Polymers thermodynamically immiscible

The aim of developing a new polymer blend is to synergistically combine the properties of the individual polymers resulting in an improved material. A general precondition to this scheme of fabrication, however, is that in order for the final blended material to have the desired properties, the final polymeric phases must form a heterophasic blend, i.e., they must have at least partial thermodynamic immiscibility. This is in contrast to the requirement that the initial reactants must form initially miscible solutions. These conditions do not seem to be met by most polyimide-epoxy systems. 

Helfand and Tagami model is based on self-consistent field that determines the configurational statistics of macromolecules in the interfacial region. At the interface, the interactions between statistic segments of polymers A and B are determined by the thermodynamic binary interaction parameter, Since the polymers are immiscible, there are repulsive enthalpic effects that must be balanced by the entropic ones that cause chains A and B to intermingle. 

The freeze drying of co-solutions of thermodynamically immiscible polymer pairs is a method of capturing kinetically the unlike molecules in molecular or segmental mixtures. PMMA/PVAc blends freeze-dried from co-solutions in benzene were reported homogeneous by dynamic mechanical and dilatometric observations. They showed a single T intermediate between those of the pure polymers [Miyata and Hata, 1970]. Further dilatometric and differential calorimetric data corroborated the findings of homogeneity [Ichihara et al., 1971]. 

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). 

Block polymers and polymer blends deserve now a great intere because of their multiphase character and their related properties. The thermodynamic immiscibility of the polymeric partners gives rise indeed to a phase separation, the extent of which controls the detailed morphology of the solid and ultimately its mechanical behavior. The advent of thermoplastic elastomers and high impact resins (HIPS or ABS type) illustrates the importance of the industrial developments that this type of materials can provide. In selective solvents, and depending on molecular structure, concentration and temperature, block polymers form micelles which influence the rheological behavior and control the morphology of the material. 

Polymer components and solid particulate fillers are thermodynamically immiscible... 

However, it is recognized that most polymer blends are both thermodynamically immiscible and technologically incompatible, and hence produce multiphase systems with... 

Poly(ethylene-octene) Copolymer/PLA Blends Poly(ethylene-octene) copolymer, a thermoplastic polyolefin elastomer (TPO), was melt blended with PLA at a ratio of 20/ 80 wt% [10]. The difference in polarities of the two polymers led to thermodynamic immiscibility and phase separation of the final blends as determined by the Molau test. Therefore, a copolymer of TPO-gra//-PLA (TPO-PLA synthesized via functionalization of TPO and MA with benzoyl peroxide (BPO), followed by esterification of the MA-functionalized TPO (TPO-MAH) with PLA using 4-dimethylaminopyridine (DMAP) as a catalyst) was introduced to improve the compatibility of the TPO/PLA blends. The use of 5 wt% TPO-... 

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