Blend miscible, PVME

Miscibility doors can be observed when the homopolymer A is miscible with the homopolymer consisting of segments of type 2. Usually, only very near to the miscibility-immiscibility boundary can a temperature dependence of the phase behavior be seen, i.e. an LCST occurs. Figure 5 shows examples for miscibility doors. Further systems are listed in Table 1. Miscibility doors were also observed for blends of styrene copolymers and polyfvinyl methyl ether) (PVME) (Fig. 6, Table 2). In contrast to PPO/PS systems blends of PVME and PS... 

It must be noted that the crosslinks themselves pose multiple problems relative to the corresponding blends in determining the actual miscibility of the systems. (1) The chemical nature of the crosslinks (both in PVME and PS) must always be different from that of the main chain, hence the heats of interaction and Flory s value will be changed. While this can be minimized, it cannot be made zero. Thus, while the blends of PVME and PS teter on the edge of miscibility, chemical alterations such as... 

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. 

It has been found in the study of PVME and SBS triblock copolymer that solubility of PVME in PS block copolymer domains is larger than in PS homopolymer. This may indicate that the mixing enthalpy has an effect on the blend miscibility [Xie et al., 1993]. The behavior has been attributed to the effect of PB segments in SBS. The phase equilibria and miscibility in polymer blends containing random or block copolymer was reviewed [Roe and Rigby, 1987]. More recent data are presented in Chapter 4 Interphase and Compatibilization by Addition of a Compatibilizer in this Handbook. 

Differential scanning calorimetry (DSC) experiments indicated that atactic polystyrene and polyvinyl methyl ether (PVME) form miscible blends [8,9]. Syndiotactic and isotactic polystyrene when blended with PVME, phase separate at aU temperatures above the glass transition temperature of PVME. Only weak van der Waals interactions between the phenyl rings in polystyrene with the methoxy group of PVME were detected using 2-dimensional nuclear magnetic resonance (NMR) spectroscopy. 

DRS was used to study the dynamics of hydrogen-bonded polymer blends of poly(2,3 dimethylbutadiene (DMB) [86%]-co-hexafluoro-2-hydroxyl-2-propyl)styrene (HFS) [14%]) copolymer with PVME [42]. The copolymer was capable of forming strong intermolecular hydrogen bonds, while minimizing the degree of intramolecular association, and its blends with PVME were miscible over the entire... 

SANS measurements on blends of PVME/PS have been reported in a number of studies [187-192]. PS/PVME is a widely studied blend, at least partly due to the lest behavior well-documented by various characterization methods. The results show miscibility in the region classified as single phase by more conventional methods. The difference in the lest temperature ( 40 °C) of deuterated PS/PVME versus PS/PVME blends was noted, yielding a relatively small effect, thus justifying the use of deuterated polymers to model hydrogenated polymer blends [187,192]. Additional SANS studies include PMMA/PVF2 [187], PS/P(nBMA) [189], PB(different vinyl contents)/PS [193],polyaniline/PA6 [194] and chlorinated PE/PMMA [195] blends as well as citations noted in Table 5.1. 

Figure 10.7 The phase diagram (a) and the glass transition temperatures (b) of a PSC/PVME mixture obtained, respectively, by light scattering and differential scanning calorimetry (DSC). Irradiation experiments were performed in the miscible region at 127 C indicated by (X) in the figure of trans-cinnamic acid-labeled polystyrene/poly(vinyl methyl ether) blends.

A more complex but faster and more sensitive approach is polarization modulation (PM) IRLD. For such experiments, a photoelastic modulator is used to modulate the polarization state of the incident radiation at about 100 kHz. The detected signal is the sum of the low-frequency intensity modulation with a high-frequency modulation that depends on the orientation of the sample. After appropriate signal filtering, demodulation, and calibration [41], a dichroic difference spectrum can be directly obtained in a single scan. This improves the time resolution to 400 ms, prevents artifacts due to relaxation between measurements, and improves sensitivity for weakly oriented samples. However, structural information can be lost since individual polarized spectra are not recorded. Pezolet and coworkers have used this approach to study the deformation and relaxation in various homopolymers, copolymers, and polymer blends [15,42,43]. For instance, Figure 7 shows the relaxation curves determined in situ for miscible blends of PS and PVME [42]. The (P2) values were determined... 

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,... 

Fig. 6. Miscibility doors of PVME/SMMA blends having different blend ratios ( ) 80/20, ( ) 50/50, (A) 35/65, ( ) 20/80 [36]...

SAN AN content 12wt%, PVME content in the blend 80 wt%, LCST behavior for all miscible blends [37]... 

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. ... 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

The PVME/PS semi-I, semi-II and sequential IPNs are slightly hazy or turbid, indicating phase separation, whereas the corresponding blends are clear and miscible. 

Cimmino and co-workers [25,28] investigated by means of solid-state NMR and DSC the dependence of miscibility on composition and temperature in sPS/ PVME blends. The blends, prepared by casting a solution from o-dichloroben-zene at 130 °C, are found to be immiscible for PVME>20 wt%, in contrast with the miscibility found for aPS/PVME blends. In fact, DSC experiments show two rg values corresponding to an sPS-rich phase (83 17 wt%) and a PVME-rich phase (13 87 wt%). The lack of miscibility is also confirmed by the absence,... 

Later, Mandal and Woo [29] demonstrated that this system is miscible, and exhibits a behavior equivalent to aPS/PVME blends. The previously found immiscibility is due to the relatively low value of the lower critical solution temperature, which in 50 50 wt% blends induces a phase separation already at temperatures of ca 120 °C. In fact, OM, SEM and DSC, applied to blends (70 30 and 50 50 wt%) prepared by casting films from 1-2% solutions of chloronaphthalene at about 120°C, or by precipitation from the same solution with w-heptane, show a substantial homogeneity. However, OM measurements, performed at various temperatures on a series of samples, show a cloud point at ca 120 °C and above, indicating the onset of segregation. At higher temperature (samples briefly treated at 300 °C and then quenched), DSC shows two Fgs at —30 °C (attributed to PVME) and at 95 °C (attributed to sPS), shifted with respect to the pure compounds and corresponding to two partially miscible phases, one rich in PVME and the other rich in sPS. Under slow cooling the process appears to be reversible. 

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... 

The materials analyzed were blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in various ratios. The two components are miscible in all proportions at ambient temperature. The photooxidation mechanisms of the homo-polymers PS and PVME have been studied previously [4,7,8]. PVME has been shown to be much more sensitive to oxidation than PS and the rate of photooxidation of PVME was found to be approximately 10 times higher than that of PS. The photoproducts formed were identified by spectroscopy combined with chemical and physical treatments. The rate of oxidation of each component in the blend has been compared with the oxidation rate of the homopolymers studied separately. Because photooxidative aging induces modifications of the surface aspect of the material, the spectroscopic analysis of the photochemical behavior of the blend has been completed by an analysis of the surface of the samples by atomic force microscopy (AFM). A tentative correlation between the evolution of the roughness measured by AFM and the chemical changes occurring in the PVME-PS samples throughout irradiation is presented. 

For simplicity, assuming that the close-packed volume of a PS mer (vps) is equal to that of a PVME mer (vPVME), the binary polymer blend is miscible [20] when... 

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