Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Polystyrene/poly(vinyl methyl ether) (PS/PVME) phase diagram was assessed by rheological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several rheological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to T_s whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing.     

Cloud point curves for poly(vinyl methyl ether) and monodisperse polystyrene mixtures

The compatibility behaviour of poly(vinyl methyl ether) (PVME) and monodisperse polystyrene (PS) is studied for solution cast films. The molecular weight of monodisperse PS ranges from 2100 to 2 000 000 whereas the PVME used is polydisperse and has weight-average molecular weight of 51 500. When cast from toluene solution, the mixtures undergo phase separation at elevated temperatures. The cloud point curves move to markedly lower temperatures with increasing molecular weight which is similar to the lower critical solution temperature (LCST) behaviour for polymer solutions. They move to lower temperatures until the molecular weight of PS reaches about 51 500.The effect of molecular weight distribution on the cloud point of equal amounts of PS and PVME mixtures simulated by mixing two monodisperse polystyrenes of different molecular weight for PS part is accurately predicted by using weight-average molecular weight for PS in this range. However, if the molecular weight of PS exceeds about 110 000 the molecular weight dependence of cloud point temperature is reversed and the prediction for polydisperse polymer by using weight-average molecular weight fails. This phenomenon is discussed from several viewpoints including the possibility of the effect of chain entanglement.Mixtures of PVME and PS of M_w = 20 400 were also cast from an ‘incompatible’ solvent, trichloroethylene. Compatibility is found to be dependent on composition and even phase-separated samples show at least one cloud point, indicating at least partial mixing of the two polymers. Finally, it is demonstrated that crosslinking of compatible films can be achieved by electron irradiation to form true interpenetrating networks. The cloud point temperatures are increased drastically after crosslinking.     

Study of the nonlinear phase‐separation behavior of a polystyrene/poly(vinyl methyl ether) blend using small‐angle light scattering

The thermally induced phase‐separation behavior of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was studied mainly using time‐resolved small‐angle light scattering, as a function of temperature and heating rate. Under a non‐isothermal field, the dependence of the critical temperature on heating rate deviated obviously from linearity, even at very low heating rates. Such a nonlinear dependence was consistent with the deviation from linearity of the temperature dependence of the isothermal phase‐separation behavior in a wider temperature range from 100 to 140 °C. It was also found that a Williams–Landel–Ferry (WLF)‐like equation could be employed to describe the temperature dependence of the apparent diffusion coefficient (D_app) and the relaxation time (τ) of normalized scattering intensity at the early stage of spinodal decomposition (SD), as well as τ of phase behavior at the late stage of SD for the PS/PVME blend. The equilibrium phase‐separation temperature could hardly be established through the conventional linear extrapolation of heating rate or D_app to zero at the early stage of SD. The successful use of the WLF‐like function for PS/PVME blends extends the applicability of the time–temperature superposition principle for describing the phase‐separation behavior of binary polymer mixtures over a relatively large temperature range. Copyright © 2010 Society of Chemical Industry     

Effect of thermal history on the molecular orientation in polystyrene/poly(vinyl methyl ether) blends

The effect of thermal history on the orientation and relaxation behavior of blends of polystyrene with poly(vinyl methyl ether) (PS/PVME) has been studied using polarization modulation infrared linear dichroism (PM-IRLD) and differential scanning calorimetry (DSC). DSC shows that miscible PS/PVME blends containing 70% of PS can be physically aged at temperatures above their mean glass transition temperature (T_g). PM-IRLD measurements reveal that both components become more oriented upon stretching at 51 °C (8 °C above T_g) if the sample is aged at the deformation temperature prior to stretching. Room-temperature aging can also lead to an increased orientation if the heating time at 51 °C is kept short. Moreover, PS and PVME develop a larger orientation in phase-separated blends than in miscible ones, and their relaxation is hindered. The results have been interpreted considering the morphology of the samples, including the presence of concentration fluctuations in miscible blends, and the effect of the local environment on the rigidity of the chains.     

Zum thermodynamischen verhalten von polystyrol (PS)/poly(vinylmethylether) (PVME)-blends

The polymer blend system PS/PVME shows a phase behaviour with lower critical separation temperature (LCST behaviour), which was simulated and discussed with the help of the model of Dee and Walsh as well as by means of the continuous thermodynamics. The results show that the Prigogine equation of state is able to fit advantageously the real PVT behaviour in the polymer melt. The spinodal curve used by the Dee/Walsh model gives a very good conformity with the results of the cloud point measurements. The model simulations show an increase of the compatibility of this polymer system with increasing pressure. By means of the continuous thermodynamics the influence of polydispersity on the phase behaviour of the blend system could be made clear. A marked shift of the critical point from minimum is seen because of the broad molecular mass distribution of PVME.     

Phase separation in polystyrene-poly(vinylmethylether) blends: a a fluorescence emission analysis

Fluorescence emission of labels appears to be a new technique for the investigation of the LCST behaviour of polystyrene-poly(vinylmethylether) (PS-PVME) blends. Indeed, heating ternary blends of PVME/PS/labelled PS results in sharp increases in the fluorescence intensity, which occur simultaneously with their phase separation. Specific interactions between the anthracenic units of the labelled PS and the ether functions of PVME, are responsible for the fluorescence quenching, which occurs in the compatible blends. Quenching drops as phase separation proceeds, because of the lowering of the probability for label-PVME interactions in the two-phase state. By relating the phase separation curves obtained in this way to those acquired by the classical light scattering method, it is shown that fluorescence experiments may allow determination of both spinodal and binodal curves, provided that heating rate is appropriate.     

Orientation and relaxation in uniaxially stretched poly(vinyl methyl ether)-atactic polystyrene blends

Infrared measurements of the dichroic ratio of polystyrene and poly(vinyl methyl ether) absorption bands allow us to determine chain orientation for each component in their compatible blends. Influence of strain rate and temperature of stretching on orientation of both polymer chains in blends containing up to 25% PVME has been studied. Mechanical relaxation master curves at a reference temperature T=T_g+40°C have also been determined. Results are compared to previous results obtained in PS-PPO compatible blends. Although PPO and PVME chains behave differently PS chains behaviour is similar in the two types of blends and interpreted in terms of a hindrance of relaxation of PS chains induced by a modification of friction coefficients due to the molecular interactions which are at the origin of compatibility.     

Miscibility and interactions in polystyrene and sodium sulfonated polystyrene with poly(vinyl methyl ether) PVME blends. Part II. FTIR

The miscibility and specific interactions of polystyrene (PS) and sodium sulfonated polystyrene (Na-SPS) with poly(vinyl methyl ether) (PVME) blends (ranging from 10 to 90% PS by weight) were examined experimentally by FTIR spectroscopy. The FTIR studies at different temperatures have shown that changes in spectra of polymer blends, as reported in the literature can be explained by temperature changes in pure homopolymers. This indicates that molecular interactions, which are responsible for miscibility, are not detectable by infrared absorptions and are therefore of unspecific strength and location. The FTIR of SPS/PVME blends show that sulfonate groups of PS affect polymer miscibility through changes in configuration of molecules, rather than through direct interaction with the PVME.     

Effect of shear memory on the coarsening behaviour of polystyrene and poly(vinyl methyl ether) blend

The effect of shear memory on the coarsening behaviour of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend which shows a typical lower critical solution temperature (LCST)-type phase diagram has been thoroughly investigated for the near critical composition (PS/PVME=30/70) using a time-resolved light scattering technique. The measurements were carried out at 135 °C (20 °C above the quiescent cloud point) at two different directions, parallel and normal to the direction of flow. Different shear memories were generated in the melt using a simple shear apparatus of parallel plate geometry. The coarsening process was influenced to a great extent by the shear history of the blend over the time scale of the measurement. The average domain size of the dispersed particles obtained from the analysis of the light scattering data on the basis of Deby Bueche theory was found to be shear memory dependent. The coarsening process was elevated and suppressed at low and high shear memory, respectively. This behaviour was attributed to the shift of the cloud point observed under same values of shear rates. In addition, the coarsening behaviour of this blend was found to be flow direction independent due to the very high viscosity ratio of the blend, which led to in turn rather circular domains of PS in PVME matrix without any elongation or orientation in the direction of flow. Furthermore, the coarsening process for all the measured samples was followed the general power low, regardless the shear history and the flow direction of the blends. This result indicated that; the shear could only retard or elevate the rate of domain growth without any effect on the coarsening mechanism.     

Synthesis and morphological studies of polyisoprene-block-polystyrene-block-poly(vinyl methyl ether) triblock terpolymer

The triblock terpolymer (PI-b-PS-b-PVME) consisting of polyisoprene (PI), polystyrene (PS) and poly(vinyl methyl ether) (PVME) was synthesized by coupling reaction between living PI-b-PS anion and end-chlorinated PVME prepared via living cationic polymerization. This polymer is an amphiphilic block polymer and unique in a sense that it exhibits complex phase behavior because PS and PVME have a lower critical solution temperature (LCST)-type phase diagram while PI and PS (or PVME) have an UCST-type phase diagram. This unique architecture would result in a step-wise microphase separation to form a three-phase microdomain structure. It was observed by transmission electron microscopy with ultrathin sections that the toluene-cast film of PI-b-PS-b-PVME has a two-phase lamellar structure consisting of PI microdomains and mixed PS/PVME microdomains. Applying a drop of water onto the ultrathin sections induced further microphase separation between PS and PVME within the lamellar microdomains resulting in the three-phase structure. Water is a selective solvent for PVME and might have lowered the order-disorder temperature between PS and PVME. This step-wise microphase separation may be a new technique to control microphase-separated structures in triblock terpolymers.     

Isothermal crystallization study on aqueous solution of poly(vinyl methyl ether) by DSC method

A study on the isothermal crystallization of water in aqueous solutions of poly(vinyl methyl ether) (PVME) was carried out by the differential scanning calorimetry (DSC). The influence of PVME concentration (49.5, 44.5 and 39.5 v%) and the crystallization temperature (T_c) on crystallization rate G, crystallization enthalpy (ΔH_c) and melting enthalpy (ΔH_m) was investigated. Avrami equation cannot be used to describe the crystallization process of water in aqueous PVME solution. Within the measured temperature range, the crystallization rate G increases with the crystallization temperature T_c and with the decreasing PVME content. The crystallization enthalpy ΔH_c linearly increases with the degree of supercooling. The influence of T_c on the ΔH_c becomes more marked with increasing PVME concentration. For 49.5 and 44.5 v% PVME solutions, the amount of water arrested in solution during the isothermal crystallization and the final concentration of PVME-rich phase increase linearly with the T_c, whereas for 39.5 v% PVME solution, these two values almost do not change with T_c. The amount of frozen water in the subsequent cold crystallization is approximately proportional to the initial T_c. The approximately constant ΔH_m for a given concentration at the different initial isothermal crystallization temperatures suggests that the total amount of ice from the first isothermal crystallization and the second cold crystallization is same. The quantitative relation of the amount of frozen water in the cold crystallization and the initial T_c demonstrates that PVME/water complexes are thermodynamically unstable.     

Effect of nano-CaCO3 on polymorphic behavior in syndiotactic polystyrene for non-isothermal crystallization

Syndiotactic polystyrene (sPS)/nano-CaCO₃ composites were prepared on a twin screw extruder for the first time. Differential scanning calorimeter and wide-angle X-ray diffraction were used to investigate the effect of maximum melting temperature (T_max) and the content of nano-CaCO₃ on the crystal forms and melting behavior of sPS for non-isothermal crystallization. The results indicated that the increasing T_max decreases the crystallization temperature of sPS and facilitates the formation of β-crystal. The addition of nano-CaCO₃ changes the melting behavior and crystal form of melt-crystallized sPS and facilitates the formation of β-crystal. The increase in the content of nano-CaCO₃ decreases crystallization temperature of sPS and increases the content of β-crystal, which was similar to the effect of increasing T_max. Pure β-crystal in sPS/nano-CaCO₃ composites can be obtained at lower melting temperature due to the effect of nano-CaCO₃.     

Phase behavior of poly(ε-caprolactone)/ poly (vinylidene fluoride) blends

The miscibility of blends of poly (ε-caprolactone) (PCL)/poly(vinylidene fluoride) (PVDF) was studied by measuring the cloud point, melting point depression and crystallization kinetics. Lower critical solution temperature (LCST) behavior was observed at PCL-rich compositions, whilst it was not observed at high compositions of PVDF. However it is possible that an LCST could exist below the melting point of PVDF. From analysis of the melting point depression, the Flory interaction parameter x₁₂, was calculated from the Nishi-Wang equation and the value was found to be-1.5. The crystallization rate of PCL increased with increasing amount of PVDF in the blend. The spinodal curve for PCL/PVDF blends was simulated by using the lattice-fluid theory.     

Deformation studies of polystyrene/poly(vinyl methyl ether) blends by mechanical-vibrational spectroscopy

We have analyzed the deformation behavior of compatible and incompatible polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends by a combination of mechanical and vibrational spectroscopy. Macroscopic properties and segmental orientation were found to be sensitive to molecular weight, strain rate, and temperature of measurement above the glass-transition temperature. Considerably different orientation functions were found for the PS and PVME components. For the experiments carried out above the T_g of the blends, the deformation behavior measured was consistent with expectations of a rubbery network.     

The mechanical properties of styrene-butadiene-styrene (SBS) triblock copolymer blends with polystyrene (PS) and styrene-butadiene copolymer (SBR)

Measurements were made of linear viscoelastic properties and nonlinear stress-strain properties of phase-separated styrene-butadiene-styrene (SBS) copolymers and their blends with several homopolymer polystyrenes (PS) and one random copolymer (SBR). Torsion pendulum testing yielded shear moduli G′, G″, and Rheovibron experiments produced tensile moduli E′, E″, over a 220°K range of temperature, both at low frequencies. For pure copolymers and their PS blends, G′ and E′ correlated quite well with the total PS content, but G″ and E″ were more sensitive to how the additive was distributed. Results suggest that a PS additive whose molecular weight (M) is less than that of the copolymer PS-block (M_s) causes expansion of both the interphase and the homogeneous PS-rich phase, while an additive with M > M_s mixes less well with these phases (probably forming separate domains of pure PS) and is less effective in enhancing the linear moduli. The blending with SBB produced reduction in G′ but a broad midrange peak in G″, suggesting that SBR was localized almost entirely within an expanded interphase. Tensile stress-strain data were obtained with an Material Testing System at room temperature. For PS blends, properties did not correlate well with the total PS content, the blends being always weaker than the SBS of the same overall composition. The amount of set also increased with PS content in the blends. Cyclic tests to increasing strain showed progressive structural alterations (as for the host SBS), with blend behavior resembling host properties more closely with each new cycle. When SBR was the additive, amounts as small as 1 percent reduced the curves by 15 percent. The yield stress was eliminated entirely with an addition of 10 percent SBR, but for all cases the set was the same. Results are discussed in terms of interphase force barriers to chain flow.     

Effect of rheological parameters on the miscibility and polymer–filler interactions of the black-filled blends of polyethylene–vinyl acetate and polychloroprene

Miscibility of 30 phr loaded black-filled (N110) blends of polyethylene-vinyl acetate (EVAc, VAc content 28%) and polychloroprene (CR) are investigated through shear and dynamic deformations. Both shear (η_a) and dynamic elongational (η′_E) viscosities are conducive to their miscibility as both show positive deviation for all blends, though dynamic out-of-phase (η″_E) viscosity shows negative-positive deviation. Both η_a and η′_E follow the power law relationship with shear rate (γ˙_wa) and frequency (ω), respectively. Both storage (E′) and loss (E″) modulii increases with frequency. The higher dissipative energy at around 11 Hz may be due to its syncronization with molecular vibrations of the polymer segments. The effect of rheological parameters like strain rate and temperature on the relative change in shear (RV_S) and dynamic elongational (RV_D) viscosities is reported for the variation of blend composition with 30 phr loaded black-filled compounds. The variation of both RV_S and RV_D follows a third order polynomial equation with carbon black loading in 50/50 EVAc/CR blend; all the polynomial constants are function of temperature and strain rate. © 1996 John Wiley & Sons, Inc.     

Pulsed electron beam irradiation of dilute aqueous poly(vinyl methyl ether) solutions

A dilute aqueous solution of the temperature-sensitive polymer, poly(vinyl methyl ether) (PVME), was irradiated by a pulsed electron beam in a closed-loop system. At temperatures, below the lower critical solution temperature (LCST), intramolecular crosslinked macromolecules, nanogels, were formed. With increasing radiation dose D the molecular weights M_w increase, whereas the dimensions (radius of gyration R_g, hydrodynamic radius R_h) of the formed nanogels decrease. The structure of the PVME nanogels was analyzed by field emission scanning electron microscopy (FESEM) and globular structures with d=(10-30) nm were observed. The phase-transition temperature of the nanogels, as determined by cloud point measurements, decreases from T_cr=36 °C (non-irradiated polymer) to T_cr=29 °C (c_p=12.5 mM, D=15 kGy), because of the formation of additional crosslinks and an increase in molecular weights. The same behavior was observed for a pre-irradiated PVME (γ-irradiation) with higher molecular weight due to intermolecular crosslinks. After pulsed electron beam irradiation the molecular weight again slightly increases whereas the dimension decreases. Above D=1 kGy the calculated ρ-parameter (ρ=R_g/R_h) is in the range of ρ=0.5-0.6 that corresponds to freely draining globular structures.     

Excimer fluorescence study on the miscibility of poly(vinyl methyl ether) and styrene-butadiene-styrene triblock copolymer

The excimer fluorescence of a triblock copolymer, styrene-butadiene-styrene (SBS) containing 48 wt% polystyrene was used to investigate its miscibility with poly(vinyl methyl ether) (PVME). The excimer-to-monomer emission intensity ratio I_M/I_E can be used as a sensitive probe to determine the miscibility level in SBS/PVME blends: I_M/I_E is a function of PVME concentration, and reaches a maximum when the blend contains 60% PVME. The cloud point curve determined by light scattering shows a pseudo upper critical solution temperature diagram, which can be attributed to the effect of PB segments in SBS. The thermally induced phase separation of SBS/PVME blends can be observed by measuring I_M/I_E, and the phase dissolution process was followed by measuring I_M/I_E at different times.     

Glass transitions and interactions in polymer blends containing poly(4-hydroxystyrene) brominated

The miscibility and interactions of binary blends of poly(4-hydroxystyrene) brominated (P4HSBR) with poly(?-caprolactone) (PCL), poly(vinyl acetate) (PVA) and poly(vinyl methylether) (PVME) are investigated by means of differential scanning calorimetry (DSC). Glass transition temperatures, T_gs, are used to assess the miscibility of these systems. All of them were found to be miscible over the whole composition range. T_gs of the blends are lower than Fox predictions, in contrast to the results previously obtained for systems involving poly(4-hydroxystyrene) (P4HS). The melting of PCL in the blends was studied. From the melting temperature depression of PCL in the blends the polymer-polymer interaction parameter was obtained and compared with the ones obtained for P4HS/PCL and poly(4-hydroxystyrene-co-methoxystyrene) (P4HSM)/PCL systems. The best interactions are achieved in P4HS/PCL and the bromination or methoxylation of the P4HS worsen the interactions with the PCL. The presence of a cusp in the T_g-composition curve was analysed in terms of the Kovacs' theory in systems with P4HS and P4HSBR.     

13C NMR characterization of intermolecular interactions for polymers. Part 3. Solvent effect on the blend compatibility of poly(vinyl methyl ether) and polystyrene

The solvent has an influence on the homogeneity of the poly(vinyl methyl ether)-polystyrene, PVME-PS blends Prepared by drying cosolutions. This influence has been analyzed in terms of the competition among polymer-polymer and polymer-solvent interactions. Model solutions have been prepared in which intermoleeular interactions correspond to the interactions in this blend and in some of the cosolutions. These interactions in the model solutions have been detected and identified by applying Rummens' method. The 13C NMR spectra have been determined for PVME and for styrene oligomer dissolved in n-alkanes, cyclohexane, diethyl ether, isopropyl methyl ether, diisopropyl ether, and chloroform, and for PVME dissolved in benzene, toluene, and cumene. The chemical shifts have been plotted against the parameter g² = [(n₂² ? 1)/(n₂² + 1)]², where n₂ is the refractive index of the solvent. If the structural segment represented by certain carbon and some solvent has an interaction that is stronger than dispersive, the chemical shift for this carbon will deviate from the line formed by its shifts in n-alkane solutions, these deviations indicate characters and intensities of the intermoleeular interactions. Results indicate that cyclohexane exhibits weak interactions with both of the polymers and does not interfere with their mutual interaction, leading to a compatible blend. Results also suggest that benzene and toluene interact in the PVME in the same manner as PS. This leads to a gradual increase of the number of polymer-polymer interactions as the concentration of the polymers is increased by solvent removal, resulting in a compatible blend. Chloroform apparently interacts more strongly with PVME than with PS but interacts strongly enough with both to restrict interaction among the two polymers. As the concentration of polymers in the cosolution is increased, PS forms a separate phase. This leads to an inhomogeneous blend when the solvent is evaporated.