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-N, (-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.