A precursor formulation comprising, before curing, a hydroxyl-terminated polybutadiene (HTPB) prepolymer or a hydroxyl-terminated polyether (HTPE) prepolymer, an oxidizer, a dimer fatty diol, and an isocyanate curative. A solid propellant comprising a reaction product of the HTPB prepolymer or HTPE prepolymer, the dimer fatty diol, and the isocyanate curative is also disclosed, as is a rocket motor comprising a case and a solid propellant in the case, the solid propellant comprising the reaction product and an oxidizer. A method of reducing a burn rate of a solid propellant is also disclosed.