss tangent in the vicinity of gel point. The cg, viscoelastic exponent, n and front factor, S were determined to be 11.3 wt%, 0.677 and 0.55 Pa-s0.677, respectively.

Micelles of a Diblock Copolymer of Styrene and Ethylene Oxide in Mixtures of 2,6-Lutidine and Water

We studied the micelle formation of a diblock copolymer of styrene and ethylene oxide in mixtures of 2,6-dimethylpyridine (2,6-lutidine) and water. Micelles are formed in a broad solvent composition range with a volume fraction of water ranging from 0.05 to 0.85, where neither polystyrene nor polyethylene oxide homopolymers are soluble. The diffusion behavior of pure solvent mixtures and in solutions of copolymer micelles is reported. In LTD/water mixtures, two diffusive processes corresponding to self-difusion and two modes belonging to mutual diffusion and diffusion of solvent clusters have been found. In copolymer solutions, the mode of copolymer micelle diffusion replaces the mode of solvent cluster diffusion. Quasielastic light scattering, small-angle neutron scattering, and pulsed-field gradient NMR have been employed in our study.

Synthesis and Characterization of ABC-type Star and Linear Block Copolymers of Styrene, Isoprene, and 1,3-Cyclohexadiene

Mikto three-arm, ABC-type star copolymers of styrene, isoprene, and 1,3-cyclohexadiene were synthesized by anionic polymerization using 1,3-bis(1-phenylvinyl)benzene (MDDPE) as linking precursor. A polystyrene macromonomer was prepared by monoaddition of polystyryllithium toward MDDPE. The resulting macromonomer was coupled with polyisoprenyllithium through the remaining double bond in MDDPE moiety, forming a diblock copolymer of styrene and isoprene. The diblock copolymer possessed a living center of diphenylethyllithium, which subsequently initiated the polymerization of a small amount of isoprene (“seeding”) and 1,3-cyclohexadiene. It was found that, without the “seeding” process, diphenylethyllithium was not able to initiate the polymerization of 1,3-cyclohexadiene. The resulting macromonomer and star polymers were characterized by gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and 1H NMR spectroscopy. In addition, linear ABC-type triblock copolymers of the corresponding monomers with different sequences were also synthesized. Microphase separation of the linear and star copolymers was investigated by differential scanning calorimetry and transmission electron microscopy.

Structural effects of type of intercalant in poly (4‐vinylpyridine) nanocomposites: compatible homopolymer or block copolymer

Abstract4‐vinylpyridine monomer was mixed with organophilic montmorillonite (MMT) clay and polymerized in the presence of free‐radical initiator. MMT clay was rendered organophilic by means of ion‐exchanging sodium cations for low‐molecular‐weight quaternized poly(4‐vinylpyridine) (P4VP) homopolymer and diblock copolymers of styrene and quaternized 4‐vinylpyridine (SVP) with different sequence lengths. The swelling behaviour of the MMT clay was studied by X‐ray diffraction (XRD). After the cation exchange, the resulting organophilic clays showed an expansion of interlayer distance indicating the nanoscale ordering of intercalant polymer and MMT layers. The nanocomposite materials, when moulded, exhibited improved thermal stability and dynamic mechanical properties compared with neat P4VP. The composite, having longer ionic segments in its organophilic MMT, showed exfoliated nanocomposite structure as well as higher stiffness and damping properties at higher temperatures even for MMT loading as low as 2 wt%. Copyright © 2006 Society of Chemical Industry

Comparative study of self-assembled ZnO nanostructures in poly(styrene–acrylic acid) diblock copolymers—[PS] m/[PAA] n—on Si and SiO 2/Si surfaces

A comparative study of the structural characteristics exhibited by the self-assembled ZnO nanoclusters developed on Si and SiO 2/Si surfaces using diblock copolymers of styrene–acrylic acid, [PS] m /[PAA] n , with block repeat unit ratios m/n of 159/63 and 106/17, is reported. These copolymer systems are expected to have self-assembled nanosized spherical domains of the minority acid blocks in solid phase but with domain sizes dependent on their respective block ratios and molecular block lengths. Templating of the ZnO nanoclusters with these copolymer systems enabled the development of the nanoclusters with two different size distributions on the Si and SiO 2/Si surfaces. The templating process involved the incorporation of a ZnCl 2 precursor into the functional group of the acid blocks in liquid phase at room temperature, application of the doped solution onto the surfaces by spin-casting for the formation of the thin nanocomposite film with ZnCl 2 nanoclusters and subsequent conversion into ZnO by a dry ozone process. The ZnO nanoclusters in the [PS] 159/[PAA] 63 copolymer and [PS] 106/[PAA] 17 copolymer were found to have a size distribution of 250–350 and 40–140 nm, respectively. Over-doping with ZnCl 2 precursor resulted in increased size of nanoclusters due to agglomeration in both copolymer systems.

Electron spin resonance investigation of molecular motions in oil‐extended styrene–butadiene–styrene block copolymers. I. The temperature dependence of resonance spectra: Glass, narrowing, and inflection temperatures

AbstractSpin‐probe research into nanometer‐scale molecular motions occurring in oil‐extended styrene–butadiene–styrene diblock copolymers within the glass‐transition range is reported. Complex resonance spectra are deconvoluted, and their intricate temperature dependence, resulting from the convolution of individual spectra due to nitroxide molecules located in different phases of the block copolymers, is analyzed. It is proved that a Boltzmann sigmoid accurately describes the temperature dependence of outer line separation. The characteristic inflection point of each sigmoid is used to assign an inflection temperature to each phase of the block copolymers. The inflection temperature coincides with the narrowing temperatures, within the experimental error. It is concluded that the inflection temperature is estimated with a higher accuracy than the narrowing temperature and that it allows a more profound analysis of molecular motions. The anomalous dependence of the glass, narrowing, and inflection temperatures for spin probes immobilized within the hard phase on the oil content has been assigned to morphological modifications, on the nanometer scale, induced by oil molecules added to the block copolymers. The experimental data demonstrate the sensitivity of spin‐probe data to modifications of the nanometer‐size architecture of block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1960–1971, 2004