Fractionation in a Phase-Separated Polydisperse Polymer Mixture

If a solution of polydisperse A- and B-polymers undergoes phase separation, the molar mass distribution of the A-polymers in the A-rich phase becomes different from that in the B-rich phase. This phenomenon is known as fractionation. Here, we compare experimental results on fractionation with Flory−Huggins theory and computer simulations. We study the degree of fractionation f ( m ) ≡ ρ A in B ( m )/ρ A in A ( m ), in which ρ A in A ( m ) is the density of A-polymers with molar mass m in the A-rich phase and ρ A in B ( m ) that of A-polymers in the B-rich phase. We find that f ( m ) obeys the simple scaling f ( m ) ∼ exp(− km ), where k is a temperature-dependent constant.