Synthesis and Characterization of Styrene-Isoprene Diblock Copolymers

A simple reusable apparatus for the synthesis of up to 40 g quantities of poly(styrene-b-isoprene) diblock copolymers of reasonably low (1.2 to 1.5) polydispersity has been described. The diblock copolymers synthesized were characterized by gel permeation chromatography (GPC), membrane osmometry, viscosimetry, and nuclear magnetic resonance (NMR) spectroscopy. Number-average molecular weights (M _n) calculated from the raw GPC chromatographs of the diblock copolymers using the summation method and M versus elution volume plots for polystyrene and polyisoprene standards agree well with those measured experimentally with osmometry. It is suggested that for polydisperse block copolymers this method is simpler than the use of a universal calibration curve. Mark-Houwink constants K ans a for polyisoprene having 18% (1,2-), 66% (3,4-), and 16% (1,4-) microstructure were found to be 3.2 × 10^?4 dL/g and 0.67, respectively, in THF at 25°C. In toluene at 30°C, K = 2.0 × 10^?4 dL/g and α = 0.7 were obtained. The diblock copolymers had 26% (1,2-), 60% (3,4-), and 14% (1,4-) microstructure in the isoprene segments, and the values of K and a for these copolymers (PS > 50%, M 20.0 × 10³) in THF at 25°C were 9.0 × 10^?5 dL/g and 0.75. For M < 20.0 × 10³ the value of α was 0.5. The experimental values of [η] were found to be lower than those calculated theoretically, presumably due to the polydisperse nature and the biellipsoidal configuration of the diblock copolymers.     

Probe diffusion in homogeneous diblock copolymers

Forced Rayleigh scattering was used to investigate the diffusion of a photoreactive dye molecule in two homogeneous poly(styrene-b-isoprene) (SI) diblock copolymers with overall molecular weights of approximately 2000. Although diffusion rates were intermediate to TTI transport in homopolymer polystyrene (PS) and polyisoprene (PI), system dynamics appear to be largely dictated in each case by the PI block. The size of the polymer jumping unit, on the other hand, is evaluated from a free-volume analysis of the data, and is found to be governed predominantly by the PS component of the copolymer. The mechanism for tracer diffusion in low-molecular-weight block copolymers appears analogous to transport in a high molecular weight SI diblock copolymer (M_n = 13,600) that has been solvated sufficiently in toluene to be microstructurally disordered. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1739–1746, 1998     

Effect of the solvent upon the diffusion coefficient of polydisperse polystyrene and styrene-acrylonitrile copolymer in dilute solution

A laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene-acrylonitrile copolymer solutions at room temperature. Data were obtained in the concentration range from 0.01 to 2.0 g polymer per 100 cm³ solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. The samples were polydisperse polystyrenes of weight average molecular weights between 80,000 and 350,000 and polydisperse copolymers of weight average molecular weights between 200,000 and 800,000. The SAN copolymers were random copolymer samples containing 24% by weight acrylonitrile. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) = D₀(1+k_Dc). Values of D₀ could be explained with a modified Kirkwood-Riseman expression. Values of the parameter k_D obtained from the slopes could be interpreted using the two-parameter theory approach as suggested by Vrentas and Duda. The value of k_D is positive for high-molecular-weight polymers and negative for low-molecular-weight polymers. For a particular polymer, the molecular weight at which k_D changes sign is greater for poor solvents than for good solvents. Observed values of D₀ were 1 × 10^?7 to 7 × 10^?7 cm²/sec.     

Synthesis of hybrid dendritic‐linear block copolymers with dendritic initiators prepared by convergent living anionic polymerization

Hybrid dendritic‐linear block copolymers were made in one‐pot by convergent living anionic polymerization. Dendritic polystyrene macroinitiators were synthesized by slowly adding a mixture of either vinylbenzyl chloride (VBC) or 4‐(chlorodimethylsilyl)styrene (CDMSS) and styrene (1 : 10 molar ratio of coupling agent to styrene) to a solution of living polystyryllithium. The addition was ceased prior to the addition of a stoichiometric amount of coupling agent to retain a living chain end. To the living dendritically branched polystyrene was then added either styrene or isoprene to polymerize a linear block from the dendritic polystyrene. The resulting copolymers were characterized by gel permeation chromatography coupled with multiangle laser light scattering (GPC‐MALLS), which clearly demonstrated the formation of diblock copolymers. The diblock copolymers were further characterized by ¹H NMR, which showed the presence of the two blocks in the case of dendritic polystyrene‐block‐linear polyisoprene. The measurement of intrinsic viscosity showed that the dilute solution properties of the block copolymers are greatly influenced by the dendritic portion. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 152–161, 2001     

Solution properties of styrene-p-chlorostyrene diblock copolymers—II. Light scattering studies in a selective solvent

Conformational behaviour of styrene-p-chlorostyrene diblock copolymers in cumene (a good solvent for polystyrene but a θ solvent for poly-p-chlorostyrene) was studied over the temperature range 15–60° by light scattering, osmotic pressure and intrinsic viscosity measurements. Two samples of copolymer (AB-4 and AB-2) were used. The composition of the samples was c. 50 mol% of styrene and the number-average molecular weights were 27.7 × 10⁴ for the AB-4 and 19.5 × 10⁴ for the AB-2. It was found that below 40° the number-average molecular weight of the AB-4 sample seemed to increase gradually with decreasing temperature and around 40°, marked decreases in the osmotic second virial coefficient and intrinsic viscosity were observed. The Zimm plot for the AB-2 sample was fairly normal at 40°. It seems that the temperature where an anomaly becomes evident in Zimm plots is dependent on the molecular weight of the sample. The experimental results for the diblock copolymers could be understood from the view that intermolecular association took place to some extent in the solutions on lowering the temperature giving rise to multi-molecular micelles.     

Triblock copolymers in a selective solvent: Dilute and semi-dilute solutions

Triblock copolymers polystyrene-polyisoprene-polystyrene were studied in dilute and semi-dilute solutions in a selective solvent, i.e. a non-solvent for polystyrene and a good solvent for polyisoprene. The mass of the copolymer is equal to 1.6×10⁵g/mol and it contains 70% of polyisoprene. At a concentration C equal to 1.6×10⁻³ g/cm³ triblock aggregation occurs. Experiments performed on dilute solutions¹ plead in favor of loose and polydisperse aggregates rather than spherical micelles: 1) the form factor of the aggregates shows a smooth decrease at qR<1; 2) internal modes are observed by quasi-elastic light scattering; 3) specific viscosity measurements show that the internal concentration of unimers and aggregates are identical; 4) the unimer concentration and the aggregation number depend on the copolymer concentration. In semi-dilute solutions² (C>3×10⁻² g/cm³), dynamical properties are strongly affected by the temperature. Viscosity and longest relaxation time increase by a factor 10⁵ as the temperature decreases from 50°C to 5°C, whereas the plateau modulus G remains independent of the temperature and proportional to the concentration. Small angle neutron scattering experiments reveal a cubic structure having a unit cell dimension d independent of the temperature and varying as C^−1/3 leading to G∼1/d³. Quasi-elastic light scattering experiments performed on this system show a wide relaxation function extending over 7 decades of time. These results argue for a lattice made of polystyrene nodes linked together by the polyisoprene middle blocks, the dynamics being governed by the glass transition of the nodes.     

Polymethylene‐b‐polystyrene diblock copolymer: Synthesis,property, and application

The design and synthesis of well‐defined polymethylene‐b‐polystyrene (PM‐b‐PS, M_n = 1.3 × 10⁴–3.0 × 10⁴ g/mol; M_w/M_n (GPC) = 1.08–1.18) diblock copolymers by the combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) was successfully achieved. The ¹H NMR spectrum and GPC traces of PM‐b‐PS indicated the successful extension of PS segment on the PM macroinitiator. The micellization behavior of such diblock copolymers in tetrahydrofuran were characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM) techniques. The average aggregate sizes of PM‐b‐PS diblock copolymers with the same length of PM segment in tetrahydrofuran solution (1.0 mg mL^?1) increases from 104.2 nm to 167.7 nm when the molecular weight of PS segment increases. The spherical precipitated aggregates of PM‐b‐PS diblock copolymers with an average diameter of 600 nm were observed by AFM. Honeycomb porous films with the average diameter of 3.0 μm and 6.0 μm, respectively, were successfully fabricated using the solution of PM‐b‐PS diblock copolymers in carbon disulfide via the breath‐figure (BF) method under a static humid condition. The cross‐sections of low density polyethylene (LDPE)/polystyrene (PS)/PM‐b‐PS and LDPE/polycarbonate (PC)/PM‐b‐PS blends were observed by scanning electron microscope and reveal that the PM‐b‐PS diblock copolymers are effective compatilizers for LDPE/PS and LDPE/PC blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1894–1900, 2010     

Viscosity of concentrated solutions of polystyrene and poly(vinyl acetate) (empirical equations)

The viscosity of solutions of polystyrene with M _w from 2.8 × 10⁴ to 7.8 × 10⁵ in toluene and of poly(vinyl acetate) with M _w from 2 × 10⁴ to 1.4 × 10⁵ in butyl acetate at 30–80°C is measured. The dependence of the activation energy of the viscous flow of the solutions on the molecular weight of the polymers and solution concentration is examined. This dependence is approximated by a cubic polynomial for polystyrene solutions and by a quadratic polynomial for poly(vinyl acetate) solutions. The dependences of the solution viscosity on the concentration, molecular weight, and temperature are approximated by exponential equations in which the exponents are sums of polynomials. The coefficients of the polynomials are determined.     

Polystyrene degradation induced by stresses resulting from the freezing of its solutions

Solutions of polystyrene in p-xylene were frozen in liquid nitrogen. No changes in molecular weight and distribution were caused by freezing solutions for a series of narrow distribution polystyrenes with molecular weights of near 2 × 10⁶ and lower. Likewise a commercial polystyrene of M?_w = 234,000 showed no change, even after 45 cycles of freezing and thawing. However, an ultrahigh molecular weight polystyrene (M?_w = 7.3 × 10⁶) showed appreciable degradation even after a few freezing cycles of its solutions. The changes in molecular weight and distribution were analyzed by gel-permeation chromatography. The results depended very much on the choice of solvent, cooling rate, and concentration. The extent of degradation was found to depend on polymer concentration in two distinct ways. Indeed, two different degradation mechanisms have been distinguished at low and at high concentrations. The change between mechanisms took place between 1.0 and 2.5 g/l. for polystyrene in p-xylene. This appears to provide a rare measure of polymer-polymer interactions (entanglements) in dilute solutions. Degradation in the entanglement region proceeded via a random chain-scission mechanism as tested by the Scott method. In contrast, at low concentrations degradation was characterized by the formation of appreciable amounts of low molecular weight polystyrene. The presence of an antioxidant (Ionol) during freezing did not change the extent of degradation significantly.     

Styrene and isoprene friction factors in styrene–isoprene matrices

Monomeric friction factors, Ξ, for polystyrene (PS), polyisoprene (PI), and a polystyrene–polyisoprene (SI) diblock copolymer have been determined as a function of temperature in four poly(styrene-b-isoprene-b-styrene-b-isoprene) tetrablock copolymer matrices. The Rouse model has been used to calculate the friction factors from tracer diffusion coefficients measured by forced Rayleigh scattering. Within the experimental temperature range the tetrablock copolymers are disordered, allowing for measurement of the diffusion coefficient in matrices with average compositions determined by the tetrablock copolymers (23, 42, 60, and 80% styrene by volume). Remarkably, for a given matrix composition the styrene and isoprene friction factors are essentially equivalent. Furthermore, at a constant interval from the system glass transition temperature, T_g, all of the friction factors (obtained from homopolymer, diblock copolymer, and tetrablock copolymer dynamics) agree to within an order of magnitude. This is in marked contrast to results for miscible polymer blends, where the individual components generally have distinct composition dependences and magnitudes at constant T − T_g. The homopolymer friction factors in the tetrablock matrices were systematically slightly higher than those of the diblock, which in turn were slightly higher than those of the homopolymers in their respective melts, when all compared at constant T − T_g. This is attributed to the local spatial distribution of styrene and isoprene segments in the tetrablocks, which presents a nonuniform free energy surface to the tracer molecules. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3079–3086, 1998     

Molecular weight standards from sulfonation of polystyrene

Polystyrene was sulfonated with sulfur trioxide–triethyl phosphate complexes in dichloroethane, the object being to prepare polystyrene sulfonates substantially free of sulfone links between polymer chains. Variations in the sulfone content with reaction conditions were conveniently followed by exclusion chromatography, the sulfone peak appearing at about twice the molecular weight of the main peak. The desired products were obtained from polystyrenes with molecular weights between 1.1 × 10⁵ and 8.7 × 10⁵ by using (at ?20 to +25°C) a 5:1 excess of a 1.5:1 complex, the last at a concentration of 0.5M. Completely soluble polystyrene sulfonate was also obtained from polystyrene of molecular weight 2.05 × 10⁶. Requirements for the successful use of the 1.5:1 complex include careful purification of the dichloroethane and, if 2 g or more polystyrene is to be sulfonated, formation of the complex at ?20°C. A method is given for measuring the sulfonating capability of the reagent before adding the polymer.     

Dilute-solution properties of ring polystyrenes

The temperature Θ_A2 at which the second virial coefficient A₂ is zero for ring polystyrenes is 28.5°C in cyclohexane, independent of molecular weight in the range 2 × 10⁴ to 4.5 × 10⁵. This cannot be explained solely by the Candau–Rempp–Benoit theory, which takes into account the effect of segment density on Θ_A2 The radius of gyration of a ring is found to be approximately one-half that of a linear polymer with the same molecular weight. The intrinsic viscosities [η] and intrinsic translational friction coefficients [f] of ring polystyrenes with molecular weights ranging from 7 × 10³ to 4.5 × 10⁵ have been measured in cyclohexane at 34.5°C (Θ, the Flory theta temperature for linear polystyrenes) and in toluene (a good solvent). The results are compared with those for linear polystyrene. It is found that the Mark–Houwink exponent is less than one-half in cyclohexane at Θ. In toluene it is 0.67 compared to 0.73 for linear polystyrene. The hydrodynamic measurements suggest that large rings are less expanded than the linear polymers with the same molecular weight, contrary to many predictions.     

Arborescent polystyrene‐graft‐poly(tert‐butyl methacrylate) copolymers: Synthesis and enhanced polyelectrolyte effect in solution

A technique is described for the preparation of arborescent graft copolymers containing poly(tert‐butyl methacrylate) (PtBMA) segments. For this purpose, tert‐butyl methacrylate is first polymerized with 1,1‐diphenyl‐2‐methylpentyllithium in tetrahydrofuran. The graft copolymers are obtained by addition of a solution of a bromomethylated polystyrene substrate to the living PtBMA macroanion solution. Copolymers incorporating either short (M_w ≈ 5000) or long (M_w ≈ 30,000) PtBMA side chains were prepared by grafting onto linear, comb‐branched (G0), G1, and G2 bromomethylated arborescent polystyrenes. Branching functionalities ranging from 9 to 4500 and molecular weights ranging from 8.8 × 10⁴ to 6.3 × 10⁷ were obtained for the copolymers, while maintaining a low apparent polydispersity index (M_w/M_n ≈ 1.14–1.25). Arborescent polystyrene‐graft‐poly(methacrylic acid) (PMAA) copolymers were obtained by hydrolysis of the tert‐butyl methacrylate units. Dynamic light scattering measurements showed that the arborescent PMAA copolymers are more expanded than their linear PMAA analogues when neutralized with NaOH. This effect is attributed to the higher charge density in the branched arborescent copolymer structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2335–2346, 2008     

Synthesis and characterization of poly[styrene‐b‐methyl(3,3,3‐trifluoropropyl)siloxane] diblock copolymers via anionic polymerization

A series of narrow molecular weight distribution (MWD) polystyrene‐b‐poly[methyl(3,3,3‐trifluoropropyl)siloxane] (PS‐b‐PMTFPS) diblock copolymers were synthesized by the sequential anionic polymerization of styrene and trans‐1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane in tetrahydrofuran (THF) with n‐butyllithium as the initiator. The diblock copolymers had narrow MWDs ranging from 1.06 to 1.20 and number‐average molecular weights ranging from 8.2 × 10³ to 37.1 × 10³. To investigate the properties of the copolymers, diblock copolymers with different weight fractions of poly[methyl(3,3,3‐trifluoropropyl)siloxane] (15.4–78.8 wt %) were prepared. The compositions of the diblock copolymers were calculated from the characteristic proton integrals of ¹H NMR spectra. For the anionic ring‐opening polymerization (ROP) of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (F₃) initiated by polystyryllithium, high monomer concentrations could give high polymer yields and good control of MWDs when THF was used as the polymerization solvent. It was speculated that good control of the block copolymerization under the condition of high monomer concentrations was due to the slowdown of the anionic ROP rate of F₃ and the steric hindrance of the polystyrene precursors. There was enough time to terminate the ROP of F₃ when the polymer yield was high, and good control of block copolymerization could be achieved thereafter. The thermal properties (differential scanning calorimetry and thermogravimetric analysis) were also investigated for the PS‐b‐PMTFPS diblock copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4431–4438, 2005     

Glass transition temperature of low molecular weight styrene–isoprene block copolymers

Different series of poly(styrene–isoprene) diblock and poly(styrene–isoprene–styrene) triblock copolymers were prepared. In each series, the low molecular weight polystyrene block was kept constant, and the molecular weight of the polyisoprene block varied. The glass transition behavior of these polymers was studied and their glass transition temperatures compared with those of the random copolymers of styrene and isoprene. It is concluded that some low molecular weight styrene-isoprene block copolymers form a single phase. Krause's thermodynamic treatment of phase separation in block copolymers was applied to the data. One arrives at a polystyrene–polyisoprene interaction parameter χ1,2 ≈ 0.1. The experimental and theoretical limitations of this result are discussed.     

Dependence of viscosity of polystyrene solutions on molecular weight and concentration

Viscosities of solutions of polystyrene in toluene were measured for concentrations up to 400 kg m^?3 at 298 K. Polymers of molecular weights ranging from 8.7 × 10³ to 2.4 × 10⁶ were used. It is observed that viscosity of the polymer solution increases with increasing concentration and molecular weight; the rate of increase is greater at higher values of the two parameters. A master curve for the system is constructed by using the experimental data for viscosity, concentration and molecular weight of the polymer. Regions of various polymer interactions in solution are identified.     

Matched ring diblock and linear triblock copolymers in dilute solution

A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light-scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 10⁴ for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (D_c) and linear triblock copolymer (D₁) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are D_c/D_l = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.     

Microstructurally Controlled Polyisoprene or Polystyrene Diblock Copolymers of rac‐Lactide

Summary: A series of new polyisoprene‐block‐polylactide and polystyrene‐block‐polylactide diblock copolymers was prepared by combining the living anionic polymerization of isoprene or styrene, and the stereoselective ring‐opening polymerization of rac‐lactide. Aluminum and yttrium‐based polystyrene or polyisoprene macroinitiators yielded isotactic‐stereoblock and heterotactic‐enriched polylactide segments, respectively. A strong influence of the microstructure of the polylactide block on the aggregation properties in solution and morphological behavior of the solid materials in thin films has been observed.

General strategy used for the preparation of the diblock copolymers, illustrated here for poly(isoprene‐block‐lactide). Poly(styrene‐block‐lactide) copolymers were prepared similarly.     

Emulsifier-free emulsion polymerization of the comonomer system styrene/tetrahydrofurfuryl metacrylate

 The emulsifier-free emulsion copolymerization of styrene and tetrahydrofurfuryl methacrylate (TMA) in aqueous phase is described. Monodisperse latex particles with diameters from about 280 to 620 nm are obtained consisting of a hydro-phobic polystyrene core and a hydrophilic poly-TMA shell. The influence of a variation of TMA, styrene and initiator (potassium persulfate) concentration in the original emulsion on particle size, molecular weight and composition of the copolymer is described. The concentration of TMA and initiator affects the number of primary particles but not the size of the final particles, whereas the styrene concentration strongly influences the particle diameter, a large size being favored by a high styrene concentration. The molecular weights of the polymers are between 6.2×10⁴ and 7.0×10⁵ g/mole. Size exclusion chromatography of polymer solutions in tetra-hydrofuran shows that high molecular weights are especially found in large particles, which are preferentially formed in emulsions with a high concentration of styrene. ¹H-NMR spectroscopy of the polymer shows that only about 50% of the initial TMA concentration are polymerized in the particles. Thus the copolymers prepared at increasing styrene concentration and constant initiator concentration of the emulsion show an increasing polystyrene content and are formed in particles of increasing size. Received: 4 June 1997 Accepted: 19 August 1997     

(Star PS)-block-(Linear PI)-block-(Star PS) Triblock Copolymers – Thermoplastic Elastomers with Complex Branched Architectures

Polystyrene-block-polyisoprene-block-polystyrene triblock copolymers were synthesized with star-shaped branching in the polystyrene phase. The block copolymers were formed through sequential anionic polymerization by first synthesizing linear polystyrene, followed by star coupling using 4-(chlorodimethylsilyl)styrene, then the polymerization of isoprene, followed by difunctional coupling with dichlorodimethylsilane. The polymerization was followed by gel permeation chromatography and the resulting copolymers were characterized by ¹H NMR spectroscopy to examine the polyisoprene microstructure.