Synthesis Of Aliphatic Polyesters And Periodic Copolymers Via Ring-Openging Copolymerization Of Cyclic Anhydride With Tetrahydrofuran Using Organic Catalyst

Aliphatic polyester are important biomaterials because of their biodegradability, biocompatibility, and acceptable mechanical strength. As a result, they are preferred over conventional plastics in industries related to drug delivery systems, tissue engineering, and commodity materials. most reports about sequence-controlled polymerization deal with radical polymerizations, such as ATRP, and use vinyl monomers as the comonomers. Therefore, developing any method including ring-opening polymerization for extending the range of monomers for use in the polyester synthesis and sequence-controlled reaction under green chemical conditions would be of great interest to polymer chemists.To synthesize polyesters and periodic copolymers catalyzed by nonafluorobutanesulfonimide (Nf2NH), we performed ring-opening copolymerizations of cyclic anhydrides with THF under initiator systems and no-initiator systems at 50-120℃. We found that in the no-initiator systems, the results of the copolymerization of cylic anhydride with THF were better than that in initiator systems, which indicated that the initiator performed negative effection on the ring-opening copolymerizations. The organic catalyst can be used as not noly initiator but also catalyst in these copolymerizations.In the no-initiator systems, at high temperature (100-120℃), the cyclic anhydrides, such as glutaric anhydride (GAn), succinic anhydride (SAn), and methylsuccinic anhydride (MSAn), copolymerized with THF via ring-opening to produce polyesters (Mn=0.8-1.9×103, Mn/Mw=2.38-3.51). Both ester and ether units were temporarily formed during this copolymerization process and subsequently, the ether units were transformed into esters by chain transfer reaction, thus giving the corresponding polyester. On the other hand, at low temperature (25-50℃), ring-opening copolymerizations of SAn, GAn and MSAn with THF produced poly(ester-ether) polymer (Mn=3.4-12.1×103, Mw/Mn=1.44-2.10). NMR and MALDI-TOF mass spectra analysis revealed that when toluene (4 M) was used as a solvent, GAn reacted with THF (unit ratio: 1:2) to produce periodic copolymers (Mn=5.9×103, Mw/Mn=2.10). It is the first report about synthesis of polyesters and periodic copolymers by ring-opening copolymerization of cyclic anhydride and THF.We have also performed model reactions to delineate the mechanism by which periodic copolymers contained both ester and ether units, were transformed into polyesters by raising the reaction temperature to 120℃. the mechanism consisted of two steps (Scheme 2). One step is the initiation and cationic propagation of the reaction in which the THF ring could be easily opened by a proton acid or a Lewis acid catalyst through cationic reaction. And the other step is the transformation reaction at high temperature, in which the transfer reaction is via nucleophilic attack of the ether oxygen on the propagating center of the cyclic anhydride, and subsequent insertion of the remaining cyclic anhydride monomer. After the chain reaction, a new oxonium ion of cyclic anhydride was generated and the ether structures transformed to ester structures.At last, we used the mechanism of the chain transformation reaction to device and successive prepared tri-units copolymers in two-steps through one-pot reaction.