Morphology of IPNs

These phenomena cannot be treated Independently, Consequently, the morphology of IPN s is often at a quasi-equlllbrlum state determined by a balance among the several kinetic factors [ l Therefore, in order to understand the domain formation process in IPN s, we should take into consideration the route taken to the final morphology as well as the chemical and physical properties of each constituent. 

This paper describes two types of novel urethane-acrylic IPNs for coating applications. The mode of preparation used was the simultaneous or SIN technique. In order to examine the effect of the soft segment on the properties and morphology of IPN coatings, the pendant hydroxy group in the hydroxyethylacrylate-butylmethacrylate copolymer was reacted with caprolactone to increase the chain length of the pendant hydroxy group. 

Figure 6.2. Selected morphologies of IPNs based on SBR and polystyrene, SBR stained with osmium tetroxide. Upper left Commercial high-impact polystyrene. Upper right, Ostromislensky s material, with no phase inversion middle left, semi-IPN, SBR crosslinked middle right, semi-11 IPN, PS crosslinked lower left, full IPN lower right, full IPN, higher crosslinking in the SBR.

By combining the TEM and MTDSC techniques, a clearer understanding of the morphology of IPNs may be obtained. From TEM measurements, phase domain size and shape and connectivity can be determined. From MTDSC measurements, the weight fraction of interphase regions can be obtained. So, the relationships between mechanical properties and IPN morphology can now, in practice, be more comprehensively investigated. 

The morphology of IPNs has been widely investigated via electron microscopy and dynamical mechanical spectroscopy. Many IPNs have dual-phase continuity, with phase domain sizes of the order of several hundred angstroms. For sound and vibration damping over broad temperature ranges, the two polymers are mixed in different extents in different parts of the material, usually in the submicron range. 

Some of the factors that control the morphology of IPNs are now reasonably clear they include chemical compatibility of the polymers, interfacial tension, crosslink densities of the networks, polymerization method, and the IPN composition. While these factors may be interrelated, they can often be varied independently. Their effects are summarized here. 

Fig. 8. A comparison of two possible morphologies of IPNs, based on (a) poly(ethyl acrylate) -ipn- poly(methyl methacrylate) and (b) poly(ethyl acrylate) -ipn-polystyrene.

The morphology of IPNs can be determined by electron microscopy. The morphology has a great influence on the physical and mechanical behaviour. The phases differ, however, in amount, size and shape, sharpening of their interface and degree of continuity. The factors affecting morphology are chemical compatibility of the polymers, interfacial tension, crosslink density of the networks, polymerization methods and IPN composition. 

The synthesis and morphology of IPN s are compared to the several other methods of preparing blends of distinguishable polymer pairs. Both components of IPN s are continuous throughout the very finely divided phase domain dim.ensions being controlled by the crosslink density. 

The morphology of IPNs is determined by the mechanism of phase separ-ation-nucleation and growth or spinodal decomposition. As was discussed above, the application of direct structural methods for studying IPNs is rather restricted due to their amorphous state and low degree of ordering. Because... 

Presently, a great deal of work is published concerning the structure of IPNs obtained using electron microscopy. From the preceding discussion it is evident that the morphology of IPNs should be determined by the following factors (1) the thermodynamic miscibility of two networks, (2) the kinetic conditions of the curing reactions, and (3) the mechanism of phase separation. In principle, three distinct features of IPN structure should be revealed. 

---