Block Copolymers Of Polystyrene Research Articles

Synthesis and Interfacial Behavior of Polystyrene−Polysaccharide Diblock Copolymers

Linear block copolymers of polystyrene and polysaccharide were synthesized using a block synthesis method with amino-terminated polystyrene and sodium cyanoborohydride as reducing agent. Different types of polysaccharides, dextrans, and maltodextrins with various molecular weights were used. IR spectroscopy indicated a successful coupling. Yields of reaction are 75-95 wt %. Attempts to couple long dextrans (Mw > 6000 Da) were not successful. Interfacial pressure measurements of monolayers of the copolymers on water showed interfacial behavior typical for amphiphilic compounds and different from the starting compounds, confirming the coupling reaction. Time-dependent hysteresis occurs between successive compression and expansion cycles. This is, to a large extent, due to the slow adsorption/desorption of the polysaccharide chains at the air-water interface and the formation of aggregates of copolymer at the interface. Aggregates are mainly formed by H-bonds between adjacent polysaccharide chains. The relaxation time for hysteresis, determined for polystyrene-dextran copolymer, was 85 min.

Enhancement of the high‐temperature utility of a polystyrene‐b‐poly(ethylene‐co‐butylene)‐b‐polystyrene block copolymer by friedel–crafts naphthoylation

AbstractA procedure was developed for the Friedel–Crafts naphthoylation of the polystyrene segments of a polystyrene‐b‐poly(ethylene‐co‐butene)‐b‐polystyrene (SEBS) triblock copolymer. It was possible to obtain up to 72% 1‐naphthoylation or 100% 2‐naphthoylation of the polystyrene segments in the copolymer. Naphthoylation could also be accomplished using trifluoromethanesulfonic acid as a catalyst. The naphthoylated products were characterized by 1H‐NMR spectroscopy, size‐exclusion chromatography, and dynamic mechanical thermal analysis. The mechanical properties of the original and naphthoylated polymers were measured from 25 to 125°C. The results obtained indicate that naphthoylation enhances the tensile properties of the polymers at elevated temperatures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1289–1295, 2003

Structural characterization and surface modification of sulfonated polystyrene–(ethylene–butylene)–styrene triblock proton exchange membranes

Structural characteristics and membrane performance of polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene (sSEBS) copolymer proton exchange membranes in water-swollen and different ratio of water/methanol-swollen are studied by small angle X-ray scattering (SAXS), ATR FT-IR, AFM. SAXS profile of sSEBS membrane showed that microstructure was a hexagonally cylindrical structure and it was maintained in the existence of methanol in water until 30 wt.%. As the main interest was on the development of proton exchange membranes for fuel cells operating at lower temperature with liquid methanol feed, a selective thin layer was introduced on the top of sSEBS membrane by simple plasma treatment in the presence of maleic anhydride in order to prevent methanol crossover. Both methanol permeability and proton conductivity gradually decreased with increasing loading amounts of maleic anhydride. Hydrophobic anhydride properties on the top of sSEBS membrane act as a barrier for methanol but also for proton, resulting in decreasing methanol permeability and proton conductivity. The hydrolysis of anhydride groups to carboxylic acid provides a facilitated transport site for the proton. After hydrolysis, the proton conductivity was recovered and the recovery rate of proton conductivity by hydrolysis was higher than that of methanol permeability.

Characterization of aqueous micellar solutions of amphiphilic block copolymers of poly(acrylic acid) and polystyrene prepared via ATRP. Toward the control of the number of particles in emulsion polymerization

A series of diblock, triblock and star-block copolymers composed of polystyrene and poly(acrylic acid) were synthesized by ATRP. The structure of the copolymers, the size of the blocks and the composition were varied, keeping however a short polystyrene block and a poly(acrylic acid) content larger than 60 mol% to allow solubility in alkaline water. Their micellization was studied by static and dynamic light scattering and the influence of their structural characteristics on the aggregation number, N agg, was examined at low salt concentration and alkaline pH. It was shown that micelles were in thermodynamic equilibrium and that N agg followed the power law N agg∼ N A −0.9 N S 2 (with N A, the total number of acrylic acid units in the copolymer and N S, the total number of styrene units), that is characteristic of amphiphile micelles formed from strongly segregated block copolymers. Moreover, N agg was independent of salt concentration in the investigated range. The same copolymers were previously used as stabilizers in emulsion polymerization [Macromolecules 34 (2001) 4439]. The final latex particle concentration, N p, was compared with N m, the initial micelle concentration. This enabled us to conclude that among the block copolymers studied, those with high acid content behaved like low molar mass surfactants. In contrast, those with low acid content formed stable micelles that could be directly nucleated to create latex particles, allowing a good control over N p.

Effect of Casting Solvent on Morphology and Physical Properties of Partially Sulfonated Polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene Copolymers

The effect of casting solvent on the morphology of sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS) was investigated using transmission electron microscopy and small-angle X-ray scattering. Proton conductivities and methanol permeabilities were measured and the related impact on morphological changes is discussed. SSEBS is transformed from a well-ordered lamellar to a disordered structure as the concentration of MeOH in MeOH/THF mixtures increases.

Adhesion properties of UV crosslinked polystyrene- block-polybutadiene- block-polystyrene copolymer and tackifier mixture

The peel and tack properties of mixtures of polystyrene- block-polybutadiene- block-polystyrene (SBS) and a tackifier were investigated after these were crosslinked by ultraviolet (UV) irradiation at various amounts of benzophenone (BP) as a photoinitiator and trimethylolpropane mercaptopropionate (TRIS) as a crosslinking agent. The degree of crosslinking of polybutadiene (PB) block in the SBS mixture was qualitatively estimated from the amount of gel fraction as well as the change in the glass transition temperature of the PB block. The crosslinking of the PB block was done within 3 min after UV irradiation and the peel strength of crosslinked specimens was as low as 45[percnt] of specimens without crosslinking. Nano-tack and bulk tack properties as well as the surface tension of mixtures were measured depending upon amounts of BP and TRIS.

Proton conductivities and methanol permeabilities of membranes made from partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene copolymers

A series of partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene copolymers (SSEBS) was synthesized and the sulfonation was characterized qualitatively by a Fourier transform-infra red (FT-IR) and quantitatively by an elementary analysis. The membranes from synthesized SSEBS were prepared by solution casting method and their proton conductivities and methanol permeabilities were measured. It was found that the proton conductivity and methanol permeability increase abruptly when the sulfonation degree on polystyrene end blocks exceeds 15 mol% and the proton conductivity equivalent to that of Nafion 117 is obtained for SSEBS with 34 mol% sulfonation while the methanol permeability is decreased more than a half. The water and methanol uptakes of SSEBS and Nafion membranes were directly evaluated and the results showed that, in both cases, the membranes favors methanol much more than water, indicating that it would not be an easy task to develop a promising proton exchange membrane from SSEBS which could be utilized for the direct methanol fuel cell (DMFC). The microstructures of SSEBS and Nafion membranes were examined by small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) and the difference between them is discussed too.

Surface visco-elastic moduli of a Langmuir film of a polystyrene-polydimethyl siloxane block copolymer at the air-ethyl benzoate interface.

Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier, but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry, the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration of 3.1 mg m(-2).

Synthesis and Gas Permeability of Block Copolymers Composed of Poly(styrene-co-acrylonitrile) and Polystyrene Blocks

Radical copolymerization of a mixture of styrene (S) and acrylonitrile (AN) at azeotropic composition (63 mole % of S and 37 mole % of AN) at 125 °C in the presence of dibenzoyl peroxide and 2,2,6,6-tetramethylpiperidin-1-yloxyl (TEMPO) gave TEMPO-terminated S-AN copolymers with narrow molecular weight distributions. Both the linear semilogarithmic time-conversion and molecular weight-conversion dependences indicated a quasiliving copolymerization process. Polymerization of styrene initiated with the synthesized macroinitiators containing reversibly bound terminal TEMPO groups yielded film-forming poly(styrene-co-acrylonitrile)-block-polystyrene copolymers. Using the resulting diblock copolymer as a macroinitiator in copolymerization of S and AN, a triblock copolymer of the A-B-A type was obtained. Films of the block copolymers were prepared by casting chloroform solutions and their permeabilities (P) to nitrogen, oxygen, methane, carbon dioxide, and hydrogen were determined. The films showed high selectivities to oxygen (PO2/PN2 > 6). The block copolymers behaved as single-phase homogeneous materials.

Polymer Nanocomposites: Molecular Dynamics Simulations of Polystyrene and Polystyrene-Polyisoprene Block Copolymer Nanocomposites

AbstractMolecular dynamics simulations were used to study the interlayer structure and dynamics of polystyrene (PS) and polystyrene-polyisoprene (PS-PI) block copolymers intercalated in organically modified layered silicates. In the case of PS the polymer chains displace the aliphatic surfactant chains and reside adjacent to the silicate layers. The electrostatic interactions between the aromatic rings on the PS chains and the silicate surface drive the intercalation of the polymer into the host galleries. PI, which lacks such electrostatic interactions, is immiscible (does not intercalate) with the host. There appears to be a minimum number of PS mers for intercalation of PS-PI copolymers to take place. The intercalated copolymer appears to structure inside the host galleries with the PS mers adjacent to the silicate layers and the corresponding PI away from the surface and towards the middle of the gallery. Using the mean square displacements we find that PS is the least mobile species in the galleries with the surfactant chains been the most mobile of all.

Blends of Butyl and Bromobutyl Rubbers and Polystyrene—Polyisobutylene—Polystyrene (PS—PIB—PS) Block Copolymers with Improved Processability and Physical Properties

Abstract An investigation of the effects of polystyrene—polyisobutylene linear triblock and three-arm star block thermoplastic elastomers on the processability and properties of butyl and bromobutyl rubbers was undertaken. All properties improved, with the exception of bromobutyl adhesion, which remained acceptable. The green strength of raw polymer blends improved by 30–80% and 5–20% improvement was seen on the carbon black compounds. Die swell was reduced by as much as 60% for compounds containing a triarm-star block. Tear strength doubled and air permeability decreased (by about) 20–40%. Fatigue life improved dramatically (20-fold on 300% crack growth and 80-fold on 600% crack growth). The cured blends can be viewed as interpenetrating networks of the chemically crosslinked rubber and the physically crosslinked thermoplastic elastomers.

Phase morphologies and mechanical properties of high‐impact polystyrene (HIPS) and polycarbonate blends compatibilized with polystyrene and polyarylate block copolymer

AbstractPhasemorphology and mechanical properties of blends of high‐impact polystyrene (HIPS) and polycarbonate (PC) blends compatibilized with a polystyrene (PS) and polyarylate (PAr) (PS–PAr) block copolymer were investigated. Over a broad range of composition from 50/50 through 30/70, HIPS/PC blends formed cocontinuous structures induced by the flow during the extrusion or injection‐molding processes. These cocontinuous phases had heterogeneity between the parallel and perpendicular directions to the flow. The micromorphology in the parallel direction to the flow consisted of stringlike phases, which were highly elongated along the flow. Their longitudinal size was long enough to be longer than 180 μm, while their lateral size was shorter than 5 μm, whereas that in the perpendicular direction to the flow showed a cocontinuous phase with regular spacing due to interconnection or blanching among the stringlike phases. The PS–PAr block copolymer was found to successfully compatibilize the HIPS/PC blends. The lateral size of the stringlike phases could be controlled both by the amount of the PS–PAr block copolymer added and by the shear rate during the extrusion or injection‐molding process without changing their longitudinal size. The HIPS/PC blend compatibilized with 3 wt % of the PS–PAr block copolymer under an average shear rate of 675 s−1 showed a stringlike phase whose lateral size was reduced almost equal to the rubber particle size in HIPS. The tensile modulus and yield stress of the HIPS/PC blends could be explained by the addition rule of each component, while the elongation at break was almost equal to that of PC. These mechanical properties of the HIPS/PC blends can be explained by a parallel connection model independent of the HIPS and PC phases. On the other hand, the toughness factor of the HIPS/PC blends strongly depended on the lateral size of the stringlike phases and the rubber particle size in the HIPS. It was found that the size of the string phases and the rubber particle should be smaller than 1.0 μm to attain a reasonable energy absorbency by blending HIPS and PC. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2347–2360, 2001

Synthesis and characterization of conducting block copolymers of thiophene-ended polystyrene with polypyrrole

4,4' Azobis (4-cyano3-thiophenemethyl pentanate (ACTMP) was synthesized from 3-Thiophenemethanol and 4,4'-Azobis (4-cyanopentanoyl chloride). ACTMP was further used in the synthesis of polystyrene with thiophene terminal groups (TPSt) at both ends. Conducting block copolymers of TPSt and pyrrole (TPSt/PPy) were electrochemically prepared using several supporting electrolytes. Characterization of these block copolymers were performed.

Structure/property relationships in polystyrene–polyisobutylene–polystyrene block copolymers

Structure/property relationships of polystyrene–polyisobutylene–polystyrene (PS–PIB–PS) triblock copolymer made by different processes were studied using dynamic mechanical analysis (DMA). The PS–PIB–PS films were composed of approximately 30% polystyrene end-blocks. Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) confirm that a self-assembled, segregated cylindrical morphology forms in the copolymer. DMA was used as a tool to investigate the structure–property relationships in these polymers. Modified PS–PIB–PS copolymers were also characterized. Modifications of the copolymers were carried out by conversion of approximately 20 mol% of the polystyrene end-blocks to styrene sulfonic acid. The modified copolymers exhibited distinctly different thermal characteristics than the unmodified copolymers, which were most notable in the storage modulus and tan δ data. The presence of sulfonic acid groups disrupted the morphology and solvent sorption characteristics of the copolymers. Dynamic mechanical behavior is discussed as it relates to the morphology of the PS–PIB–PS copolymers formed via different processing methods and chemical modification.

Thermal-initiating potentialities of poly(methyl methacrylate) peroxide: Metamorphosis of block-into-block copolymer and comparative studies on surface texture and morphology

This is the first report concerning the use of vinyl polyperoxide, namely, poly(methyl methacrylate) peroxide (PMMAP), as a thermal initiator for the synthesis of active polymer PMMAP-PS-PMMAP by free-radical polymerization with styrene. The polymerizations have been carried out at different concentrations of macroinitiator PMMAP. The active polymers have been characterized by 1H NMR, DSC, thermogravimetric analysis, and gel permeation chromatography. PMMAP-PS-PMMAP is further used as the thermal macroinitiator for the preparation of another block copolymer, PMMA-b-PS-b-PMMA, by reacting the active polymers with methyl methacrylate. The block copolymers have been synthesized by varying the concentrations of the active polymers. The mechanism of block copolymers has been discussed, which is also supported by thermochemical calculations. Studies on the surface texture and morphology of the block copolymer of polystyrene (PS) and PMMA material have been carried out using scanning electron microscopy. Furthermore, in this article, a blend of the same constituent materials (PS and PMMA) in proportions (v/v) similar to that contained in block copolymers has been formulated, and the morphology and surface textures of these materials were also investigated. A comparative microscopical evaluation between two processing methods was done for a better understanding of the processing route dependence of the microstructures. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 546–554, 2001

Microphase Separation in Normal and Inverse Tapered Block Copolymers of Polystyrene and Polyisoprene. 1. Phase State

We have investigated the influence of composition gradients on the microdomain structure and viscoelastic properties of tapered block copolymers by (i) varying the amount of interfacial material and (ii) the block sequence. Normal tapered and inverse tapered triblock copolymers of polystyrene and polyisoperne with a tapered midblock have been synthesized via anionic polymerization with a nearly symmetric composition and compared with the corresponding diblock copolymers. We found that increasing the amount of tapered material within the interface systematically increases the compatibility. Block sequencing is found to be an important factor controlling compatibility. Inverse tapered block copolymers are much more compatible than the corresponding normal tapered block copolymers. Results presented here could be used as a guideline for preparing copolymers with controlled compatibility at the synthesis level.

Radical telomerization of vinyl acetate with chloroform. Application to the synthesis of poly(vinyl acetate)-block-polystyrene copolymers by consecutive telomerization and atom transfer radical polymerization

This paper demonstrates that radical telomerization and atom transfer radical polymerization (ATRP) can be combined in a two-step procedure to prepare poly-(vinyl acetate)-block-polystyrene (PVOAc-b-PSt) diblock copolymers. The first step consists in telomerizing VOAc with chloroform, leading to trichloromethyl-terminated VOAc telomers CCl3(VOAc)nH. A detailed 1H NMR analysis shows that nearly pure telomer structures are obtained over a broad range of DPn values (up to at least 60 units). When ATRP of styrene is initiated with a model telomer adduct (CCl3CH2CH2OAc), molecular weights increase linearly with monomer conversion and match theoretical values. Moreover, polydispersities are consistently low (1.22 < Mw/Mn < 1.38) throughout polymerization. Similarly, VOAc telomers (DPn = 9 and 62) are good ATRP macroinitiators. The high purity of the resulting diblock copolymers is confirmed by GPC using RI/UV dual detection.

Preparation of block copolymers of polystyrene and poly (t-butyl acrylate) of various molecular weights and architectures by atom transfer radical polymerization

Block copolymers of polystyrene and poly(t-butyl acrylate) were prepared using atom transfer radical polymerization techniques. These polymers were synthesized with a CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine catalyst system and had predictable molecular weights based on the degree of polymerization, as calculated from the initial ratio of monomer to initiator. The final polydispersities were low (1.10 < Mw /Mn < 1.3) for all the homopolymers and block copolymers. Polymers of various chain architectures were prepared, ranging from linear AB diblocks to three-armed stars composed of AB diblocks on each arm. The key to controlled synthesis with this catalyst system was the choice of the solvent, temperature, and concentrations of catalyst and deactivator. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2274–2283, 2000

Copolymerization and addition of styrene andN-phenylmaleimide in the presence of nitroxide

The copolymerization and addition reaction of styrene (S) with N-phenylmaleimide (PMI), either neat or in xylene, have been found to proceed at 125°C in the presence of 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO) radicals. TEMPO-terminated alternating S-PMI copolymers and comonomer adducts were obtained. The amounts of the low molecular weight compounds increased with the increasing content of PMI in the initial mixture. The reaction suggests formation of monofunctional unimolecular initiators. In the autopolymerization of neat comonomers, a mediating role of TEMPO was observed. The synthesized copolymers containing TEMPO end groups were used as macroinitiators to initiate polymerization of styrene. The molecular weight distributions of resulting poly(styrene-alt-N-phenylmaleimide)-block-polystyrene copolymers indicated the presence of both low molecular weight termination products and some copolymer precursor. The copolymers and comonomer adducts were characterized using the nitrogen analysis, size-exclusion chromatography (SEC), and NMR spectroscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1093–1099, 2000

Inner core segment design for drug delivery control of thermo-responsive polymeric micelles

Modification of the thermo-responsive behavior of polymeric micelles for specific drug delivery functions was investigated using combinations of micellar inner cores and outer shell polymer chemistries. Polymeric micelles comprised of AB block copolymers of PIPAAm (poly( N-isopropylacrylamide)) with either PBMA (poly(butyl methacrylate)) or PSt (polystyrene) were employed. PIPAAm–PBMA and PIPAAm–PSt block copolymers formed a core-shell micellar structure after dialysis of the block copolymer solutions in organic solvents against water at 20°C. The hydrophobic drug, adriamycin, (ADR) was loaded into the inner core of the polymeric micelles by dialysis. The polymers showed reversible intermicellar dispersion/aggregation in response to temperature cycles through an outer polymer shell lower critical solution temperature (LCST for PIPAAm=32.5°C), observed by DLS (dynamic light scattering) and transmittance measurements. Upon heating above the LCST, PIPAAm–PBMA micelles exhibited an abrupt increase in micropolarity and an abrupt decrease in microrigidity sensed by pyrene and 1,3- bis(1-pyrenyl)propane (PC 3P), respectively. In contrast, PIPAAm–PSt micelles maintained constant values with lower micropolarity and higher microrigidity than those of PIPAAm–PBMA micelles over the temperature range 20 to 40°C. From these results, structural deformations produced by outer shell polymer structural change with temperature cycles through the LCST are proposed for the PBMA core possessing a lower T g (ca. 20°C) than the outer shell PIPAAm LCST. The PSt core with a much higher T g (ca. 100°C) than the outer shell LCST retained its structure, regardless of outer shell changes. PIPAAm–PBMA micelles released ADR only when heated above the LCST, while PIPAAm–PSt micelles did not. Cell cultures treated with PIPAAm–PBMA micelles loaded with ADR showed high in vitro cytotoxicity when heated above the LCST, while PIPAAm–PSt micelles loaded with ADR expressed very low in vitro cytotoxicity irrespective of temperature change through the LCST. The nature of hydrophobic segments comprising the micelle inner core offers an important control point for thermo-responsive drug release and the drug activity of the thermo-responsive polymeric micelle.