Thermo-sensitive transition of monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) films to micellar-like nanoparticles

Monomethoxy poly(ethylene glycol)-block-poly(trimethylene carbonate) (mPEG(3)-PTMC(11), M(n) of mPEG=3.1 x 10(3) and M(n) of PTMC=10.8 x 10(3)g/mol) was synthesized by ring-opening polymerization of TMC using mPEG(3) as an initiator and stannous octoate as a catalyst. The block copolymer has a broad melting range with a peak at 49.5 degrees C and a heat of fusion of 47.6J/g. The heat of fusion normalized to the mPEG content is higher than that of the mPEG(3) polymer, suggesting that PTMC segments are also semi-crystalline. The mPEG(3)-PTMC(11) films were stable in water at room temperature, whereas at 37 degrees C the film specimens disintegrated and the amphiphilic block copolymer self-assembled into micellar-like nanoparticles with average sizes up to 210nm. The critical association concentration (CAC) of the formed micellar-like particles is 1.35 x 10(-3)mg/ml. The average size and polydispersity index of the formed mPEG(3)-PTMC(11) nanoparticles depend on temperature and storage time: the values decrease with increases in temperature and in storage time. By co-dissolving dexamethasone with mPEG(3)-PTMC(11) during the film preparation, micellar-like nanoparticles loaded with dexamethasone can be obtained after the film to micellar-like nanoparticles transition. A high loading efficiency of 93.3 wt.% was achieved. The sustained release of the drug was complete in 20d.