Tri-block copolymers of linear poly(ethylene glycol) (PEG) and hyperbranched poly-3-ethyl-3-(hydroxymethyl)oxetane (poly-TMPO) are reported. The novel dumb-bell shaped polyethers were synthesized in bulk with cationic ring-opening polymerization utilizing BF3OEt2 as initiator, via drop-wise addition of the oxetane monomer. The thermal properties of the materials were successfully tuned by varying the amount of poly-TMPO attached to the PEG-chains, ranging from a melting point of 54 degrees C and a degree of crystallinity of 76% for pure PEG, to a melting point of 35 degrees C and a degree of crystallinity of 12% for the polyether copolymer having an average of 14 TMPO units per PEG chain. The materials are of relatively low polydispersity, with M-n/M-w ranging from 1.2 to 1.4. The materials have been evaluated for usage with the energetic oxidizer ammonium dinitramide. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6191-6200, 2009