Polystyrene Polybutadiene Research Articles

A scaling model for the prediction of micellization of diblocks in polymer melts

A scaling model is proposed for A–B diblock copolymers in homopolymer melts based on the minimization of free energy. Competition between the migration of block copolymer to the A and B homopolymer interface and formation of micelles in the B phase has been modeled. Sample calculations done for polystyrene (PS), polybutadiene (PB), and PS–PB diblock copolymers support experimental observation for the onset of micellization and for the aggregation number of a micelle. The model is relatively simple and testable. It can be used as a predictive tool, once knowledge of three scaling factors is obtained. This would allow a priori calculation of the block copolymer concentration needed for full coverage of the homopolymer interface.

Relaxations in lamellar polystyrene–polybutadiene diblock copolymer. Thermally stimulated depolarization current study

The samples of the polystyrene-polybutadiene (PSPB) diblock copolymers with lamellar structure were investigated by integral and partial thermally stimulated depolarization current (TSDC) measurements in the 160–303 K range, and compared to the analogous investigation performed on a homopolymer sample of polystyrene (PS). The current peak, which appeared at 187 K, was found to be a dipolar relaxation α peak caused by the glass transition in the PB phase. The space-charge relaxation, distributed in the 220–260 K range and split into two parts – denoted as β 1 and β 2, was attributed to the possible local motion of the phenyl rings in the PS phase. The current maxima of the β relaxations significantly increased and shifted to the lower temperatures in the copolymer samples due to the PS–PB interfaces. The occurrence of doubleness and the relative distance between β 1 and β 2 was discussed. The relative numbers of the relaxing dipoles ( N) vs. E a were approximated. The energy width ( ω) was significantly increased in the copolymers due to the released motions at the glass–liquid PS–PB interfaces.

Impact and tensile properties of SEBS copolymer compatibilized PS/HDPE blends

In this study, polystyrene–hydrogenated polybutadiene–polystyrene (SEBS) triblock copolymer was used as a compatibilizer for the blends of polystyrene (PS) and high-density polyethylene (HDPE). The morphology and static mechanical and impact properties of the blends were investigated by means of scanning electron microscopy, uniaxial tension, and instrumented falling-weight impact measurements. Tensile tests showed that the yield strength of the PS/HDPE/SEBS blends decreases considerably with increasing HDPE content. However, the elongation at break of the blends tended to increase significantly with increasing HDPE content. The excellent tensile ductility of the HDPE-rich blends resulted from shield yielding of the matrix. Charpy impact measurements indicated that the impact strength of the blends increases slowly with HDPE content up to 50 wt %; thereafter, it increases sharply with increasing HDPE content. The impact energy of the HDPE-rich blends exceeded that of pure HDPE, implying that the HDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of SEBS compatibilizer. The correlation between the impact property and morphology of the blends is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1099–1108, 1998

Impact and tensile properties of SEBS copolymer compatibilized PS/HDPE blends

In this study, polystyrene–hydrogenated polybutadiene–polystyrene (SEBS) triblock copolymer was used as a compatibilizer for the blends of polystyrene (PS) and high-density polyethylene (HDPE). The morphology and static mechanical and impact properties of the blends were investigated by means of scanning electron microscopy, uniaxial tension, and instrumented falling-weight impact measurements. Tensile tests showed that the yield strength of the PS/HDPE/SEBS blends decreases considerably with increasing HDPE content. However, the elongation at break of the blends tended to increase significantly with increasing HDPE content. The excellent tensile ductility of the HDPE-rich blends resulted from shield yielding of the matrix. Charpy impact measurements indicated that the impact strength of the blends increases slowly with HDPE content up to 50 wt %; thereafter, it increases sharply with increasing HDPE content. The impact energy of the HDPE-rich blends exceeded that of pure HDPE, implying that the HDPE polymer can be further toughened by the incorporation of brittle PS minor phase in the presence of SEBS compatibilizer. The correlation between the impact property and morphology of the blends is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1099–1108, 1998

Synthesis, homopolymerization, and block copolymerization ofN-ethyl-2-ethynyl-pyridinium trifluoromethanesulfonate with styrene and butadiene

A novel acetylenic monomer 2-N-ethyl pyridinium trifluoromethane sulfonate (2EPyEtTf) was synthesized and polymerized. Diblock copolymers of 2EPyEtTf with styrene and with butadiene were prepared. Initiation of the polymerization by living anionic polystyryl - -Li + and polybutadienyl - -Li + (Scheme 1) resulted in polystyrene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate) (PS 57 PA 8 ), and polybutadiene-block-poly(N-ethyl-2-ethynylpyridinium trifluoromethanesulfonate)(PB 30 PA 8 ). These amphiphilic block molecules contain rigid, conjugated, and strongly hydrophilic polyacetylene chain fragments attached to hydrophobic polystyrene or flexible polybutadiene chain fragments. The structure of these copolymers was studied by FTIR, UV-visible, and NMR spectroscopy. GPC and viscometry were also used to obtain information on the molecular mass and the molecular mass distribution. Thermal behavior was investigated by means of TGA and DSC. Both block copolymers were shown to form stable monolayers at the air-water interface. The positively charged rigid polyacetylene portion of the copolymer is believed to be partially submerged, while the more flexible hydrophobic chains are forced out of the water. Multilayers of PB 30 PA 8 deposited using the Langmuir-Blodgett technique were found to be less uniform than in the case of the previously reported polystyrene-block-poly(2E-PyMeTf)(PS 12 PA 4 ) copolymer (Balogh et al., Macromolecules, 29, 1996). Polycation-polyanion self-assembly deposition was also investigated, using polystyrenesulfonate (PSS) as polyanion. While PS 57 PA 8 /ASS layer-by-layer deposition was not uniform, it was found that PB 30 PA 8 /ASS gave homogenous and stable films on hydrophilic glass substrates.

Condutividade elétrica de misturas de poliestireno/polibutadieno e poliestireno/copolímero em bloco de estireno-butadieno contendo negro de fumo.

RESUMO: A condutividade elétrica de compósitos contendo negro de fumo extra condutor em sistemas envolvendo poliestireno/ polibutadieno (PS/PBD) e poliestireno/copolímero em bloco de estireno-butadieno (PS/SB) foi investigada. A mistura PS/SB apresentou menores limiares de percolação do que misturas PS/PBD. Análises através de microscopia eletrônica de varredura indicaram que, no caso das misturas PS/PBD, as partículas de negro de fumo estão aglomeradas e não formam um caminho contínuo, característico de condução elétrica. Investigações a respeito da formação de interações físicas entre polímero-negro de fumo (bound rubber) indicaram também maior adesão entre polímero-NF quando se utilizou o sistema PS/PBD.

Thermal annealing of roll-cast triblock copolymer films

Polystyrene—polybutadiene—polystyrene triblock copolymers were roll-cast from toluene solutions to form globally oriented films. Microstructural changes following thermal annealing of films with cylindrical and lamellar morphology were monitored using two-dimensional small angle X-ray scattering, transmission electron microscopy and thermomechanical analysis. The microdomains in the unannealed films of cylindrical morphology were found to be assembled on a distorted hexagonal lattice, due to the roll-casting flow field. Thermal annealing significantly improved the alignment and packing of the cylinders, increased grain size, reduced the number of morphological defects and resulted in a 12% decrease in the area per junction. The microstructure of the unannealed films of lamellar morphology was observed to be composed of many small grains with low-angle helicoid surface twist boundaries. Annealing significantly reduced the number of grains and twist boundaries and resulted in a 7% decrease in the area per junction. Molecular models are presented for the relaxation of the chains during the annealing process in both cylindrical and lamellar morphologies based upon 2-D SAXS data and thermomechanical analysis.

The dynamics of symmetric polystyrene–polybutadiene diblock copolymer melts studied above and below the order–disorder transition using dynamic light scattering

This communication describes dynamic light scattering measurements on three low molar mass symmetric polystyrene–polybutadiene diblock copolymer melts. Above but close to the order–disorder transition, four modes contribute to the time-dependent correlation function. In the depolarized geometry there is a very fast, broad relaxation typifying the segmental reorientational dynamics and a slower, single-exponential mode related to chain orientation and stretching. In the polarized experiments two additional processes are seen: the heterogeneity mode related to the self-diffusion of individual copolymer molecules and a slow mode representing the translational diffusion of large (≂100 nm) clusters. Just below the order–disorder transition (ODT), the slowest mode is shifted to very long times. The heterogeneity mode gives rise to depolarized scattering below the ODT because of the anisotropy induced by the lamellar structure. With the lowest molar mass copolymer above the ODT, it could be seen that the amplitude of the mode related to chain orientation and stretching decreases the deeper the sample is in the disordered state. A new subtraction technique was used for data analysis.

Effect of Solvent Quality on Pure and Mixed Brushes

AbstractWe investigate, theoretically and experimentally, the effect of solvent quality on pure, one‐component, and two‐component brushes. Both mean‐field and self‐consistent field models are developed, and their predictions compared to surface forces experiments on polystyrene and mixed polystyrene–polybutadiene brushes. We find that in pure brushes the structure and interactions between surfaces are highly sensitive to solvent quality. In a good solvent, the brush is extended and the interactions are repulsive, while in a poor solvent the brush is “collapsed” and the interactions are strongly attractive. Mixing two incompatible chains significantly reduces the sensitivity of the brush to solvent properties. While one of the chains collapses in a selective solvent, the other chain remains solvated, thus providing long‐range repulsive interactions between surfaces. Our experiments show that the interactions between surfaces carrying a 1:1 mixed brush of styrene–butadiene are repulsive even in hexane, a poor solvent for polystyrene. Theoretically, we calculate that incorporating only 10% of an equi‐molecular‐weight chain into a collapsed brush can eliminate attractive interactions between surfaces.

Microphase separation of block copolymer solutions in a flow field

AbstractFilms of polystyrene–polybutadiene–polystyrene (PS/PB/PS) triblock copolymer and polystyrene‐poly(ethylene/propylene) (PS/PEP) diblock copolymer were cast from toluene solutions subjected to hydrodynamic flow at room temperature using a device based on a novel casting method we term ‘roll‐casting.’ Polymer solutions were rolled between two corotating eccentric cylinders while at the same time the solvent was removed at a controlled rate. As the solvent evaporated, the block copolymers microphase separated into globally oriented structures. A discussion of the flow field that develops during roll‐casting is presented and specific attention is given to the importance of the shear and elongation rates present. For the triblock and diblock, respectively, the processed structures consisted of polystyrene cylinders assembled on a hexagonal lattice in a polybutadiene matrix, and unidirectional lamellae of alternating polystyrene and polyethylene/propylene. Small‐angle x‐ray scattering (SAXS) and transmission electron microscopy (TEM) indicated the near single‐crystal structure both types of films. SAXS also showed the styrene cylinders and the alternating lamellae to be packed closer together in roll‐cast films than in simple quiescently cast films. A molecular orientation mechanism is proposed to describe both these results as well as the changes in packing and in macroscopic sample dimensions measured after complete solvent evaporation and after sample annealing. © 1993 John Wiley & Sons, Inc.

Gas solubility and diffusion in a polystyrene–polybutadiene block copolymer

AbstractOver the temperature range of 20 to 90°C, the equilibrium solubility of methane or argon in a star‐branched polystyrene–polybutadiene (SB) block copolymer can be reliably estimated from a volume‐fraction‐weighted average of the homopolymer solubilities; the value of heat of solution for SB block copolymer lies between the two values associated with the constituent homopolymers. Diffusion coefficients for gases in the block copolymer are bracketed by the homopolymer values over the range of temperature employed, but the activation energies for diffusion in SB are higher than either of the homopolymer values. The anomalous temperature dependence and the inability of a computer simulation to reproduce experimental diffusion coefficients supported the concept of a temperature‐dependent restriction on chain mobility in the polybutadiene regions of the block copolymer. This β factor embodies the relative reduction in the rate of gas diffusion through the B regions of the copolymer compared to B homopolymer; β has a value of about 2–3 at room temperature but decreases to unity when the polystyrene chains become mobile at the polystyrene Tg.

Studies on polybutadiene rubber (PBR)-polystyrene (PS) interpenetrating polymer networks

Elastomer-plastomer blends based on polybutadiene rubber (PBR) and polystyrene (PS) giving interpenetrating networks (IPNs) were studied. The semi IPNs were formed by allowing the initially formed elastomer (PBR) network to swell in styrene monomer and then completing polymerization of the monomer through the swollen elastomer network. For full interpenetrating network formation selected low doses of divinylbenzene (DVB) was used in the monomer styrene and copolymerization of the styrene-DVB system through the monomer swollen elastomer network was effected subsequently. Dicumyl peroxide (DCP) was used to form the initial PBR network and benzoyl peroxide (Bz2O2) was used as the initiator for the polymerization of styrene or styrene-DVB mixture. Effects of variation of DCP dose, DVB dose and PBR-PS blend ratio on the physical-mechanical properties of the blends were examined. The full IPNs exhibited higher tensile strength and modulus while the semi IPNs exhibited greater toughness. A PBR-PS blend ratio of around 50∶50 to 40∶60 resulted in blends morphologically characterized by spherical domains of PBR encompassed by PS phase appearing fibrillar in nature and a synergism in the toughness property was most prominent in blends of this blend ratio range. For PBR>50%, the elastomer phase is apparently the continuous phase, while it is just the reverse for PBR<40 to 50% in general.

Carbon dioxide diffusion and solubility in a polystyrene-polybutadiene block copolymer with a highly oriented lamellar morphology

Abstract : Solubility and diffusion coefficients for CO2 in polystyrene polybutadiene (SB) block copolymer films were measured in a pressure decay sorption apparatus at 1 atm over a temperature range of 20 to 90 C. The morphology of the block copolymer specimens consisted of alternating S and B lamellae of approximately 100 angstrom thickness with excellent long range orientation perpendicular to the surface of the 0.02 to 0.05 cm thick films. Diffusion behavior in the copolymer was simulated using homopolybutadiene and homopolystyrene data along with a finite difference model based on the well- ordered morphology. Comparisons of model predictions with the measured values of the effective diffusion coefficient for CO2 in the copolymer revealed that the diffusion coefficient of CO2 in the polybutadiene region of the copolymer was lower than in homopolybutadiene by a factor of 1.9 at 20 C. This difference disappeared at the glass transition temperature of the polystyrene in SB. This temperature-dependent reduction of CO2 diffusion in the polybutadiene regions of the block copolymer results from restrictions on chain motions of the polybutadiene blocks arising from their connection to polystyrene blocks. (aw)

Morphological changes in SBS block copolymers caused by oil extension as determined by absolute small angle x-ray scattering

A series of SBS block copolymers diluted with different amounts (0–60 wt%) of three different kinds of oil were investigated: 1) lithene PM (a low molecular weight polybutadiene); 2) a paraffinic mineral oil with its electron density close to that of the polybutadiene (PB) phase; 3) a highly aromatic mineral oil with an electron density close to the polystyrene (PS) phase. All the oils seem to go into the polybutadiene matrix. Paraffinic oil and lithene form a homogeneous phase with PB; the aromatic oil at low concentrations mixes with the PB phase with a high level of inhomogeneity, while at higher concentration partial phase separation occurs. In the undiluted polymer, styrene forms cylinders in hexagonal packing. The distance between cylinders (about 43 nm) is not significantly changed upon dilution up to 33 wt%. Previously proposed changes in the morphology of PS domains at larger oil contents can be related to observed changes in the long period, in the segment length distributions, and in the homogeneities of the phase (density fluctuations). The electron density difference obtained for pure SBS is lower than the theoretical one calculated from the densities of pure PS and pure PB. Dilution by paraffinic oil improves the phase separation.

Compatibility studies of polystyrene–polybutadiene blends by thermal analysis

AbstractIn order to examine the behavior of incompatible blends of polystyrene and polybutadiene, the glass transition temperature, the melting point, and the specific heat increment at the glass transition temperature for atactic polystyrene (a‐PS), isotactic polystyrene (i‐PS), polybutadiene (PBD), and blends of a‐PS/PBD and i‐PS/PBD were determined by use of a differential scanning calorimeter. Blends were prepared by solution casting, freeze‐drying, and milling. Weight fractions of polystyrene in the blends ranged from 0.95 to 0.05. The glass transition temperature of polystyrene changed with weight fraction in the blends, and with blending preparation methods; the glass transition temperature of polybutadiene remained essentially unchanged. The specific heat increment at the glass transition temperature of PBD decreases linearly with increasing proportions of PS in the PS/PBD blend for the broad and narrow molecular weight distribution polybutadience polymers, whereas the specific heat increment for PS did not decrease with increasing proportions of PBD in the PS/PBD blend. These results suggest that the polybutadiene dissolves more in the polystyrene phase than does the polystyrene in the polybutadiene phase.

Partitioning of polystyrene between incompatible phases and distributional effects in the system polystyrene–polybutadiene–toluene

AbstractThe average molecular weights and the molecular weight distributions of polystyrene (PS) in the conjugate incompatible phases of the ternary system of PS and polybutadiene with toluene as solvent were studied at 23°C. Gelpermeation chromatography, with ultraviolet and differential refractive index detectors, was used for analyzing the compositions of the conjugate phases and for obtaining the molecular weight averages of PS in the phases. Both narrow and broad molecular weight distribution (MWD) polymer samples were used. The effect of broad MWD polymers is seen as one of narrowing the shape of the binodal, thus effectively increasing the compatible region. The molecular weight averages of PS in the two conjugate phases do not vary significantly in the case of the narrow MWD PS sample while for broad MWD samples the average molecular weight of PS is found to be higher in the PS‐rich phase than in the polybutadiene‐rich phase for tie lines closer to the plait point indicating a partitioning or redistribution of the molecular weight species of PS between the incompatible phases.

Calorimetric values of composite solid propellants

The calorimetric values of composite solid propellant based on polystyrene, polyphenolformaldehyde, poly(vinyl chloride) and carboxy-terminated polybutadiene were determined using combustion calorimetry in order to assess the uncertainities in their measurements. The dependence of the calorimetric values on various propellant composition was obtained. The stoichiometry of oxidizer and fuel in the propellant for complete combustion obtained experimentally were compared with the theoretical stoichiometry calculated based on the oxidizer decomposition.

Formation of worm-like micelles from a polystyrene–polybutadiene–polystyrene block copolymer in ethyl acetate

An investigation has been made of micelle formation by a polystyrene–polybutadiene–polystyrene block copolymer in ethyl acetate, which is a selectively bad solvent for polybutadiene; the number-average molecular weights of the three blocks were 12900, 66000 and 13700, respectively. As the temperature was raised dilute solutions of the copolymer in ethyl acetate showed a distinct cloud-point, which moved to higher temperatures with increases in concentration. On raising the temperature further the solutions gradually became clear again.Light scattering and electron microscopy studies showed that the onset of cloudiness was due to the formation of long worm-like micelles from spherical micelles. The clearing of solutions at higher temperatures occurred because the micelles dissociated to form copolymer molecules in the free-chain form. The cores of both types of micelle were composed of swollen polybutadiene blocks and the outer fringes of the micelles of polystyrene blocks. The spherical micelles had a fairly narrow size distribution. The worm-like micelles had a wide distribution of contour lengths but possessed a narrow size distribution in the radial direction.A second polystyrene–polybutadiene–polystyrene copolymer having shorter blocks than the first copolymer showed a similar type of solution behaviour at lower temperaturs.

Limiting conversions in two‐phase polymer reactions

AbstractThe concepts of limiting conversion in one‐phase polymer reactions have been extended to two‐phase reaction systems. The analysis of the two‐phase reaction requires the consideration of the glass transition temperature of each phase and the distribution of the reacting monomer between the phases. Predicted limiting conversions are compared with experimental data for simple polystyrene and polystyrene–polybutadiene reactions in latex form. Strong agreement is found for these comparisons.

Solvation and phase separation in ABA block copolymers

AbstractA conceptual scheme is presented for classifying the phase behavior of ABA block copolymers and solvents. The effect of solvent fraction ϕS on microphase separation is described for macroscopically homogeneous systems, but more attention is focused on the limits of solubility. A “miscibility map” is developed in terms of solubility parameters δA, δB, and δS and used to define regions of macrophase separation, complete miscibility, and partial miscibility. Combined with known triblock molecular structure, the miscibility map can be used to predict the character of solvated systems and guide the selection of solvents for special purposes. A survey of reports in the literature shows qualitative consistency with this treatment. New observations are reported on solvation of a polystyrene–polybutadiene–polystyrene polymer in numerous solvents; these are used to infer microstructural information and define the miscibility map more realistically.