Design And Synthesis Of Poly(Ester Amide)s Based On Aziridine Compounds

Poly(ester amide)s are synthetic polymeric materials which have both ester and amide groups in the main chain,gathering good biodegradability and biocompatibility of polyesters with the excellent thermal and mechanical characters of polyamides.More importantly,the properties of polymer can be precisely controlled by changing the structure and proportion of ester/amide groups in the main chain.At present,poly(ester amide)s exhibit wide application prospects in the fields of drug delivery systems,hydrogels,tissue engineering,elastomers and smart materials.Developing of efficient synthetic methods for poly(ester amide)s has always been the focus in this field.In this paper,a new method for synthesizing poly(ester amide)s was developed.Poly(ester amide)s were obtained via the copolymerization of aziridine compounds and cyclic anhydrides,followed by the deprotection for the substitutes on the N atoms groups of the resulted copolymers.(1)A new pathway for synthesizing poly(ester amide)s with aziridine compounds and cyclic anhydrides was developed.Firstly,N-substituted poly(ester amide)s were synthesized by the alternating copolymerization of N-benzyl substituted aziridines and cyclic anhydrides with MTBD as catalyst and Bn OH as initiator.Secondly,the debenzylation of the obtained N-substituted copolymers was studied.The comparative analysis of the copolymer before and after the debenzylation was carried out by ¹H NMR and GPC.The results showed that the copolymer obtained from the M3 could be efficiently oxidized by K₂S₂O₈/Na₂HPO₄ to remove the substituents on the N atoms.MALDI-TOF-MS revealed that the poly(ester amide)s synthesized by this method possess a completely alternating structure of ester and amide groups.The method has good universality and can realize the synthesis of poly(ester amide)s with different structures in the main chain.(2)The polymerization of aziridine compounds containing electron withdrawing protective groups with cyclic anhydrides and the desulfonylation of the resulted polymers were studied.The copolymerization of M6 and PA was realized with DMAP as initiator.¹H NMR and ESI-MS of the polymer showed that there was not only the alternating copolymerization of M6 and PA,but also a homopolymerization of M6 occurred in the polymerization.The effect of different initiator systems,feed ratios of monomer to initiator and reaction temperature on the selectivity of the polymer were investigated,and it was found that when DMAP was used as initiator,the feed ratio of M6/PA was 1/4 and the reaction temperature was 25?,the copolymerization ratio of M6 and PA can reach a maximum of 4.69.The reduction method using Red-Al and the acid hydrolysis method using HBr were studied respectively for the desulfonylation of the copolymer obtained by copolymerization of M6 with PA.¹H NMR and GPC of the product showed that the main chain of the copolymer was degraded in the process of deprotection.The corresponding poly(ester amide)s cannot be effectively obtained..(3)The terpolymerization of M3,M6 and PA was studied.It was found that in the presence of the organic base TBD as catalyst and Bn OH as initiator,the content of ester amide unit in copolymer was the highest.The results of reactivity ratio experiment showed that r _M3=0.95,r _M6=1.05(r refers to the ratio of chain growth rate constants between homopolymerization and copolymerization in the polymerization;r<1 indicates that the tendency of copolymerization is larger than the homopolymerization,r>1 indicates that the homopolymerization tendency is larger than the copolymerization),it showed that M3 can only copolymerize with PA alternately,while M6 can either copolymerize with PA alternately or homopolymerize itself.