The Synthesis Of Multi-responsive Azobenzene Block Copolymer And Study On Its Self-assmebly Behavior

The self-assembly aggregation of responsive amphiphilic block copolymers are widely used in the field of biological science and nanomaterial science,because it can make corresponding reversible or irreversible changes toward external environment stimuli.Compared with conventional single-or dual-stimuli-based systems,multiple responsive polymers could respond more fully and sensitively to external stimuli,which has become a hot topic in the field of polymer self-assembly.In this study,multi-responsive block copolymer,PAA-b-P(AzoMA-co-PEGMA)containing pH-,light-and reduction-responsiveness were synthesized with monomers of AzoMA,PEGMA and acrylic acid via reversible addition-framentation chain transfer polymerization(RAFT).The main contents of this article is as follows.1.Firstly,the azobenzene monomer AzoMA with polymerization activity was obtained by diazotization,azo coupling and acyl chloridization.Three kinds of copolymers of PtBA-b-P(AzoMA-co-PEGMA)s,labelled as P-1,P-2,P-3 with different structural unit ratios and molecular weights were synthesized via RAFT,then amphiphilic block copolymers of PAA-b-P(AzoMA-co-PEGMA)s,labelled as BCP-1,BCP-2,BCP-3 were obtained by further hydrolysis under the action of trifluoroacetic acid.The structures of AzoMA,PtBA,PAA-b-P(AzoMA-co-PEGMA)were characterized by FT-IR,1HNMR and GPC.The results indicated that the target block copolymers have been successfully synthesized.2.Block copolymer was dissolved in THF,then the micelles were obtained by water inducing copolymer self-assembly.The effects of concentration and ratio of hydrophobic structural units on micellar morphology and size were investigated by TEM,DLS,UV-vis and fluorescence spectra.The results showed that the size of micelles become smaller as the increasing of AzoMA segment and the effect of concentration on micellar particle size was related to the attractive and repulsive forces between the copolymer micelles.3.The pH-,light-and reduction-responsive block copolymer micelles were investigated by TEM,DLS and UV-vis.The results showed that the micelle size decrease with the decreasing of pH within a certain range.However,the particle size of micelles increased significantly when the pH was 4.The light-responsiveness of micelles was reduced.It could be explained that the isomerization behavior of azobenzene groups was obviously inhibited by the aggregation.UV absorption of micelles gradually disappeared by adding reducing agent,which suggested the dissociation of block copolymer micelles.4.Fluorescent molecular of Nile Red was selected as a hydrophobic guest molecule to study the properties of encapsulating and releasing abilities of block copolymer micelles for guest molecules.The results showed that the loading capacity of three kinds of copolymer micelles followed the order of BCP-1>BCP-2>BCP-3.At the same time,the block copolymer micelles also can release a certain amount of Nile Red under the irradiation of UV light,the reduction of Na2S2O4 as reductant,or alkaline environment.