High-temperature fourier transform infrared study of polystyrene/poly(vinyl methyl ether) blends

Fourier transform infrared (FTIR) studies of polystyrene (PS)/poly(vinyl methyl ether) (PVME) miscible blends as a function of temperature are presented. Below the lower critical solution temperature (LCST) little change is observed in the interaction spectrum obtained via digital subtraction techniques. Once above the LCST, the magnitude of the interaction spectrum decreases as a result of the phase separation process. Comparison of the behavior of the ether C? O stretching band in the reference PVME and in the blends has yielded a lower limit estimate for the interaction energy of about 0.15 kcal/mol.     

Photooxidation of blends of polystyrene and poly (vinyl methyl ether)

Photooxidation of blends of polystyrene and poly (vinyl methyl ether) was studied at 30°C. The oxygen uptake by PS was negligible but PVME oxidized readily. The induction period of oxidation of PVME was prolonged by the presence of PS. The steady state rate of oxidation of the blend was strongly influenced by the segmental mobility of the blend which also governed the kinetics and morphology of phase separation. The molecular weight of PVME decreased more slowly in the blend as PS content increased. It was believed that the reaction between PVME radicals and PS resulted in less reactive PS radicals which retarded oxidation. The PS radicals eventually underwent chain scission reactions.     

Thermal diffusivity study of polystyrene/poly(vinyl methyl ether) blends by flash radiometry

This article presents thermal diffusivity (D) measurements by flash radiometry for the polymer blend of polystyrene (PS) and poly(vinyl methyl ether) (PVME) with lower critical solution temperature (LCST) phase diagram. Dependence of D on PS content measured at 100°C coincides a phase diagram determined by a cloud point measurement. D value for the blend decreases with increasing PS content and has minimum value at the PS content around 20 wt % from which D increases again with increasing PS content. If the concentration fluctuation between two components in the miscible states at the temperature close to LCST causes the remarkable phonon scattering, the composition dependence of D would resemble the phase diagram. D for the sample in the phase-separated state is larger than that for the miscible state. The larger D in the phase-separated sample would be due to the decrease of the total surface area microscopically contacted to the counter component in the phase-separated state. Dependence of D on temperature for the phase-separated sample is quite different from that of the miscible one. On an isothermal measurement of D for PS/PVME (10 : 90) at 110°C just below the cloud point, D started to increase at time above 100 min and leveled out above 250 min. Isothermal observation of sample film by a differential interference contrast microscopy showed the creation of some structure due to the nucleation and growth of interface at 225 min and it became obvious above 250 min. Thus, the increase in D at 110°C implies that D can sensitively reflect the change in microscopic structures which follows the nucleation and growth of interface. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1869–1876, 1997     

Rheology and phase separation in polystyrene/poly(vinyl methyl ether) blends

Blends of monodisperse polystyrene and poly(vinyl-methyl-ether) of various compositions were prepared from solution in benzene. Dynamic rheological properties of these blends were studied at different temperatures below, near, and above T_s, the temperature of phase separation, and in a frequency range from 0.05 to 100 rad/s. A flattening in the storage modulus and an initial plateau for the complex viscosity were observed near and above T_s in the low-frequency region; in contrast, below T_s the behavior of the blends was similar to that of the homopolymers. The WLF superposition principle applies only at temperatures below T_s, i.e., in the miscible and homogeneous region. G″ versus G′ representations for the blends were found to be independent of temperature and to vary with composition in the miscible region but are temperature and composition-dependent in the immiscible region. It is also shown that the η″ versus η′ representation is a useful tool for characterizing phase separation of blends and is more sensitive than the classical frequency dependence of the material functions.     

Rheology of polystyrene/poly(vinyl methyl ether)blends near the phase transition

Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature T_s was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from T_s, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to T_s deviations were observed for G' at low frequencies (the so-called terminal zone). Above T_s G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near T_s can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″²) as a function of temperature were shown to be sensitive to this anomalous behavior.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Molecular weight dependence of polystyrene segmental dynamics in dilute blends with poly(vinyl methyl ether)

The segmental dynamics of backbone‐deuterated polystyrenes (d₃PS) with varying molecular weights (1.7–67 kg/mol) have been measured in blends with poly(vinyl methyl ether) (PVME). ²H NMR T₁ values at 15 and 77 MHz are reported for the pure d₃PS and for the dilute d₃PS component in PVME matrices. The temperature shift that is needed to superpose the NMR T₁ data for the pure d₃PS and the d₃PS as a dilute component in the blend ranges from 45 to 70 K. In the framework of Lodge/McLeish model, the self‐concentration value for d₃PS in these dilute blends with PVME is found to be independent of molecular weight. We thus establish for this system that the substantial influence of molecular weight on the blend segmental dynamics can be explained by homopolymer T_g differences. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2252–2262, 2007     

Effect of blend composition on diffusivity and solubility of small molecules in polystyrene/poly(vinyl methyl ether) blends

The capillary column inverse gas chromatography technique was used to determine diffusivity and solubility data for several solvents in polymer blends composed of polystyrene and poly(vinyl methyl ether) (PVME). Diffusivity behaved as expected, increasing as the concentration of PVME increased in the blend. Knowing only the free‐volume parameters for the pure polymers, the free‐volume theory was successfully applied to predict the dependence of the diffusion coefficients on the blend composition. Transport in blends above the glass transition temperature is controlled by free volume, and the effect of concentration fluctuations is minimal at the temperatures studied. Experimental data show an increase in the partition coefficient of some solvents in the blends with respect to the pure polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2071–2082, 2007     

Phase transformation in mixtures of polystyrene and poly(vinyl methyl ether)

Homogeneous films comprised of mixtures of polystyrene and poly(vinyl methyl ether) can be obtained by evaporation from a ternary solution containing toluene as the solvent. Heterogeneous films result when the solvent is trichloroethylene. The possibility that a heterogeneous film cast from trichloroethylene can be transformed to a homogeneous one by physical means is a logical expectation when the polymer-polymer interaction is favorable, though as yet no comprehensive report has appeared in the literature. We have accomplished the transformation by increasing the temperature. Optical microscopy and glass transition experiments were employed to observe the effects.     

Thermal oxidation of blends of poly(vinyl methyl ether) and modified polystyrenes

Thermal oxidation of blends of poly(vinyl methyl ether) and styrene copolymers containing hydroxyl groups as hydrogen-bond donors was studied. The hydrogen-bonding interaction provide for improved miscibility between the component polymers and more extensive crosspropagation/cross-termination reactions. In addition to their contribution to improved miscibility, phenol groups in the copolymers exhibited apparent antioxidant and prooxidant effects.     

Fourier-transform infrared study of conformational changes in plasticized poly(vinyl chloride)

Fourier-transform infrared spectroscopy has been used for the detection of conformational changes induced by plasticization in atactic poly(vinyl chloride) (PVC). The amount of short trans syndiotactic sequences decrease upon plasticization. This change depends on the amount and kind of plasticizer. Difference spectra emphasize changes in the distribution of gauche defects in the chains as a function of temperature in plasticized PVC films.     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

Fourier-transform infrared study of orientation in pure and plasticized poly(vinyl chloride)

Fourier-transform infrared spectroscopy has been used for the study of orientation of pure and plasticized PVC. The results show that orientation is independent of experimental conditions (temperature, strain rate, plasticizer) in the homogeneous deformation range. Such behavior is explained by the existence of a fringe micellar-type network with physical crosslinks. The network is partially destroyed during stretching. Furthermore, the orientation of the carbonyl group of the plasticizer is connected with PVC chain orientation.     

Temperature-sensitive poly(vinyl methyl ether) hydrogel beads

Temperature-sensitive hydrogel beads were prepared by radiation crosslinking of poly(vinyl methyl ether) PVME spheres wrapped in Ca-alginate. The obtained gel beads have diameters in the sub-millimeter or millimeter range (depending on the PVME concentration). They were characterized by sol-gel analysis, swelling measurements, and differential scanning calorimetry. The gel content g increases with increasing radiation dose D. The swelling degree Q_v decreases with increasing PVME concentration c_p and increasing D. In comparison to PVME bulkgels the phase-transition temperature of the synthesized PVME gel beads is a little decreased.     

A dielectric study of chain motions in poly(vinyl methyl ether)

The dielectric permittivity and loss of poly(vinyl methyl ether) (mol. wt. 30,000) have been measured from 12 Hz to 100 kHz at temperatures from 77 K to 320 K. Two relaxation processes, γ and β, are observed at T < T_g (245 K), and one above T_g. The Arrhenius plots of the γ and β processes have activation energies of 20 and 41 kJ mole^?1 respectively. The relaxation rate of the α process is described by the Vogel-Fulcher-Tamman equation or the William-Landel-Ferry equation. The relaxation rates of γ and β processes evaluated from the isochrones differ from those evaluated from the isothermal spectrum. The features of chain motions observed are similar to those in other polymer and rigid molecular glasses.     

Molecular dynamics and phase behavior of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether)(PS/PVME) blends induced by hydrophilic nanosilica(A200) or hydrophobic nanosilica(R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity(ΔC_p) during glass transition via modulated differential scanning calorimetry(MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.