Preparation And Properties Of Amphiphilic Fluorescent Block Copolymer Micelles Based On Cyano-Stilbene

Photo-responsive amphiphilic fluorescent block copolymers are the research hotspots in the field of intelligent polymer materials.They have potential applications in drug controlled release,biomedical materials,white light materials and other fields.Cyano-stilbene has good photoelectric properties and excellent controllability.The cistrans isomerization of cyano-stilbene will occur when stimulated by light or heat,which will affect its fluorescence.Up to now,little research has been done on the photoresponse behavior of amphiphilic fluorescent block copolymers constructed from cyano-stilbene.In this paper,a series of photo-responsive amphiphilic fluorescent block copolymers based on cyano-stilbene were designed and synthesized,and micelles were prepared by solvent-induced method in aqueous solution.The effects of the isomerization of cyano-stilbene micelles on the fluorescence properties and the effect of flexible spacers on the photo-response speed of cyano-stilbene micelles were studied.The main work of this paper includes the following aspects:1.A series of amphiphilic fluorescent block copolymers PM0PVPC1-b-MPEG were synthesized by RAFT polymerization with using polyethylene glycol monomethyl ether as hydrophilic segment and cyanostilbene-containing side-chain fluorescent polymer without flexible spacer group as hydrophobic segment.The luminescence behavior of the copolymers in THF solution,film state and micelles prepared in aqueous solution was investigated.It was found that the fluorescence emission was monomolecular in the dispersion state of the solution,and multi-peaks appeared in the fluorescence emission map of the film and micelle aggregation state.The fluorescence intensity was 20~40 times of that of the pure solution,and the AIEE effect was obvious.In THF solution,trans-cis isomerization occurs and fluorescence intensity decreases when irradiated by UV-365 nm,while cis-trans isomerization occurs when irradiated by UV-254 nm,and fluorescence intensity increases.After self-assembled into micelles in aqueous solution,trans-cis isomerization occurs when irradiated by UV-365 nm,the size of micelles becomes larger and the fluorescence intensity increases.When irradiated by UV-254 nm,cis-trans isomerization occurs,the size of micelles becomes smaller and the fluorescence intensity decreases,which indicates that the fluorescence intensity of micelles is closely related to the size and aggregation degree of aggregates.2.A series of amphiphilic fluorescent block copolymers PM6PVPC1-b-MPEG were synthesized by RAFT polymerization with using polyethylene glycol monomethyl ether as hydrophilic segment and cyanostilbene-containing side-chain fluorescent polymer with flexible spacer as hydrophobic segment.The luminescence behavior of the copolymers in THF solution,film state and micelles prepared in aqueous solution was investigated.It was found that the fluorescence emission of all samples was single molecular emission in the dispersed state of solution.In the film state,the fluorescence behavior of the block copolymer and the homopolymer PM6PVPC1 were more and more similar with the increase of hydrophobic segment content.At the same time,the longer the proportion of hydrophobic group,the lower the CMC.When the degree of polymerization of hydrophobic segment was 80,the amphiphilic fluorescent block copolymer was unable to form micelles in water because of the strong hydrophobic interaction.The fluorescence emission spectra of micelles showed multiple peaks,and the fluorescence intensity was 5~20 times higher than that of pure solution,which has obvious AIEE properties.The light-responsiveness of amphiphilic fluorescent block copolymers in solution and micelles formed in water was also studied.The results show that the trend of photo-response behavior is basically the same as that of amphiphilic fluorescent block copolymers containing non-flexible spacer group cyanostilbene.However,the introduction of flexible spacers weakens the interaction between the main and side chains.When the copolymers were stimulated by ultraviolet light,the motion of the cyanostilbene chain segment accelerates and the speed of light response accelerates.