The crystallization behaviour of a copolyester based on polyethylene terephthalate containing cyclohexanedimethanol groups was studied as a function of thermal and solvent treatment. Although the rate of crystallization as compared to homopolymer was reduced, a substantial amount of crystallinity could be introduced by prolonged treatment and a new orthorhombic crystal lattice with unit cell dimensions of a = 5.05 A ̊, b = 7.1 A ̊ and c = 10.7 A ̊ was formed in the copolyester as compared to the triclinic in the homopolymer. © 1986.