The crystalline structure exhibited by terpolymers obtained through chemical modification with benzoyl chloride from an ethylene-vinyl alcohol copolymer with a molar fraction in vinyl alcohol of 68%, EVOH68, has been studied by either wide angle X-ray diffraction or small angle X ray scattering experiments and differential scanning calorimetry. The type of crystal lattice developed has been found to be strongly dependent on modification degree and thermal history. A highly-disordered crystalline lattice with very small crystallites has been found for the quenched specimen with the highest benzoate content while the rest of fast cooled samples crystallized into an orthorhombic lattice. On the other hand, a monoclinic crystal cell has been observed in the slowly cooled specimens with low benzoate incorporation. At the last given thermal treatment, this monoclinic lattice evolves and seems to be transformed into an orthorhombic-like crystal for the terpolymer with the highest modification ratio. (c) 2007 Wiley Periodicals, Inc.