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Owing to the overdependence on fossil fuels, global effort has been initiated to identify alternate renewable sources for PET Polyethylene terephthalate (PET), a polyester of terephthalic acid (TPA) and ethylene glycol (EG). As these efforts to make PET from renewably sourced TPA and EG make inroads, alternate renewably sourced comonomers need to be identified to modulate its properties depending on the needs of the application. The goal of this work was to develop polyesters of PET with two commercially viable, renewably sourced comonomers, namely, 2,5-furandicarboxylic acid (FDCA) and isosorbide (ISB), and establish a fundamental understanding of the structure-property relationship for these polyesters.In the first part of this work, effect of copolymerization of PET with FDCA (described as PETF copolyesters) on the esterification kinetics was evaluated in detail. The presence of FDCA and esterified FDCA products during copolymerization enhanced the solubility of TPA in the reaction media and improved the esterification kinetics. The kinetics study revealed that the esterification step of PETF copolyesters can be performed at shorter times or lower temperatures to gain energy savings. Following this study, high molecular weight PETF copolyesters were synthesized and processed into continuous films. In the unoriented state, incorporation of furan units in the PET backbone reduced the crystallization rate and enhanced mechanical and barrier performance of PET. Improvement in the barrier properties was primarily attributed to the suppressed chain segment mobility due to the presence of rigid, non collinear furan ring. The PETF copolyester films were biaxially stretched to evaluate the effect of furan units on the orientation and strain induced crystallization of PET. Differential scanning calorimetric studies revealed that the furan units resulted in decreased strain induced crystallization upon orientation. However, even with lower crystallinity values, PETF copolyesters showed similar enhancement in properties as seen in the unoriented state. Analysis of amorphous phases suggested that the rigid amorphous phase trapped between the lamellae and chain folds increased by incorporation of furan units. It was proposed that this rigid amorphous fraction compensated for the loss of crystallinity upon orientation and retained the property enhancement for biaxially stretched PETF samples. Lastly, the framework developed for structure-property evaluation of PETF copolyesters was extended to the copolyesters of PET with isosorbide (PEIT copolyesters) and terpolyesters of PET with ISB and FDCA (PEITF terpolyesters). Incorporation of bulky isosorbide units improved the glass transition temperature significantly. However, mechanical and barrier performance of PET was negatively affected due the increased brittleness because of the isosorbide units. The PEITF terpolyesters exhibited intermediate properties between PETF and PEIT copolyesters. This work, which focused on understanding the fundamentals of reaction chemistry and structure property relationship for the copolyesters and terpolyesters of PET, can therefore be envisioned to provide a framework to evaluate the effect of potential comonomers on the synthesis and properties of PET relevant for packaging.