Lattice model of equilibrium polymerization. IV. Influence of activation, chemical initiation, chain scission and fusion, and chain stiffness on polymerization and phase separation

Abstract

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 Φ, Helmholtz free energy F, configurational entropy S, specific heat CV, polymerization transition temperature Tp, osmotic pressure Π, and the second and third virial coefficients, A2 and A3. The dependence of the critical temperature Tc and critical composition φc (volume fraction of associating species) on the enthalpy Δhp and entropy Δsp of polymerization and on the strength εFH of the FH effective monomer–solvent van der Waals interaction (χ=εFH/T) is also analyzed as an illustration of the strong coupling between phase separation and polymerization. For a given polymerization model, both Tc and φc, normalized by their values in the absence of polymerization, are functions of the dimensionless “sticking energy” hε≡(|Δhp|/R)/(2εFH) (where R is the gas constant) and Δsp.