Synthesis of biodegradable pentaarmed star-block copolymers via an asymmetric BIS-TRIS core by combination of ROP and RAFT: From star architectures to double responsive micelles

Biodegradable star-shaped poly(E-caprolactone) and poly(epsilon-caprolactone-b-L-lactide) (5sPCL-b-PLLA) with five arms were synthesized by ring-opening polymerization (ROP) from an asymmetric BIS-TRIS core via core-first strategy. Subsequently, a series of amphiphilic and double responsive star-block copolymers were synthesized by Z-RAFT star polymerization of N,N-dimethylamino-2-ethyl methacrylate (DMAEMA) from the star-shaped macro-RAFT agent, which was prepared by attaching 3-benzyl-sulfanylthiocarbonylthiocarbonylsufanylpropionic acid (BSPA) to 5sPCL-b-PLLA using a simple two-step reaction sequence GPC and H-1 NMR data demonstrated the polymerization courses are under control The molecular weight of 5sPCL-b-PLLA-b-DMAEMA increased with the monomer conversion, and the molecular weight distribution was in the range of 119-1.37. The spherical micelles with degradable core and pH/thermo-double sensitive shell had been prepared from the aqueous medium of the amphiphilic star-shaped copolymers by dialysis method Both pH and thermal-responsive behaviours of copolymer micelles obtained in this study were investigated. The micelle size and morphology were measured by DLS, AFM and TEM (C) 2010 Elsevier Ltd All rights reserved