Study On Nonmetallic Lewis Pairs Mediated Controllable Ring-Opening Polymerization Of NCAs

Due to theirs’ unique secondary structure,Excellent self-assembly performance,and good biocompatibility,polypeptides have important applications in the field of bioengineering,such as siRNA delivery,tissue engineering scaffolds and so on.The most commonly used method of preparation of polypeptides,is ring-opening polymerization(ROP)of a-amino acid N-carboxyanhydrides(NCAs).In order to prepare polypeptides with different topologies and functional groups,it is essential to develop different strategies to construct catalyst systems to mediate controllable/living ROP of NCAs.Despite the emergence of some "living"polymerization systems,which can be widely used are very little.Therefore,the development of new catalyst systems,especially the use of organocatalyst is important.In this paper,we used the strategy of using Lewis acid and large steric hindrance primary amine to form Frustrated Lewis Pair,to initiate controllable ROP of Glu-NCA.First,an internal standard method was used to establish a simple and efficient method for calculating the conversion rate of polymerization of Glu-NCA.Fmes2BF/aniline has been found to be FLP by screening a series of different steric hindrance,acidic borane,which could be used for initiating the ROP of Glu-NCA.Subsequently,the reaction conditions such as emissions of carbon dioxide produced by the reaction,are optimized and the conversion of the polymerization reaction was raised to 99%.Under the optimum reaction conditions,PBLG with Mn=1.19 kg/mol and D = 1.28 was obtained.The results show that the molecular weight of the polymer is linearly related to the molecular weight distribution(R2 = 0.9626)during the polymerization of Glu-NCA initiated by Fmes2BF/aniline.The ring opening polymerization of Glu-NCA initiated by Fmes2BF/aniline was monitored by ’H NMR spectroscopy and 11B NMR spectroscopy.The capture of the signal changes indicated that Fmes2BF interacted with the terminal amino group at the polymer chain,so that FLP was formed.At the same time,the intermediates of Glu-NCA ring-opening reaction were prepared,and the above-mentioned speculation was verified by the results of 11B NMR,after the interaction between the intermediate system and Fmes2BF.The "FLP-intermediate"chain growth mechanism was proposed on the base of mechanism investigation.