Phase separation during the formation of three-dimensional polymers

Phase separation during the formation of three-dimensional polymers in the presence of inert diluents, by crosslinking of linear polymers, or by polymerization of multifunctional monomers, was treated under the assumption of thermodynamic equilibrium by using the Flory theory of swelling equilibria and rubber elasticity. The separation begins when the maximum swelling of the network in the diluent or diluent-monomer mixture drops to the degree of dilution of the network; the two quantities remain equal even after separation of phases. The network formed in this way is a composite one. Relations have been derived for the dependence of composition and volume of the network phase upon initial conditions and degree of crosslinking or extent of polymerization. The results of calculations for binary and ternary model systems are discussed with respect to syneresis or formation of porous structures, as two possible modes of phase separation.