Preparation of nanomaterials by ring opening polymerization and self-assembly of angelw: N-heterocyclic anhydrides in aqueous phase

1、 Background the preparation of nano materials with special properties by self-assembly of aliphatic polymers is an important research direction in the field of nano synthesis Among the polymers involved, natural or chemically synthesized polypeptide structure is a new kind of biomaterial In the synthesis of nanodrugs, because amphiphilic peptides can form unique nanostructures by intermolecular or intramolecular interactions, precise design of amphoteric peptide polymers is the direction of researchers Up to now, the most feasible method of peptide synthesis is the ring opening polymerization of N-heterocyclic anhydrides (NCA) However, there are still many problems in this reaction: the purification of substrate is more complex, the substrate is more sensitive to water, and many toxic reagents such as DMF are involved in the reaction How to simply realize the ring opening polymerization of N-heterocyclic anhydrides, and at the same time realize the self-assembly process to prepare nano materials with special topological structure are "two big mountains" pressing on nano researchers (source: angelw Chem Int ed.) 2 Recently, Colin bonduele and s é Bastien lecommandoux, University of Bordeaux, France, used hydrophilic macromolecular initiator to realize one-step open-loop polymerization of N-heterocyclic anhydrides in water phase, and prepared nano materials with core-shell structure of nano size Relevant research results were published in angelw Chem Int ed (10.1002 / anie 201912028) (source: angelw Chem Int ed.) in previous reports, the preparation of nanomaterials by polypeptides is mainly divided into two steps: the ring opening polymerization of NCA and the self-assembly process of block polymers How to realize the two-step reaction at the same time is the research goal of the author After in-depth analysis of the reaction process, the author proposed two conditions to achieve the above objectives: the polymerization speed is greater than the hydrolysis speed of NCA; the formed short polymer micelles have a protective effect on the monomer NCA to avoid its hydrolysis After careful screening, peg with amino terminal was selected as the initiator of macromolecule (source: angelw Chem Int ed.) in view of the hydrolysis of NCA, the author found that the pH of reaction solution has a great relationship with the hydrolysis rate of NCA When sodium bicarbonate solution with pH = 8 is selected as the reaction solvent, the hydrolysis process of NCA can be well inhibited, and the ring opening polymerization of NCA can be realized quickly The molecular weight of the polymerized block polymer determined by GPC shows that the reaction has good controllability and the conversion rate of the reaction can be as high as 90% At the same time, the author found that the reaction solution changed greatly before and after polymerization Before polymerization, the reaction liquid is a milky white liquid with a solid content of 7% However, after polymerization, the typical blue characteristics of nano colloids can be observed The results of dynamic light scattering showed that the prepared nano materials were micelles with an average value of 80 nm In addition, the block polymers with different solid content are analyzed and it is found that the polymers with higher solid content will have larger hydraulic diameter D H (source: angelw Chem Int ed.) Moreover, the molecular weight of the peg segment of the block polymer will have a great impact on the topological structure of its nanomaterials When the molecular weight of PEG segment is small, needle like nanomaterials are mainly prepared; when the molecular weight of PEG segment is increased, worm like nanomaterials can be prepared 3 The conclusion of the study is that the aqueous ring opening polymerization of NCA is realized by using the PEG chain modified by amino group, and the self-assembly process of block polymer is realized at the same time This laid a foundation for the application of such nano materials in the future