PS-PVME

Figure 7 Relaxation of orientation measured simultaneously for both components in miscible PS/PVME blends following a rapid deformation (1 m/s) to a draw ratio of 2 at Tg +15°C. The time-resolved dichroic difference spectra were acquired using PM-IRLD. Reproduced with permission from Pellerin et al. [42]. Copyright 2000 American Chemical Society.

C NOE spectroscopy under MAS was used for probing polymer miscibility in polymer blends, polystyrene/polyvinyl methyl ether (PS/PVME) [42], This study takes advantage of the fact that crosspeaks appear only between spins that are neighbours of each other,... 

Winter et al. [119, 120] studied phase changes in the system PS/PVME under planar extensional as well as shear flow. They developed a lubrieated stagnation flow by the impingement of two rectangular jets in a specially built die having hyperbolic walls. Change of the turbidity of the blend was monitored at constant temperature. It has been found that flow-induced miscibility occurred after a duration of the order of seconds or minutes [119]. Miscibility was observed not only in planar extensional flow, but also near the die walls where the blend was subjected to shear flow. Moreover, the period of time required to induce miscibility was found to decrease with increasing flow rate. The LCST of PS/PVME was elevated in extensional flow as much as 12 K [120]. The shift depends on the extension rate, the strain and the blend composition. Flow-induced miscibility has been also found under shear flow between parallel plates when the samples were sheared near the equilibrium coexistence temperature. However, the effect of shear on polymer miscibility turned out to be less dramatic than the effect of extensional flow. The cloud point increased by 6 K at a shear rate of 2.9 s. ... 

In Ref. [120] the first time has been reported on flow-induced phase separation in polymer blends. When PS/PVME blends were exposed to shear or extensional flow at lower temperatures, 20 to 30 K below the equilibrium coexistence temperature, phase separation was observed in both flow regimes. As the authors suggest, the stress, rather than the deformation rate, appears to be the most important parameter in flow-induced phase separation. 

After the examination of the PS photooxidation mechanism, a comparison of the photochemical behavior of PS with that of some of its copolymers and blends is reported in this chapter. The copolymers studied include styrene-stat-acrylo-nitrile (SAN) and acrylonitrile-butadiene-styrene (ABS). The blends studied are AES (acrylonitrile-EPDM-styrene) (EPDM = ethylene-propylene-diene-monomer) and a blend of poly(vinyl methyl ether) (PVME) and PS (PVME-PS). The components of the copolymers are chemically bonded. In the case of the blends, PS and one or more polymers are mixed. The copolymers or the blends can be homogeneous (miscible components) or phase separated. The potential interactions occurring during the photodegradation of the various components may be different if they are chemically bonded or not, homogeneously dispersed or spatially separated. Another important aspect is the nature, the proportions and the behavior towards the photooxidation of the components added to PS. How will a component which is less or more photodegradable than PS influence the degradation of the copolymer or the blend We show in this chapter how the... 

In the AES and PS-PVME blends, no interaction in terms of nature or reactivity of the photoproducts formed was detected. All the blends contained an elastomeric phase which has been shown always to be the most oxidizable component. EPDM and PVME degrade in the first few hours of irradiation and the photoproducts resulting from the oxidation of SAN or PS accumulate at longer irradiation times. However, the styrene units are oxidized faster in the blends than in the homopolymer PS or in SAN. In addition, in the PVME-PS blends rich in PS polymer, the PS retarded the photodegradation of PVME. 

Fig.6. Phase diagram of PS/PVME blend [23] where the line represents the calculated results using the simulated equation-of-state parameters with (,= 1.00066 and filled circles represent experimental spinodal data [37]...

As an example of atomistic modeling for multiphase polymer systems, miscibility of PEO/SAA and PS/PVME blends are investigated. For PEO/SAA blends, the effect of sequence distribution of copolymer on the miscibility of blends is analyzed by calculating the interaction energy parameters. It is observed that both the sequence distribution and the composition significantly affect the degree of miscibility. For a fixed composition, there exists an optimal range of sequence distribution for which the blend system is miscible. The sequence distri-... 

For PS/PVME blends, the thermodynamic properties are calculated by MD and MM, from which the characteristic parameters of the equation-of-state theory, p, vsp, and T are determined based on the physical meaning of the para-... 

Both blends are known to be compatible at ambient temperature (7,8). PS/PVME shows phase separation at high temperatures (Lower Critical Solution Temperature, LCST)... 

Materials(PS/PVME). Atactic PS of weight-average molecu-... 

In the other PS/PVME system, the complete temperature range of interest was accessible. The typical linear behavior of In Vg° versus 1/T for PS with =17,500 g/mol was obtained between 120 C and 210 C. Thus, all blends of PS/PVME and the pure PVME were measured in this temperature range. Five different probes (acetone, ethyl acetate, cyclohexane, n-octane, and ethyl benzene) were used to get X23 As observed in the PS/PPE blends, X23 scattered depending on the probe. Because of the limited number of probes and their different chemical nature, no systematical probe dependence could be detected. Thus, the different X23 values were averaged. 

The preceding studies on the configuration of aryl vinyl polymer chains in dilute, miscible blends and on the kinetics of phase separation in concentrated blends were based on the implicit assumption that the Initial solvent cast blend represented an equilibrium state. In the final section of this paper we explore this question with new data on the effect of the casting solvent on the fluorescence behavior of PS/PVME blends. Our objectives are to determine first whether the fluorescence observables are sensitive to differences in as-cast films and then to identify the true equilibrium state. 

These early studies demonstrated that excimer fluorescence is a useful addition to the battery of experimental tools available to study solid state polymer blends. However, the longer range goal of explaining the significance of the absolute value of R was not realized because there was insufficient companion information about the thermodynamics of the blends. The PS/PVME blend does not suffer from this limitation, and thus provides an excellent system for characterization of the photophysies under conditions for which miscibility or immiscibility are firmly established. In this section we examine results for PS/PVME as well as more recent work on dilute blends containing P2VN that are believed to be miscible. 

Fig. 3. Dependence of the probability of eventual monomer decay M on the concentration of polystyrene in a PS/PVME blend. (Reproduced from Reference 9. Copyright 1982 American Chemical Society.

Fig. 4. Phase diagrams determined using a turbidimetric technique for PS/PVME blends having monodisperse PS molecular weights of 100,000 and 1,800,000 and PVME molecular weight of 44,600.

Dependence of the observed excimer to monomer intensity ratio on polystyrene concentration for PS/PVME blends cast from tetrahydrofuran (circles) and toluene (squares) with the fluorescence spectra measured before (open symbols) and after (filled symbols) annealing at 383 K for 10 hours,... 

Dependence of the excimer band position on time of annealing at 383 K for PS/PVME blends cast from toluene (open symbols) and tetrahydrofuran (filled symbols) for polystyrene concentration of 30% (squares) and 70% (circles). Data are plotted relative to the excimer band position of annealed toluene cast films. 

In the above, we have seen that a certain interpolymer interaction is required for different polymers to be miscible. Here, we will see that high resolution NMR enables us to locate interacting regions in component polymers. One of the most useful methods is the nuclear Overhauser effect (NOE) between H— H and H—NOE can be observed between spins whose distances are less than about 0.5 nm. The one- (ID) and two-dimensional (2D) NOE experiments have been used to reveal the spatial structure of biomolecules in solutions. Of course, these can be applied to locate interacting regions in a blend in solution and in solids [3]. For example, Crowther et al. [22] and Mirau et al. [23] applied NOE experiments to polystyrene/poly(vinyl methyl ether) (PS/PVME) in a toluene solution, and show that the interpolymer NOE signals between the aromatic protons of PS and the methoxy protons of PVME can be observed at polymer concentrations higher than 25 wt%. In the solid state, Heffner and Mirau [24] measured 2D H— H NOESY (NOESY nuclear Overhauser effect spectroscopy) spectra of 1,2-polybutadi-ene and polyisoprene (1,2-PB/PI) and observed NOE cross-peaks between these component polymers. White and Mirau observed interpolymer NOE interactions between the H spins of PVME and the spins of deuterated... 

Line broadening of CP/MAS signals is often observed at the temperature range of Tg + 30 to Tg -I- 60 K. For PS/PVME = 50/50, line broadening of the resonance for the CH carbon of PVME on blending with PS was... 

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