Polythioether prepolymers that have a low nucleation temperature. The symmetry of the polythioether prepolymers is modified by including pendent groups extending from the backbone of the polythioether prepolymer chain and/or the symmetry is modified by including segments having a different number of —C(R)2— groups between heteroatoms. The polythioether prepolymers are stable at low temperature storage conditions for an extended period of time. Compositions prepared using the low nucleation temperature polythioether prepolymers are useful as sealants.