Novel reverse thermoresponsive injectable poly(ether carbonate)s

Abstract

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 C _i (minimal gelation concentration) and T _i (minimal gelation temperature) of these systems was investigated. The copolymers were characterized by GPC, ¹H-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 °C, poly(ether carbonate) water solutions (15%) attained viscosities between 25 000 and 150 000 Pa.s.