Rheological properties of novel thermo-responsive polycarbonates aqueous solutions

Abstract

Thermo-responsive multiblock polycarbonates were facilely synthesized by covalently binding poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) blocks, using triphosgene as coupling agent and pyridine as catalyst. The aqueous solutions of thermo-responsive polycarbonates were investigated by rheological measurements. Steady-state shear measurements reveal that the polycarbonate solutions exhibit shear-thinning behavior and the hydrophilic content has a pronounced effect on the flow behavior of the polycarbonates aqueous solutions. The shear viscosity decreases with increasing poly(ethylene oxide) (PEO) composition. The increase of viscosity with increasing concentration is probably attributed to the formation of stronger network owing to interchain entanglement of PEO block at higher concentration. When the flow curves are fitted to the power law model, flow index is obtained to be less than 1, as exhibiting typical pesudoplastic fluid. The viscoelastic properties of the system also show close dependence on the composition of polycarbonates. Temperature sweep confirms that the multiblock polycarbonates exhibit thermo-responsive properties. For 7% aqueous solution of polycarbonate with composition ratio of EO to PO of 1/1, the sol-gel transition occurs at 37 °C, which makes the system suitable as an injectable drug delivery system.

Keywords

polycarbonates / thermo-responsive / rheological measurements / viscosity / gel