Polymer blends, from ternary systems

One way to overcome such problems is to consider solvent(l)/polymer(2)/ polymer(3) ternary systems any method that determines either AG or its derivatives should make it possible to calculate Xi3- Thus, for example, osmotic pressure measurements were used to characterize PS/PVME blends dissolved in either toluene or ethylbenzene (Shiomi et al. 1985). The Xi3 was found to depend on the blends composition. Elimination of the solvent effects gave X23/E1 = —10 (7.41 — 11.0103). Thus, the system was expected to remain miscible up to a PVME volume fraction of 03 = 0.67. Osmotic pressure has also been used to determine X23 = 0.070 for PS with poly(p-chloro styrene) in toluene, 2-butanone, and cumene (Ogawa et al. 1986). For the same system, X23 = 0.087 was calculated from intrinsic viscosity measurements. Thus, the system is thermodynamically immiscible. More recently, osmotic pressure measurements in cyclohexanone of a ternary system resulted in X23ipoly(vinylchloride-co-vinylacetate) blends with a series of acrylic copolymers (Sato et al. 1997). 

Qipeng demonstrated that PCL/PVME blends were also characterised by single, composition-dependent TgS (Sect. 18.2). Similarly, all ternary blends of the three polymers exhibited single glass transition temperatures which agreed with values calculated from l/T=I(w/Tgj), an extension of Eq. (23) to multiple components. The author concluded that the polymers were miscible in all proportions but made no reference to the occurrence of PCL crystallisation in the samples. Cloud points were also determined in PCL/PVME and phenoxy/PVME blends PCL/phenoxy blends remained clear to 200 °C. All ternary systems exhibited cloud points and the minimum of the connecting surface was 108 °C at a PCL/phenoxy/PVME composition of 25/25/50. 

Like the spinodals and binodals of ternary and quaternary polymer blends were calculated with the method(Horst 1995 Horst Wolf, 1992) (the knowledge of the first and second derivatives of AG with respect to the composition variables is not required), the spinodals and the binodals of the PEO/P(EO-b-DMS) system were calculated with the SL theory under different pressures. Figure 15 shows the calculated results of the spinodals and the binodals compared with the experimental data as showed in Figure 14. The dashed and the solid lines represent the spinodals and the binodals calculated with the SL theory under indicated pressures, respectively the open circles represent the experimental data, respectively, which were obtained from Figure 14. In Figure 4 the qualitative agreement between the spinodals and the binodals calculated and the experimental cloud points is acceptable at different pressure. From Figure 15, it can be seen that the critical temperatures (T ) calculated by means of FL theory under different pressure increase with pressure. 

When Zhao and Choi (51] also discussed the solvent-dependence of they found that the problem had essentially originated from an incorrect choice of reference volumes used when calculating the binary interaction parameter between various solvents and the pure polymers, and their blends. Traditionally, in Flory-Hu ins theory the molar volume of the solvent (Vi) is taken as the reference volume (Vo). This problem is valid for ternary systems, and differences in the values of the X parameter originate from the lattice size used. Zhao and Choi [51] have proposed the use of a common reference volume, calculating x zi from the equation ... 

The solvent in the blends can increase the mobility of the polymer molecules and decrease the interaction force between the macromolecules. From Figure 15.18, it can be seen that the solvent in an immiscible polymer pair can decrease the free energy level of the system and increase the miscibility of the two polymers. Therefore, the solvent concentration can influence the resultant pattern in the spinodal decomposition indeed, the solvent concentration can be changed to investigate the influence of solvent composition on the morphology of phase separation. The morphology evolution of ternary systems with different solvent composition is shown in Figure 15.22 in this case the initial condition is the same. 

The ternary model was established to investigate the effects of a solvent in polymer blends during phase separation. In cases of constant solvent concentration it emerged that, the less solvent that was in solution, the slower was the evolution of the morphology in phase separation. This effect was due to the polymers being immiscible with each other, but both being miscible with the solvent. The addition of a solvent decreased the free energy level in the blend, which in turn slowed down the evolution of phase separation. The mechanism of phase separation with solvent evaporation was further complicated by dynamic solvent evaporation from the ternary system. 

Then in section III, we analyze the liquid-liquid phase separation of polymer blends in solvents of various quality. Particular emphasis is put on the case of a common good solvent and on the discussion of the critical properties of demixing which are very unusual as the critical behavior is not of the mean-field type (except for very long chains and low incompatibility degrees) and is als very different from that of low molecular weight ternary mixtures. We also focus on well- demixed systems and consider the interfacial properties following the work of Broseta et al. ... 

The addition of homopolymers further enhances the tolerance of mismatching and allows chemical epitaxy of stractures more complex than the typical bulk phases of block copolymers. Stoykovich et al. introduced a ternary blend to further extend their surface-directed method. Such a blend system enables the block copolymer lamellae to conform to substrate stripe arrays with sharp bends. In the imblended block copolymer S3 tem, a high strain builds up in the polymer film at sharp comers of the chemical pattern because the comer-to-comer distance is much larger than the natural periodicity of the block copolymer. Successful replication of arrays of tilt boundaries with 45° and 90° angles was observed as a result of the redistribution of the homopolymer. (The polymer blend includes 20% PMMA homopolymer, 20% PS homopolymer, and 60% symmetric PS-b-PMMA.) Homopolymers are depleted above commensurate regions and concentrated above the distorted regions of the pattern to reduce the strain from incommensurability. 

Crystallization of Blends The first polymer blend was made from two polymeric mbbers in 1846, but polymer blend technology and a scientific understanding of the underlying principles controlling the compatibility (or lack of) in polymer mixtures (alloys as they have been named recently) has taken place only in the latter part of the current century. Many blends are non-crystalline but our interest in this document is focused on the kinetics of phase transformations of binary and ternary systems that receives more attention annually. Some of these systems can be very complicated, often comprised of multiple phases that m involve homopolymers, copolymers, mesophases and the like. Polymorphism and even isomorphism may occur... 

In another study, it was successfully reported an intimate ternary blend system of poly(carbonate) (PC)/poly(methyl methacrylate ) (PMMA)/poly (vinyl acetate) (PVAc) obtained by the simultaneous coalescence of the three guest polymers from their common y-cyclodextrin (y-CD) inclusion complex (IC). The thermal transitions and the homogeneity of the coalesced ternary blend were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) [50]... 

We also observed that the PC chains possess a preferred ability to form inclusion compounds with y-CD in solution, when competing with PMMA and PVAc. From the XH NMR spectrum of the coalesced 1 1 1 PC/PMMA/PVAc blend (not shown), the molar ratio of PC PMMA PVAc was determined to actually be 1.6 1 1.4 compared to the initial molar ratio of 1 24 24, respectively, used in solution to form their common y-CD-IC. Despite the initial 1 24 24 PC PMMA PVAc molar ratio in solution, the PC component in the coalesced PC/PMMA/PVAc blend is still prevalent over the PMMA and PVAc components, which indicates that there may be additional factors that govern the inclusion process from a multiguest system. We believe that this very strong preference of the host y-CD molecules for PC chains, rather than the other two possible guests, is due to their different hydrophobicities. Although the final molar ratio of the coalesced ternary blend can be somewhat controlled by modifying the initial molar ratio of polymers in their common solution, our eventual aim is to be able to adjust, as desired, the constituent polymer ratios in coalesced ternary blends. 

The determination of the experimental variables for apphcation of this approach is based on analysis of FTIR data on the blends and is covered in the references noted above. The application of the association model to determine or predict the phase behavior of interacting polymer systems include poly(2,6-dialkyl-4-vinyl phenol) blends with poly(n-alkyl methacrylates) and ethylene-vinyl acetate copolymers [217], poly(4-vinyl phenol)/poly(hydroxybutyrate) blends [218] and poly(4-vinyl phenol) in ternary blends with PEMA and PMMA [219] as weU as a number of examples in [92]. The determination of the equihbrium constants Ka and Kb) from FTIR data has been reported for ethylene-methacryhc add copolymers with polyethers [118] and ethylene-methacrylic add copolymers with poly(2-vinyl pyridine) [220]. 

Figure 4.31 Phase behavior of ternary blend of PCI7SAN/SMA (reproduced (replotted) from Defieuw.G., Groeninckx,G.and Reynaers, H., in ContemporaryTopics in Polymer Science Vol.6 Multiphase Macromolecular Systems, Culbertson, B. M. (Ed.) (1989), Plenum Press, New York, p. 423, with kind permission of Springer Science and Business Media)...

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