PS/PVME mixtures

Figure 8. Compressibility of PVME/COi, PS-PVME 50-50 blend/COi, and PS/PVME mixtures at 20 C calculated using the Sanchez-Lacombe equation of state.

It has been proved that the nature of solvent used for casting in the preparation of the blend influences the compatibility and related properties of PS-poly(vinyl methyl ether) (PVME) mixtures." Clear films of PS-PVME mixtures were obtained on casting from solvents like benzene, toluene, etc., while visually incompatible films result upon casting from trichloroethylene and chloroform. Blends of PVC and LNR/epoxidized liquid natural rubber (ELNR) were prepared using a common solvent, 2-butanone. ° Another research group prepared PVC/NR blends using THE as the solvent. ... 

In the first category, polystyrene (PS) and poly(vinyl methyl ether) (PVME) have been reported to be compatible when films are cast from suitable solvents.5 But phase separation can be induced in a compatible film simply by heating the mixture to about 150°C. Subsequent slow cooling of the phase-separated mixture resTilts in a compatible film. The thermally induced phase separation behavior of PS-PVME mixture indicates the existence of LOST. The presence of UCST was not reported, althoTigh, according to Patterson s theory, if LOST exists, UCST should also exist. 

The origin of the change in fluorescence emission at the temperature T lies in the photophysical process itself, i.e. in quenching phenomena, the extent of which shoj ld depend on the nature of the molecules next to the label. In fact, PS is surrounded by a mixture of PS and PVME in the homogeneous blends, but mainly by PS molecules in the phase-separated systems. Thus, a simple explanation of the change in fluorescence intensity would be that PS emission is greater in PS than in PS-PVME mixtures or, in other words, that PVME is responsible for the quenching of the fluorescence emission. 

Hre butterfly patterns were observed at various tempera-mres and concentrations and for various solvents such as DOP, tydohexane, and diethyl malonate, which are theta solvents for PS at 35°C, as wdl as dibutyl phthalate and tricresyl phosphate, which are good solvents for PS. The patterns were also observed for semidilute solutions of polyethylene with paraflin as the solvent (athermal solution) and for sheared colloidal srrspensions. They are thus quite general for sheared dynamically asymmetric systems. The butterfly pattern was also formd for PS/PVME mixtures by Mani et and Gerard et and for other polymer mixtures. ... 

Fig. 10.27. CP/MAS spectra taken at several contact times of deuterated-PS/PVME = 50/50 at 240 K. Spectra (a-d) are a mechanical mixture before heating and (e-h) are after heating to 403 K for 30 min. The additional resonances in the aromatic region are due to carbons of d8-PS which have been polarized from the protons of PVME. (Reprinted with permission from Ref. [130]. 1987 John Wiley, New York.)...

There is growing evidence that t-T superposition is not valid even in miscible blends well above the glass transition temperature. For example, Cavaille et al. [1987] reported lack of superposition for the classical miscible blends — PS/PVME. The deviation was particularly evident in the loss tangent vs. frequency plot. Lack of t-T superposition was also observed in PI/PB systems [Roovers and Toporowski, 1992]. By contrast, mixtures of entangled, nearly mono-dispersed blends of poly(ethylene-a/f-propylene) with head-to-head PP were evaluated at constant distance from the glass transition temperature of each system, homopolymer or blend [Gell et al, 1997]. The viscoelastic properties were best described by the double reptation model , viz. Eq 7.82. The data were found to obey the time-temperature superposition principle. 

The observed cloud points of mixtures of PS with PVME are plotted in Figure 1. The LCST behavior of PS/PVME blends is well known . The specific interaction between PS and PVME, giving rise to their compatibUity, was reported to reside on the phenyl group of the styrene monomer and CCXDH3 of PVME. 

Figure 1 also shows the cloud points of the mixtures of P(S-co-oMeSl) or P(S8-co-oMeS2) with PVME. One can discern a clear indication of the effect of the addition of o-methylstyrene on the compatibility of PS/PVME blends. The copolymers are less compatible with PVME than PS is, and the cloud points of mixtures containing copolymers are shifted downward by 5 - 10 C for... 

Cowie, J.M.G., Devlin, B.G., McEwen, I.J. Surface enrichment in PS/PVME blends 2. The effect of specific interactions in the bulk mixture. Polymer 34, 4130-4135 (1993)... 

This accessory was used to image, in situ, the phase separation of a homogeneous LCST PS/PVME (50/50 w/w) polymer blend. A homogeneous mixture was cast directly onto the diamond, which was the ATR crystal used for the measurements. The resultant FTIR images are presented in Fig. 10.8 (Section 3.2), showing the distribution of both PS and PVME, before and after exposure to 60 bar of CO2. Following exposure to CO2 it can be seen that phase separation occurs, resulting in domains of ca. 200 pm [135]. 

PS/PVME (Shibayama et al. 1985). Within the temperature range in which % is negative these mixtures are miscible for all molecular weights. Because of the specific nature of the interactions both the temperature and the composition dependence of x may be complex, and phase diagrams may have LCSTs, UCSTs or both. 

For nearly athermal systems, the proportionality factors, S. and Sy, are taken as equal to 1. Thus, for the systems without strong interactions, the binary parameters are weU approximated by the geometric and algebraic averages. For example, for PS/PVME blends, the assumption 5 = 5v = 1 resulted in 0.1 % deviation for the experimental values of the cross-parameters (Xie et al. 1992 Xie and Simha, 1997, private communication ). In contrast, it is to be expected that for systems with strong intermolecular interactions such mixture rules may fail and experimental values for the cross-factors may have to be found. However, least squares lit of Eqs. 2.42 and 2.43 to experimental values of CO2 miscibilities in PS (in a wide range of P and T) yielded values for and Sy close to 1 (Xie et al. 1997). 

Here, w is the mixture composition. The results indicate that the compressibility of the mixture increases with increase in CO2 pressure. This occurs for two reasons a) CO2 is a high free volume diluent that increases compressibility of the mixture relative to that of the pure polymer and b) CO2 sorption in the mixture increases with pressure. We did not calculate the compressibility of the PS/CO2 binary as PS is below the glass transition temperature at these conditions although it is expected to be quite small. Also shown in the figure is the compressibility of a PS/PVME blend under the influence of hydrostatic pressure only calculated using the Sanchez-Balasz modification to the SL-EOS. ... 

Schwahn et al [175] were the first to report a transition from mean-field to non-mean-field behavior in polymer mixtures on the basis of SANS results obtained from a PS-poly(vinyl methyl ether) (PVME) mixture. Subsequently, Bates et al. [176] quantitatively verified these conclusions using a model polyisoprene-poly(ethylene-propylene) mixture above the upper critical solution temperature (Tc = 38 °C), which revealed a transition from y = 2v = 1 (mean-field behavior) toy = 1.26 (non-mean-field behavior) approximately 30 °C above the critical temperature. These SANS crossover studies established the limitations of mean-field theory, which has been used extensively for evaluating polymer-qx)lymer thermodynamics, and similar crossover phenomena have been investigated via SANS for polymers in small-molecule solvents (e.g. polystyrene in cyclohexane) and supercritical media (e.g. polydimethylsiloxane in CO2), as described in Section 7.6.4... 

Flgure5.26 2D NOE spectrum of a 40% (w/w) equal weight mixture of PS/PVME at 65 °C (0.1s mixing time).The intrachain PS and PVME connectivities are in the upper part and the interchain in the lower part of the spectrum (reproduced (replotted) with permission from reference Mirau, P. A.,Tanaka, H.and Bovey, E A.,Macromolecules (1988) 21, p. 2929, copyright (1988) American Chemical Society)... 

So far, the tacticity effect on polymer mixtures has been investigated mainly for the special systems where hydrogen bonding interaction is dominant, such as poly (vinyl chloride)/poly(methyl metacrylate) (PVC/PMMA) [1] or poly-styrene/poly(vinyl methyl ether) (PS/PVME) [2] mixtures. However, recently, there has been an interest in the effect of tacticity on polymer mixtures without specific interaction such as polyolefin/polyolefin [3] or polystyrene/ deuterated polystyrene mixtures [4,5]. 

Both the one-dimensional random walk model described in Section 4.1 and the three dimensional model to be considered here are attempts to provide analytical predictions of M and, hence, for the experimental Id/Iji results. We wish to emphasize, however, that it is possible to obtain an experimental measurement of M through straightforward use of Equation (11) and data for a miscible mixture [80]. This is shown in Figure 8 for the 100 K PS/PVME blend cast from toluene. 

Static quenching of PS fluorescence emission has been discovered in PS-PVME blends. Although such phenomenon is generally uncommon in pol3rmer mixtures, we have recently jjbserved similar quenching effects in poly(dimethylphenylene oxide)-PS mixtures and also in blends of chlorinated polyethylene and anthracene-labelled poly(methylmethacry-late). 

In view of the fact that a binodal curve constructed from equilibrium thermodynamics (i.e., from the Flory-Huggins theory) determines the boundary between the homogeneous and inhomogeneous regions in a mixture of two liquids, the presence of microheterogeneity discussed above in this and preceding sections for PS/PaMS and PS/PVME blend systems may be attributable to dynamic composition fluctuations near the critical point. However, the extent of dynamic composition fluctuations would vary with blend system. 

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