The Synthesis And Self-Assembly Of Amphiphilic Dithienylethene Diblock Copolymer

Amphiphilic block copolymers containing photoresponsive dithienylethenegroups have self-assembly and photoresponsive properties, which can be potentiallyapplied in many fields such as optical information storage, optical switches, opticalsensors and light-controlled release, etc. This dissertation includes synthesis ofamphiphilic dithienylethene diblock copolymers, characterization of their structuresand properties, study of their self-assembly and photoresponsive properties. The mainachievements of this thesis are summarized as follows.A series of amphiphilic diblock copolymers (PEGx-b-PSDTEy) containingphotochromic dithienylethene (DTE) pendants had been synthesized by reversibleaddition fragmentation chain transfer (RAFT) radical polymerization with PEG asmacro-chain transfer agent. The molecular weight, structures and properties of thesediblock copolymers were carefully characterized by GPC, NMR, UV–vis and DSCmeasurements. The analyses results indicated that the diblock copolymers possessedwell-defined structures and narrow molecular weight distributions. The1H NMRanalyses verified that nearly100%percent of the DTE pendants in the diblockcopolymers were underwent photochemical ring-closing and-opening reactions whenirradiated with UV and visible light respectively. The chain length of diblockcopolymers had a great influence on the photoresponsive properties ofdithienylethene pendants. Fluorescence spectra results indicated that DTE pendants inthe diblock copolymers could effectively control the fluorescence intensity ofRhodamin B and realize the reversible photo-modulated fluorescence quench andemission.Amphiphilic dithienylethene diblock copolymer (PEGx-b-PSDTEy) canself-assemble to hollow vesicle-like structures or colloidal spheres with solid interiorsprepared by gradually adding deionized water to their THF solutions. The proportionbetween hydrophilic and hydrophobic blocks and the self-assembly condition showedeffect to the size and internal structure of the colloidal spheres self-assemblies, which were characterized by using laser light scattering (LLS) and TEM methods. The twooptical isomers of the PEG43-b-PSDTE29showed entirely different self-assemblybehaviors. Hollow vesicle-like structures were formed by gradually adding deionizedwater to the colorless PEG43-b-PSDTE29open(DTE in open form) THF solution. Underthe same condition, the aggregates formed in the blue PEG43-b-PSDTE29close(DTE inclosed form) solution were the colloidal spheres with solid interiors. Theisomerization of DTE pendants could cause the deformation of the vesicle-likestructures but unchanged morphology of colloidal spheres. Above result demonstratesa kind of novel photo-modulated self-assembly behavior and morphology of theaggregates of amphiphilic diblock copolymer.