This research effort is directed at examining the engineering process variables on the mechanical properties of aromatic polyesters and copolyesters. The proposal was submitted in response to NSF 96-4, NSF-CONACyT Collaborative Research opportunities. It is an extension and augmentation of an already successful cooperative research program in polymer engineering between the University of Tennessee and the Universidad Autonoma de San Luis Potosi. Basic research studies will be under taken to determine the relations between morphological control variables and critical mechanical properties and to extend those results to the processing characteristics of the materials. It is proposed to determine the behavior of the polymers and copolymers as a function of cooling rate and nucleating agents and to relate the structures generated to the mechanical properties. Successful completion of the effort will increase the basic knowledge on the control of the mechanical properties during industrial processing. The Oak Ridge National Laboratory (ORNL) has agreed to participate in the project by conducting specific analysis.