Alternating Copolymerization Of Aziridines And Cyclic Anhydrides

Poly（ester-amide）s,of which the main chains contain alternatively distributed ester and amide,have been widely applied in the area of biomedicine materials,smart materials etc,due to their good biodegradable and mechanical properties.Herein,we developed a novel strategy of synthesizing poly（ester-amide）s via the copolymerization of cyclic anhydrides and aziridine derivatives.Compared with the conventional synthetic methods,such as the byproduct unavoidable polycondensation or monomer structures limited ring opening polymerization,the newly developed method showed many advantages including easily access to aziridine derivatives,tunable structures of the resultant copolymers,efficient and controllable copolymerization behaviors.The detail comments are as follows:（1）An efficient method for synthesizing aziridine derivatives was developed.The benzyl protected aziridine derivatives were synthesized through the condensation of benzaldehyde and hydramine compounds,the corresponding product was reduced by sodium borohydride（NaBH₄）,followed by the cyclization reaction and afforded the corresponding aziridine derivatives.This synthetic method exhibited many advantages including readily available starting materials,moderate reaction condition and high product yields.The easily accessible hydramines enriched structures of the resultant copolymers,which provided the chance of tuning the properties of the resulting polymers.（2）The alternating copolymerization of the anhydrides and aziridine derivatives were successfully obtained usingorganic base/benzyl alcohol（BnOH）as catalyst.With the 2-methyl-N-benzylaziridine（MBnAz）and phthalic anhydride（PA）as model monomers,and BnOH as initiator,the organic base N-methyl-1,5,7-triazabicyclododecene（MTBD）exhibited excellent activity in catalyzing the copolymerization after catalyst screening experiments.The conversion of MBnAz reached to 73%after the copolymerization for 10 h,affording the resulted copolymers with the molecular weight（M_n）of 13.6 kg/mol and a narrow distribution of molecular weight（D）of 1.14.The MALDI-TOF spectrum revealed the perfectly alternating structures of the copolymers.The study on the polymerization process exhibitedthe linear increase in M_n with monomer conversion,accompanied with the narrowD,indicating well-controlled nature of the copolymerization.Furthermore,the second-feed experiment exhibited the living copolymerization character of the copolymerization.The in-situ IR experiment proved no induce period of the copolymerization,the synchronously increase in the intensity of the peaks representing ester and amide.The glass transition temperature of the PA/MBnAz copolymers was determined as 118℃,with the decomposition temperature up to 257℃.The aziridine derivatives with different structures can copolymerize with anhydrides,providing the corresponding copolymers with alternating structures,suggesting the excellent universality of this method for obtaining poly（ester amide）s with diverse structures.（3）The efficient polymerization of N-p-toluenesulfonylaziridine and cyclic acid anhydride to poly（ester amide）s with ester bond and amide bond in the main chain was obtained.Using 4-dimethylaminopyridine（DMAP）as the initiator for 2-methyl-N-p-toluenesulfonylaziridine（MTsAz）and PA polymerization for 0.5 h,the conversion rate of MTsAz reached to 95%,the molecular weight of the polymer was 21.1 kg/mol,and the molecular weight distribution was1.15.The electrospray mass spectrogram shows that the DMAP is the terminal part of resulting polymer with a two-component structures.The polymer has an alternating structures of aziridine derivatives and anhydrides and also with a homopolymerization structures of aziridine derivatives,respectively.