Compatibilization in Phase-Separated IPNs

The general condtision may be drawn that by formation of IPNs filler plays simnltaneously two roles—it affects the reaction rates, which changes the conditions of phase separation, and directly influences the phase separation due to adsorption of components at the interface. 

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The advantageous properties of IPNs come from co-continuity and excellent compatibilization (obtained by co-reactions) that result in fine dispersions. Often IPNs do not possess co-continuity of networks rather one phase forms fine droplets (10-100 nm diameter) dispersed in another phase. IPNs with specific topological network structure provide smaller domains of phase-separated materials. Their miscibility level gives rise to a multiphase polymer system with ordered variety of domain structure ranging from a nanometre to... 

Simultaneous IPNs involve monomers or reactive oligomers and crosslinkers of two or more reactive systems. These systems are generally chosen such that the reaction of one component does not interfere with or is involved with the reactions of the second component. Otherwise, grafting reaction would compete with interlocking ring formation as the method of compatibilization. An example of a simultaneous IPN is the reaction of free radical polymers (such as polyacrylates) in the presence of condensation polymers such as polyurethanes, as has been the subject of many investigations [171-174]. A PU/PMMA simultaneous IPN exhibited transparency and showed only limited phase separation below 30% PMMA [171]. This IPN... 

It was shown that introduction of various amounts of HEMA into the starting system leads to the formation of a semi-IPN which is characterized by a single temperature transition based on DMA and DSC data [310,353]. The position of this transition depends on the system composition and on the kinetic conditions of the reaction (rates of formation of both components). The kinetic measurements have shown that during reaction in the presence of HEMA no phase separation proceeds, as follows from the hght scattering data. In this case the final system has a one-phase structure due to the formation of a thermodynamically miscible ternary system and to the grafting of PU chains onto PS macromolecules via the third component. The reaction compatibilization was studied more thoroughly for semi-IPN PU/PS in the presence of OUDM [311]. 

The IPNs, as a rule, undergo in the course of curing nonequilibrium microphase separation due to thermodynamic incompatibility of the constituent networks. IPNs present two-phase systems with phases of varying composition. All such systems are characterized by the existence of two relaxation maxima corresponding to the constituent phases. Up to now there are only scattered works where the compatibilization of IPNs is considered. The improvement of compatibility of two networks comprising IPNs may be reached either by grafting one network to the other [148,336-339] or by introducing compatibilizers of the same type, as were used for blends of linear polymers [339,340]. 

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