CALCULATION OF PHASE-DIAGRAMS NOT REQUIRING THE DERIVATIVES OF THE GIBBS ENERGY DEMONSTRATED FOR A MIXTURE OF 2 HOMOPOLYMERS WITH THE CORRESPONDING COPOLYMER

A method is presented which allows the calculation of phase diagrams (spinodal, binodal and tie lines) on the basis of the Gibbs energy of mixing Delta G. No derivatives of Delta G with respect to the composition variables are required. This method is particularly useful in cases where the composition dependence of Delta G is very complex and no analytical representation of the derivatives can be given. The method is applied to a ternary mixture of two homopolymers with a copolymer consisting of the same monomers. The sequence distribution of the copolymer is kept constant between random and purely alternating, and phase diagrams are calculated for different chemical compositions of the copolymer. The complex phase separation behavior resulting for a 1:1 copolymer becomes much simpler as one monomeric unit starts to predominate in the copolymer.