NUCLEAR-MAGNETIC-RESONANCE LINESHAPE STUDIES OF INTERPENETRATING POLYMER NETWORKS

In the so-called in situ sequential interpenetrating polymer networks (IPNs), the two networks are formed after each other, and the network formed first is thought to impede gross phase separation in the final material. This is contrary to the other type of IPNs (in situ simultan eous), in which the formation of both networks is initiated at once an d proceeds to completion more or less simultaneously. In order to veri fy more accurately this assumption, which is not inconsistent with tra nsmission electron microscopy findings, a solid-state nuclear magnetic resonance lineshape analysis technique has been used to investigate t he degree of phase dispersion of IPNs of both types composed of an ela stomeric polyurethane (PUR) (25 wt%) and a crosslinked poly(methyl met hacrylate). The results confirm that such IPNs, when prepared sequenti ally, have a higher degree of phase dispersion than those obtained by the simultaneous synthesis method. Furthermore, in the corresponding n eat PUR networks, built up from aromatic pluriisocyanate and poly(oxyp ropylene glycol) (POPG), the rigid crosslink points are not composed o f isocyanate only, but include some oxypropylene mers; it appears that the amount of the rigidified part is the same, whatever the molecular weight of POPG.