DETERMINATION OF AN INTERPENETRATING NETWORK STRUCTURE BY SMALL-ANGLENEUTRON-SCATTERING

Small-angle neutron scattering (SANS) was used to study the effects of cross-link density on the structure of in situ sequential interpenetr ating polymer networks (IPNs). The system investigated is a PSD (deute rated polystyrene-co-divinylbenzene) network built within a matrix net work of PUR (polyurethane). The scattering can be approximated by the Debye-Bueche law with a q(-4) dependence at intermediate values of wav e vector q, with departures from it at both low and very large values of q. At low q, this Debye-Bueche law yields a value of the structure factor S(q-->0) and a correlation length xi. At large q, it yields a v alue of the specific area S/V S being the total area and V the total v olume. As the cross-link density of either network of the IPN increase s, S(q-->0) and xi decreases, while S/V increases. The measured xi is in the range 20 to 80 Angstrom and the values of SIV correspond to 100 -300 m(2)/gm, indicating a rather finely divided material. The quantit y S(q-->0), after being divided by volume xi(3), allows us to estimate the contrast. The existence of a maximum in S(q) is discussed for the most cross-linked samples. With increasing cross-link density of the networks, it seems that the size of phase-separated regions is decreas ing, indicating that the IPN structure freezes earlier in the evolutio n of the separation kinetics. However, from comparison of effective co ntrast and maximum contrast between ''pure phases'' (i.e. made of pure PSD and the other of pure PUR), it seems that the content of the sepa rated regions is closer to ''pure phases'' when the cross-linking is h igher. At this stage of the analysis, the effects of complicated topol ogical connectivity between the two networks were neglected.