Four p)lyurethane networks based on polypropylene glycols and a triisocyanate, were swollen in polypropylene glycols (diluents) having n:olecu1ar weights of 400, 2000 and 4000. The effect of n:o:Lecular weight of network chains and the penetrants (diluents) on the 

diffus:ton coefficients were examined and compared with the predictions of the reptation concept. It was found that diffusion coefficients varied linearly with M-1 of the penetrants and approximately linearly with M,: of the network chains. It was shown that reptatiort does not take place in these systems. Equilibrium swelling was compared with the predictions of scaling theory and the resulting problems were discussed.