Hydroxyl-terminatedpolybutadiene(HTPB)-based allophanate-urethane networks were prepared by reacting HTPB with di-isocyanates, such as toluene-di-isocyanate (TDI), isophorone-di-isocyanate (IPDI), and 4,4'-di(socyanatocyclohexyl)methane (H12MDI) at stoichiometric ratios (r-values) ranging from 1.0 to 1.5. The networks were characterized for mechanical and swell properties. The network parameters, such as "X," which is the fraction of urethane groups involved in the allophanate formation, and effective chain length (L-X) were calculated from experimental crosslink density values determined from swell data, using alpha-model equations developed by Marsh. Excellent linear correlations were obtained between mechanical properties and the calculated network parameters. (c) 2006 Wiley Periodicals, Inc.