The synthesis of sustainable polymers is a hot topic but a challenging issue in the field of polymer chemistry. In this report, we report on the synthesis of polyesters from cationic copolymerization of aldehydes (and acetals)[1-2] with cyclic anhydrides through using a series of catalyst/initiator. Aldehydes and cyclic anhydrides are two important types of oxygen-rich compounds that can also be derived from biomass, and acetals can be derived from diol and formaldehyde. This report presents a new family of alternating aldehydes and cyclic anhydrides through cationic mechanism, including aldehyde (acetal)/cyclic anhydride copolymers with fully alternated sequence, especially, sea water degradable the formaldehyde/cyclic anhydride copolymers with AB/ABB sequence[3], and flame-retardant chloral/cyclic anhydride copolymers [4] will be highlighted. The cationic polymerization is versatile and has successfully synthesized polyesters with new structures, which can potentially be used in the manufacture of plastics and rubbers. At high temperatures, these polymers could be degraded to the initial aldehydes and cyclic anhydrides, and the recovery rate exceeds 90%, thus achieving efficient closed-loop recovery of the monomers. The oxygen-rich polyester synthesized from biomass demonstrates the concept of low-carbon polymers.