Degree of phase separation

The appearance of any appreciable degree of phase-separation in the copolymer should be reflected in different TgS of the two phases. But Braun and coworkers [159] observed only single TgS in the reported range of 0-57.0 mol% of ethylene in the copolymer. This may constitute a criticism of the ideas put forward here. 

Typically IPNs exhibit some degree of phase separation in their structure depending on how miscible the component polymers are. However, because the networks are interconnected such phase separation can occur only to a limited extent, particularly by comparison with conventional polymer blends. Polymer blends necessarily have to be prepared from thermoplastics IPNs may include thermosets in their formulation. 

By using a thermodynamic model based on the formation of self-associates, as proposed by Singh and Sommer (1992), Akinlade and Awe (2006) studied the composition dependence of the bulk and surface properties of some liquid alloys (Tl-Ga at 700°C, Cd-Zn at 627°C). Positive deviations of the mixing properties from ideal solution behaviour were explained and the degree of phase separation was computed both for bulk alloys and for the surface. 

IPNs can be prepared by either the "sequential" or the "simultaneous" technique. IPNs synthesized to date exhibit varying degrees of phase separation depending primarily on the compatibility of the component polymers (4-7). 

DMA can be applied to a wide range of materials using the different sample fixture configurations and deformation modes (Table 23.1) [10,11]. This procedure can be used to evaluate by comparison to known materials (a) degree of phase separation in multicomponent systems (b) amount type, and dispersion of filler (c) degree of polymer crystallinity, (d) effects of certain pretreatment and (e) stiffness of polymer composites [8,11]. 

The copolymer composition in miniemulsion copolymerization of vinyl acetate and butyl acrylate during the initial 70% conversion was found to be less rich in vinyl acetate monomer units [34]. Miniemulsion polymerization also allowed the synthesis of particles in which butyl acrylate and a PMMA macromonomer [83, 84] or styrene and a PMMA macromonomer [85] were copolymerized. The macromonomer acts as compatibilizing agent for the preparation of core/shell PBA/PMMA particles. The degree of phase separation between the two polymers in the composite particles is affected by the amount of macromonomer used in the seed latex preparation. 

The remarkable properties of amorphous block polymers, particularly poly (styrene-b-diene), have been studied extensively in recent years. Many studies (10,35,36,37,38) suggest that the degree of phase separation depe nds on the length of, the number of, and the chemical composition of the blocks. 

IPN polymers may also exhibit varying degrees of phase separation depending on the compatibility of the polymer components used in their synthesis. With highly incompatible polymers, the thermodynamic forces leading to phase separation are so powerful that it occurs substantially before the kinetic ramifications can prevent it. In these cases, little phase mixing would be gained. 

If, as suggested by FTIR data, the situation here involves two, essentially separate, phases of OA and DPPC, one might expect a two-stage collapse in isotherms of mixed monolayers of these two components. Although it has been concluded that in the gel phase, complete separation of oleic acid and DPPC is unlikely (Lewis and Hadgraft, 1990), there is evidence from biphasic-type collapse pressures of OA/DPPC monolayers that a fair degree of phase separation does occur. It is well established that some degree of phase separation is likely in most biphasic systems, and there are several excellent review articles on this theme (e.g., Jain, 1983). 

Fig. 10. The degree of phase separation as a function of centrifugal acceieration, a, where g is acceleration due to gravity (Adapted from Merzhanov and Yukhvid, 1990).

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