Synthesis and self-assembly behaviors of the ABC miktoarm star terpolymer

The ABC miktoarm star terpolymer MPEG-PTHF( -PDMA) was synthesized by the combination of click chemistry, atom transfer radical polymerization ( ATRP ) and cationic ring opening polymerization ( CROP ) . A block copolymer of poly( ethylene glycol) ( PEG ) and poly( N, N-dimethylaminoethyl methacrylate) ( PDMA) which bears an azido at diblock junction ( MPEG-N₃ ( -PDMA) ) was first prepared by atom transfer radical polymerization. Then, an alkynyl-terminated narrow distributed polytetrahydrofuran (PTHF-Alk) was synthesized as another building block via cationic ring opening polymerization. The well- defined ABC miktoarm star shaped terpolymer was afforded by clicking MPEG-N₃ ( -PDMA) onto the chain end of PTHF-Alk. The structure of the star terpolymer was characterized by the FTIR,NMR and SEC/MALLS. The self-assembly behavior of the polymer were investigated by dynamic light scattering ( DLS) and transmission electron microscopy ( TEM ) . This star shaped terpolymer consists of a hydrophobic PTHF chain, a hydrophiphilic PEG chain and another stimuli-responsive PDMA chain. It can self-assemble into micelles with different sizes and morphologies at various pH values, such as 5. 0 ,7. 4 and 9. 5. The micellar size also exhibits temperature-dependence at pH 7.4 and 9.5. The variation of size and morphology of the micelles with the solution pH and temperature is ascribed to the pH- And thermo-responsive properties of the PDMA block.