The modification of poly(ethylene terephthalate) with 1,4-cyclohexanedimethanol and the modification of poly(1,4-wcyclohexylanedimethanol terephthalate) with ethylene glycol or isophthalic acid retard the crystallization of the copolyester backbone, and over a wide range of comonomer concentrations, very slowly crystallizing, essentially amorphous copolyesters are formed. These amorphous copolyesters possess attractive physical properties such as toughness, low color, and chemical resistance, and since their first commercial introduction in 1977, these copolyesters have become the basis of a large and growing plastics business for Eastman Chemical Co. (C) 2004 Wiley Periodicals, Inc.