In accordance with the regular folded chain crystallite model, an expression for the melting point depression of crystalline polymer in diluent was derived by extending the treatment given by Flory. The equation obtained is which reduces for very large x and considerably large ζ to where Tm⁰ is the melting point of the pure polymer of infinite fold length and chain length, Tm⁰(l) is tne melting point of the pure polymer of fold length l, Tm(l) is the melting point for the polymer of fold length l in the presence of diluent, ΔHᵤ is the heat of fusion per mole of repeating unit, Vᵤ and V₁ are the molar volumes of the polymer repeating unit and the diluent, respectively, x is the degree of polymerization, v₁ and v₂ are the volume fractions of the diluent and the polymer, respectively, ζ is the fold length in number of repeating units, σₑ is the end surface free energy per unit volume, Δhf is the heat of fusion per unit volume, and X₁ is the diluent-polymer interaction parameter. The model used here was discussed in relation to the fringed micelle model
