Calculation of critical points not requiring the derivatives of the Gibbs energy demonstrated for a mixture of two homopolymers with the corresponding copolymer

The method for the calculation of phase diagrams (spinodal, binodal and tie lines) exclusively on the basis of the Gibbs energy of mixing, Delta G, with no need of calculating its derivatives with respect to the composition variables was extended to determine the critical conditions and the condition of the stability of the critical points. 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. Three critical lines were found within a very small interval of the copolymer composition.