Polyethylene terephthalate (PET) is a widely used thermoplastic polymer, but its excessive use and poor waste management pose environmental challenges. Enzymatic degradation of PET offers a potential solution that is ecofriendly and yields monomers suitable for the synthesis of plastics. In 2016, Yoshida et al. discovered a PET degrading enzyme (PETase) from sediment-dwelling bacteria, Ideonella sakaiensis ( Science 2016, 351 (6278), 1196−1199). It was found that the enzymatic degradation rate of PET increases with reduced crystallinity, suggesting that this parameter may be amenable to tuning. To investigate the interplay between substrate crystallinity and chemical structure on the efficiency of PET degradation, we synthesized PET, PET copolymers (e.g., polyethylene terephthalate-co-ethylene isophthalate, P(ET-co-EI), poly(ethylene terephthalate-co-ethylene phthalate), P(ET-co-EP)), and branched PET that have been used in packaging. These polymers have good properties for injection molding and oxygen scavenging, respectively. The polymers were synthesized from aryl chloride and ethylene glycol. Size, composition, randomness, thermal properties, and crystallinity of all polymers were determined. The polymers were then enzymatically degraded to compare the efficiency of PETase on different PET substrates. Our study demonstrates that, while chemical modification reduces crystallinity, the influence of chemical structures (the kinks and branches) on the binding of the PETase, and hence the enzymatic degradation, is more significant than the effect of crystallinity.