Phase Diagrams of Crystalline Polymer Blends

Matkar et al. have hypothesized what would happen to crystalline blend phase diagrams if one relaxes the last assumption of the Floty diluent theory of crystalline polymer solutions, namely, the complete rejection of polymeric solvent from the crystalline phase [66, 67]. In addition, Xu et al. have developed a new theory for a binary crystalline polymer blends based on a combination of liquid-liquid phase separation and solid-liquid phase transition by taking into consideration the coupling interaction between the solid crystal and amorphous liquid phase [71]. 

Phase Diagram Calculation of a Crystalline/Amorphous Polymer Blend 

Determination of Crystal-Amorphous Interaction in Crystalline/Amorphous Blends 

In the Matkar-Kyu model, the crystal-amorphous interaction parameter was assumed to be inversely proportional to the absolute temperature, that is, Xca = coAHu/RT, where AH is heat of fusion of the crystal in the pure state and T is absolute temperature. However, the analytical solution for the melting point depression was not sought in their original approach [66, 67]. This deficiency has been remedied recently by Rathi et ol. [75] for a crystalline/amorphous blend by solving the combined FH/PF free energies and obtaining an analytical expression from the equilibrium conditions, viz., df/d i = 0 and/(i )) = 0 as described below  

It can be anticipated that Eq. (4.27) should be valid for a small molecule system, but in the case of crystalline polymer blends its applicability may be limited to high crystalline polymer compositions. From a plot of 1 — T /J versus ( — ([)), one can determine Xca directly from the slope (Be) as follows  

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The possible entrapment of solvent in polymer crystals has been demonstrated by Malik et al., who investigated blends of syndiotactic polystyrene (s-PS) with organic solvents such as naphthalene, benzene, toluene, and so on [63]. Subsequently, the phase diagrams of these polymer-solvent systems, thus established, exhibited the liquidus and solidus lines, showing crystalline phases of s-PS and/or its modifications such as crystallo-solvates, in which the solvent molecules were trapped in the s-PS crystals [63-65]. The experimental evidence has led to the suggestion of possible entrapment of solvent in polymer crystals, forming solvated crystals [63]. 

Morphology Development in Relation to Phase Diagram of Crystalline/Amorphous Polymer Blends... 

A general summary of the topic phase diagrams of polymers is given by Porter RS, Jonza JM, KimuraM, DesperCR, George ER (1989) A Review of Phase Behavior in Binary Blends Amorphous, Crystalline, Liquid Crystalline, and On Transreaction. Polymer Eng Sd 29 55-62. 

The phase diagram of two-crystalline polymer blends such as that of PEO/diacrylate (DA) reveals a solid-liquid coexistence gap bound by the solidus and liquidus lines intersecting with the upper critical solution temperature (UCST) (Figure 4.18) [79]. The liquidus closely matches with the melting transition points, showing isotropic (I), the coexistence of crystal + liquid (Cri + I), and crystal + crystal (Cri + 0-2) regions. The two horizontal lines represent the monotectic line (upper) and the... 

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