Polyurethane-containing semi-IPNs

In papers reviewed in this section, the thermoplastic polyurethane elastomer was used [27-52] as a linear component of semi-IPNs in which, as already mentioned in Section 1, the second component should be a chemically crosslinked polymer. As a second component the polyurethane [27], polyepoxyisocyanurate [28-33] and polycyanurate [34-52] networks were used. Once again, it is important to note that if the thermoplastic PU forms a continuous phase, the final semi-IPNs exhibit the properties and behavior of thermoplastic elastomers. 

The viscoelastic properties of semi-IPNs based on a thermoplastic polyurethane (TPU) and a chemically crosslinked polyurethane (PU network) formed in the TPU solution, as well as of the same semi-IPNs filled with (-Fe203 powder have been studied by Brovko et al. [27]. The TPU (molar mass 40000 g/mole) was synthesized from poly (1,4-butylene) glycol adipate (molar mass 1000 g/ mole), 4,4 -methylenebis(phenyl isocyanate) and 1,4-butane diol as a chain extender. The PU network was based on a vinyl chloride/vinyl acetate/vinyl alcohol terpolymer with an adduct of 1,1,1-trimethylolpropane and 2,4-toluene diisocyanate the appropriate for crosslinking NCO/OH ratio was chosen to be 0.55. The non-filled semi-IPNs exhibited only one situated between those of TPU and PU network. Therefore, the components of the semi-IPNs may be assumed to be compatible. It was found that the semi-IPNs filled with a small amount of Fe20g (up to 1.4 vol%) exhibited one shifted toward higher 

The semi-IPNs filled with 6.5 to 10.5 vol% of -Fe203 are characterized by dual phase continuity. A very important characteristic of the phase separation in the IPNs is the degree of segregation, a, giving the fraction of material, which undergoes phase separation. When a = 1, the system is fully phase-separated at a = 0, it is fully miscible. The value of a can be estimated from the characteristic maxima of the mechanical loss curves according to the equation proposed by Rosovitsky and Lipatov in [59]  

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Polyurethane-containing semi-IPNs with immiscible components... 

A few papers dealing with silicone latex IPNs have appeared. Frisch et al. [ 111 ] patented a process whereby two emulsions were prepared the first contained a hydroxyl-terminated PDMS and stannous octoate, the second a crosslinked polyurethane, poly(urethaneurea) or polyacrylate latex. The two lattices were blended and a film was cast and cured at 120 °C. The mechanical properties were found to be enhanced, especially in the case of the polyacrylate/PDMS IPN. Noteworthy is the fact that semi-IPNs such as the thermally stable... 

The silicone semi-IPNs consist of mixing a hydride-containing silicone prepolymer and a vinyl-functionalized silicone polymer into a thermoplastic matrix such as PA, PBT, thermoplastic polyurethane (TPU), or styrene-ethylene/butylene-styrene (S-EB-S) block copolymer elastomer. The two silicone prepolymers coreact in the thermoplastic matrix during melt extrusion and injection molding to form a partially cross-linked network within the thermoplastic matrix. 

In this chapter, structure-property relationships in new thermoplastic apparent IPNs (AIPNs) and in semi-IPNs containing a polyurethane thermoplastic elastomer are discussed. 

A curable epoxy resin containing a crosslinked elastomeric latex " yields a special type of sequential IPN. The elastomers mentioned include SBR, EPR, NBR, silicone rubber, and PEA. Hawkins " described an epoxy/polyurethane semi-SIN, and Mendoyanis " revealed an epoxy/liquid rubber SIN. The liquid rubbers were based on polysulfide rubber or polyethylene. The final products could be extended to 400% at... 

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