Phase Diagrams of Reacting Systems

The microheterogeneous structure of IPNs arises as a result of the thermodynamic immiscibility (corresponding to the positive value of thermodynamic interaction parameter x) that appears in the course of IPN formation and leads to the microphase separation of the system. 

In spite of this, an attempt has been made to construct a phase diagram for the curing semi-IPN based on poly(butyl methacrylate) (PBMA) and styrene-divinylbenzene (DVB) copolymer (Fig. 1) [53]. The system polystyrene (PS)/PBMA shows limited compatibility at low concentrations and low molecular mass of components, and full incompatibility at higher concentrations and molecular weights. With increasing conversion, the quality of the solvent (mixture of styrene and DVB) becomes poorer in relation to PBMA. As a result, after reaching a certain degree of conversion, the system can no 

Recently, phase diagrams of ternary IPNs have been obtained [54]. The semi-IPNs based on cross-linked polyurethane (PU) and linear poly(vinyl acetate) (PVA) have been investigated by adding the third component, PBMA. The phase diagram was constructed using the Flory-Huggins theory for 

In other work [55-59] a partly complete phase triangle diagram of the polymerization of styrene plus cross-linker in the presence of cross-linked polybutadiene has been constructed based on the data of transmission electron microscopy (TEM). This diagram shows the intercept with the binodal and spinodal curves at constant temperature. 

The comparison of the phase behavior of semi-IPNs based on almost miscible polymers—linear PS and poly-a-methylstyrene cross-linked by DVB and mixtures of the corresponding homopolymers—has shown that for homopolymer blends only one glass transition is observed, its position obeying the Fox equation. Simultaneously, for semi-IPNs there were two glass transitions, far from the glass transition temperatures of the components, for the same compositions where linear blends are miscible. A difference in phase behavior between blends and semi-IPNs seems to be evident. However, no phase diagrams allow one to determine the mechanism of phase separation. 

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