Synthesis and micellization of amphiphilic multi-branched poly(p-dioxanone)-block-poly(ethylene glycol)

A novel multi-branched crystalline-coil block copolymer composed of hydrophilic polyethylene glycol (PEG) block and multi-branched crystallisable poly(p-dioxanone) (PPDO) block was prepared. Firstly, multi-branched PPDO was prepared via polycondensation of AB2-type HOOC-PPDO-2OH precursor, which was synthesized by using 2,2-bis(hydroxymethyl)propionic acid as initiator for ring opening polymerization of p-dioxanone; then the multi-branched PPDO-b-PEG copolymer was obtained by coupling the end hydroxyl group of multi-branched PPDO with carboxylated mPEG using dicyclohexylcarbodiimide as dehydrator. The molecular structures of polymers formed in each step were characterized by NMR and GPC. The results confirmed the successful preparation of the target product, and the molecular characteristics of the multi-branched PPDO, such as chain length of the blocks and branch density, could be facilely controlled. In addition, the micelle of the copolymer in aqueous solution was investigated by fluorescent probe, TEM, DLS, DSC and NMR. The results indicated that the copolymer in aqueous solution can form “star anise”-like micelles and the micellization behavior was determined by the composition and molecular architecture of the copolymer.