Homo-IPNs physical crosslinks

Because of the special swelling and mutual dilution effects encountered in sequential IPN s, special equations were derived for their rubbery modulus and equilibrium swelling. The new equations were used to analyze polystyrene/polystyrene homo-IPN swelling and rubbery modulus data obtained by four different laboratories. In the fully swollen state, there was no evidence for IPN related physical crosslinks, but some data supported the concept of network I domination. In the bulk state, network I clearly dominates network II because of its greater continuity in space. The analysis of the data concerning the possible presence of added physical crosslinks in the bulk state yielded inconclusive results, but this latter is of special interest for modern network theories. 

Through the use of sequentially polymerized homo-interpenetrating polymer networks, IPN s, a method will be described below to detect changes, if any, in the physical crosslink density, provided that such physical crosslinks actually do contribute to the retractive and swelling forces. 

While there is some evidence for new physical crosslinks, unfortunately the data do not permit a reasonable conclusion either way. Only the modulus data of Shibayama and Suzuki indicates the presence of any added physical crosslinks contributing to the rubbery modulus. Siegfried, Manson, and Sperling s data. Fig. 5b, indicate fewer physical crosslinks in the homo-IPN than in the corresponding single networks, because the data lies to the left of the line. 

Figures 4.2,4.3, and 4.4 show the modulus predicted by equation (4.8) vs. Young s modulus, E (experiment). As with the swelling data, the network imperfections and the contributions of the physical crosslinks, if any, were minimized by determining the two crosslink levels required for E (theory) on the separate homopolymer networks. Unfortunately, Millar did not report modulus data for his polystyrene/polystyrene homo-IPNs.

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