Preparation Of Amphiphilic Azobenzene-Containing Block Copolymers And Investigation Of Their Properties

Amphiphilic azobenzene-containing block copolymer combined the properties of azobenzene and amphiphilic block copolymer, which showed interesting photo-responsive behaviors in solution. These polymers attacked more and more researching interest for their novel ability as the building block of photo-sensitive materials. In this thesis, the RAFT polymerization behavior of three azobenzene vinyl monomers containing different substitutes was investigated firstly. Then, the amphiphilic block copolymers of these azobenzene polymers with DMAEMA and PEGMA were synthesized through the chain extension method. The properties of these polymers in solution were investigated thereafter. The details were showed as following:(1) Three well-defined azobenzne homopolymers, e.g. poly{6-[4-phenylazo -phenoxy)hexylmethacrylate} (PPHMA), poly{6-[4-(4-methoxyphenylazo) phenoxy]hexylmethacrylate} (PMHMA) and poly{6-[4-(4-cyanophenylazo) phenoxy] -hexylmethacrylate} (PCHMA), were synthesized via RAFT polymerization using CPDN as the RAFT agent and AIBN as the initiator. The polymerization showed characteristics of living/controlled behavior. Using these azobenzene homopolymers as the macro-RAFT agents, the amphiphilic diblock copolomers were prepared by chain extension using DMAEMA as the second monomer. The polymer structure was characterized via NMR technique. The light responsive behaviors of the homopolymer and their diblock copolymers in their solution were also investigated.(2) The amphiphilic azobenzene block copolymer, poly(6-(4-phenylazophenoxy) hexylmethacrylate-b-poly((2-dimethylamino)ethyl methacrylate)) (P(PHMA)-b- (PEGMA)) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization technique. The polymerization behavior showed that it was conducted in a controlled living manner. The obtained amphiphilic block copolymer showed strong fluorescence emission in water/tetrahydroforan(THF) solution with minor relationship with UV-vis irradiation. Further investigation showed that such copolymer emitted strong fluorescence in THF after UV-vis irradiation. The change of fluorescence emission behavior of the amphiphilic block copolymer both in water/THF and THF solution was caused by the formation and size changing of aggregation originated by the photo-isomerization of azobenzene chromophore.