Novel reverse thermoresponsive injectable poly(ether carbonate)s

The water solutions of polymers displaying reverse thermal gelation (RTG), such as poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblocks, exhibit a pronounced viscosity increase as temperature rises, within a very narrow temperature interval. Unfortunately, the viscosity increase attained by these solutions is not large enough, resulting in systems displaying limited stability and short residence times. This paper introduces a new family of reverse thermoresponsive alternating [A-B](n) block copolymers, comprising poly(ethylene oxide) (PEO), and poly(propylene oxide) (PPO) chains, using phosgene as the molecule connecting both components. The effect of various compositional and structural parameters on both the Ci (minimal gelation concentration) and Ti (minimal gelation temperature) of these systems was investigated. The copolymers were characterized by GPC, (1)H-NMR, FT-IR, and DSC and the rheological behavior of the water solutions was studied using a Brookfield viscometer. The water systems were also studied by dynamic light scattering (DLS) and fluorescence spectroscopy. The copolymers developed exhibited clearly superior rheological properties, when compared to existing RTG-displaying PEO-PPO-PEO triblocks. For example, while the viscosity of a 15% water solution of the commercially available Pluronic F-127 achieved 5000 Pa.s, at 37 degrees C, poly(ether carbonate) water solutions (15%) attained viscosities between 25 000 and 150 000 Pa.s.