The influence of thermal activation, chemical initiation, chain fragmentation, and chain stiffness on basic thermodynamic properties of equilibrium polymerization solutions is systematically investigated using a Flory-Huggins type lattice model. The properties treated include the average chain length L, extent of polymerization Phi, Helmholtz free energy F, configurational entropy S, specific heat C-V, polymerization transition temperature T-p, osmotic pressure Pi, and the second and third virial coefficients, A(2) and A(3). The dependence of the critical temperature T-c and critical composition phi(c) (volume fraction of associating species) on the enthalpy Deltah(p) and entropy Deltas(p) of polymerization and on the strength epsilon(FH) of the FH effective monomer-solvent van der Waals interaction (chi=epsilon(FH)/T) is also analyzed as an illustration of the strong coupling between phase separation and polymerization. For a given polymerization model, both T-c and phi(c), normalized by their values in the absence of polymerization, are functions of the dimensionless "sticking energy" h(epsilon)equivalent to(\Deltah(p)\/R)/(2epsilon(FH)) (where R is the gas constant) and Deltas(p). (C) 2003 American Institute of Physics.