The diol and dicarboxylic acid in polyester synthesis are significant independent variables that relate directly to the structure-property-dependent variables of polyesters. The choice of the stereoisomers of the diol in the polyester synthesis can significantly alter the mechanical and thermal performance. Terephthalate polyesters prepared from the proper ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and 1,3-propanediol have superior impact resistance when compared to ballistics grade polycarbonate. In addition these polymers exhibit very strong self-healing behavior that is activated by heat. These copolymers were all produced with a mixture of cis and trans isomers with a ratio of 43/57, respectively. This study reports research conducted to determine the structure-property relationships that can be attributed to the stereoisomers of the CBDO monomer. The polyester prepared with 99 % cis (CBDO) monomer has significantly improved mechanical and thermal performance when compared with the polyester prepared with a 43:57 mixture of cis and trans isomers or 100 % trans isomer. Thermal gravimetric analysis and differential scanning calorimetry demonstrated that the cis CBDO polymer exhibit a much higher T (g) (99 A degrees C for cis and 69 A degrees C for the trans 84.5 A degrees C for the mixed polymer) and better thermal stability than the trans form of the polymer (onset of decomposition of trans at 345 and 360 A degrees C for cis). Dynamic mechanical analysis and the Notched Izod demonstrated that the cis form of the polymer was much tougher than the trans form. Wide angle X-ray diffraction showed that the trans form was semicrystalline and the cis form was amorphous. The Notched Izod impact was 1070 J/m for the cis CBDO-based copolymer with the trans form having an impact factor of 841 J/m with the mixed polymer exhibiting an intermediate value of 944 J/M. Molecular modeling supports the experimental evidence that the choice of stereoisomers for the diol significantly influences the molecular architecture of the polyesters. The molecular architecture of polyesters in addition to polar attraction and molecular weight variables provides a dramatic increase in mechanical and thermal performance.