Miscible blend

As fully described below, sPS has been found to be miscible with aPS, PPE, PYME, TMPC and styrene-l,l-diphenylethylene copolymer. Generally the reported investigations deal with the effect of the second component on crystalline features of sPS, such as polymorphic behavior, crystallization kinetics, morphology and growth rate of crystallites. Just one study reports on toughening sPS by adding suitable components. 

For sPS/PPE blends, DSC and DMTA measurements give a single Tg value [16-19], intermediate between those of the components and dependent on composition. The Tg values of sPS and PPE being very different from each other (98 and 220 °C, respectively), this result constitutes an unambiguous proof of blend miscibility within the whole composition range. 

The same techniques cannot be applied to the case of sPS/aPS blends, as the two components have similar Tg values (less than 10 °C difference). A higher resolution of close Tg values can be derived from the isothermal heat capacity curves, measured in the vicinity of Tg by modulated DSC [20]. Furthermore, sPS and aPS, when annealed separately below Tg, exhibit in both DSC and modulated DSC distinct endothermic transitions owing to the enthalpy recovery [20,21]. Both methods, when applied to the sPS/aPS blends, give a single temperature for all compositions in agreement with the presence of a miscibility between the components. 

Additional information on the miscibility of sPS/aPS blends was gained by measuring with DSC the crystallization kinetics and the melting and crystallization peaks [20]. 

The addition of miscible components (PPE, aPS, etc.) to sPS may affect the distribution of a and structures formed from melt-crystallized samples. 

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Mischmetal [62379-61-7] Misch metal [8049-20-5] Misch metal hydride Miscible blend Miscible liquids... 

Most of the polymer s characteristics stem from its molecular stmcture, which like POE, promotes solubiUty in a variety of solvents in addition to water. It exhibits Newtonian rheology and is mechanically stable relative to other thermoplastics. It also forms miscible blends with a variety of other polymers. The water solubiUty and hot meltable characteristics promote adhesion in a number of appHcations. PEOX has been observed to promote adhesion comparable with PVP and PVA on aluminum foil, cellophane, nylon, poly(methyl methacrylate), and poly(ethylene terephthalate), and in composite systems improved tensile strength and Izod impact properties have been noted. 

Changes in heat capacity and measurement of T for blends have been used to determine components of copolymers and blends (126—129), although dynamic mechanical analysis has been found to give better resolution. Equations relating T of miscible blends and ratios of components have been developed from dsc techniques, eg, the Fox equation (eq. 1), where f the blend, or is the weight fraction of component 1 or 2,... 

Fig. 2. Glass-transition temperature, T, for two commercially available, miscible blend systems (a) poly(phenylene oxide) (PPO) and polystyrene (PS) (42) ...

Miscible blends of high molecular weight polymers often exhibit LOST behavior (3) blends that are miscible only because of relatively low molecular weights may show UCST behavior (11). The cloud-point temperatures associated with Hquid—Hquid phase separation can often be adequately determined by simple visual observations (39) nevertheless, instmmented light transmission or scattering measurements frequendy are used (49). The cloud point observed maybe a sensitive function of the rate of temperature change used, owing to the kinetics of the phase-separation process (39). 

Table 2. Examples of Random Copolymers That Form Miscible Blends with Other Polymers When Corresponding Homopolymers Do Not...

There are many examples known where a random copolymer Al, comprised of monomers 1 and 2, is miscible with a homopolymer B, comprised of monomer 3, even though neither homopolymer 1 or 2 is miscible with homopolymer 3, as illustrated by Table 2. The binary interaction model offers a relatively simple explanation for the increased likelihood of random copolymers forming miscible blends with other polymers. The overall interaction parameter for such blends can be shown (eg, by simplifying eq. 8) to have the form of equation 9 (133—134). 

Miscible Blends. Sometimes a miscible blend results when two polymers are combined. A miscible blend has only one amorphous phase because the polymers are soluble in each other. There may also be one or more crystal phases. Simple theory (26) has supported the empirical relation for the permeabihty of a miscible blend. Equation 18 expresses this relation where is the permeabihty of the miscible blend and ( ) and are the volume fractions of polymer 1 and 2. 

Plasticized polymers have been observed to behave like miscible blends. The permeabiUties of oxygen, carbon dioxide, and water vapor in a vinybdene chloride copolymer increase exponentially with increasing plasticizer (4,5,28). About 1.6 parts plasticizer per hundred parts polymer is enough to double the permeabiUty. 

After a temptative structure-based classification of different kinds of polymorphism, a description of possible crystallization and interconversion conditions is presented. The influence on the polymorphic behavior of comonomeric units and of a second polymeric component in miscible blends is described for some polymer systems. It is also shown that other characterization techniques, besides diffraction techniques, can be useful in the study of polymorphism in polymers. Finally, some effects of polymorphism on the properties of polymeric materials are discussed. 

In the fourth section the influence of comonomeric units on the polymorphic behavior of some polymers is described. In particular it is shown that comonomeric units can produce changes in the solid-solid transition temperatures as well as variations of the crystalline forms, which can be obtained for a given crystallization procedure. In the same section, some recent studies, showing that the polymorphic behavior of some polymers can be altered in particular miscible blends, are also reviewed. 

However, a few cases of miscible blends have been described recently in the literature in which, in particular conditions, the polymorphic behavior of a polymer appears to be altered. 

When two polymers interact or react with each other, they are likely to provide a compatible, even a miscible, blend. Epoxidized natural rubber (ENR) interacts with chloro-sulfonated polyethylene (Hypalon) and polyvinyl chloride (PVC) forming partially miscible and miscible blends, respectively, due to the reaction between chlorosulfonic acid group and chlorine with epoxy group of ENR. Chiu et al. have studied the blends of chlorinated polyethylene (CR) with ENR at blend ratios of 75 25, 50 50, and 25 75, as well as pure rubbers using sulfur (Sg), 2-mercapto-benzothiazole, and 2-benzothiazole disulfide as vulcanizing agents [32]. They have studied Mooney viscosity, scorch... 

Nando, G.B. Reactive Miscible Blends from Ethylene Copolymers and Specialty Rubbers, 156th Meeting of the Rubber Division, American Chemical Society, Orlando EL, September 1999, Paper No. 55. 

Some preliminary results indicate that the functionalized polymers form miscible blends with poly(methyl methacry1 ate). 

Now, let s look at a polymeric system. To begin with, the motion in polymer chains is hindered. The massive size of the polymer itself and the intermolecular forces within the chains create an inflexible system, especially when compared to the aqueous systems with which we are most familiar. Secondly, the entropy of mixing is not actually as great as that seen in typical solution formation. Polymers are inherently highly entropic, so the benefit of mixing them together is modest. Therefore, any two polymers that form a miscible blend depend primarily... 

Likewise, poly (methyl methacrylate) and polyfvinylidene fluoride), the chemical structures of which are shown in Fig. 10.2, make a miscible blend because of the strong specific interactions between the oxygen atoms on the methacrylate and the fluoride group in the vinylidene fluoride group. 

One of the difficulties in working with miscible blends is that they are often very temperature-sensitive. The temperature sensitivity depends on the components of the blend, but once you pass the region of stability, the two components will separate and the material becomes an... 

Though both miscible and immiscible blends are composite materials, their properties are very different. A miscible blend will exhibit a single glass transition temperature that is intermediate between those of the individual polymers. In addition, the physical properties of the blends will also exhibit this intermediate behavior. Immiscible blends, on the other hand, still contain discrete phases of both polymers. This means that they have two glass transition temperatures and that each represents one of the two components of the blend. (A caveat must be added here in that two materials that are immiscible with very small domain sizes will also show a single, intermediate value for Tg.) In addition, the physical properties... 

How do entropic and enthalpic effects determine the miscibility of polymers in blends Which term dominates the formation of a miscible blend ... 

In Fig. 10.4 there is a temperature range in which two polymers form a miscible blend. Why do the polymers separate into distinct phases at both high and low temperatures ... 

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