Blends 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.

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. 

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-... 

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. 

Fig. 10.3. Component-ratio dependence of the Xe NMR chemical shifts in PS/PVME blends. Circles express the measured shifts. A solid line represents the calculated chemical shifts using a simple weighted sum of the volumes of pure PS and PVME. Crosses are the calculated chemical shift using the observed total volumes of the blends measured by Shiomi et al. [50] (Reprinted with permission from Ref. [45]. 1997 Elsevier, Amsterdam.)...

For nearly athermal systems, the proportionality factors, S and S, are taken as equal 1. Thus, for the systems without strong interactions the binary parameters were well approximated by the geometric and algebraic averages. For example, for PS/PVME blends the assumption = 1... 

In systems 1-solvent, 2-polymer, and 3-poly-mer, any method that determines either AG or its derivatives should make it possible to calculate Thus, for example, osmotic pressure measurements were used to characterize PS/PVME blends... 

The relation between rheology and morphology during late stages of SD in PS/PVME blends was investigated by means of several techniques [Polios et al., 1997]. The results were interpreted using Doi-Ohta [1991] theory. 

PS and PVME are a rather unique pair of polymers that are dissimilar, both chemically and in their response to irradiation, yet they form miscible blends over the entire range of composition. McHerron and Wilkes [1993] report on the effects of dose, blend composition and the state of miscibility on the gel content obtained on electron irradiation of PS/PVME blends (Table... 

Table 11.56. Gel fraction of PS/PVME blends on electron irradiation [McHerron and Wilkes, 1993]...

As discussed in Chapter 2 of this Handbook, the osmotic pressure can provide one of the most direct methods of determination of interaction parameter. The estimation of these interaction parameters is applied to PS/PVME blends in toluene and ethyl benzene respectively [Shiomi et al., 1985]. It is observed that in toluene varied with composition from -0.044 to h-0.0093, while in ethyl benzene it increased with PVME content from -0.06 to 0.027. 

As aging tends to lead to changes in the packing density of the system, PALS was used to study the blends as it will provide qualitative estimate of the free volume in the system. The stress relaxation results were confirmed qualitatively using PALS. It was found that PS/PPE and PS/PVME blends were less dense than PS, while PMMA/PEG was denser than PMMA, thereby making chain relaxation easier in the former and more difficult in the latter. 

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